Breast Cancer DOI 10.1007/s12282-013-0504-0
ORIGINAL ARTICLE
Radiation exposure during sentinel lymph node biopsy for breast cancer: effect on pregnant female physicians Fuyo Kimura • Mana Yoshimura • Kiyoshi Koizumi Hiroshi Kaise • Kimito Yamada • Ai Ueda • Norio Kohno
•
Received: 5 July 2013 / Accepted: 17 October 2013 Ó The Japanese Breast Cancer Society 2013
Abstract Background The radionuclide (RN) method employed for sentinel lymph node biopsy is generally safe for adult medical care workers. However, the number of pregnant medical care workers who attend surgery has recently been increasing, along with the increasing number of female surgeons. In particular, female surgeons are concerned about the position of a surgeon’s lower abdominal region being close to the RN injection site. We measured the exposure dose of the lower abdominal region in medical care workers and investigated the possible exposure effect on fetuses. Methods A dose of 99mTc-phytic acid (37 MBq) was subcutaneously injected into the areola of the nipple of patients. Scintigraphy and surgery were performed after 1
and 4 h, respectively. At the time of the local injection, a personal dosimeter measured the exposure dose in the surgeon, first and second assistants, anesthesiologist, and scrub nurse. Results The median exposure doses were 3, 1, 1, 0, and 0 lSv in the surgeon, first and second assistants, anesthesiologist, and scrub nurse, respectively. Protective clothing reduced the mean exposure dose by 66 %. Conclusions In surgeons, the exposure dose from daily life activities (1 mSv/year) corresponds to the dose received after performing 333 surgeries (using 3 lSv as the median). However, the maximum value measured was 24 lSv; at this value, the total exposure dose exceeds 1 mSV in the 42nd surgery. Medical care workers can further reduce their exposure dose by paying attention to the surgical procedure and to their posture and position.
F. Kimura (&) H. Kaise K. Yamada A. Ueda N. Kohno Department of Breast Oncology, Tokyo Medical University Hospital, 6-7-1 Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan e-mail: [email protected]
Keywords Sentinel lymph node biopsy Exposure dose Pregnant medical care workers
H. Kaise e-mail: [email protected]
Introduction
K. Yamada e-mail: [email protected]
Performing a sentinel lymph node biopsy eliminates the need for lymph node dissection in patients judged as being negative for axillary lymph node metastasis [1]. Test methods include the radionuclide (RN) method, the dye method (using a dye such as indigo carmine or indocyanine green), or a combination of these. The results of studies comparing the dye and combination methods have demonstrated that the two methods are equivalent [2]. However, in other studies, the identification rate and falsenegative rate of the combination method were superior to those of the dye method alone [3, 4]. In one report, only dye or only RN was incorporated into the sentinel lymph
A. Ueda e-mail: [email protected] N. Kohno e-mail: [email protected] M. Yoshimura K. Koizumi Department of Radiology, Tokyo Medical University Hospital, Tokyo, Japan e-mail: [email protected] K. Koizumi e-mail: [email protected]
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node at a rate of approximately 10 % in the combination method [5]. Based on these findings, the combination method is recommended. The safety of the RN method for breast cancer during pregnancy has previously been discussed. With the recent advancement of a woman’s age at childbirth, the incidence of breast cancer accompanying pregnancy has increased. The uterine-absorbed dose during sentinel lymph node biopsy in breast cancer patients has previously been reported as ranging from 1.67 lGy to 4.3 mGy, which shows a marked variation. However, studies have confirmed the safety of the RN method employed for sentinel lymph node biopsy for pregnant breast cancer patients [6– 8]. In previous reports on the safety for medical care workers, the absorbed dose rate to a surgeon’s trunk was 8–13.3 lSv/h when 41.1–46 MBq of 99mTc was used, thereby confirming its safety [9, 10]. However, with the recent increase in the number of female surgeons, the occasions of pregnant female surgeons performing surgery have increased. In the case of an early pregnancy, a surgeon could operate without being aware of her pregnancy. As the position of the surgeon’s lower abdominal region is close to the RN injection site during a sentinel lymph node biopsy, many female surgeons are concerned about the exposure effect on fetuses. We measured the exposure dose to investigate the degree of exposure effect on female surgeons.
Fig. 1 Positions of the surgeon, first and second assistants, scrub nurse, and anesthesiologist
Materials and methods
using the Aloka Curiemeter IGC-3 (Hitachi Aloka Medical, Ltd., Tokyo, Japan). The normal dose was controlled at 37 MBq. At the time of the local injection, the equivalent dose was measured at the abdominal surface using the Aloka MyDose (Hitachi Aloka Medical, Ltd.) personal dosimeter for the surgeon, first and second assistants, anesthesiologist, and scrub nurse (Fig. 1). The effect of protective clothing on the surgeon was also investigated. The surgeon wore protective clothing equivalent to 0.25 mm lead. Personal dosimeters were attached to the inside and outside of the protective clothing at the abdominal level. A verbal and written explanation of the study was given to the subjects and informed consent was obtained in accordance with the ethical standards of the Helsinki Declaration of 1975.
Accuracy control of the personal dosimeter
Evaluation of measured values
To prevent electrocautery noise-induced measurement errors, the absence of a noise effect was confirmed at the surgery (other than in a sentinel lymph node biopsy) before measuring the exposure dose. The ambient dose rate was also measured in our hospital facility using a personal dosimeter which was placed for 1, 2, and 24 h. Measurements were performed for 4 days, and then the means were calculated. The accuracy of the personal dosimeter was analyzed by comparing the measured value at 30 min at a site 10 cm from the source of radioactivity (i.e., 37 and 18.5 MBq in 0.5 cc of liquid) with the calculated value.
The measured values of the personal dosimeter at each standing position were analyzed using univariate analysis. Bivariate analysis was performed for the operative time and injected dose. The exposure dose was measured in 4 surgeons and compared using the Student t test at a significance level of P \ 0.05. We used JMP 9.0.0 software for the statistical analyses.
Results Accuracy control of the personal dosimeter
Measurement methods The subjects who participated in the study included 146 medical staff members involved in biopsies between June 29, 2011, and June 29, 2012. A dose of 99mTc-phytic acid was subcutaneously injected into the areola of the patient’s nipple. Scintigraphy was performed after 1 h, and surgery was carried out after 4 h. The injected dose was measured
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The dose of 37 MBq of technetium (99mTc) (0.5 cc) was determined at a 10-cm distant site after 30 min. The measured value was doubled to express it as lSv/h, and then compared with the calculated value. The dose of 37 MBq of 99mTc at 10 cm from the point source was calculated using the following formula: 0.0213 9 37/ 0.12 = 78.81 lSv/h; the measured value was 48 lSv/h.
Breast Cancer
The dose of 18.5 MBq at 10 cm from the point source was calculated as 0.0213 9 18.5/0.12 = 39.4 lSv/h; the measured value was 22 lSv/h. A slight deviation may have existed because the measured substance was not the true point source; however, the values were roughly consistent. The ambient dose rate was 0.052 lSv/h; 0.0213 (lSv m2 MBq-1 h-1) is the 1 cm dose equivalent rate of 99m Tc. Measured values by category of work The surgeon had the highest exposure dose per surgery, and the median value was 3 lSv (range 1–24 lSv). This median value was followed by 1 lSv (0–7 lSv) in the first assistant, 1 lSv (0–3 lSv) in the second assistant, 0 lSv (0–1 lSv) in the scrub nurse, and \1 lSv in the anesthesiologist. The exposure dose was least in the anesthesiologists and \1 lSv in all surgeries (Fig. 2). We also investigated the exposure dose at the time of the RN injection. However, it was 0 lSv because of the short time exposure. Measured values while wearing protective clothing For the dose-reducing effect of protective clothing, the median exposure doses on the body surface per surgery were 1 lSv inside and 4 lSv outside the protective clothing. This shows a median 66 % reduction (Fig. 3). The injected dose was 46 MBq in 1 person who had an exposure dose of 24 lSv. This amount of exposure may have
been due to the shortened distance between the surgeon’s abdominal region and the injected site resulting from an axillary dissection while the resected breast was turned over. Relationships among the operative time, dose, and surgeon No significant relationship was observed between the injected dose and the exposure dose, as the injected dose did not markedly vary between surgeries (Fig. 4a). No significant association was noted between the exposure dose and the operative time, because all surgeries had a short operative time (Fig. 4b). The exposure doses for the 4 surgeons are presented individually. Only patients who underwent a partial mastectomy with sentinel lymph node biopsy or who underwent an axillary dissection and mastectomy with sentinel lymph node biopsy were included. The surgeons’ mean exposure doses were 2.0 lSv (surgeon A), 5.8 lSv (surgeon B), 4.1 lSv (surgeon C), and 5.0 lSv (surgeon D) (Fig. 5). The exposure dose differed only in surgeon A. Among the surgeons, there was no significant difference in the mean operative time or in the injected dose. The distance of a surgeon’s abdominal region from the injection site was measured during the operation, during flap preparation, and during sentinel lymph node biopsy. The mean was then calculated. Surgeon A tended to stand away from the injection site compared with the other surgeons. To investigate whether the low value resulted from the distance from the injection site, the
Fig. 2 Exposure dose values of the surgeon, first and second assistants, scrub nurse, and anesthesiologist. The median exposure doses on the surgeon, first and second assistants, scrub nurse, and anesthesiologist are 3, 1, 1, 0, and 0 lSV, respectively
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Fig. 3 Dose-reducing effect of protective clothing. Protective clothing reduces the exposure dose by 66 %
personal dosimeters were placed at sites that were 28 and 36 cm away from the injection site. The exposure dose was measured 4 h after the 37 MBq injection. The exposure dose rate was 3 lSv/h at the 28-cm site and 1 lSv/h at the 36-cm site. The values were similar and were obtained by multiplying by the mean operative time.
Discussion Radiation exposure causes various base exchanges and single- and double-strand breaks in the DNA. It is believed that 1 Gy radiation causes 25–40 double-strand breaks (DSB) [11, 12]. Endogenous sources such as free radicals often cause this type of DNA damage, but cells effectively repair it. Eighty percent of radiation-induced DSBs are repaired within 30 min. However, some DSBs may persist unrepaired, leading to mutation, carcinogenesis, and even cell death. A high linear energy transfer (LET) radiation–induced DSB has a greater effect than a low LET-induced radiation DSB. High LET radiation causes lethal or stable rearrangement in cells, making repair difficult. 99mTc-phytic acid emits low LET radiation, and its effect on cells is small. The effect of radiation on fetuses is different from its effect on children and adults. Fetuses are readily affected by low-dose radiation. The effect varies, moreover, depending on the time during the fetal period that the exposure occurs, and the effect is irreversible.
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The effect on DNA is divided into stochastic and deterministic effects. Stochastic effects are caused by single-cell injury and induce mutation. The stochastic effect on germ-line cells becomes hereditary, and on somatic cells leads to cancerization. On the other hand, deterministic effects are caused by the injury to many cells. The deterministic effect on germ-line cells includes infertility, and on somatic cells leads to tissue and organ injury, anomaly, and abortion. There is no threshold for stochastic effects, but a threshold exists for deterministic effects. The threshold varies, depending on the timing. The lowest threshold is reportedly 100 mGy. The probability of causing no anomaly at an exposure dose lower than 100 mGy is 97 %, which is close to the risk at 0 mGy [13]. In the Ordinance on Prevention of Ionizing Radiation Hazards, the equivalent dose limit for the period between the time of a diagnosis of pregnancy and the delivery is set at 2 mSv for the abdominal surface for occupationally exposed pregnant women [14]. On the other hand, the International Commission on Radiological Protection (ICRP) specifies that the effective dose limit for a product of conception during pregnancy should not exceed approximately 1 mGy [13], with the goal of setting a limit for fetuses that is equivalent to or lower than the effective dose limit for the general public, because the fetus does not decide to be exposed to radiation, although the mother selected an occupation involving exposure to radiation. The median exposure dose in a single breast cancer surgery accompanied by sentinel lymph node biopsy was 3 lSv; using this value, the total exposure of 333 surgeries would be 1 mSv. The data were collected from the body surface; the actual exposure dose in fetuses may be lower. However, this was the median value, and the exposure dose (based on one surgery) reached a maximum of 24 lSv per surgery. The exposure dose varied among the surgeons when the differences in the operative time and the surgeons were investigated. The three factors that reduce external exposure are time, distance, and shielding. The exposure dose is inversely proportional to the square of the distance and directly proportional to the time. The exposure dose is reduced by maintaining a slight distance from the patient, rather than by shortening the time. Therefore, it is important that surgeons pay attention to their posture and position since these factors may change the exposure dose. It was difficult to detect a significant difference among the surgical procedures because only a few patients received axillary dissection. However, in the case of total mastectomy, axillary dissection while the breast is turned over may not be preferable because the surgeon’s abdominal region is close to the injection site, thereby increasing the exposure dose. We investigated the effect of protective clothing, and obtained a 66 % reduction in the exposure dose.
Breast Cancer Fig. 4 Relationships between the operative time and the exposure dose and between the exposure dose and the injected dose. There is no significant difference between the exposure dose and the operative time because the operative time is short. There is no association between the exposure dose and the injected dose because the injected dose does not markedly differ among the surgeries
the exposure dose readily changes as the distance between the surgeon’s abdominal region and the injection site changes in accordance with the surgeon’s posture and the surgical procedure. The maximum exposure was 24 lSv; at this value, the total exposure exceeds 1 mSv with the 42nd surgery. Any increase in the occupational exposure of medical staffs due to a sentinel procedure should be minimal, particularly in the case of pregnant women. If pregnant women attend the surgery, sufficient attention should be paid to the surgical procedure and their posture. Acknowledgments The authors are indebted to Associate Professor Edward Barroga of the Department of International Medical Communications of Tokyo Medical University for their editorial review of the English manuscript. Fig. 5 Differences in the exposure dose among the surgeons. Only surgeon A has a major difference in the mean exposure dose. There are no marked differences in the mean operative time or the injected dose among the surgeons. The distance between the abdominal region and the injection site is short only in surgeon A
Technetium emits an electromagnetic wave, the gamma (c) ray. Substances with a heavy specific gravity are generally used for shielding, and 10-cm-thick lead (11.3 g/cm3) attenuates c-rays to approximately 1/100 to 1/1000. In diagnostic nuclear medicine, the usefulness of protective clothing against diagnostic X-rays is reportedly low in procedures that use relatively high-energy photons, such as the positron nuclides used for positron emission tomography (PET). On the other hand, a 50 % shielding effect can be expected as a 0.25-mm lead equivalent for low-energy nuclides such as technetium [15]. Protective clothing containing no lead (which reduces its weight) has recently become available and exhibits a shielding effect comparable to the lead used in the X-ray field. However, it should be noted that the effect is insufficient in the field of diagnostic nuclear medicine [15]. The mean exposure dose of the surgeon during surgery was 3 lSv. The effective dose limit for fetuses in daily activities is 1 mSv/year, which corresponds to the total exposure a surgeon receives with 333 surgeries (using an exposure dose of 3 lSv per surgery). Using an X-ray protector could provide a dose-reducing effect. However,
Conflict of interest The authors declare no sources of financial support for this work. No funding was received for this work from any organization.
References 1. Lyman GH, Giuliano AE, Somerfield MR, Benson AB 3rd, Bodurka DC, Burstein HJ. American Society of Clinical Oncology guideline recommendations for sentinel lymph node biopsy in early-stage breast cancer. J Clin Oncol. 2005;23:7703–20. 2. Morrow M, Rademaker AW, Bethke KP, Talamonti MS, Dawes LG, Clauson J, et al. Learning sentinel node biopsy: results of a prospective randomized trial of two techniques. Surgery. 1999;126:714–20. 3. Noguchi M, Motomura K, Imoto S, Miyauchi M, Sato K, Iwata H, et al. A multicenter validation study of sentinel lymph node biopsy by the Japanese Breast Cancer Society. Breast Cancer Res Treat. 2000;63:31–40. 4. McMasters KM, Tuttle TM, Carlson DJ, Brown CM, Noves RD, Glaser RL, et al. Sentinel lymph node biopsy for breast cancer: a suitable alternative to routine axillary dissection in multi-institutional practice when optimal technique is used. J Clin Oncol. 2000;18:2560–6. 5. Goyal A, Newcombe RG, Chhabra A, Mansel RE, ALMANAC Trialists Group. Factors affecting failed localization and false negative rates of sentinel node biopsy in breast cancer—results of the ALMANAC validation phase. Breast Cancer Res Treat. 2006;99:203–8. 6. Spanheimer PM, Graham MM, Sugg SL, Weigel RJ. Measurement of uterine radiation exposure from lymphoscintigraphy
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7.
8.
9.
10. 11.
indicates safety of sentinel lymph node biopsy during pregnancy. Ann Surg Oncol. 2009;16:1143–7. Keleher A, Wendt R 3rd, Delpassand E, Stachowiak AM, Kuere HM. The safety of lymphatic mapping in pregnant breast cancer patients using Tc-99m sulfur colloid. Breast J. 2004;10:492–5. Pandit-Taskar N, Dauer LT, Montgomery L, St Germain J, Zanzonico PB, Divgi CR. Organ and fetal absorbed dose estimates from 99mTc-sulfur colloid lymphoscintigraphy and sentinel node localization in breast cancer patients. J Nucl Med. 2006;47:1202–8. Japanese Society of Nuclear Medicine. The guidelines in the proper use of radiopharmaceuticals. C. Sentinel node detection and lymphoscintigraphy. (Japanese Society of Nuclear Medicine web site) 77–94. 2001. http://www.jsnm.org/guideline/20040714. Accessed Feb 1 2013. Stratmann SL, McCarty TM, Kuhn JA. Radiation safety with breast sentinel node biopsy. Am J Surg. 1999;178:454–7. Stenerlow B, Karlsson KH, Cooper B, Rydberg B. Measurement of prompt DNA double-strand breaks in mammalian cells without
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including heat-labile sites: results for cells deficient in nonhomologous end joining. Radiat Res. 2003;159:502–10. Prise KM, Schettino G, Folkard M, Held KD. New insights on cell death from radiation exposure. Lancet Oncol. 2005;6:520–8. International Commission on Radiological Protection (ICRP). Pregnancy and medical radiation. ICRP publication no. 84. Ann ICRP. 2000;30:1–43. Japan Industrial Safety and Health Association. A commentary of the ordinance on prevention of ionizing radiation hazards. Tokyo: Sun graphics Ltd; 2011. p. 35–56. Fukuda A, Koshiba K, Yamaguchi I, Takahashi M, Kitabayashi K, Matsubara K, et al. Shielding effect of clinical X-ray protector and lead glass against annihilation radiation and gamma rays of 99mTC (in Japanese with English abstract). Nihon Hoshasen Gijutu Gakkai Zasshi. 2004;60:1723–9.
ORIGINAL ARTICLE
Radiation exposure during sentinel lymph node biopsy for breast cancer: effect on pregnant female physicians Fuyo Kimura • Mana Yoshimura • Kiyoshi Koizumi Hiroshi Kaise • Kimito Yamada • Ai Ueda • Norio Kohno
•
Received: 5 July 2013 / Accepted: 17 October 2013 Ó The Japanese Breast Cancer Society 2013
Abstract Background The radionuclide (RN) method employed for sentinel lymph node biopsy is generally safe for adult medical care workers. However, the number of pregnant medical care workers who attend surgery has recently been increasing, along with the increasing number of female surgeons. In particular, female surgeons are concerned about the position of a surgeon’s lower abdominal region being close to the RN injection site. We measured the exposure dose of the lower abdominal region in medical care workers and investigated the possible exposure effect on fetuses. Methods A dose of 99mTc-phytic acid (37 MBq) was subcutaneously injected into the areola of the nipple of patients. Scintigraphy and surgery were performed after 1
and 4 h, respectively. At the time of the local injection, a personal dosimeter measured the exposure dose in the surgeon, first and second assistants, anesthesiologist, and scrub nurse. Results The median exposure doses were 3, 1, 1, 0, and 0 lSv in the surgeon, first and second assistants, anesthesiologist, and scrub nurse, respectively. Protective clothing reduced the mean exposure dose by 66 %. Conclusions In surgeons, the exposure dose from daily life activities (1 mSv/year) corresponds to the dose received after performing 333 surgeries (using 3 lSv as the median). However, the maximum value measured was 24 lSv; at this value, the total exposure dose exceeds 1 mSV in the 42nd surgery. Medical care workers can further reduce their exposure dose by paying attention to the surgical procedure and to their posture and position.
F. Kimura (&) H. Kaise K. Yamada A. Ueda N. Kohno Department of Breast Oncology, Tokyo Medical University Hospital, 6-7-1 Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan e-mail: [email protected]
Keywords Sentinel lymph node biopsy Exposure dose Pregnant medical care workers
H. Kaise e-mail: [email protected]
Introduction
K. Yamada e-mail: [email protected]
Performing a sentinel lymph node biopsy eliminates the need for lymph node dissection in patients judged as being negative for axillary lymph node metastasis [1]. Test methods include the radionuclide (RN) method, the dye method (using a dye such as indigo carmine or indocyanine green), or a combination of these. The results of studies comparing the dye and combination methods have demonstrated that the two methods are equivalent [2]. However, in other studies, the identification rate and falsenegative rate of the combination method were superior to those of the dye method alone [3, 4]. In one report, only dye or only RN was incorporated into the sentinel lymph
A. Ueda e-mail: [email protected] N. Kohno e-mail: [email protected] M. Yoshimura K. Koizumi Department of Radiology, Tokyo Medical University Hospital, Tokyo, Japan e-mail: [email protected] K. Koizumi e-mail: [email protected]
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node at a rate of approximately 10 % in the combination method [5]. Based on these findings, the combination method is recommended. The safety of the RN method for breast cancer during pregnancy has previously been discussed. With the recent advancement of a woman’s age at childbirth, the incidence of breast cancer accompanying pregnancy has increased. The uterine-absorbed dose during sentinel lymph node biopsy in breast cancer patients has previously been reported as ranging from 1.67 lGy to 4.3 mGy, which shows a marked variation. However, studies have confirmed the safety of the RN method employed for sentinel lymph node biopsy for pregnant breast cancer patients [6– 8]. In previous reports on the safety for medical care workers, the absorbed dose rate to a surgeon’s trunk was 8–13.3 lSv/h when 41.1–46 MBq of 99mTc was used, thereby confirming its safety [9, 10]. However, with the recent increase in the number of female surgeons, the occasions of pregnant female surgeons performing surgery have increased. In the case of an early pregnancy, a surgeon could operate without being aware of her pregnancy. As the position of the surgeon’s lower abdominal region is close to the RN injection site during a sentinel lymph node biopsy, many female surgeons are concerned about the exposure effect on fetuses. We measured the exposure dose to investigate the degree of exposure effect on female surgeons.
Fig. 1 Positions of the surgeon, first and second assistants, scrub nurse, and anesthesiologist
Materials and methods
using the Aloka Curiemeter IGC-3 (Hitachi Aloka Medical, Ltd., Tokyo, Japan). The normal dose was controlled at 37 MBq. At the time of the local injection, the equivalent dose was measured at the abdominal surface using the Aloka MyDose (Hitachi Aloka Medical, Ltd.) personal dosimeter for the surgeon, first and second assistants, anesthesiologist, and scrub nurse (Fig. 1). The effect of protective clothing on the surgeon was also investigated. The surgeon wore protective clothing equivalent to 0.25 mm lead. Personal dosimeters were attached to the inside and outside of the protective clothing at the abdominal level. A verbal and written explanation of the study was given to the subjects and informed consent was obtained in accordance with the ethical standards of the Helsinki Declaration of 1975.
Accuracy control of the personal dosimeter
Evaluation of measured values
To prevent electrocautery noise-induced measurement errors, the absence of a noise effect was confirmed at the surgery (other than in a sentinel lymph node biopsy) before measuring the exposure dose. The ambient dose rate was also measured in our hospital facility using a personal dosimeter which was placed for 1, 2, and 24 h. Measurements were performed for 4 days, and then the means were calculated. The accuracy of the personal dosimeter was analyzed by comparing the measured value at 30 min at a site 10 cm from the source of radioactivity (i.e., 37 and 18.5 MBq in 0.5 cc of liquid) with the calculated value.
The measured values of the personal dosimeter at each standing position were analyzed using univariate analysis. Bivariate analysis was performed for the operative time and injected dose. The exposure dose was measured in 4 surgeons and compared using the Student t test at a significance level of P \ 0.05. We used JMP 9.0.0 software for the statistical analyses.
Results Accuracy control of the personal dosimeter
Measurement methods The subjects who participated in the study included 146 medical staff members involved in biopsies between June 29, 2011, and June 29, 2012. A dose of 99mTc-phytic acid was subcutaneously injected into the areola of the patient’s nipple. Scintigraphy was performed after 1 h, and surgery was carried out after 4 h. The injected dose was measured
123
The dose of 37 MBq of technetium (99mTc) (0.5 cc) was determined at a 10-cm distant site after 30 min. The measured value was doubled to express it as lSv/h, and then compared with the calculated value. The dose of 37 MBq of 99mTc at 10 cm from the point source was calculated using the following formula: 0.0213 9 37/ 0.12 = 78.81 lSv/h; the measured value was 48 lSv/h.
Breast Cancer
The dose of 18.5 MBq at 10 cm from the point source was calculated as 0.0213 9 18.5/0.12 = 39.4 lSv/h; the measured value was 22 lSv/h. A slight deviation may have existed because the measured substance was not the true point source; however, the values were roughly consistent. The ambient dose rate was 0.052 lSv/h; 0.0213 (lSv m2 MBq-1 h-1) is the 1 cm dose equivalent rate of 99m Tc. Measured values by category of work The surgeon had the highest exposure dose per surgery, and the median value was 3 lSv (range 1–24 lSv). This median value was followed by 1 lSv (0–7 lSv) in the first assistant, 1 lSv (0–3 lSv) in the second assistant, 0 lSv (0–1 lSv) in the scrub nurse, and \1 lSv in the anesthesiologist. The exposure dose was least in the anesthesiologists and \1 lSv in all surgeries (Fig. 2). We also investigated the exposure dose at the time of the RN injection. However, it was 0 lSv because of the short time exposure. Measured values while wearing protective clothing For the dose-reducing effect of protective clothing, the median exposure doses on the body surface per surgery were 1 lSv inside and 4 lSv outside the protective clothing. This shows a median 66 % reduction (Fig. 3). The injected dose was 46 MBq in 1 person who had an exposure dose of 24 lSv. This amount of exposure may have
been due to the shortened distance between the surgeon’s abdominal region and the injected site resulting from an axillary dissection while the resected breast was turned over. Relationships among the operative time, dose, and surgeon No significant relationship was observed between the injected dose and the exposure dose, as the injected dose did not markedly vary between surgeries (Fig. 4a). No significant association was noted between the exposure dose and the operative time, because all surgeries had a short operative time (Fig. 4b). The exposure doses for the 4 surgeons are presented individually. Only patients who underwent a partial mastectomy with sentinel lymph node biopsy or who underwent an axillary dissection and mastectomy with sentinel lymph node biopsy were included. The surgeons’ mean exposure doses were 2.0 lSv (surgeon A), 5.8 lSv (surgeon B), 4.1 lSv (surgeon C), and 5.0 lSv (surgeon D) (Fig. 5). The exposure dose differed only in surgeon A. Among the surgeons, there was no significant difference in the mean operative time or in the injected dose. The distance of a surgeon’s abdominal region from the injection site was measured during the operation, during flap preparation, and during sentinel lymph node biopsy. The mean was then calculated. Surgeon A tended to stand away from the injection site compared with the other surgeons. To investigate whether the low value resulted from the distance from the injection site, the
Fig. 2 Exposure dose values of the surgeon, first and second assistants, scrub nurse, and anesthesiologist. The median exposure doses on the surgeon, first and second assistants, scrub nurse, and anesthesiologist are 3, 1, 1, 0, and 0 lSV, respectively
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Fig. 3 Dose-reducing effect of protective clothing. Protective clothing reduces the exposure dose by 66 %
personal dosimeters were placed at sites that were 28 and 36 cm away from the injection site. The exposure dose was measured 4 h after the 37 MBq injection. The exposure dose rate was 3 lSv/h at the 28-cm site and 1 lSv/h at the 36-cm site. The values were similar and were obtained by multiplying by the mean operative time.
Discussion Radiation exposure causes various base exchanges and single- and double-strand breaks in the DNA. It is believed that 1 Gy radiation causes 25–40 double-strand breaks (DSB) [11, 12]. Endogenous sources such as free radicals often cause this type of DNA damage, but cells effectively repair it. Eighty percent of radiation-induced DSBs are repaired within 30 min. However, some DSBs may persist unrepaired, leading to mutation, carcinogenesis, and even cell death. A high linear energy transfer (LET) radiation–induced DSB has a greater effect than a low LET-induced radiation DSB. High LET radiation causes lethal or stable rearrangement in cells, making repair difficult. 99mTc-phytic acid emits low LET radiation, and its effect on cells is small. The effect of radiation on fetuses is different from its effect on children and adults. Fetuses are readily affected by low-dose radiation. The effect varies, moreover, depending on the time during the fetal period that the exposure occurs, and the effect is irreversible.
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The effect on DNA is divided into stochastic and deterministic effects. Stochastic effects are caused by single-cell injury and induce mutation. The stochastic effect on germ-line cells becomes hereditary, and on somatic cells leads to cancerization. On the other hand, deterministic effects are caused by the injury to many cells. The deterministic effect on germ-line cells includes infertility, and on somatic cells leads to tissue and organ injury, anomaly, and abortion. There is no threshold for stochastic effects, but a threshold exists for deterministic effects. The threshold varies, depending on the timing. The lowest threshold is reportedly 100 mGy. The probability of causing no anomaly at an exposure dose lower than 100 mGy is 97 %, which is close to the risk at 0 mGy [13]. In the Ordinance on Prevention of Ionizing Radiation Hazards, the equivalent dose limit for the period between the time of a diagnosis of pregnancy and the delivery is set at 2 mSv for the abdominal surface for occupationally exposed pregnant women [14]. On the other hand, the International Commission on Radiological Protection (ICRP) specifies that the effective dose limit for a product of conception during pregnancy should not exceed approximately 1 mGy [13], with the goal of setting a limit for fetuses that is equivalent to or lower than the effective dose limit for the general public, because the fetus does not decide to be exposed to radiation, although the mother selected an occupation involving exposure to radiation. The median exposure dose in a single breast cancer surgery accompanied by sentinel lymph node biopsy was 3 lSv; using this value, the total exposure of 333 surgeries would be 1 mSv. The data were collected from the body surface; the actual exposure dose in fetuses may be lower. However, this was the median value, and the exposure dose (based on one surgery) reached a maximum of 24 lSv per surgery. The exposure dose varied among the surgeons when the differences in the operative time and the surgeons were investigated. The three factors that reduce external exposure are time, distance, and shielding. The exposure dose is inversely proportional to the square of the distance and directly proportional to the time. The exposure dose is reduced by maintaining a slight distance from the patient, rather than by shortening the time. Therefore, it is important that surgeons pay attention to their posture and position since these factors may change the exposure dose. It was difficult to detect a significant difference among the surgical procedures because only a few patients received axillary dissection. However, in the case of total mastectomy, axillary dissection while the breast is turned over may not be preferable because the surgeon’s abdominal region is close to the injection site, thereby increasing the exposure dose. We investigated the effect of protective clothing, and obtained a 66 % reduction in the exposure dose.
Breast Cancer Fig. 4 Relationships between the operative time and the exposure dose and between the exposure dose and the injected dose. There is no significant difference between the exposure dose and the operative time because the operative time is short. There is no association between the exposure dose and the injected dose because the injected dose does not markedly differ among the surgeries
the exposure dose readily changes as the distance between the surgeon’s abdominal region and the injection site changes in accordance with the surgeon’s posture and the surgical procedure. The maximum exposure was 24 lSv; at this value, the total exposure exceeds 1 mSv with the 42nd surgery. Any increase in the occupational exposure of medical staffs due to a sentinel procedure should be minimal, particularly in the case of pregnant women. If pregnant women attend the surgery, sufficient attention should be paid to the surgical procedure and their posture. Acknowledgments The authors are indebted to Associate Professor Edward Barroga of the Department of International Medical Communications of Tokyo Medical University for their editorial review of the English manuscript. Fig. 5 Differences in the exposure dose among the surgeons. Only surgeon A has a major difference in the mean exposure dose. There are no marked differences in the mean operative time or the injected dose among the surgeons. The distance between the abdominal region and the injection site is short only in surgeon A
Technetium emits an electromagnetic wave, the gamma (c) ray. Substances with a heavy specific gravity are generally used for shielding, and 10-cm-thick lead (11.3 g/cm3) attenuates c-rays to approximately 1/100 to 1/1000. In diagnostic nuclear medicine, the usefulness of protective clothing against diagnostic X-rays is reportedly low in procedures that use relatively high-energy photons, such as the positron nuclides used for positron emission tomography (PET). On the other hand, a 50 % shielding effect can be expected as a 0.25-mm lead equivalent for low-energy nuclides such as technetium [15]. Protective clothing containing no lead (which reduces its weight) has recently become available and exhibits a shielding effect comparable to the lead used in the X-ray field. However, it should be noted that the effect is insufficient in the field of diagnostic nuclear medicine [15]. The mean exposure dose of the surgeon during surgery was 3 lSv. The effective dose limit for fetuses in daily activities is 1 mSv/year, which corresponds to the total exposure a surgeon receives with 333 surgeries (using an exposure dose of 3 lSv per surgery). Using an X-ray protector could provide a dose-reducing effect. However,
Conflict of interest The authors declare no sources of financial support for this work. No funding was received for this work from any organization.
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