Radiation Protection Dosimetry (2014), Vol. 159, No. 1–4, pp. 137 –140 Advance Access publication 29 May 2014
doi:10.1093/rpd/ncu170
APPLICABILITY OF EPR/ALANINE DOSIMETRY FOR QUALITY ASSURANCE IN PROTON EYE RADIOTHERAPY B. Michalec1, *, G. Mierzwinska1, M. Ptaszkiewicz1, U. Sowa1, L. Stolarczyk1 and A. Weber2 1 The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, ul. Radzikowskiego 152, 31-342 Krakow, Poland 2 Charite´ - Universita¨tsmedizin Berlin, Department of Ophthalmology CBF, BerlinProtonen am HelmholtzZentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany *Corresponding author: [email protected]
INTRODUCTION Proton ocular radiotherapy is an effective method of eye cancer, mainly uveal melanoma, treatment. This kind of radiation therapy is an attractive alternative for enucleation and plaque therapy (brachytherapy). It is aimed at destroying the primary tumour while conserving the eye, often with useful vision(1). As in each kind of radiation therapy, the precise determination of the therapeutic depth dose distribution is a necessary condition for successful use of the method in the clinical practice. Nowadays, the clinical proton dosimetry is mainly based on ionisation chambers. The proton dosimetry protocol TRS 398 also provides ionisation chamber dosimetry, based on calibration in a 60Co beam in terms of absorbed dose to water(2). The extended uncertainty for the primary dosimetry in radiotherapy should not exceed 5 %. This condition, extremely difficult to fulfil by passive dosemeters, can be easily reached with ionisation chambers. Moreover, ionisation chambers, as active dosemeters, are on-line proton beam monitors and their signal is used to stop the proton beam when the fraction dose has been already delivered to the target volume. On the other hand, the current signal from the ionisation chamber is registered only in a digital form; hence, there is no physical record of the delivered dose. Therefore, there is no possibility to reproduce or repeat the dose measurement after irradiation, which could be crucial in some doubtful situations. Electron paramagnetic resonance (EPR)/alanine dosimetry used as one of the quality assurance (QA) or/and quality control (QC) methods during proton irradiation is a potential tool for recording the patient dose in its physical form as stable radiation-induced radicals trapped in the crystal structure of alanine. The concentration of these radicals, proportional to
the absorbed dose over a therapeutic range of doses, can be estimated quantitatively using EPR spectrometry. Various properties of alanine as a dosimetric tool have previously been reported: tissue equivalence(3), independence on environmental agents, except for high humidity and intense light exposure(4), signal stability meant as low fading(3) and non-destructive read-out(5). The last feature enables the registration both fractional and cumulative (total) dose with the same detector. It also makes the repeating of the dose read-out possible. This paper describes the implementation of the patient QA system based on EPR/alanine dosimetry at the facility for proton eye radiotherapy at the Institute of Nuclear Physics (IFJ PAN) in Krakow (Poland). MATERIAL AND METHODS Alanine detectors In the study, the commercially available pellet-shaped detectors (4.8 mm in diameter, 3.0 mm height), consisting of 96 % alanine and 4 % binder by weight made by Synergy Health (former name Gamma Service), were used. Irradiations Irradiations of the detectors were performed at IFJ PAN, at the facility for eye cancer treatment, by proton beam from the AIC-144 cyclotron as well as at the ‘twin’ facility of the Charite´ at Helmholtz-Zentrum Berlin (HZB). Irradiations were performed in the therapy regime. Detectors used for QA measurements could not disturb the depth dose distribution delivered to the tumour volume. Detectors were then placed in beam but not in the tract, on the inner side of the final,
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at Dalhousie University on June 20, 2015
A new quality assurance and quality control method for proton eye radiotherapy based on electron paramagnetic resonance (EPR)/alanine dosimetry has been developed. It is based on Spread-Out Bragg Peak entrance dose measurement with alanine detectors. The entrance dose is well correlated with the dose at the facility isocenter, where, during the therapeutic irradiation, the tumour is placed. The unique alanine detector features namely keeping the dose record in a form of stable radiation-induced free radicals trapped in the material structure, and the non-destructive read-out makes this type of detector a good candidate for additional documentation of the patient’s exposure over the therapy course.
B. MICHALEC ET AL.
beam-forming, collimator. Three alanine pellets were collocated on the collimator’s circuit at 1208. They registered the entrance dose, which is correlated with the dose delivered to the isocenter of the facility, where the centre of a tumour irradiated in the SpreadOut Bragg Peak (SOBP) is placed. At IFJ PAN facility, alanine detectors were irradiated with an entrance dose in four different SOBPs (Figure 1) characterised by following parameters:
The facility was calibrated for the dose of 15 CGE (Cobalt Grey Equivalent) at the facility isocenter in each of four cases. During irradiation of alanine pellets with entrance dose at the collimator, another three alanine detectors were also placed at the isocenter for dose delivery control as well as for comparison between the ‘alanine dose’ and ‘ionisation chamber dose’. At HZB facility, detectors were irradiated with an entrance dose in three different SOBPs characterised by the following parameters: (1) modulation 10 mm, range 31 mm, (2) modulation 15 mm, range 31 mm, (3) modulation 31 mm, range 31 mm. The facility was calibrated for the dose 15 Gy at the facility isocenter in each case. There was no alanine pellets placed at the isocenter during irradiation (therapeutic conditions). EPR measurements and dose read-out EPR measurements were performed using the Bruker ESP 300 spectrometer, at IFJ PAN. Alanine read-out
Figure 1. SOBPs used for irradiations of alanine detectors. Squares, RM010; plus symbols, RM005; circles, RM021; triangles, RM029.
RESULTS AND DISSCUSSION Detectors used for patient QA cannot in any case disturb the therapeutic depth dose distribution. The influence of placing alanine pellets at the reverse side of patient collimator during dose to tumour delivery was investigated with 2D TL detectors. The dose distribution at the plane of isocenter was measured with and without detectors at collimator (Figure 2). No significant difference between the dose distribution registered in the presence and in the absence of alanine pellets was found. Doses measured with alanine pellets at the IFJ PAN facility isocenter demonstrated compatibility with transmission chamber dose (on-line dose measurements in the therapy mode) within 0.3–2.6 %. The entrance dose, averaged of three detectors, registered for specified modulation widths with alanine pellets shows the linear correlation with modulation value at both facilities—IFJ PAN and HZB (Figure 3). Clearly visible shift between the line for IFJ PAN facility and HZB facility reflects differences in facility calibration doses—15 CGE at IFJ PAN and 15 Gy at HZB. Figure 4 shows the dependence between entrance dose/isocenter dose ratio and modulation width. The dependence is also linear. Considering the uncertainties, it is the same for both facilities. This relation enables the determination of the dose delivered to the tumour knowing the entrance dose registered with alanine pellets (Equation 1).
Figure 2. Dose distribution at the plane of the facility isocenter without (A) and with (B) alanine pellets at the inner side of final collimator.
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(1) modulation 10 mm, range 29.3 mm [SOBP produced be range modulator no. 10 (RM010)], (2) modulation 15 mm, range 29.3 mm (RM021), (3) modulation 21.8 mm, range 29.3 mm (RM029), (4) modulation 29.3 mm, range 29.3 mm (RM005).
parameters were as follows: microwave power 7.93 mW, modulation amplitude 9.77 G, modulation frequency 100 kHz, receiver gain 2` 104, time constant 327.68 ms, conversion time 20.48 ms, magnetic field resolution 1024 points. Each measurement was performed in accumulating mode, with three sample scans to improve the signal-to-noise ratio. The alanine spectrum consists of five spectral lines, and the peak-to-peak amplitude of the central line is considered to be the dosimetric signal(6). The dose is estimated from the calibration curve. Its construction has been previously described(7).
EPR/ALANINE DOSIMETRY FOR QUALITY ASSURANCE
ACKNOWLEDGEMENTS This work was done as a part of the project, ‘EPR/ alanine dosimetry for radiotherapeutic ion beams’, carried out in the frames of the PARENT—BRIDGE Program. FUNDING
Figure 4. Entrance dose—isocenter dose ratio vs. modulation width for circles, IFJ PAN facility (solid line); diamond HZB facility (dashed line).
This study was supported by the Foundation for the Polish Science, co-financed from EU structural funds under Action 1.2 ‘Strengthening the human resources potential of science’ of the Innovative Economy Operational Program 2007–13. REFERENCES
1
Diso ¼ Dentr ð0:027 M þ 0:26Þ
ð1Þ
where D iso, dose estimated at the isocenter; D entr, entrance dose registered at the collimator; M, modulation. CONCLUSIONS AND FUTURE PERSPECTIVES In this study, the authors confirmed the applicability of EPR/alanine dosimetry as a potential element of the QC and QA system of patient in proton radiotherapy. The entrance dose registered with alanine pellets is well correlated with the dose delivered to the isocenter and depends on SOBP modulation width. Alanine detectors placed on the reverse side of patient collimator do not disturb the depth dose distribution, and they can be used as additional documentation of the patient’s exposure over the therapy course. As EPR read-out of the stable radiation-induced free-radical
1. Damato, B., Kacperek, A., Chopra, M. and Errington, R. D. Proton beam radiotherapy of choroidal melanoma: the Liverpool – Clatterbridge experience. Int. J. Radiat. Oncol. Biol. Phys. 62(5), 1405– 1411 (2005). 2. International Atomic Energy Agency. Absorbed dose determination in external beam radiotherapy. An international code of practice for dosimetry based on standards of absorbed dose to water. Technical Reports Series No. 398 (2000). 3. Schauer, D. A., Iwasaki, A., Romanyukha, A. A., Swartz, H. M. and Onori, S. Electron paramagnetic resonance (EPR) in medical dosimetry. Radiat. Measur. 41, 117–123 (2007). 4. Peimel-Stuglik, Z. and Fabisiak, S. Use of alanine-EPR dosimeter for measurements of absorbed doses in range 0.5– 10 kGy applied in food irradiation (in Polish). Raporty ICHTJ Seria B nr 10/2001 (2001). 5. Ciesielski, B., Schultka, K., Kobierska, A., Nowak, R. and Peimel-Stuglik, Z. In vivo alanine/EPR dosimetry in daily clinical practice: a feasibility study. Int. J. Radiat. Oncol. Biol. Phys. 56(3), 899–905 (2003). 6. ISO/ASTM International. Practice for use of alanine-EPR dosimetry system. ISO/ASTM 51607:2004(E) (2004).
139
Downloaded from http://rpd.oxfordjournals.org/ at Dalhousie University on June 20, 2015
Figure 3. The entrance dose registered by alanine detectors vs. modulation width. Circles, IFJ PAN facility (solid line); diamond HZB facility (dashed line).
signal does not destroy it, it is possible to control the dose accumulated in the alanine detector by its consecutive irradiation. Keeping in mind that SOBP fields are formed by the superposition of multiple, successively range-shifted, and individually weighted pristine Bragg peaks, also these with low energies, the authors have not observed in this study any effects that could be connected with widely reported decrease in relative effectiveness of alanine for proton energies of ,10 MeV.(7 – 9) Before the implementation of this QA/QC system, it is going to be tested also for different proton ranges. Then, it is planned to be implemented at the existing facility for proton eye radiotherapy as well as at the new (still under construction) facility called Cyclotron Center Bronowice equipped with proton cyclotron Proteus 235 for treating all neoplastic sites using a 230MeV proton beam, a rotating proton gantry, and active Bragg peak spreading technique.
B. MICHALEC ET AL. 7. Michalec, B., Mierzwinska, G., Sowa, U., Nowak, T., Ptaszkiewicz, M. and Swakon, J. Alanine dosimetry of 60MeV proton beam at IFJ PAN in Krakow, Poland – preliminary results. Nukleonika 57(4), 503– 506 (2012). 8. Fattibene, P., De Angelis, C., Onori, S. and Cherubini, R. Alanine response to proton beams in the 1,6-6,1 MeV
energy range. Radiat. Protect Dosim. 101(1–4), 465–468 (2002). 9. Olsen, K. J. and Hansen, J. W. The response of the alanine dosemeter to low energy protons and high energy heavy charged particles. Radiat. Protect. Dosim. 31(1– 4), 81–84 (1990).
Downloaded from http://rpd.oxfordjournals.org/ at Dalhousie University on June 20, 2015
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doi:10.1093/rpd/ncu170
APPLICABILITY OF EPR/ALANINE DOSIMETRY FOR QUALITY ASSURANCE IN PROTON EYE RADIOTHERAPY B. Michalec1, *, G. Mierzwinska1, M. Ptaszkiewicz1, U. Sowa1, L. Stolarczyk1 and A. Weber2 1 The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, ul. Radzikowskiego 152, 31-342 Krakow, Poland 2 Charite´ - Universita¨tsmedizin Berlin, Department of Ophthalmology CBF, BerlinProtonen am HelmholtzZentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany *Corresponding author: [email protected]
INTRODUCTION Proton ocular radiotherapy is an effective method of eye cancer, mainly uveal melanoma, treatment. This kind of radiation therapy is an attractive alternative for enucleation and plaque therapy (brachytherapy). It is aimed at destroying the primary tumour while conserving the eye, often with useful vision(1). As in each kind of radiation therapy, the precise determination of the therapeutic depth dose distribution is a necessary condition for successful use of the method in the clinical practice. Nowadays, the clinical proton dosimetry is mainly based on ionisation chambers. The proton dosimetry protocol TRS 398 also provides ionisation chamber dosimetry, based on calibration in a 60Co beam in terms of absorbed dose to water(2). The extended uncertainty for the primary dosimetry in radiotherapy should not exceed 5 %. This condition, extremely difficult to fulfil by passive dosemeters, can be easily reached with ionisation chambers. Moreover, ionisation chambers, as active dosemeters, are on-line proton beam monitors and their signal is used to stop the proton beam when the fraction dose has been already delivered to the target volume. On the other hand, the current signal from the ionisation chamber is registered only in a digital form; hence, there is no physical record of the delivered dose. Therefore, there is no possibility to reproduce or repeat the dose measurement after irradiation, which could be crucial in some doubtful situations. Electron paramagnetic resonance (EPR)/alanine dosimetry used as one of the quality assurance (QA) or/and quality control (QC) methods during proton irradiation is a potential tool for recording the patient dose in its physical form as stable radiation-induced radicals trapped in the crystal structure of alanine. The concentration of these radicals, proportional to
the absorbed dose over a therapeutic range of doses, can be estimated quantitatively using EPR spectrometry. Various properties of alanine as a dosimetric tool have previously been reported: tissue equivalence(3), independence on environmental agents, except for high humidity and intense light exposure(4), signal stability meant as low fading(3) and non-destructive read-out(5). The last feature enables the registration both fractional and cumulative (total) dose with the same detector. It also makes the repeating of the dose read-out possible. This paper describes the implementation of the patient QA system based on EPR/alanine dosimetry at the facility for proton eye radiotherapy at the Institute of Nuclear Physics (IFJ PAN) in Krakow (Poland). MATERIAL AND METHODS Alanine detectors In the study, the commercially available pellet-shaped detectors (4.8 mm in diameter, 3.0 mm height), consisting of 96 % alanine and 4 % binder by weight made by Synergy Health (former name Gamma Service), were used. Irradiations Irradiations of the detectors were performed at IFJ PAN, at the facility for eye cancer treatment, by proton beam from the AIC-144 cyclotron as well as at the ‘twin’ facility of the Charite´ at Helmholtz-Zentrum Berlin (HZB). Irradiations were performed in the therapy regime. Detectors used for QA measurements could not disturb the depth dose distribution delivered to the tumour volume. Detectors were then placed in beam but not in the tract, on the inner side of the final,
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at Dalhousie University on June 20, 2015
A new quality assurance and quality control method for proton eye radiotherapy based on electron paramagnetic resonance (EPR)/alanine dosimetry has been developed. It is based on Spread-Out Bragg Peak entrance dose measurement with alanine detectors. The entrance dose is well correlated with the dose at the facility isocenter, where, during the therapeutic irradiation, the tumour is placed. The unique alanine detector features namely keeping the dose record in a form of stable radiation-induced free radicals trapped in the material structure, and the non-destructive read-out makes this type of detector a good candidate for additional documentation of the patient’s exposure over the therapy course.
B. MICHALEC ET AL.
beam-forming, collimator. Three alanine pellets were collocated on the collimator’s circuit at 1208. They registered the entrance dose, which is correlated with the dose delivered to the isocenter of the facility, where the centre of a tumour irradiated in the SpreadOut Bragg Peak (SOBP) is placed. At IFJ PAN facility, alanine detectors were irradiated with an entrance dose in four different SOBPs (Figure 1) characterised by following parameters:
The facility was calibrated for the dose of 15 CGE (Cobalt Grey Equivalent) at the facility isocenter in each of four cases. During irradiation of alanine pellets with entrance dose at the collimator, another three alanine detectors were also placed at the isocenter for dose delivery control as well as for comparison between the ‘alanine dose’ and ‘ionisation chamber dose’. At HZB facility, detectors were irradiated with an entrance dose in three different SOBPs characterised by the following parameters: (1) modulation 10 mm, range 31 mm, (2) modulation 15 mm, range 31 mm, (3) modulation 31 mm, range 31 mm. The facility was calibrated for the dose 15 Gy at the facility isocenter in each case. There was no alanine pellets placed at the isocenter during irradiation (therapeutic conditions). EPR measurements and dose read-out EPR measurements were performed using the Bruker ESP 300 spectrometer, at IFJ PAN. Alanine read-out
Figure 1. SOBPs used for irradiations of alanine detectors. Squares, RM010; plus symbols, RM005; circles, RM021; triangles, RM029.
RESULTS AND DISSCUSSION Detectors used for patient QA cannot in any case disturb the therapeutic depth dose distribution. The influence of placing alanine pellets at the reverse side of patient collimator during dose to tumour delivery was investigated with 2D TL detectors. The dose distribution at the plane of isocenter was measured with and without detectors at collimator (Figure 2). No significant difference between the dose distribution registered in the presence and in the absence of alanine pellets was found. Doses measured with alanine pellets at the IFJ PAN facility isocenter demonstrated compatibility with transmission chamber dose (on-line dose measurements in the therapy mode) within 0.3–2.6 %. The entrance dose, averaged of three detectors, registered for specified modulation widths with alanine pellets shows the linear correlation with modulation value at both facilities—IFJ PAN and HZB (Figure 3). Clearly visible shift between the line for IFJ PAN facility and HZB facility reflects differences in facility calibration doses—15 CGE at IFJ PAN and 15 Gy at HZB. Figure 4 shows the dependence between entrance dose/isocenter dose ratio and modulation width. The dependence is also linear. Considering the uncertainties, it is the same for both facilities. This relation enables the determination of the dose delivered to the tumour knowing the entrance dose registered with alanine pellets (Equation 1).
Figure 2. Dose distribution at the plane of the facility isocenter without (A) and with (B) alanine pellets at the inner side of final collimator.
138
Downloaded from http://rpd.oxfordjournals.org/ at Dalhousie University on June 20, 2015
(1) modulation 10 mm, range 29.3 mm [SOBP produced be range modulator no. 10 (RM010)], (2) modulation 15 mm, range 29.3 mm (RM021), (3) modulation 21.8 mm, range 29.3 mm (RM029), (4) modulation 29.3 mm, range 29.3 mm (RM005).
parameters were as follows: microwave power 7.93 mW, modulation amplitude 9.77 G, modulation frequency 100 kHz, receiver gain 2` 104, time constant 327.68 ms, conversion time 20.48 ms, magnetic field resolution 1024 points. Each measurement was performed in accumulating mode, with three sample scans to improve the signal-to-noise ratio. The alanine spectrum consists of five spectral lines, and the peak-to-peak amplitude of the central line is considered to be the dosimetric signal(6). The dose is estimated from the calibration curve. Its construction has been previously described(7).
EPR/ALANINE DOSIMETRY FOR QUALITY ASSURANCE
ACKNOWLEDGEMENTS This work was done as a part of the project, ‘EPR/ alanine dosimetry for radiotherapeutic ion beams’, carried out in the frames of the PARENT—BRIDGE Program. FUNDING
Figure 4. Entrance dose—isocenter dose ratio vs. modulation width for circles, IFJ PAN facility (solid line); diamond HZB facility (dashed line).
This study was supported by the Foundation for the Polish Science, co-financed from EU structural funds under Action 1.2 ‘Strengthening the human resources potential of science’ of the Innovative Economy Operational Program 2007–13. REFERENCES
1
Diso ¼ Dentr ð0:027 M þ 0:26Þ
ð1Þ
where D iso, dose estimated at the isocenter; D entr, entrance dose registered at the collimator; M, modulation. CONCLUSIONS AND FUTURE PERSPECTIVES In this study, the authors confirmed the applicability of EPR/alanine dosimetry as a potential element of the QC and QA system of patient in proton radiotherapy. The entrance dose registered with alanine pellets is well correlated with the dose delivered to the isocenter and depends on SOBP modulation width. Alanine detectors placed on the reverse side of patient collimator do not disturb the depth dose distribution, and they can be used as additional documentation of the patient’s exposure over the therapy course. As EPR read-out of the stable radiation-induced free-radical
1. Damato, B., Kacperek, A., Chopra, M. and Errington, R. D. Proton beam radiotherapy of choroidal melanoma: the Liverpool – Clatterbridge experience. Int. J. Radiat. Oncol. Biol. Phys. 62(5), 1405– 1411 (2005). 2. International Atomic Energy Agency. Absorbed dose determination in external beam radiotherapy. An international code of practice for dosimetry based on standards of absorbed dose to water. Technical Reports Series No. 398 (2000). 3. Schauer, D. A., Iwasaki, A., Romanyukha, A. A., Swartz, H. M. and Onori, S. Electron paramagnetic resonance (EPR) in medical dosimetry. Radiat. Measur. 41, 117–123 (2007). 4. Peimel-Stuglik, Z. and Fabisiak, S. Use of alanine-EPR dosimeter for measurements of absorbed doses in range 0.5– 10 kGy applied in food irradiation (in Polish). Raporty ICHTJ Seria B nr 10/2001 (2001). 5. Ciesielski, B., Schultka, K., Kobierska, A., Nowak, R. and Peimel-Stuglik, Z. In vivo alanine/EPR dosimetry in daily clinical practice: a feasibility study. Int. J. Radiat. Oncol. Biol. Phys. 56(3), 899–905 (2003). 6. ISO/ASTM International. Practice for use of alanine-EPR dosimetry system. ISO/ASTM 51607:2004(E) (2004).
139
Downloaded from http://rpd.oxfordjournals.org/ at Dalhousie University on June 20, 2015
Figure 3. The entrance dose registered by alanine detectors vs. modulation width. Circles, IFJ PAN facility (solid line); diamond HZB facility (dashed line).
signal does not destroy it, it is possible to control the dose accumulated in the alanine detector by its consecutive irradiation. Keeping in mind that SOBP fields are formed by the superposition of multiple, successively range-shifted, and individually weighted pristine Bragg peaks, also these with low energies, the authors have not observed in this study any effects that could be connected with widely reported decrease in relative effectiveness of alanine for proton energies of ,10 MeV.(7 – 9) Before the implementation of this QA/QC system, it is going to be tested also for different proton ranges. Then, it is planned to be implemented at the existing facility for proton eye radiotherapy as well as at the new (still under construction) facility called Cyclotron Center Bronowice equipped with proton cyclotron Proteus 235 for treating all neoplastic sites using a 230MeV proton beam, a rotating proton gantry, and active Bragg peak spreading technique.
B. MICHALEC ET AL. 7. Michalec, B., Mierzwinska, G., Sowa, U., Nowak, T., Ptaszkiewicz, M. and Swakon, J. Alanine dosimetry of 60MeV proton beam at IFJ PAN in Krakow, Poland – preliminary results. Nukleonika 57(4), 503– 506 (2012). 8. Fattibene, P., De Angelis, C., Onori, S. and Cherubini, R. Alanine response to proton beams in the 1,6-6,1 MeV
energy range. Radiat. Protect Dosim. 101(1–4), 465–468 (2002). 9. Olsen, K. J. and Hansen, J. W. The response of the alanine dosemeter to low energy protons and high energy heavy charged particles. Radiat. Protect. Dosim. 31(1– 4), 81–84 (1990).
Downloaded from http://rpd.oxfordjournals.org/ at Dalhousie University on June 20, 2015
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