- Email: [email protected]
SP-0619 PRIMO: A GRAPHICAL ENVIRONMENT FOR THE AUTOMATIC SIMULATION OF VARIAN AND ELEKTA LINACS WITH PENELOPE
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take place. The committee selects the proposals taking in consideration some criteria defined for clinical and preclinical researches as the scientific relevance of the proposal, the expertise of the researcher in the field and the ability to take part to the clinical activity, the feasibility of the project, the potential impact on patient referral, the potential to improve existing facilities, the impact on hadron therapy on the whole. The facilities will provide personnel, training courses, equipment and labs to satisfy the needs of the research groups. Researchers going to CNAO or HIT for clinical researches may bring or not patients but they will act as observers if they are not entitled by national laws to perform medical activities. In the website of the ULICE project, researchers concerned find instructions on the application and on the rules about transnational access to the facilities. More details can be addressed to [email protected].
SYMPOSIUM: MC PLATFORMS, GETTING MC EASY FOR ROUTINE USE IN MP SP-0617 SMCP - AN EFFICIENT MONTE CARLO TREATMENT PLANNING SYSTEM P. Manser1 1 Inselspital Universität Bern, Div. of Med. Radiation Physics, Bern, Switzerland Monte Carlo (MC) methods are seen as the most accurate method to calculate dose distributions in radiation therapy. Due to its statistical nature, however, MC methods lack of efficiency and thus its clinical implementation is limited. Several approaches were developed in order to improve efficiency while not compromising the accuracy. As an example, the macro MC method [1] for electron beams was developed and successfully implemented in clinical routine. Nevertheless, for photon beams, the need to speed up MC simulations is even more pronounced. Thus, in this presentation, the Swiss Monte Carlo Plan (SMCP) [2] is used to demonstrate the potential of an efficient and accurate MC treatment planning system. SMCP is an efficient and flexible MC platform for dose calculations of photon beams. It is based on a GUI-framework with different methods for the simulation of the radiation transport in a linear accelerator’s treatment head. By this means, not only 3DCRT but also more complex delivery techniques such as IMRT or VMAT [3] can be managed. Dose calculation within the patient is performed using different radiation transport methods and is linked to a commercially available treatment planning system (Eclipse, Varian Medical Systems). References: [1] H. Neuenschwander et al., Phys. Med. Biol., 107-25, 1992 [2] M.K. Fix et al., Phys. Med. Biol., N425-N437, 2007 [3] P. Manser et al., Med. Phys., 3240, 2010
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radiotherapy dosimetry problems. These problems include the investigation of perturbation effects and the generation of correction factors for absolute and relative dosimetry. The methodology to assess the contribution of systematic uncertainties to results is explained. Some features of the new EGSnrc release with relevance for ion chamber calculations are discussed. SP-0619 PRIMO: A GRAPHICAL ENVIRONMENT FOR THE AUTOMATIC SIMULATION OF VARIAN AND ELEKTA LINACS WITH PENELOPE L. Brualla1, M. Rodriguez2, J. Sempau2 1 Universitätsklinikum Essen, Strahlenklinik, Essen, Germany 2 Universitat Politècnica de Catalunya, Institut de Tècniques Energètiques, Barcelona, Spain Purpose: The accurate Monte Carlo simulation of a linac requires a detailed description of its geometry and the application of elaborate variance-reduction techniques (VRTs). Here, we introduce a new system based on the codes PENELOPE, penEasy, penEasyLinac and a graphical user interface (GUI) that encompasses all these pieces in a single user-friendly environment, called PRIMO. Methods: PENELOPE is a set of general-purpose subroutines for the Monte Carlo simulation of electron and photon transport. penEasy is a general-purpose, well structured, main program for PENELOPE that includes several source models, tallies, VRTs and the possibility of combining quadric and voxelised geometries. penEasyLinac is a complementary tool that generates the input files required for the simulation of certain Varian and Elekta linacs with PENELOPE/penEasy. PRIMO is the uppermost layer of the simulation system (see figure). It consists of a GUI that allows users to define the configuration of the simulated machine, that is, irradiation mode, beam nominal energy, jaw positions, position of every leaf of the multileaf collimator (photon mode) or type of electron applicator (electron mode). All the other parameters, those of the simulation and application of VRTs, are automatically selected by the system without user intervention. Users can edit and modify configuration files if desired. The automatically selected parameters are optimised for each particular linac configuration. Finally, PRIMO incorporates graphical and numerical tools for the analysis of phase-space files and dose distributions tallied during the simulations.
SP-0618 EGSNRC FOR THE INVESTIGATION OF IONIZATION CHAMBERS IN RADIOTHERAPY DOSIMETRY J. Wulff1 1 Technische Hochschule Mittelhessen, Institut fuer Medizinische Physik und Strahlenschutz, Giessen, Germany The EGSnrc code system has been used for the investigation of ion chamber dosimetry in electron/photon radiotherapy for more than a decade. Already the very first version of EGSnrc included the elaborate electron transport algorithm capable of calculating artifactfree ion chamber response at the 0.1% level (relative to crosssections). This made EGSnrc one of the few general purpose codes available for these types of simulations. Since its initial release several enhancements have been made to the physics back-end, but more importantly a C++ interface with a geometry and particle source library was incorporated into the system. Subsequently tailored applications for efficient calculation of ion chamber response have been released. In conjunction with the functionality of BEAMnrc to calculate the fluence output of typical radiotherapy machines, the system can be understood as a valuable tool for dosimetry research. The simulation setup is mainly text-file based and requires some syntax learning, but the platform allows the investigation of complex problems in photon/electron dosimetry even for a novice user. This talk summarizes the features of EGSnrc for accurate ion chamber calculations and explains how different variance reduction techniques are employed for an efficient simulation of ion chambers in typical
Results: A demanding test for a linac simulator is the computation of absorbed dose distributions produced by relatively small far-from-axis photon fields. As an example, we have simulated a 3x5 cm2 field located 12 cm away from the beam axis of a Varian Clinac 2100 C/D. This field requires the largest possible over-travel distances for both set of jaws. Comparison of the simulated results with experimental data via the gamma test shows that there are no voxels with gamma index larger than unity using the 0.2 cm and 2% criteria. The simulation of this off-axis field, starting at the bremsstrahlung target and ending with the dose estimation in a water phantom reached 2%
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statistical uncertainty (1 SD) in 3.1 hours using a single core of a desktop computer. Conclusion: Two new PENELOPE-based MC tools, penEasy and penEasyLinac, and a graphical user interface, PRIMO, are presented. Combined, they make the accurate and efficient simulation of various Elekta and Varian linacs (including their electron applicators and MLCs) possible, even for users with little or no experience in Monte Carlo methods. Furthermore, the modular structure of our codes facilitates the development of new functionalities (e.g., tallies, source models and VRTs) by advance users.
SYMPOSIUM: RESEARCH
COMPARISON
STUDIES:
ONGOING
SP-0620 ICORG 09-06 AN ONGOING PROSPECTIVE RANDOMISED TRIAL COMPARING 3D RT WITH IMRT FOR THE TREATMENT OF ENDOMETRIAL CANCER L. O'Sullivan1, O. McArdle1, J. Gilmore1, L. Walsh2, C. Gillham1 1 St Luke's Hospital, Department of Radiotherapy, Dublin, Ireland Republic of 2 Mid Western Cancer Centre, Department of Radiotherapy, Limerick, Ireland Republic of Objectives: The primary objective of this trial is to compare the rate of >Grade 2 acute gastrointestinal (GI) and genitourinary (GU) toxicity across the two arms (3D CRT and IMRT). Secondary objectives include examining the feasibility of using IMRT for pelvic nodal irradiation, comparing late GI and GU toxicity and documenting the overall survival rate. In addition, this trial aims to establish an image-guided pathway for gynaecological cancer, including investigating the effects of bladder and rectal filling protocols on the Planning Target Volume. Finally, this trial aims to gather Quality of Life (QoL) data on this group of patients. Methods: Once patients have given consent as per ICH-GCP guidelines, they are randomised to either the 3D CRT or IMRT Arm. All patients are prescribed external beam radiotherapy of 45Gy/25# followed by 11Gy/2# vaginal vault brachytherapy. Acute (assessed weekly while on radiotherapy) and late (assessed at routine intervals post radiotherapy) toxicity is graded according to the NCI-CTCAE, Version 3.0. Patients are asked to adhere to bladder filling (540ml of water) and rectal consistency (dietary guidelines +/- laxatives) protocols and the effects of these protocols are assessed via on-treatment KV conebeam CT imaging. The EORTC QLQ C30 and CX24 modules are used to assess QoL. Results: 18 of the target accrual of 142 evaluable patients have been accrued to date. Recruitment of the 20th patient will trigger an interim analysis of the set-up displacements and organ volume consistencies. SP-0621 3-YEARS FOLLOW-UP OF A MODERATE HYPOFRACTIONATION SCHEME WITH ENDORECTAL BALLOON FOR EBRT OF THE PROSTATE G. McColl1, M. Kunze-Busch1, P. van Kollenburg1, E. van Lin1, J. Kaanders1 1 Radboud University Nijmegen Medical Center, Radiotherapy, Nijmegen, The Netherlands Purpose: To retrospectively assess the long-term outcome and morbidity of a 70Gy hypofractionation scheme combined with gold marker based correction and a daily endorectal balloon (ERB) for prostate cancer. Materials: Between 2006 and 2011, 207 patients (median age 67 years) were irradiated in Nijmegen using this regimen. 121 patients (58.5%) received hormonal treatment (6 months neo-adjuvant). 7% of the patients were classified as low risk, 18% intermediate risk and 75% high risk. All patients received three trans-rectally implanted gold markers for position verification and correction. Originally, a 3-field CRT technique was used with an online position correction protocol in AP direction (n=92), with the introduction of 5-field IMRT and a daily online-protocol in 3 directions in 2008 (n=82). Since 2010 patients are treated using singular anterior semi-arc VMAT (n=33). A 100cc airfilled ERB, to reduce ano-rectal toxicity, has been used throughout. 70Gy in 28 fractions of 2.5Gy over a total period of 7 weeks, 4 times a
week, was prescribed. This scheme is biologically equivalent to 78Gy in 2Gy fractions (assuming an α/ß ratio of 3Gy). Before commencing treatment and during follow-up, patients were asked to fill out an EPIC (Expanded Prostate Cancer Index Composite) questionnaire to assess acute and late toxicity. PSA relapse was defined according to the Phoenix definition (absolute nadir+2ng/ml). Patients were seen every 6 months, and from the third year of followup, yearly. Results: The median follow-up time was 35 months (range 3- 66 months). The three-year PSA relapse free survival rates were 92% for low risk, 89% for intermediate and 76% for high risk (fig.1). Radiotherapy was given as planned with ERB in all patients with none of the patients having to stop use during treatment. Acute rectal toxicity grade 2 was seen in 3.8% of the patients, mostly increase in frequency. No grade 3 complaints were observed. Acute urinary symptoms grade 2 were seen in 4.7%, consisting mostly of an increase in nocturia. Acute grade 3 complaints were observed in 4.7% of the patients and consisted mainly of daily use of incontinence pads. After three years, five patients (5.6%) suffered grade 2 rectal toxicity and four patients had a grade 3 rectal toxicity, mostly an increase in uncontrolled leakage or some blood loss. Nine patients (10%) had a grade 2 urinary toxicity i.e. increase in nocturia, frequency and some haematuria. A grade 3 urinary toxicity was seen in 12 of the patients, mostly incontinence. The three-year actuarial cumulative rates of grade 3 rectal and grade 3 urinary toxicity were 4.4% and 13.2% respectively. Conclusions: This regimen of 70Gy/2.5Gy moderate hypofractionated radiotherapy with ERB and gold marker-based online position verification was tolerated well with favourable acute toxicity. After 3 years, mostly urinary symptoms were reported. Rectal toxicity was low, compared to literature. So far, the PSA relapse free survival is promising, seen in the light of the majority of high-risk patients, although longer follow-up is required. It is a feasible and convenient treatment scheme for both patients and a busy department and has already led the way to taking part in several randomised hypofractionation studies (the Dutch HYPRO and the FLAME study). For patients, outside these trials, 70Gy/2.5Gy remains our standard regimen.
fig.1 SP-0622 SHAPE VARIATION OF THE CLINICAL TARGET VOLUME IN RECTAL CANCER: COMPARISON BETWEEN SHORT-COURSE AND LONG-COURSE RT J. Nijkamp1, M. Swellengrebel2, B. Hollmann1, R. de Jong1, C.A.M. Marijnen3, C. van Vliet-Vroegindeweij1, B. van Triest1, M. van Herk1, J.J. Sonke1 1 The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Radiation Oncology, Amsterdam, The Netherlands 2 The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Hepatology, Amsterdam, The Netherlands 3 Leiden University Medical Center, Clinical Oncology, Leiden, The Netherlands Purpose: For early stage rectal cancer, RT is often given in 5 fractions of 5 Gy in one week (SCRT), while for locally advanced rectal cancer 25 fractions of 2 Gy are given in 5 weeks in combination with chemotherapy (LCRT). The most important geometric uncertainties for RT of rectal cancer are CTV delineation variation and CTV shape variation. With different fractionation schemes, treatment duration and the use of chemotherapy in LCRT, CTV shape variation might be
take place. The committee selects the proposals taking in consideration some criteria defined for clinical and preclinical researches as the scientific relevance of the proposal, the expertise of the researcher in the field and the ability to take part to the clinical activity, the feasibility of the project, the potential impact on patient referral, the potential to improve existing facilities, the impact on hadron therapy on the whole. The facilities will provide personnel, training courses, equipment and labs to satisfy the needs of the research groups. Researchers going to CNAO or HIT for clinical researches may bring or not patients but they will act as observers if they are not entitled by national laws to perform medical activities. In the website of the ULICE project, researchers concerned find instructions on the application and on the rules about transnational access to the facilities. More details can be addressed to [email protected].
SYMPOSIUM: MC PLATFORMS, GETTING MC EASY FOR ROUTINE USE IN MP SP-0617 SMCP - AN EFFICIENT MONTE CARLO TREATMENT PLANNING SYSTEM P. Manser1 1 Inselspital Universität Bern, Div. of Med. Radiation Physics, Bern, Switzerland Monte Carlo (MC) methods are seen as the most accurate method to calculate dose distributions in radiation therapy. Due to its statistical nature, however, MC methods lack of efficiency and thus its clinical implementation is limited. Several approaches were developed in order to improve efficiency while not compromising the accuracy. As an example, the macro MC method [1] for electron beams was developed and successfully implemented in clinical routine. Nevertheless, for photon beams, the need to speed up MC simulations is even more pronounced. Thus, in this presentation, the Swiss Monte Carlo Plan (SMCP) [2] is used to demonstrate the potential of an efficient and accurate MC treatment planning system. SMCP is an efficient and flexible MC platform for dose calculations of photon beams. It is based on a GUI-framework with different methods for the simulation of the radiation transport in a linear accelerator’s treatment head. By this means, not only 3DCRT but also more complex delivery techniques such as IMRT or VMAT [3] can be managed. Dose calculation within the patient is performed using different radiation transport methods and is linked to a commercially available treatment planning system (Eclipse, Varian Medical Systems). References: [1] H. Neuenschwander et al., Phys. Med. Biol., 107-25, 1992 [2] M.K. Fix et al., Phys. Med. Biol., N425-N437, 2007 [3] P. Manser et al., Med. Phys., 3240, 2010
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radiotherapy dosimetry problems. These problems include the investigation of perturbation effects and the generation of correction factors for absolute and relative dosimetry. The methodology to assess the contribution of systematic uncertainties to results is explained. Some features of the new EGSnrc release with relevance for ion chamber calculations are discussed. SP-0619 PRIMO: A GRAPHICAL ENVIRONMENT FOR THE AUTOMATIC SIMULATION OF VARIAN AND ELEKTA LINACS WITH PENELOPE L. Brualla1, M. Rodriguez2, J. Sempau2 1 Universitätsklinikum Essen, Strahlenklinik, Essen, Germany 2 Universitat Politècnica de Catalunya, Institut de Tècniques Energètiques, Barcelona, Spain Purpose: The accurate Monte Carlo simulation of a linac requires a detailed description of its geometry and the application of elaborate variance-reduction techniques (VRTs). Here, we introduce a new system based on the codes PENELOPE, penEasy, penEasyLinac and a graphical user interface (GUI) that encompasses all these pieces in a single user-friendly environment, called PRIMO. Methods: PENELOPE is a set of general-purpose subroutines for the Monte Carlo simulation of electron and photon transport. penEasy is a general-purpose, well structured, main program for PENELOPE that includes several source models, tallies, VRTs and the possibility of combining quadric and voxelised geometries. penEasyLinac is a complementary tool that generates the input files required for the simulation of certain Varian and Elekta linacs with PENELOPE/penEasy. PRIMO is the uppermost layer of the simulation system (see figure). It consists of a GUI that allows users to define the configuration of the simulated machine, that is, irradiation mode, beam nominal energy, jaw positions, position of every leaf of the multileaf collimator (photon mode) or type of electron applicator (electron mode). All the other parameters, those of the simulation and application of VRTs, are automatically selected by the system without user intervention. Users can edit and modify configuration files if desired. The automatically selected parameters are optimised for each particular linac configuration. Finally, PRIMO incorporates graphical and numerical tools for the analysis of phase-space files and dose distributions tallied during the simulations.
SP-0618 EGSNRC FOR THE INVESTIGATION OF IONIZATION CHAMBERS IN RADIOTHERAPY DOSIMETRY J. Wulff1 1 Technische Hochschule Mittelhessen, Institut fuer Medizinische Physik und Strahlenschutz, Giessen, Germany The EGSnrc code system has been used for the investigation of ion chamber dosimetry in electron/photon radiotherapy for more than a decade. Already the very first version of EGSnrc included the elaborate electron transport algorithm capable of calculating artifactfree ion chamber response at the 0.1% level (relative to crosssections). This made EGSnrc one of the few general purpose codes available for these types of simulations. Since its initial release several enhancements have been made to the physics back-end, but more importantly a C++ interface with a geometry and particle source library was incorporated into the system. Subsequently tailored applications for efficient calculation of ion chamber response have been released. In conjunction with the functionality of BEAMnrc to calculate the fluence output of typical radiotherapy machines, the system can be understood as a valuable tool for dosimetry research. The simulation setup is mainly text-file based and requires some syntax learning, but the platform allows the investigation of complex problems in photon/electron dosimetry even for a novice user. This talk summarizes the features of EGSnrc for accurate ion chamber calculations and explains how different variance reduction techniques are employed for an efficient simulation of ion chambers in typical
Results: A demanding test for a linac simulator is the computation of absorbed dose distributions produced by relatively small far-from-axis photon fields. As an example, we have simulated a 3x5 cm2 field located 12 cm away from the beam axis of a Varian Clinac 2100 C/D. This field requires the largest possible over-travel distances for both set of jaws. Comparison of the simulated results with experimental data via the gamma test shows that there are no voxels with gamma index larger than unity using the 0.2 cm and 2% criteria. The simulation of this off-axis field, starting at the bremsstrahlung target and ending with the dose estimation in a water phantom reached 2%
S243
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statistical uncertainty (1 SD) in 3.1 hours using a single core of a desktop computer. Conclusion: Two new PENELOPE-based MC tools, penEasy and penEasyLinac, and a graphical user interface, PRIMO, are presented. Combined, they make the accurate and efficient simulation of various Elekta and Varian linacs (including their electron applicators and MLCs) possible, even for users with little or no experience in Monte Carlo methods. Furthermore, the modular structure of our codes facilitates the development of new functionalities (e.g., tallies, source models and VRTs) by advance users.
SYMPOSIUM: RESEARCH
COMPARISON
STUDIES:
ONGOING
SP-0620 ICORG 09-06 AN ONGOING PROSPECTIVE RANDOMISED TRIAL COMPARING 3D RT WITH IMRT FOR THE TREATMENT OF ENDOMETRIAL CANCER L. O'Sullivan1, O. McArdle1, J. Gilmore1, L. Walsh2, C. Gillham1 1 St Luke's Hospital, Department of Radiotherapy, Dublin, Ireland Republic of 2 Mid Western Cancer Centre, Department of Radiotherapy, Limerick, Ireland Republic of Objectives: The primary objective of this trial is to compare the rate of >Grade 2 acute gastrointestinal (GI) and genitourinary (GU) toxicity across the two arms (3D CRT and IMRT). Secondary objectives include examining the feasibility of using IMRT for pelvic nodal irradiation, comparing late GI and GU toxicity and documenting the overall survival rate. In addition, this trial aims to establish an image-guided pathway for gynaecological cancer, including investigating the effects of bladder and rectal filling protocols on the Planning Target Volume. Finally, this trial aims to gather Quality of Life (QoL) data on this group of patients. Methods: Once patients have given consent as per ICH-GCP guidelines, they are randomised to either the 3D CRT or IMRT Arm. All patients are prescribed external beam radiotherapy of 45Gy/25# followed by 11Gy/2# vaginal vault brachytherapy. Acute (assessed weekly while on radiotherapy) and late (assessed at routine intervals post radiotherapy) toxicity is graded according to the NCI-CTCAE, Version 3.0. Patients are asked to adhere to bladder filling (540ml of water) and rectal consistency (dietary guidelines +/- laxatives) protocols and the effects of these protocols are assessed via on-treatment KV conebeam CT imaging. The EORTC QLQ C30 and CX24 modules are used to assess QoL. Results: 18 of the target accrual of 142 evaluable patients have been accrued to date. Recruitment of the 20th patient will trigger an interim analysis of the set-up displacements and organ volume consistencies. SP-0621 3-YEARS FOLLOW-UP OF A MODERATE HYPOFRACTIONATION SCHEME WITH ENDORECTAL BALLOON FOR EBRT OF THE PROSTATE G. McColl1, M. Kunze-Busch1, P. van Kollenburg1, E. van Lin1, J. Kaanders1 1 Radboud University Nijmegen Medical Center, Radiotherapy, Nijmegen, The Netherlands Purpose: To retrospectively assess the long-term outcome and morbidity of a 70Gy hypofractionation scheme combined with gold marker based correction and a daily endorectal balloon (ERB) for prostate cancer. Materials: Between 2006 and 2011, 207 patients (median age 67 years) were irradiated in Nijmegen using this regimen. 121 patients (58.5%) received hormonal treatment (6 months neo-adjuvant). 7% of the patients were classified as low risk, 18% intermediate risk and 75% high risk. All patients received three trans-rectally implanted gold markers for position verification and correction. Originally, a 3-field CRT technique was used with an online position correction protocol in AP direction (n=92), with the introduction of 5-field IMRT and a daily online-protocol in 3 directions in 2008 (n=82). Since 2010 patients are treated using singular anterior semi-arc VMAT (n=33). A 100cc airfilled ERB, to reduce ano-rectal toxicity, has been used throughout. 70Gy in 28 fractions of 2.5Gy over a total period of 7 weeks, 4 times a
week, was prescribed. This scheme is biologically equivalent to 78Gy in 2Gy fractions (assuming an α/ß ratio of 3Gy). Before commencing treatment and during follow-up, patients were asked to fill out an EPIC (Expanded Prostate Cancer Index Composite) questionnaire to assess acute and late toxicity. PSA relapse was defined according to the Phoenix definition (absolute nadir+2ng/ml). Patients were seen every 6 months, and from the third year of followup, yearly. Results: The median follow-up time was 35 months (range 3- 66 months). The three-year PSA relapse free survival rates were 92% for low risk, 89% for intermediate and 76% for high risk (fig.1). Radiotherapy was given as planned with ERB in all patients with none of the patients having to stop use during treatment. Acute rectal toxicity grade 2 was seen in 3.8% of the patients, mostly increase in frequency. No grade 3 complaints were observed. Acute urinary symptoms grade 2 were seen in 4.7%, consisting mostly of an increase in nocturia. Acute grade 3 complaints were observed in 4.7% of the patients and consisted mainly of daily use of incontinence pads. After three years, five patients (5.6%) suffered grade 2 rectal toxicity and four patients had a grade 3 rectal toxicity, mostly an increase in uncontrolled leakage or some blood loss. Nine patients (10%) had a grade 2 urinary toxicity i.e. increase in nocturia, frequency and some haematuria. A grade 3 urinary toxicity was seen in 12 of the patients, mostly incontinence. The three-year actuarial cumulative rates of grade 3 rectal and grade 3 urinary toxicity were 4.4% and 13.2% respectively. Conclusions: This regimen of 70Gy/2.5Gy moderate hypofractionated radiotherapy with ERB and gold marker-based online position verification was tolerated well with favourable acute toxicity. After 3 years, mostly urinary symptoms were reported. Rectal toxicity was low, compared to literature. So far, the PSA relapse free survival is promising, seen in the light of the majority of high-risk patients, although longer follow-up is required. It is a feasible and convenient treatment scheme for both patients and a busy department and has already led the way to taking part in several randomised hypofractionation studies (the Dutch HYPRO and the FLAME study). For patients, outside these trials, 70Gy/2.5Gy remains our standard regimen.
fig.1 SP-0622 SHAPE VARIATION OF THE CLINICAL TARGET VOLUME IN RECTAL CANCER: COMPARISON BETWEEN SHORT-COURSE AND LONG-COURSE RT J. Nijkamp1, M. Swellengrebel2, B. Hollmann1, R. de Jong1, C.A.M. Marijnen3, C. van Vliet-Vroegindeweij1, B. van Triest1, M. van Herk1, J.J. Sonke1 1 The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Radiation Oncology, Amsterdam, The Netherlands 2 The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Hepatology, Amsterdam, The Netherlands 3 Leiden University Medical Center, Clinical Oncology, Leiden, The Netherlands Purpose: For early stage rectal cancer, RT is often given in 5 fractions of 5 Gy in one week (SCRT), while for locally advanced rectal cancer 25 fractions of 2 Gy are given in 5 weeks in combination with chemotherapy (LCRT). The most important geometric uncertainties for RT of rectal cancer are CTV delineation variation and CTV shape variation. With different fractionation schemes, treatment duration and the use of chemotherapy in LCRT, CTV shape variation might be