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430 MIMic IMRS delivery system
Posters
$188 efficient and safe delivery of radiotherapy by considering the treatment as an entity instead of as a series of separate beams. An effort of TPS- and R&V-companies is needed to make the SB-technique available to more clinics.
2004 - Q4
8000
[] standard
ooo4ooo 16000-io i I =
• actual (SB)
0 A
B Linac C
D
429 T e n t a t i v e of comparison of I M R T delivery m o d e s for h e a d and neck cancer using a s i m u l t a n e o u s i n t e g r a t e d boost M. Tomse~, N. De Patoul U. C. L. -St-Luc University Hospital, Radiation oncology department, Brussels, Belgium Intensity modulated radiation therapy (IMRT) plays an important role in the treatment of patients with head and neck cancer. As the hitjhly conformal dose distribution that is achievable with IMRT makes it possible to envisage an increase in physical dose while still maintaining the dose to the OAR at a reasonable level, several options could be considered to attain this objective. This has been possible thanks to the rising of quality of inverse treatment planning systems employing very powerful algorithms, focused either on optimisation either on dose calculations. Optimal fluences are found for each beam by the input of dose volume constraints and will generate different shapes of beams using whether a dynamic or a static collimation. Linacs today are capable to treat in IMRT patients using the "step and shoot" or the dynamic delivery or both. This study tries to compare both delivery techniques (step and shoot and dynamic), with ELEKTA (step and shoot only possible) and VARIAN (step and shoot and dynamic) linacs using the same inverse planning system, ECLIPSE (VARIAN), in which both kinds of beam delivery exist, and is the result of a collaboration of 2 sites owning original equipment, i.e. Centre Val d'Aurelles in Montpellier, France (ECLIPSE and VARIAN linacs) and St-Luc University Hospital, U.C.L. in Brussels, Belgium (ECLIPSE and ELEKTA linacs). Same patients have been exchanged in terms of images and volumes and were chosen to belong to same category,say moderately advanced (T2N0, T2N1, T3N0) squamous cell carcinomas (SCC) of the oropharynx, larynx and hypopharynx, treated using a simultaneous integrated boost approach. Obviously, same dose volume objectives (and/or same optimal fluence files) have been fixed as well as the maximum iterations and of course the geometrical parameters and beam energy. Treatment plans are performed according to such protocol, and analysis has been realized reporting parameters derived from dose volume histograms and will be discussed here.
430 M I M i c I M R S delivery system G. Kralik St. Elizabeth cancer Institute, Radiation Physics, Bratislava, SIovak Rapublic Radiosurgery is a one time application of high Dose of radiation to a stereotactically defined target volume. Treatment delivery involves multiple stereotactically targeted, arced fields. The goal of radiosurgery is deliver a high dose to the target by minimal dose to normal tissue just a few millimeters away. Since 1993 is used in St.Elisabeth cancer Institute in Bratislava the stereotactic radiosurgery on linac. Till 30.03.2005 we have treated 650 patients with brain tumor, metastases, recidives and AV Malformations with Leibinger stereotaxy collimators system on Clinac2100 C of Varian accelerator. Since March of 2005 we prepare a Nomos MIMIC (with BEAK) stereotaxy IMRS delivery system with Corvus treatment planning system and autocrane positioning of cauch. From the reason of continuity by transformation of Stereotactic radiosurgery we use in the first step the Leibinger fixation and positioning system with autocrane mowing system on a new Clinac 600C/D. The poster brings the first experience by planning, verification and realisation of treatment with a new system. 431 C o m p a r i n g isocentric and p r o x i m i t y e l e c t r o n - M L C t h e r a p y - a d v a n t a g e s and d i s a d v a n t a g e s L. Olofsson, M. Karlsson, M. Karlsson Ume~ university, department of radiation sciences, radiation physics, Ume~, Sweden B a c k g r o u n d and Purpose: It is well known that the proximity geometry, where the electron collimator is situated with the last plane of collimation close to the skin of the patient, produces the smallest penumbras. However, when used in a multisegmented electron treatment, such as electron IMRT, the overlapping bremsstrahlung leakage becomes an increasingly important problem to consider. This leakage dose contribution can easily increase with a factor of 10 - 15 with the addition of both intensity and electron energy modulation in electron IMRT. The aim of this study was to analyse the significance of the bremsstrahlung leakage-dose contribution and electron penumbra comparing the proximity and isocentric collimation geometries and to investigate how it can be reduced using the photon-MLC to partially shield an add-on electron-MLC from bremsstrahlung. M a t e r i a l s and methods: The two collimation geometries, both based on a standard dual scattering foil treatment head design, were investigated using Monte Carlo methods. Both leakage dose profiles and the integral leakage dose contribution to a 30x30x30 cm 3 water phantom was analysed using 9.6 and 22.5 MeV electrons. Results: It was found that the electron-MLC leakage could generate an integral dose (dose x volume) 1.5 times larger than the integral dose from radiation passing the collimator opening. The leakage dose could be reduced by more than a factor of 6 using the photon collimator to partially shield the electron MLC from bremsstrahlung. For the isocentric collimation geometry a smaller margin between the photon and electron collimator field sizes can be used, compared to the proximity geometry, still avoiding perturbation of the electron beam penumbra or output. It was also found that, with the same margin, the electron-MLC leakage-dose contribution was approximately 75 % higher for the proximity geometry. Conclusions: Although the narrow penumbras of the proximity collimation geometry is best for the single electron field treatment the reduced bremsstrahlung leakage dose is a clear advantage for the isocentric geometry in multisegmented treatments such as the electron-IMRT. Also, the isocentric collimation geometry is more suitable for combined
$188 efficient and safe delivery of radiotherapy by considering the treatment as an entity instead of as a series of separate beams. An effort of TPS- and R&V-companies is needed to make the SB-technique available to more clinics.
2004 - Q4
8000
[] standard
ooo4ooo 16000-io i I =
• actual (SB)
0 A
B Linac C
D
429 T e n t a t i v e of comparison of I M R T delivery m o d e s for h e a d and neck cancer using a s i m u l t a n e o u s i n t e g r a t e d boost M. Tomse~, N. De Patoul U. C. L. -St-Luc University Hospital, Radiation oncology department, Brussels, Belgium Intensity modulated radiation therapy (IMRT) plays an important role in the treatment of patients with head and neck cancer. As the hitjhly conformal dose distribution that is achievable with IMRT makes it possible to envisage an increase in physical dose while still maintaining the dose to the OAR at a reasonable level, several options could be considered to attain this objective. This has been possible thanks to the rising of quality of inverse treatment planning systems employing very powerful algorithms, focused either on optimisation either on dose calculations. Optimal fluences are found for each beam by the input of dose volume constraints and will generate different shapes of beams using whether a dynamic or a static collimation. Linacs today are capable to treat in IMRT patients using the "step and shoot" or the dynamic delivery or both. This study tries to compare both delivery techniques (step and shoot and dynamic), with ELEKTA (step and shoot only possible) and VARIAN (step and shoot and dynamic) linacs using the same inverse planning system, ECLIPSE (VARIAN), in which both kinds of beam delivery exist, and is the result of a collaboration of 2 sites owning original equipment, i.e. Centre Val d'Aurelles in Montpellier, France (ECLIPSE and VARIAN linacs) and St-Luc University Hospital, U.C.L. in Brussels, Belgium (ECLIPSE and ELEKTA linacs). Same patients have been exchanged in terms of images and volumes and were chosen to belong to same category,say moderately advanced (T2N0, T2N1, T3N0) squamous cell carcinomas (SCC) of the oropharynx, larynx and hypopharynx, treated using a simultaneous integrated boost approach. Obviously, same dose volume objectives (and/or same optimal fluence files) have been fixed as well as the maximum iterations and of course the geometrical parameters and beam energy. Treatment plans are performed according to such protocol, and analysis has been realized reporting parameters derived from dose volume histograms and will be discussed here.
430 M I M i c I M R S delivery system G. Kralik St. Elizabeth cancer Institute, Radiation Physics, Bratislava, SIovak Rapublic Radiosurgery is a one time application of high Dose of radiation to a stereotactically defined target volume. Treatment delivery involves multiple stereotactically targeted, arced fields. The goal of radiosurgery is deliver a high dose to the target by minimal dose to normal tissue just a few millimeters away. Since 1993 is used in St.Elisabeth cancer Institute in Bratislava the stereotactic radiosurgery on linac. Till 30.03.2005 we have treated 650 patients with brain tumor, metastases, recidives and AV Malformations with Leibinger stereotaxy collimators system on Clinac2100 C of Varian accelerator. Since March of 2005 we prepare a Nomos MIMIC (with BEAK) stereotaxy IMRS delivery system with Corvus treatment planning system and autocrane positioning of cauch. From the reason of continuity by transformation of Stereotactic radiosurgery we use in the first step the Leibinger fixation and positioning system with autocrane mowing system on a new Clinac 600C/D. The poster brings the first experience by planning, verification and realisation of treatment with a new system. 431 C o m p a r i n g isocentric and p r o x i m i t y e l e c t r o n - M L C t h e r a p y - a d v a n t a g e s and d i s a d v a n t a g e s L. Olofsson, M. Karlsson, M. Karlsson Ume~ university, department of radiation sciences, radiation physics, Ume~, Sweden B a c k g r o u n d and Purpose: It is well known that the proximity geometry, where the electron collimator is situated with the last plane of collimation close to the skin of the patient, produces the smallest penumbras. However, when used in a multisegmented electron treatment, such as electron IMRT, the overlapping bremsstrahlung leakage becomes an increasingly important problem to consider. This leakage dose contribution can easily increase with a factor of 10 - 15 with the addition of both intensity and electron energy modulation in electron IMRT. The aim of this study was to analyse the significance of the bremsstrahlung leakage-dose contribution and electron penumbra comparing the proximity and isocentric collimation geometries and to investigate how it can be reduced using the photon-MLC to partially shield an add-on electron-MLC from bremsstrahlung. M a t e r i a l s and methods: The two collimation geometries, both based on a standard dual scattering foil treatment head design, were investigated using Monte Carlo methods. Both leakage dose profiles and the integral leakage dose contribution to a 30x30x30 cm 3 water phantom was analysed using 9.6 and 22.5 MeV electrons. Results: It was found that the electron-MLC leakage could generate an integral dose (dose x volume) 1.5 times larger than the integral dose from radiation passing the collimator opening. The leakage dose could be reduced by more than a factor of 6 using the photon collimator to partially shield the electron MLC from bremsstrahlung. For the isocentric collimation geometry a smaller margin between the photon and electron collimator field sizes can be used, compared to the proximity geometry, still avoiding perturbation of the electron beam penumbra or output. It was also found that, with the same margin, the electron-MLC leakage-dose contribution was approximately 75 % higher for the proximity geometry. Conclusions: Although the narrow penumbras of the proximity collimation geometry is best for the single electron field treatment the reduced bremsstrahlung leakage dose is a clear advantage for the isocentric geometry in multisegmented treatments such as the electron-IMRT. Also, the isocentric collimation geometry is more suitable for combined