JOURNAL OF MAGNETIC RESONANCE IMAGING 41:1528–1540 (2015)

Original Research

Early Response to Chemoradiotherapy for Nasopharyngeal Carcinoma Treatment: Value of Dynamic Contrast-Enhanced 3.0 T MRI Dechun Zheng, MS,1 Yunbin Chen, MD,1* Xiangyi Liu, MS,1 Ying Chen, BS,1 Luying Xu, BS,2 Wang Ren, MS,1 Weibo Chen, MSc,3 and Queenie Chan, PhD4 Purpose: To prospectively evaluate the dynamic contrast-enhanced magnetic resonance imaging (DCEMRI) value for predicting early nasopharyngeal carcinoma (NPC) chemoradiotherapy (CRT) response.

markers for NPC patients receiving CRT therapy following NAC. Key Words: DCE-MRI; nasopharyngeal carcinoma; neoadjuvant chemotherapy; radiation therapy; therapy response J. Magn. Reson. Imaging 2015;41:1528–1540. C 2014 Wiley Periodicals, Inc. V

Materials and Methods: Forty-two patients with advanced NPC were recruited and received three DCEMRI exams before treatment (Pre-Tx), as well as 3 days (Day 3-Tx) and 40 days (Day 40-Tx) after chemotherapy initiation (two neoadjuvant chemotherapy cycles, NAC). We used DCE-Tool to measure primary tumor kinetic parameters (Ktrans, Kep, ve, and vp) using the extended Tofts model. Kinetic parameters and corresponding changes were compared between responders and nonresponders after NAC or CRT treatment using Student’s t or Mann–Whitney U tests. Results: Response to two NAC cycles correlated with short-term local control (P ¼ 0.01). Compared to the nonresponder group, the responder group presented with significantly larger DKtrans(0–3), DKep(0–3), and Dvp(0–3) values after NAC (P < 0.05). The complete response group after CRT exhibited significantly lower Ktrans(Day 40-Tx) and larger DKtrans(0–3) values than the residual group (P ¼ 0.05). High sensitivity (range: 74.1%–90%) and moderate-to-high specificity (range: 50%–84.3%) distinguished nonresponders from responders grouping after NAC or CRT, with diagnostic efficiency ranging from 69.3%–88%. Conclusion: Our study showed kinetic parameter changes earlier after chemotherapy were potential

1 Department of Radiology, Fujian Medical University Teaching Hospital, Fujian Provincial Cancer Hospital & Institute, Fuzhou, Fujian, People’s Republic of China. 2 Department of Radiation Oncology, Fujian Medical University Teaching Hospital, Fujian Provincial Cancer Hospital & Institute, Fuzhou, Fujian, People’s Republic of China. 3 Philips Healthcare, Shanghai, People’s Republic of China. 4 Philips Healthcare, Hong Kong. The first two authors are co-first authors and contributed equally to this work. Contract grant sponsor: Natural Science Foundation of Fujian Province; Contract grant number: 2012J01330. *Address reprint requests to: Y.C., No.420, Fuma Road, Fuzhou, Fujian, People’s Republic of China 350014. E-mail: [email protected] Received May 30, 2014; Accepted July 21, 2014. DOI 10.1002/jmri.24723 View this article online at wileyonlinelibrary.com. C 2014 Wiley Periodicals, Inc. V

NASOPHARYNGEAL CARCINOMA (NPC) has become a territorial epidemic in southern China and Southeast Asia (1). As a result of advances in radiation therapy equipment and multimodal therapy for locally advanced NPC, the 5-year overall survival rate of NPC has improved substantially, ranging from 75%–83.5% according to the latest studies from southern China (2,3). However, locoregional relapses and distant metastases following aggressive chemoradiotherapy (CRT) for advanced NPC remain significant clinical problems. Neoadjuvant chemotherapy (NAC) has been used for reducing overall tumor volume and boosting radiation therapy (RT) sensitivity in patients with NPC and other malignancies, thereby facilitating local control and reducing the distant metastases rate (4,5). A recent study found out that NAC prior to concurrent chemoradiotherapy improved survival of nasopharyngeal carcinoma patients (6). RT or CRT following NAC has been a routine practice for advanced NPC patients in our hospital since 2004 (7). There is a clear and strong need for radiologists to identify earlier predictive markers where they can determine earlier if patients were sensitive or not to the chemoradiotherapy regimen. Although molecular markers, such as Bcl-2, Ki-67, p53, and CD31 have potential, but have not yet gained clinical significance as outcome predictors (8). Magnetic resonance imaging (MRI) has recently been proposed as a potential noninvasive imaging technique to predict and monitor early chemoradiotherapy response (9–13). Compared to computed tomography (CT) and positron emission tomography (PET), MRI provides improved morphological and functional imaging; it retains the advantages of having

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higher spatial resolution and no ionizing radiation. Evaluating treatment effectiveness by size reduction is generally inaccurate (14) and a delay of several weeks to months after treatment is common. Several functional MRI techniques have emerged, affording qualitative and quantitative metrics for early therapy response assessment to malignancies by providing complementary information based on underlying biological changes. These include vascularity and oxygenation (dynamic contrast-enhanced MRI [DCEMRI]), cellularity (diffusion-weighted imaging [DWI]), and biochemical changes (magnetic resonance spectroscopy [MRS]), all potential mediators of chemoradioresistance. MRS has limitations in its extracranial application. Both DCE-MRI and DWI have been proven to be valuable predictors for treatment response and identifying disease relapse, especially in head and neck cancer, breast cancer, and cervical cancer (9–13). Studies of breast cancer showed an early increase in apparent diffusion coefficient (ADC) values after only one or two cycles of neoadjuvant chemotherapy (13). Kim et al (15) reported that the average pretreatment Ktrans value in the complete response groups of head and neck squamous cell carcinoma was significantly higher than the partial response group. A recent clinical study discovered that the change ratio of the ADC value after 2 weeks of radiation therapy was an independent prognostic factor for the short-term effect of intensity-modulated radiotherapy (IMRT) in NPC (16). However, the ADC value is an indirect marker reflecting tumor vascularity and permeability status, both of which are widely recognized to be associated with pharmaceutical delivery as well as tissue hypoxia. Conversely, DCE-MRI directly provides biological markers to investigate tumor vascularity, permeability, and oxygenation, which are important factors for both chemotherapy and radiation therapy sensitivity. Whether or not DCE-MRI can be used in the individualized treatment for NPC remains unknown. Hence, our prospective study probed the feasibility of using serial DCE-MRI to depict early response to NAC and CRT and to evaluate its potential to define individualized treatment regimens in advanced NPC.

MATERIALS AND METHODS Patient Population and Treatment The study protocol was approved by the Regional Committee for Medical and Health Research Ethics, and all recruited patients signed written informed consent. Between May 2012 and December 2013, 42 newly-diagnosed NPC patients with no prior treatment were recruited and referred for chemoradiotherapy. One patient was excluded from the study because of a serious motion artifact on pretreatment MRI exams. Hence, analysis of MRI data was completed on 41 patients (33 males and 8 females, mean age: 46.4 6 13.1 years). All patient TNM statuses were determined by radiologists, with reference to the latest 7th edition of the Union for International Cancer Control-American Joint Committee on Cancer (UICC-AJCC) staging sys-

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tem. The selected individuals were candidates for either two cycles (n ¼ 32) or three/four cycles (n ¼ 9) of neoadjuvant chemotherapy (all patients fulfilled treatment in 21 6 3.2 days per cycle). In each cycle, 31 patients were given a dose of 100 mg/m2 cisplatin (DDP, Qilu Pharmaceutical, Shandong, China) on days 1, 2, and 3, plus 135 mg/m2 taxol (PTX, Hainan Chuntch Pharmaceutical, Hainan, China) on day 1, while the other 10 patients were given a dose of 100 mg/m2 cisplatin on days 1, 2, and 3, plus 1000 mg/m2 gemcitabine (GEM, Jiangsu Hansoh Pharmaceutical, Jiangsu, China) on days 1 and 8. After finishing neoadjuvant chemotherapy, two patients refused further radiation therapy. The remaining 39 patients then received accelerated radiation treatment with an average total dose of 6975 cGy/32 fractions (220 cGy/ fraction) over a period of 44–53 days. Among 39 patients, 22 were given concurrent chemotherapy (100 mg/m2 DDP on days 1 and 22 during the radiation treatment course). Follow-up was performed to assess whether or not some patients experienced relapse. The median follow-up term was 7.8 months (range: 4–10 months). Although a posttreatment follow-up of 6 months may reflect long-term or overall survival, the current study focused on predicting and assessing local control of primary disease. Additional therapeutic strategies done at the end of chemoradiotherapy for residual lesions, which included boost dose radiotherapy, adjuvant chemotherapy, or cycle cytokineinduced killer (CIK) immunotherapy, made it difficult to assess the neoadjuvant chemotherapy role. Thus, the status at the end of chemoradiotherapy was used as the clinical endpoint in this study. The criterion for a complete response (CR) was the absence of visible and viable tumor based on the MRI assessment and/ or pharyngorhinoscopy. All partial response (PR) or stable disease (SD) patients were confirmed by MRI examination according to RECIST 1.1 criteria (17), in which a reduction of the longest diameter of primary tumor larger or equal to 30% after NAC or CRT was considered PR and the others who did not reach 30% as SD. After two NAC cycles, CR and PR patients were categorized as responders and SD patients were categorized as nonresponders. Based on MR examination at the end of CRT, CR patients were classified as responders; PR and SD patients who presented as residual disease on MR examination were classified as nonresponders. All subjects were prospectively scheduled to receive four MRI exams during the treatment course. This included exams before treatment (Pre-Tx), the 3rd day (about 60 hours after IV chemotherapy, Day 3-Tx) and 40th day (at the end of two cycles of NAC, Day 40-Tx) after NAC initiation and at the end of CRT (within 1 week after completion of CRT, Post-Tx). All efforts were made to minimize possible MRI exams associated variables, although it was difficult to keep the exact timing of serial MRI scans for all patients. Variances at every scan timepoint were mainly due to the large variability in the clinical conditions of patients for the oncological radiologist to implement therapy and to perform MRI exams.

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MRI Protocols and Procedures In this study, we used a 3.0 T whole-body multitransmit scanner system (Achieva TX, Philips Healthcare, Best, The Netherlands) and a 16-channel neurovascular coil. The DCE-MRI used a 3D-T1-fast field echo (FFE) sequence. The following parameters were used in the DCE-MRI: time of repetition (TR): 13 msec; time  of echo (TE): 2.6 msec; two different flip angles (5 for  precontrast scan, and 15 for the dynamic scan [80 dynamics]); number of signal averages (NSA): 4 for the precontrast scan and 2 for the dynamic scan; field of view (FOV): 240  180 mm; slab thickness: 80 mm; acquisition matrix: 160  119; 22 slices were available. Imaging was performed at a spatial resolution of 1.5  1.5  3.6 mm3. The temporal resolution of the dynamic scans was 4.8 sec. The total duration of DCE-MRI sequences was 7.5 min. The routine imaging protocols for NPC in our hospital included axial and sagittal T1-weighted imaging (T1WI), axial and oblique coronal T2-weighted imaging (T2WI) with fat suppression using a short-inversion-time (TI ¼ 180 msec) inversion recovery (STIR) technique, axial diffusion weighted imaging (DWI); and axial and oblique coronal T1WI with fat suppression using spectral presaturation with inversion recovery (SPIR) technique images that were acquired after acquisition of DCEMRI sequences. Some major parameters of T2WI, T1WI, and DWI are detailed as follows: TR/TE for T1WI: 550/8.1 msec, for T2WI: 6000/70 msec, for DWI: 4500/100 msec; FOV for axial imaging: 240  230 mm; for coronal: 340  240 mm; slices thick/ gap: 5/1 mm; b value for DWI: 0, 800 s/mm2. The routine and DCE-MRI protocols were carried out on recruited patients within 1 week before treatment. They received DCE-MRI and T2WI at Day 3-Tx and Day 40-Tx timepoints during chemoradiotherapy. Only routine MRI protocols were implemented at the end of CRT. Scan procedures were implemented as follows: First, five routine sequences, including the axial and sagittal T1WI, axial and oblique coronal T2WI with fat saturation using STIR and DWI sequences were performed before the DCE-MRI scan. Next, a precontrast T1 FFE scan and a DCE-MRI T1 FFE scan were performed. Gd-DTPA (Magnevist, Bayer Schering, Berlin, Germany) was administered in a bolus dose of 2.0 ml/kg (or 0.1 mmol/kg) at a rate of 2.0 ml/sec by power injector followed by 10 ml of a saline flush at the 8th dynamic scan. Finally, axial and oblique coronal T1WI contrast-enhanced scans were then repeated after the DCE-MRI scan. MRI Data Analysis DCE-MRI data were analyzed with dedicated software (DCE-Tool, v. 5.3, Philips Healthcare) according to the following steps: 1. A robust precontrast T1 map was calculated using image data acquired from different flip angles described by Wang et al (18) and dynamic T1 maps were calculated using the method described by Daldrup et al (19).

Zheng et al.

2. The Gd-DTPA concentration was calculated from signal intensities as described by Hittmair et al (20); it assumed a linear relation between concentration and 1/T1, and a known relaxation rate of the gadolinium (Gd) compound (the longitudinal relaxation rate of Gd-DTPA used in this study was 4.95 l/mmol/sec). 3. Pharmacokinetic modeling used a two compartment model based on the extended Tofts model (21); it included a vascular component which was implemented as a linear version developed by Murase (22). The DCE-MRI series were analyzed on a region of interest (ROI) basis by using the arterial input function established by Benjaminsen et al (23). DCE-MRI data were processed by a radiologist (D.Z.) with 7 years of experience in head and neck radiology. After a rigid registration was processed, a pooled arterial input function (AIF) based on an established method (24) was obtained from every patient used for the modeling procedure. The Gd concentration was then acquired in this procedure and similar Gd concentrations were ascertained during processing different timepoints for each patient. A built-in T10 value of blood fluid equal to 1550 msec was automatically used for kinetic analysis. After the largest section of the nasopharyngeal lesion was determined, the following output maps were then calculated automatically: Ktrans (the volume transfer constant of GdDTPA), Kep (rate constant), ve (the extracellular volume fraction of the imaged tissue), and vp (the blood volume fraction). On the basis of the Ktrans maps, three different ROIs (including the other adjacent up and down slices) covering the whole primary nasopharyngeal tumor (excluding peripheral fat, artifacts, and blood vessels) were delineated separately to review corresponding values of Ktrans, Kep, ve, and vp for further analysis. All ROI sizes were recorded as well. The longest nasopharyngeal lesion diameter was determined on the largest transverse section in Pre-Tx, Day 40-Tx, and Post-Tx to assess respective therapeutic response after neoadjuvant chemotherapy and chemoradiotherapy. Fifteen patients’ data on the Day 40-Tx timepoint were excluded for parameter analysis either because they began radiation therapy the day when processing MRI exams (n ¼ 6) or attained CR (n ¼ 9). Statistical Analysis Data were analyzed using SPSS 15.0 software (Chicago, IL). The parameters from three different timepoints were marked using the following form: Parameter(time-point). Changes of kinetic parameters during NAC and CRT were defined according to the formula: Dparameter(0-X) ¼ (Pre-Tx value – Day X-Tx value), where "X" represented the timepoint of taking the MRI examination; and Dparameter(3–42) ¼ (Day 3Tx value – Day 42-Tx value) represented the mathematical difference of MRI kinetic parameters derived during and after NAC. Experimental data were presented as an arithmetic mean 6 standard deviation (SD) unless otherwise stated. After two NAC cycles, primary tumor shrinking ratios was calculated based

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Table 1 Differences in NAC or CRT Responses Between Stage III and IV Patients Residual after CRT Nonresidual (Responder) Residual (Nonresponder)

After two cycles NAC Responder Nonresponder Total Responder Nonresponder Total

Total

Clinical stage III

IV

Total

13(12) 4 17(16) 2 4 6 23

11(10) 3 14(13) 1 3 4 18

24(22) 7 31(29) 3 7 10 41

The numbers in parentheses exclude two patients who withdrew after chemoradiotherapy. CRT, chemoradiotherapy; NAC, neoadjuvant chemotherapy.

on RECIST 1.1 criteria according to the formula: shrinking ratio ¼ the longest diameter at Pre-Tx – its corresponding product at Day 40-Tx / the longest diameter at Pre-Tx. Fisher’s exact test was used to exam the correlation short-term control and response to two NAC cycles treatments. The Shapiro–Wilk test was performed first for diagnosing the normality of data distribution of each parameter. Then statistical comparisons between responders and nonresponders after two NAC cycles and at the end of CRT were carried out using the independent-samples t-test or Mann–Whitney U test accordingly. The receiver operating characteristic (ROC) analyses were used to evaluate the diagnostic efficacies of parameters as predictive imaging markers for the response to chemoradiotherapy. The P-value was considered significant if it was 0.05 or less at the confidence interval (CI) of 95%. RESULTS Clinical Results This study included 38 non-keratinizing undifferentiated squamous cell carcinomas and 3 nonkeratinizing differentiated squamous cell carcinomas according to the WHO classification. As there were only two stage IVb patients in our study, accounting for 4.9% of all subjects, we merged stage IVa and IVb patients into stage IV during statistical analysis. After two NAC cycles, the responses to NAC ranged from 3.57% to 100%, with an average of 48.66 6 33.38% (66.2 6 26.9% for the responder group vs. 14.8 6 10.4% for the nonresponder group, P ¼ 0.001). There were nine patients (with five patients from stage III and four from stage IV) who achieved CR, 18 patients (with 10 patients from stage III and 8 from stage IV) who achieved PR, and the other 14 patients (with eight patients from stage III and six from stage IV) remained in SD after two NAC cycles. A total of 29 patients were categorized as CR (with no evidence of residual disease) and 10 patients as PR (with evidence of residual disease) after chemoradiotherapy. For the latter, six patients were at stage III and four were at stage IV. Further details are shown in Table 1.

The response to NAC significantly correlated with short-term control after CRT (P ¼ 0.01). We found there were 50% (7 of 14) of nonresponder patients after two NAC cycles who presented with residual disease at the end of CRT, and only 12% (3 of 25) from responder patients who presented with residual disease. Further analysis shown in Table 2 indicated patients who had residual disease (PR, n ¼ 10) after CRT presented with significantly lower (P ¼ 0.001) shrinking ratios after two NAC cycles (18.2 6 13.9%) than that of CR patients (58.5 6 31.9%). In our study, there were nine patients who achieved CR for corresponding primary lesions; six were excluded because of initiated radiation therapy or discontinued radiation therapy. In this subgroup (n ¼ 26), the nonresponders (n ¼ 6) who presented as residual disease had a significantly lower shrinking ratios than the responders (19.4% vs. 52.7%, P ¼ 0.017). There were no significant correlations between clinical stage and therapy responses assessed after two NAC cycles or at the end of aggressive CRT treatment (P > 0.50). After an average 7.8 months follow-up, no patient was found to have locoregional relapse or distant metastasis.

DCE-MRI Findings We found that stage III NPC patients had smaller primary mass (232 6 130 pixels) ROI size than stage IV patients (430 6 221 pixels) prior to pretreatment. Stage III NPC patients had higher Kep values than stage IV patients in primary mass at baseline (P ¼ 0.011), and Ktrans, ve, vp values showed no significant differences (P > 0.05) between groups. The differences of kinetic features at Pre-Tx and Day 3-Tx and corresponding changes (including changes between Pre-Tx and Day 3-Tx, between PreTx and Day 40-Tx, and between Day 3-Tx and Day 40-Tx) with responder (CRþPR) and nonresponder (SD) groups after two NAC cycles were investigated and compared; key results were presented in Table 3. There were equality of variances of Ktrans(Pre-Tx) and Kep(Pre-Tx) parameters (P > 0.15) but not for other parameters (P < 0.15) between responder and nonresponder groups after two NAC cycles. Compared to the baseline DCE-MRI, we found that the Ktrans, Kep, and vp values of the responders showed a significant

Table 2 Shrinking Ratio of Primary Tumor After Chemoradiotherapy Subject Overall (N¼39) Subgroup (N¼26)

Residual

N

Mean 6 SD (% z)

t test

P value

Yes * No y Yes No

10 29 6 20

18.23 6 13.89 58.47 6 31.94 19.44 6 17.39 52.70 6 29.86

3.84

0.001

2.58

0.017

*Residual disease within nasopharynx was proven by MRI examination. y Complete response to aggressive chemoradiotherapy. z Response ratio of two cycles of neoadjuvant chemotherapy. SD, standard deviation.

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Table 3 Differences in Response After Two Cycles of Neoadjuvant Chemotherapy Parameters trans

K

(Day 3-Tx)

Kep(Day

3-Tx)

DKtrans(0–3) DKep(0–3) Dvp(0–3) Dvp(3–40)

Group

N

Mean 6 SD (min1)*

T/Uy

P value

Responder Nonresponder Responder Nonresponder Responder Nonresponder Responder Nonresponder Responder Nonresponder Responder Nonresponder

27 14 27 14 27 14 27 14 27 14 18 8

0.403 6 0.168 0.533 6 0.190 0.583 6 0.290 0.797 6 0.349 0.068 6 0.105 0.078 6 0.220 0.071 6 0.195 0.111 6 0.325 0.009 6 0.054 0.0316 0.071 0.009 6 0.054 0.0536 0.122

2.229

0.032

2.090

0.043

2.891

0.006

2.243

0.031

1.991

0.053 (0.045) 0.072 (0.045)

y

1.886 y

*Unit of Ktrans and Kep kinetic parameters and their mathematical difference. Results from Mann-Whitney U test result analysis.

y

decrease as early as 3 days after NAC initiation, while there was no obvious decrease at 3 days after NAC among nonresponders. The Ktrans(Day 3-Tx), Kep(Day 3-Tx), DKtrans(0–3), DKep(0–3), and Dvp(0–3) values in the responder group were significantly higher than those in the nonresponder group (P < 0.05). The Ktrans, Kep, and vp at baseline did not show significant differences between responder and nonresponder groups. There were no significant difference between responder and nonresponder groups for the ve at baseline (2.33 6 2.77 vs. 0.93 6 0.32, respectively) and its changes in the early stage of NAC. Boxplots in Fig. 1a–f (grouping by response to NAC) showed that the Ktrans(Day 3-Tx), Kep(Day 3-Tx), DKtrans(0–3), DKep(0–3), and Dvp(0–3) values were valuable parameters to distinguish responder from nonresponder patients for two NAC cycles. However, Ktrans(Day 3-Tx) and Kep(Day 3-Tx) values partially overlapped between responder and nonresponder groups. Hence, more subjects are needed to further study and determine if it was an appropriate parameter for early prediction of chemotherapy response. As the trend graphs show in Fig. 2b–d (grouping by response to NAC), at the end of NAC most of the patients corresponding Ktrans and Kep values continued to decrease in comparison with Pre-Tx and Day 3-Tx timepoints except for vp. The vp values in the responders were only slightly revised as compared to Day 3-Tx timepoints, while significantly decreased in nonresponders. Corresponding changes Dvp(3–40) value showed a significant difference between responders and nonresponders (0.009 vs. 0.053, P ¼ 0.045). Twenty-six patients’ MR materials were available to carry out statistical analysis after excluding 15 patients at the Day 40-Tx timepoint whose MRI data were not available for parameter analysis. Figure 3a shows that the CR patients had a significantly higher shrinking ratio than those presented with residual lesions. The quantitative DCE-MRI parameters at PreTx, Day 3-Tx, Day 40-Tx, and changes between them were investigated and compared between responder and nonresponder groups according to assessment at the end of CRT, as shown in Table 4. There was equality of variance between Ktrans(Pre-Tx) and Ktrans(Day

parameters (P > 0.15) but not for DKtrans(0–40) after CRT (P ¼ 0.036). Compared to baseline, the Ktrans value decreased more in responders than nonresponders. The Ktrans(Day 3-Tx) and Ktrans(Day 40-Tx) values were lower in the responder group than the nonresponder group (P ¼ 0.05). Furthermore, we found that the change in DKtrans(0–3) values of responder patients were significantly higher than those of nonresponder patients after CRT (P ¼ 0.05). Boxplots in Fig. 3b–d (grouping by response to aggressive CRT) showed that Ktrans(Day3-Tx), Ktrans(Day40-Tx), and DKtrans(0–3) values were valuable parameters distinguishing PR from CR patients for CRT. However, the other kinetic parameters did not prove significantly different between responder and nonresponder groups. Further ROC analyses were conducted to investigate diagnostic efficacies of kinetic parameters in the early prediction of NAC and/or CRT sensitivity of NPC. The results of the diagnostic efficacy of the above parameters are shown in Table 5 and Fig. 4. A generally higher sensitivity and moderate-to-high specificity were acquired from Ktrans(Day3-Tx), Kep(Day3-Tx), DKtrans(0–3), DKep(0–3), Dvp(0–3), and Dvp(3–40) to separate nonresponders from responders early during NAC treatment. It was also acquired from separating the shrinking ratio of two NAC cycles as well as the Ktrans(Day3-Tx), Ktrans(trans Day40-Tx), and DK (0–3) parameters to separate nonresponders from responders early during CRT treatment, which ranged from 74.1–90.0% for sensitivity and 50–84.3% for specificity, respectively. We also conclude from Table 5 that the diagnostic efficiency of the above parameters, except for Ktrans(Day 3-Tx) and Ktrans(Day 40-Tx), were significant metrics for predicting NAC and/or CRT response (P < 0.05). Figure 5 showed representative responder and nonresponder NPC patients’ MRI morphological and functional performance before, during, and after treatment. 40-Tx)

Study Biases of Clinical and MRI Exams During Therapy The pretreatment MRI examinations were conducted on average 3.1 6 1.8 days (range: 1–7 days) before chemotherapy; and 3.6 6 0.8 days (range: 3–5 days)

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Figure 1. Boxplots (a–f) show differentiation of Ktrans(Day 3-Tx), DKtrans(0-3), DVp(0–3), Kep(Day 3-Tx), DKep(0–3), and DVp(3–40) between responder and nonresponder patient groups by the response to two cycles of NAC. The horizontal line is a median (50th percentile) of the measured kinetic values, where the top and bottom of the box represent the 25th and 75th percentiles, respectively. Whiskers indicate the range from the largest to smallest observed data points within the 1.5 interquartile range presented by the box. From Fig. 1 we concluded that kinetic parameters change after 3 days of NAC between responder and nonresponder groups (P < 0.05), in which DKtrans(0–3) and DKep(0–3) were potential discriminative markers while Ktrans(Day 3-Tx), Kep(Day 3-Tx), Dvp(0–3), and Dvp(3–40) values showed slight to moderate overlaps.

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Figure 2. Graphs (a) show overall change in Ktrans, Kep, and vp values before as well as 3 days and 40 days after NAC treatment initiation. b–d: Different trends of Ktrans, Kep, and vp values before and after NAC between responders (thick dark line) and nonresponders (thin gray line) patient groupings by the respective response to two NAC cycles.

for Day 3-Tx examinations and 42 6 2.7 days (range: 39–45 days) for Day 40-Tx examinations after the initiation of chemotherapy. Post-Tx scans were performed at 2.4 6 1.8 days (range: 3 days prior 4 days after completion of CRT treatment). However, the mild skewing of Pre-Tx, Day 3-Tx, Day 40-Tx, and Post-Tx MRI scans for responder and nonresponder groups showed no significant difference (P > 0.20). Thus it was assumed that these diverse results for MR scans at every given timepoint were equivalent and acceptable, allowing for effective response of the primary tumor to CRT. Kinetic parameters derived from primary masses did not show substantial changes within every given MRI scan timepoint.

The treatment continued to have a few biases among our cohorts between responder and nonresponder groups. These included stage, sex, age, regimen, and cycles of NAC, with or without implementing concurrent chemotherapy during radiation therapy. However, they maintained a general balance between different groups.

DISCUSSION This study focused on the early response to chemotherapy within a week of NPC. Interestingly, the results demonstrate that after two NAC cycles, most

Assessing NPC Chemoradiotherapy by DCE-MRI

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Figure 3. Boxplots show differentiation of Ktrans(Day 3-Tx), Ktrans(Day 40-Tx), and DKtrans(0–3) values between responder and nonresponder patient groups by the response to definite CRT (b–d). Differentiation of the tumor shrinkage ratios after two NAC cycles were presented by RECIST 1.1 criteria (a). The horizontal line is a median (50th percentile) of the measured kinetic values; the top and bottom of the box represent 25th and 75th percentiles, respectively. Whiskers indicate the range from the largest to smallest observed data points within the 1.5 interquartile range presented by the box. From Fig. 3, we found that a response to NAC was able to show patients earlier who may have residual disease after CRT (a). The kinetic parameter Ktrans value change after 3 and 40 days of NAC differed between responder and nonresponder groups (P < 0.05), in which DKtrans(0–3) were potential markers to discriminate residual patients from the complete response group patients. Although Ktrans(Day 3-Tx) values had moderate overlaps between responder and nonresponder groups after two NAC cycles, potential markers discriminated residual patients from the complete response group patients after CRT.

patients had decreases in tumor diameter and volume; however, the percentage decrease varied widely. We found that patients with residual disease after aggressive CRT presented with significantly lower response ratios at the end of two NAC cycles. This suggests that the patients who have higher sensitivity to chemotherapeutic agents may have earlier predicted short-term control of CRT, in accordance with

our recent retrospective study (25). Tumor regression was chosen as a short-term endpoint in our study because it has been shown to correlate with both local control and outcomes (26,27). This study investigated the ability of 3.0T DCE-MRI for early assessment of treatment response to NAC and CRT in NPC. We discovered that kinetic parameters changed earlier than morphological changes

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Table 4 Differences in Response After Chemoradiotherapy Parameters trans

K

Residual

N

Mean 6 SD (min1)

T/U*

P value

Yes No Yes No Yes No Yes No Yes No

6 20 6 20 6 20 6 20 6 20

0.490 6 0.125 0.450 6 0.164 0.590 6 0.208 0.417 6 0.173 0.350 6 0.098 0.264 6 0.087 0.100 6 0.121 0.033 6 0.143 0.140 6 0.041 0.186 6 0.183

0.56

0.578

2.05

0.052

2.06

0.050

2.05 * 1.05

0.052 0.023 0.584

(Pre-Tx)

Ktrans(Day

3-Tx)

Ktrans(Day

40-Tx)

DKtrans(0–3) DKtrans(0–40)

*Result from Mann-Whitney U test analysis.

during the aggressive CRT of NPC. The Ktrans and Kep values of primary tumor in the responder group presented significant decreases as early as 60 hours after NAC initiation and with a slight reverse at the end of NAC. In comparison, the patients responding poorly to chemotherapy agents (nonresponder group) showed either increases or immobility of Ktrans and Kep during the NAC process. The Ktrans(Day 3-Tx) and Kep(Day 3-Tx) values in the responder group were significantly lower than the nonresponder group; in contrast, significantly larger DKtrans(0–3), DKep(0–3), and Dvp(0–3) values were detected. These findings are in agreement with some prior studies showing that kinetic parameters that decreased earlier in therapy may be valuable indicators, resulting in better responses to chemoradiotherapy regimens. A recent study conducted by Powell et al (9) showed that seven out of nine patients had complete metabolic responses after two induction chemotherapy (IC) cycles on 18F-FDG PET/CT, in which DCE-MRI showed a significant fall in Ktrans and DW-MRI showed a rise in the ADC value following IC. There is a widely accepted theory that tumors with poor blood supply will lead to chronic hypoxia of tumor cells, thereby promoting the transfer of tumor cells into subtypes with more resistance to chemotherapy and radiation regimens. Tumors with a higher level of perfusion and permeability are likely to be better oxygenated and therefore more sensitive to radiation; they will also benefit from a higher concentration of cisplatin within the tumor, leading to better regi-

men efficiency. Hence, they have a better prognosis than hypoxic tumors. DCE-MRI could enable the quantitative assessment of tumor microcirculation properties: vessel size distribution, hyperpermeability, flow heterogeneity, and spatial distribution, and possibly endothelial biomarker upregulation (28) and hypoxia gene expression (29). Jansen et al (30) reported that the standard deviation of Ktrans derived from DCE-MRI and the mean standard uptake value (SUV) derived from 18F-FDG PET-CT were significant predictors of a short-term response in HNSCC. Recently, DCE-MRI has been proven to be able to detect tumor hypoxia in vivo (31). A study based on a xenograft model reported that pretreatment Ktrans values derived from kinetic model analysis were suppressed by combined irinotecan with cetuximab (an anti-epidermal growth factor receptor) therapy after 3 days initiation in orthotopic pancreatic tumor xenografts. The Ktrans changes in the peripheral tumor region after 3 days of therapy were linearly correlated with 21-day decreases in tumor volume (P < 0.001) (32). Many other studies probed the relationship between kinetic parameters and tumor hypoxic status by using experimental tumor models. Some researchers found that Ktrans values were lower in hypoxic tumors than those in nonhypoxic tumors (31), and nonhypoxic tumors were found to be significantly higher in sensitivity to radiation than hypoxic tumors (33). This study investigated early changes of kinetic parameters within a week after chemotherapy (NAC).

Table 5 Diagnostic Efficiency of Kinetic Parameters in Differentiating Responders From Nonresponders After NAC or CRT

NAC

CRT

Parameters

Positive state

Cutoff value (min-1)*

Sensitivity

Specificity

K (Day 3-Tx) Kep(Day 3-Tx) DKtrans(0–3) DKep(0–3) Dvp(0–3) Dvp(3–40) Shrinking Ratio (%) Ktrans(Day3-Tx) Ktrans(Day40-Tx) DKtrans(0–3)

SD SD PRþCR PRþCR PRþCR SD CR CR CR PR

0.394 0.552 0.045 0.007 0.021 0.003 30.54 0.478 0.293 0.094

78.6 85.7 77.8 74.1 77.8 75.0 75.0 83.3 83.3 90.0

63.0 59.3 71.4 71.4 57.1 72.2 50.0 75.0 60.0 84.3

tras

Area under the curve (95% CI*) 0.700 0.725 0.765 0.705 0.693 0.750 0.829 0.746 0.708 0.880

(0.518, 0.882) (0.555, 0.895) (0.580, 0.949) (0.507, 0.903) (0.504,0.883) (0.522,0.978) (0.667,0.991) (0.484, 1.000) (0.484, 0.933) (0.572, 1.000)

P value 0.038 0.019 0.006 0.033 0.045 0.046 0.016 0.073 0.128 0.028

*Unit of Ktrans and Kep kinetic parameters and their mathematical difference. NAC, neoadjuvant chemotherapy; CRT, chemoradiotherapy; CI, confidence interval; SD, stable disease; PR, partial response; CR, completed response.

Assessing NPC Chemoradiotherapy by DCE-MRI

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Figure 4. The diagnostic accuracy of different kinetic parameters (ROC, a–f) in predicting NAC or CRT of the NPC are displayed. Curve (a) shows the diagnostic accuracy of pretreatment Ktrans(Day 3-Tx) (blue) and Kep(Day 3-Tx) (green) value; curve (b) shows the diagnostic accuracy of a change of kinetic parameters between pretreatment and 3 days after NAC initiation (DKtrans(0–3), blue; DKep(0–3), green; D vp(0–3), red); curve (c) shows the diagnostic accuracy of a change of kinetic parameters between pretreatment and 40 days after NAC (Dvp(0–40), blue) between responders and nonresponders after two NAC cycles. They had similar diagnostic accuracy to discriminate between responders and nonresponders at the end of NAC. Curve (d) shows the diagnostic accuracy of the shrinkage ratio after two NAC cycles (blue); curve (e) shows the diagnostic accuracy of Ktrans(Day 3-Tx) (blue) and Ktrans(Day 40-Tx) (green) values; curve (f) shows the diagnostic accuracy of DKtrans(0–3) (blue). The DKtrans(0–3) value had higher sensitivity and specificity than Ktrans(Day 3-Tx) and Ktrans(Day 40-Tx) values to discriminate between responders and nonresponders at the end of CRT.

Our results are promising, as they imply that Ktrans and Kep may be considered direct measure markers of NAC efficiency. The Ktrans and Kep values changed early in the 3 days after therapy initiation. These results may have potential value in predicting responses to chemotherapy agents. Patients showing significant decreases in these parameters within a week after therapy initiation may be predicted to have a substantial shrinkage of tumor diameter and volume after two or more NAC cycles. Our primary result suggests that the response after two NAC cycles is a valuable timepoint to choose patients who would respond well to CRT. And kinetic parameters (ie, Ktrans value) may also be a potential approach for predicting CRT response. We found that the responder group presented with significantly lower Ktrans(Day 3-Tx) and Ktrans(Day 40-Tx) values than the nonresponder group at the end of CRT, while the Ktrans(Pre-Tx) was not between the two groups. For the latter, a larger cohort study is still warranted to validate present study findings to determine whether a higher pretreatment Ktrans value could be a valuable

predictor to correlate with a better chemoradiotherapy response in NPC patients. Chikui et al (34) reported that both the increase of the ve and the elevation of permeability Ktrans values indicated a good tumor response to CRT based on histological evaluation after CRT in oral cancer. Similar results have been shown recently (35). Although Gu et al (36) reported in their rectal cancer study that neither Ktrans or ADC values at baseline nor their corresponding changes after 2 weeks of CRT were valuable to differentiate between responders and nonresponders, their study was small in size (n ¼ 8). Accurate measurement of ve has been proven to be clinically important in assessing tumor response to treatment (34). However, we could not find an obvious change of ve in the early stages of therapy. The ve in our study was relatively high compared to that reported in the literature (12). Several possible factors may lead to overestimation of ve. Skinner et al (37) hypothesized that the greatest effects were differences in contrast agent concentration dynamics between well-vascularized and necrotic tumor regions.

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Zheng et al.

Figure 5. Images in each row are representative images from four different timepoints before and during aggressive CRT (row A ¼ baseline; row B ¼ 3 days after NAC initiation; row C ¼ at the end of two NAC cycles; row D ¼ at the end of CRT) from a nonresponder patient (T4N1M0, a) and responder patient (T4N3M0, b). The images of the central section of the primary tumor from T2WI are presented to show volume changes after two NAC cycles and at the end of CRT in comparison with the baseline. Corresponding kinetic parameters (Ktrans and Kep maps and ROI-basis values) of the primary tumor are presented to show displayed permeability changes from three given timepoints (Pre-Tx, Day 3-Tx, and Day 40-Tx). In the nonresponder patient, there was a slight change in volume (18.98%) after two NAC cycles; he was proven to have residual disease at the end of CRT (a, row D). However, a substantial change of volume was observed in the responder patient after NAC, reaching up to 40.0%, and he was proven to have CR both on MRI (b, row D) and pharyngorhinoscopy at the end of CRT. According to the ROI-based analysis of kinetic parameters (Ktrans and Kep) at pretreatment, 3 days after NAC initiation and at the end of NAC from both the nonresponder and responder, the Ktrans values from (a) and (b) were 0.46 vs. 0.47 (min1), 0.52 vs. 0.33 (min1), and 0.31 vs. 0.22 (min1), respectively. The Kep values from (a) and (b) were 0.78 vs. 0.57 (min1), 0.74 vs. 0.31 (min1), and 0.48 vs. 0.16 (min1), respectively.

According to Tofts’ latest talk, "Modelling in DCE MRI," there were two comments about high ve (38). Hence, further investigation and value analysis of ve parameters is warranted. Both pretreatment and early DCE-MRI assessment during treatment may prospectively identify patients at high risk of treatment failure. The main impetus of this study was to nontraumatically find the indicator of short-term NPC response; independent prognosis factors were determined by tumor chemotherapy and radiotherapy sensitivity, which is strongly regulated by tumor hypoxic status. In this pilot study, we discovered that the Ktrans and Kep values, as well as their early changes in the NAC course, can distinguish drug-sensitive subjects from drug-insensitive ones. Moreover, Ktrans is valuable to distinguish radiationsensitive subjects from those radiation-insensitive ones. The kinetic parameters showed moderate-tohigh values to discriminate responders and nonresponders. Consequently, these parameters could be regarded as potential prognostic image biomarkers of NPC in the clinic. Further study should focus on a

larger cohort study with the same CRT regimens. In the future, pretreatment DCE-MRI data may help distinguish tumors with good prognosis from those with poor prognosis. Utilization of DCE-MRI may allow individualized treatment planning for NPC patients and may help identify at-risk patients earlier so that they can be considered for additional biological target therapy. However, this study had several limitations. First, there were differences in sample size among different groups after NAC or CRT. Thus, these differences may induce a statistical bias in a small sample study. The estimation of a Ktrans value demarcation point in a small sample study is far from standard clinical practice. Further investigation using larger cohorts may improve the statistical power. Second, in order to employ DCE-MRI in the head and neck region, some challenges must be overcome, such as random motion, especially in children, the elderly, or other special groups who cannot remain immobile for the examination. Finally, as high temporal resolution is required after DCE-MRI processing in order to obtain

Assessing NPC Chemoradiotherapy by DCE-MRI

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