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536 Quality control of CT on rail system (FOCAL unit) with a micro-multi leaf collimator (mMLC) using new Gafchromic film for stereotactic radiotherapy
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$228 important weapon in treatment of most CNS cancers, it plays an important role especially in those who have the ability to escape from other therapies and spread to this location, such as medulloblastomas and ependymomas. The daily radiotherapy treatment is consequence of many steps, involving a complex chain, in which dosimetric planning assumes a primordial position. The goal of this work is to describe the different steps of that chain, as they are done in IPOFG-CROC,S.A., and the main reasons to have evolved from 2D to 3D methods. M e t h o d s and Materials: The patient positioning is defined in the simulator (Siemens Mevasim), and requires: wholebody vacuum cushion and a thermoplastic mask (both moulded to the patient body shape). The crucial step at this time is the alignment of the craniospinal axis through fluoroscopy and definition of the field dimensions. In both methods (2D and 3D) the Plato Planning System - Nucletron (RTS version 2.6.1) is used for dose planning. Both methods use "Feathering" technique. The main difference is that 2D uses just water calculations without considering heterogeneities or anatomical structures (only taking into account the patient sagital outline obtained through digitalisation from the lateral CT topogram) whereas in 3D method CT images are taken (Siemens Somaton Plus 4). The range is defined from head to the sacrum (slice thickness 5 mm). Then images are transferred through network to the Plato TPS where the physician draws the clinical target volumes (brain and spinal cord) and organs at risk (optic chiasm and nerves, eyes, lungs, liver, heart and kidneys). Results and Conclusions: The high resolution of CT images allows the improvement of spinal cord irradiation accuracy. The correct definition of treatment volumes and organs at risk and more precise dose calculations (by taking into account body heterogeneities) are some of the advantages. Treatment planning using the "Feathering" technique allows variation of the problematic regions, particularly field junctions. The major advantages of CT images are DVH assessment and plan addition, consequently planning optimisation. No significant difference was obtained in c r v coverage between both methods, although 3D allows reduction in field width, customized organ protections and ability to determine the anatomical location of hot spots.
and mMLC unit (Accuknife, Direx Inc., Tokyo, Japan). We have developped original alignment phantom and small steel markers (2mmcp) were implanted on its surface at certain intervals. Firstly, we have evaluated the accuracy of selfmoving CT gantry and CT resolutions for cranio-caudal directions by changing slice thickness. And then using the phantom, we have measured the accuracy and reproducibility of geometric isocenter of the linac side and the CT gantry side by scanning the phantom. We have also measured the geometric changes of the common treatment couch by weight-loaded test (up to 135kgw). To estimate dosimetric and geometric accuracies with the mMLC unit, the misalignment of the beam axes (gantry, collimator and couch rotation axis), mMLC leaf positions, and dose distributions for the verification plan were measured with new type Gafchromic films (Gafchromic-RTQA, ISP Inc., USA) and cylindrical phantom. The dose characteristics of the Gafchromic film were also evaluated. Results: The reproducibility of the self-moving CT gantry have a good agreement within lmm. Weight-load test have shown a good reliability within 2ram at the common treatment couch. The translational precision of the common treatment couch was 0.3±0.2mm at tinac side and 1.0+0.6mm at CT gantry side. The misalignments of beam axes have been kept within 0.4ram at maximum. Gap test have shown the accuracies of the mMLC leaf positions, which is needed to keep within l m m by a routine calibration. Conclusions: To practice quality control program for the FOCAL unit and the mMLC unit is essential for a regular interval to reduce systematic errors. New type radiochromic film would be useful for a verification tool as alternative to conventional film.
536 Q u a l i t y control of CT on rail system (FOCAL u n i t ) w i t h a m i c r o - m u l t i leaf c o l l i m a t o r ( m M L C ) using n e w G a f c h r o m i c film f o r s t e r e o t a c t i c r a d i o t h e r a p y
M. Oita 1, Y. Takegawa1, H. Ikushima 2, K. OsakP, S. Furutan 2, H. Yagi1, Y. Nishimoto 3, M. Tominaga3, M. Sasak/3, H. Nishitani 4 ITokushima University Faculty of Medicine, Department of Health Sciences, Tokushima, Japan 2Tokushima University School of Medicine, Department of Radiology, Tokushima, Japan 3Tokushima University Hospital, Department of Radiology, Tokushima, Japan nTokushima Univeristy School of Medicine, Department of Radiology, Tokushima, Japan Purpose: Recent years, CT on rail system was reported to be useful as a tool for image-guided radiotherapy (IGRT). This system was clinically developed with the aim of stereotactic irradiation (STI) for brain, lung, liver, prostate and other sites. Quality assurance and quality control is an important issue in CT on rail system to assure geometric accuracies. The purpose of this study is to estimate the geometric accuracies of our CT on rail system using a detachable micromulti leaf collimator (mMLC) with new type radiochromic films. Carrying out our original QC program, translational errors, setup reproducibility, beam misalignment and beam characteristics were evaluated. M e t h o d s and Materials: We have studied with CT on rail system (FOCAL unit, Toshiba Medical systems, Tokyo, Japan)
Figure1. Dose distribution of the Gafchromic film using the mMLC unit in phantom verification.
537 I n d i c a t i o n s for the I M R T protocol for Head and N e c k Tumors: purpose and reality.
T. Batej W. Duthoy, W. De Neve University Hospital, Radiotherapy, Gent, Belgium Purpose: to evaluate if all patients with a head and neck tumor are treated according to the protocol. M e t h o d s and Materials: In May 2003 a protocol for IMRT irradiation of H&N Tumors was implemented in our
$228 important weapon in treatment of most CNS cancers, it plays an important role especially in those who have the ability to escape from other therapies and spread to this location, such as medulloblastomas and ependymomas. The daily radiotherapy treatment is consequence of many steps, involving a complex chain, in which dosimetric planning assumes a primordial position. The goal of this work is to describe the different steps of that chain, as they are done in IPOFG-CROC,S.A., and the main reasons to have evolved from 2D to 3D methods. M e t h o d s and Materials: The patient positioning is defined in the simulator (Siemens Mevasim), and requires: wholebody vacuum cushion and a thermoplastic mask (both moulded to the patient body shape). The crucial step at this time is the alignment of the craniospinal axis through fluoroscopy and definition of the field dimensions. In both methods (2D and 3D) the Plato Planning System - Nucletron (RTS version 2.6.1) is used for dose planning. Both methods use "Feathering" technique. The main difference is that 2D uses just water calculations without considering heterogeneities or anatomical structures (only taking into account the patient sagital outline obtained through digitalisation from the lateral CT topogram) whereas in 3D method CT images are taken (Siemens Somaton Plus 4). The range is defined from head to the sacrum (slice thickness 5 mm). Then images are transferred through network to the Plato TPS where the physician draws the clinical target volumes (brain and spinal cord) and organs at risk (optic chiasm and nerves, eyes, lungs, liver, heart and kidneys). Results and Conclusions: The high resolution of CT images allows the improvement of spinal cord irradiation accuracy. The correct definition of treatment volumes and organs at risk and more precise dose calculations (by taking into account body heterogeneities) are some of the advantages. Treatment planning using the "Feathering" technique allows variation of the problematic regions, particularly field junctions. The major advantages of CT images are DVH assessment and plan addition, consequently planning optimisation. No significant difference was obtained in c r v coverage between both methods, although 3D allows reduction in field width, customized organ protections and ability to determine the anatomical location of hot spots.
and mMLC unit (Accuknife, Direx Inc., Tokyo, Japan). We have developped original alignment phantom and small steel markers (2mmcp) were implanted on its surface at certain intervals. Firstly, we have evaluated the accuracy of selfmoving CT gantry and CT resolutions for cranio-caudal directions by changing slice thickness. And then using the phantom, we have measured the accuracy and reproducibility of geometric isocenter of the linac side and the CT gantry side by scanning the phantom. We have also measured the geometric changes of the common treatment couch by weight-loaded test (up to 135kgw). To estimate dosimetric and geometric accuracies with the mMLC unit, the misalignment of the beam axes (gantry, collimator and couch rotation axis), mMLC leaf positions, and dose distributions for the verification plan were measured with new type Gafchromic films (Gafchromic-RTQA, ISP Inc., USA) and cylindrical phantom. The dose characteristics of the Gafchromic film were also evaluated. Results: The reproducibility of the self-moving CT gantry have a good agreement within lmm. Weight-load test have shown a good reliability within 2ram at the common treatment couch. The translational precision of the common treatment couch was 0.3±0.2mm at tinac side and 1.0+0.6mm at CT gantry side. The misalignments of beam axes have been kept within 0.4ram at maximum. Gap test have shown the accuracies of the mMLC leaf positions, which is needed to keep within l m m by a routine calibration. Conclusions: To practice quality control program for the FOCAL unit and the mMLC unit is essential for a regular interval to reduce systematic errors. New type radiochromic film would be useful for a verification tool as alternative to conventional film.
536 Q u a l i t y control of CT on rail system (FOCAL u n i t ) w i t h a m i c r o - m u l t i leaf c o l l i m a t o r ( m M L C ) using n e w G a f c h r o m i c film f o r s t e r e o t a c t i c r a d i o t h e r a p y
M. Oita 1, Y. Takegawa1, H. Ikushima 2, K. OsakP, S. Furutan 2, H. Yagi1, Y. Nishimoto 3, M. Tominaga3, M. Sasak/3, H. Nishitani 4 ITokushima University Faculty of Medicine, Department of Health Sciences, Tokushima, Japan 2Tokushima University School of Medicine, Department of Radiology, Tokushima, Japan 3Tokushima University Hospital, Department of Radiology, Tokushima, Japan nTokushima Univeristy School of Medicine, Department of Radiology, Tokushima, Japan Purpose: Recent years, CT on rail system was reported to be useful as a tool for image-guided radiotherapy (IGRT). This system was clinically developed with the aim of stereotactic irradiation (STI) for brain, lung, liver, prostate and other sites. Quality assurance and quality control is an important issue in CT on rail system to assure geometric accuracies. The purpose of this study is to estimate the geometric accuracies of our CT on rail system using a detachable micromulti leaf collimator (mMLC) with new type radiochromic films. Carrying out our original QC program, translational errors, setup reproducibility, beam misalignment and beam characteristics were evaluated. M e t h o d s and Materials: We have studied with CT on rail system (FOCAL unit, Toshiba Medical systems, Tokyo, Japan)
Figure1. Dose distribution of the Gafchromic film using the mMLC unit in phantom verification.
537 I n d i c a t i o n s for the I M R T protocol for Head and N e c k Tumors: purpose and reality.
T. Batej W. Duthoy, W. De Neve University Hospital, Radiotherapy, Gent, Belgium Purpose: to evaluate if all patients with a head and neck tumor are treated according to the protocol. M e t h o d s and Materials: In May 2003 a protocol for IMRT irradiation of H&N Tumors was implemented in our