- Email: [email protected]
Development and validation of an electron Monte Carlo model for an Elekta Synergy linear accelerator
Abstracts of the 55th Annual Congress of the SAAPMB / Physica Medica 41, Suppl. 1 (2017) S1–S15
expensive and more accurate when compared to doing these QA tests on film.
O7. Implementing a modified Winston-Lutz test for stereotactic radiotherapy at Universitas Hospital Annex D. Violante *, I. Setilo University of The Free State, Bloemfontein, South Africa * E-mail address: [email protected] (D. Violante) Introduction: The high dose delivered during stereotactic radiotherapy necessitates accurate patient positioning by performing the Winston-Lutz test in the case of a single lesion treatment. Since a single-isocentre approach in treating multiple lesions is convenient, a modified Winston-Lutz test has been proposed. This study aims to evaluate, from a quality control perspective, the single isocentre technique in treating multiple lesions in stereotactic radiotherapy. Materials and Methods: The modified Winston-Lutz test is performed on the ELEKTA Synergy linear accelerator system, using a Winston-Lutz test tool. The test is performed at isocentre and a range of off-isocentric distances (2, 4, 6, and 9 cm) representing separation between multiple lesions, where EPID images are acquired using a 3×3 cm2 field and 6 MV photon beam. The test is repeated at a series of gantry and collimator angle combinations. The deviation of the light and radiation fields at these distances are compared to the 1 mm limit, as recommended by the AAPM TG-142, using a custom MATLAB script. An off-isocentric margin is identified above which the single-isocentre treatment delivery for multiple lesions no longer adheres to recommended limits. Results: The average light/radiation field deviations were 0.46 ± 0.25, 0.66 ± 0.16, 0.67 ± 0.35, 1.02 ± 0.36 and 1.07 ± 0.39 mm for 0, 2, 4, 6 and 9 cm offset respectively. The results show a distinct increase in deviation with increasing off-isocentric distance. A linear fit attributed to the data suggests a margin of 6.7 cm. However, the limit is reached as soon as 4 cm for a particular gantry and collimator combination. Conclusion: The results indicate two different limits based on the interpretation of the quality control recommendation. The more conservative 4 cm margin is recommended for use at UHA.
S3
Results: The linac was modelled precisely according to information from ELEKTA™ under a non-disclosure agreement. A model for the upper part of the linac was created for each beam energy with moderate changes to primary and secondary scattering foil dimensions. A model for the lower part of the linac was created for each beam energy and field size which included changes to Multi-Leaf Collimator, Jaw and Applicator dimensions. Modelled unit density water phantoms for each field size were coordinately adjusted as to evaluate source-to-surface distance. Simulated data complied with criteria after fine tuning to beam parameters. Conclusion: The EGSnrc user code could successfully be utilized to develop an electron model which after some fine modifications simulated data that was able to meet the tolerance criteria.
O9. Mobile hot cell and borehole disposal integration for high activity disused radioactive sealed sources (DSRS) conditioning and final disposal N.J. Van Der Merwe * Necsa, Johannesburg, South Africa * E-mail address: [email protected] (N.J. Van Der Merwe) The International Atomic Energy Agency (IAEA) Waste Technology Section with additional support from the U.S. National Nuclear Security Agency (NNSA) through the IAEA Nuclear Security Fund has funded the design, fabrication, evaluation, and testing of a mobile hot cell intended to address the problem of high activity disused sealed radioactive sources (DSRS) in obsolete irradiation devices such as teletherapy heads and dry irradiators. Operations to condition high activity DSRS using the mobile hot cell has successfully been undertaken in various countries since April 2009. The project was initially targeting the African continent but it has now also expanded to other parts of the world such as Latin America and Asia. The mobile hot cell allows for source removal, characterization, consolidation, repackaging in stainless steel capsules as special form, and secure storage of high risk DSRS in modern long term storage shields at single sites in each IAEA Member State. The project has been expanded to include disposal using the Borehole concept. This presentation will give a brief overview of the mobile hot cell, focusing on the use of a Borehole for final disposal.
O8. Development and validation of an electron Monte Carlo model for an Elekta Synergy linear accelerator K. Sachse *, F.C.P. du Plessis University of The Free State, Department of Medical Physics, Bloemfontein, South Africa * E-mail address: [email protected] (K. Sachse) Background: Monte Carlo modelling of electron beams from linear accelerators (linac) for the use in treatment planning systems have been performed successfully by several authors in the past. This study aimed to develop and validate an accurate model of the electron beam delivery system of an ELEKTA™ Synergy linac in aid of the impending development of modulated electron radiotherapy. Methods: The EGSnrc-based BEAMnrc and DOSXYZnrc packages were used to accurately model the linac and a water phantom, respectively. Different beam setups used clinically were simulated using an Intel® Xeon® Processor. The developed model was benchmarked against a subset of measured data including central axis percentage depth dose curves, inline and crossline beam profiles and relative output factors. Measured data included commissioning and newly measured data using Gafchromic® EBT2 film placed within a Perspex mini phantom. Gamma index evaluations were performed with a 2%/2 mm tolerance criterion.
O10. Effects of telfairiaoccidentalis extract (TOE), allium cepa extract (ACE) & combined TOE/ACE formulations in radiationinduced hepatotoxic Wistar rats K.K. Sylvester * University of Nigeria Teaching Hospital, Enugu Nigeria, Enugu, Nigeria * E-mail address: [email protected] (K.K. Sylvester) Combined administration of two or more plant extracts has been speculated to be more effective than single extract as radioprotective agents in radiotherapy, hence the need for this study. 42 Wistar strain rats, weighing 150 ± 20 g, were divided into Seven groups of six rats each and fed for 21 days. Groups 1 and 2 are Normal Control and Experimental Control respectively, were fed with 100% normal rat feed/distilled water. Group 3 were fed with normal rat feed supplemented with TOE in the ratio of [50:50], while Group 4 were fed with similar diet supplemented with ACE in same ratio. Diets supplemented with varying proportions of TOE/ACE formulation [Normal feed:TOE:ACE] in the order of [50:35:15, 50:25:25 and 50:15:35] were administered orally to Groups 5, 6 and 7 respectively. All the groups, except Group 1 were exposed to total body
expensive and more accurate when compared to doing these QA tests on film.
O7. Implementing a modified Winston-Lutz test for stereotactic radiotherapy at Universitas Hospital Annex D. Violante *, I. Setilo University of The Free State, Bloemfontein, South Africa * E-mail address: [email protected] (D. Violante) Introduction: The high dose delivered during stereotactic radiotherapy necessitates accurate patient positioning by performing the Winston-Lutz test in the case of a single lesion treatment. Since a single-isocentre approach in treating multiple lesions is convenient, a modified Winston-Lutz test has been proposed. This study aims to evaluate, from a quality control perspective, the single isocentre technique in treating multiple lesions in stereotactic radiotherapy. Materials and Methods: The modified Winston-Lutz test is performed on the ELEKTA Synergy linear accelerator system, using a Winston-Lutz test tool. The test is performed at isocentre and a range of off-isocentric distances (2, 4, 6, and 9 cm) representing separation between multiple lesions, where EPID images are acquired using a 3×3 cm2 field and 6 MV photon beam. The test is repeated at a series of gantry and collimator angle combinations. The deviation of the light and radiation fields at these distances are compared to the 1 mm limit, as recommended by the AAPM TG-142, using a custom MATLAB script. An off-isocentric margin is identified above which the single-isocentre treatment delivery for multiple lesions no longer adheres to recommended limits. Results: The average light/radiation field deviations were 0.46 ± 0.25, 0.66 ± 0.16, 0.67 ± 0.35, 1.02 ± 0.36 and 1.07 ± 0.39 mm for 0, 2, 4, 6 and 9 cm offset respectively. The results show a distinct increase in deviation with increasing off-isocentric distance. A linear fit attributed to the data suggests a margin of 6.7 cm. However, the limit is reached as soon as 4 cm for a particular gantry and collimator combination. Conclusion: The results indicate two different limits based on the interpretation of the quality control recommendation. The more conservative 4 cm margin is recommended for use at UHA.
S3
Results: The linac was modelled precisely according to information from ELEKTA™ under a non-disclosure agreement. A model for the upper part of the linac was created for each beam energy with moderate changes to primary and secondary scattering foil dimensions. A model for the lower part of the linac was created for each beam energy and field size which included changes to Multi-Leaf Collimator, Jaw and Applicator dimensions. Modelled unit density water phantoms for each field size were coordinately adjusted as to evaluate source-to-surface distance. Simulated data complied with criteria after fine tuning to beam parameters. Conclusion: The EGSnrc user code could successfully be utilized to develop an electron model which after some fine modifications simulated data that was able to meet the tolerance criteria.
O9. Mobile hot cell and borehole disposal integration for high activity disused radioactive sealed sources (DSRS) conditioning and final disposal N.J. Van Der Merwe * Necsa, Johannesburg, South Africa * E-mail address: [email protected] (N.J. Van Der Merwe) The International Atomic Energy Agency (IAEA) Waste Technology Section with additional support from the U.S. National Nuclear Security Agency (NNSA) through the IAEA Nuclear Security Fund has funded the design, fabrication, evaluation, and testing of a mobile hot cell intended to address the problem of high activity disused sealed radioactive sources (DSRS) in obsolete irradiation devices such as teletherapy heads and dry irradiators. Operations to condition high activity DSRS using the mobile hot cell has successfully been undertaken in various countries since April 2009. The project was initially targeting the African continent but it has now also expanded to other parts of the world such as Latin America and Asia. The mobile hot cell allows for source removal, characterization, consolidation, repackaging in stainless steel capsules as special form, and secure storage of high risk DSRS in modern long term storage shields at single sites in each IAEA Member State. The project has been expanded to include disposal using the Borehole concept. This presentation will give a brief overview of the mobile hot cell, focusing on the use of a Borehole for final disposal.
O8. Development and validation of an electron Monte Carlo model for an Elekta Synergy linear accelerator K. Sachse *, F.C.P. du Plessis University of The Free State, Department of Medical Physics, Bloemfontein, South Africa * E-mail address: [email protected] (K. Sachse) Background: Monte Carlo modelling of electron beams from linear accelerators (linac) for the use in treatment planning systems have been performed successfully by several authors in the past. This study aimed to develop and validate an accurate model of the electron beam delivery system of an ELEKTA™ Synergy linac in aid of the impending development of modulated electron radiotherapy. Methods: The EGSnrc-based BEAMnrc and DOSXYZnrc packages were used to accurately model the linac and a water phantom, respectively. Different beam setups used clinically were simulated using an Intel® Xeon® Processor. The developed model was benchmarked against a subset of measured data including central axis percentage depth dose curves, inline and crossline beam profiles and relative output factors. Measured data included commissioning and newly measured data using Gafchromic® EBT2 film placed within a Perspex mini phantom. Gamma index evaluations were performed with a 2%/2 mm tolerance criterion.
O10. Effects of telfairiaoccidentalis extract (TOE), allium cepa extract (ACE) & combined TOE/ACE formulations in radiationinduced hepatotoxic Wistar rats K.K. Sylvester * University of Nigeria Teaching Hospital, Enugu Nigeria, Enugu, Nigeria * E-mail address: [email protected] (K.K. Sylvester) Combined administration of two or more plant extracts has been speculated to be more effective than single extract as radioprotective agents in radiotherapy, hence the need for this study. 42 Wistar strain rats, weighing 150 ± 20 g, were divided into Seven groups of six rats each and fed for 21 days. Groups 1 and 2 are Normal Control and Experimental Control respectively, were fed with 100% normal rat feed/distilled water. Group 3 were fed with normal rat feed supplemented with TOE in the ratio of [50:50], while Group 4 were fed with similar diet supplemented with ACE in same ratio. Diets supplemented with varying proportions of TOE/ACE formulation [Normal feed:TOE:ACE] in the order of [50:35:15, 50:25:25 and 50:15:35] were administered orally to Groups 5, 6 and 7 respectively. All the groups, except Group 1 were exposed to total body