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463 The application of Co-60 calibrated plane-parallel chambers in electron dosimetry
Posters
$200 water phantom at clinical relevant condition using a new type of gafchromic film. Materials and m e t h o d : Recently the Gafchromic EBT has been introduced commercially in film dosimetry for external beam therapy including IMRT. The high spatial resolution, weak energy dependence and near tissue-equivalence of EBT films make them suitable for measurement of dose distributions in radiation outside a multileaf collimated beam. In this work, an Fpson GT 12000, flatbed scanner has been used to study the FBT response in a dose interval of 0-8 Gy. A 36-bit colour-scale mode along with colour image splitting into its red, green and blue components (RGB) is suggested as an improvement over formerly employed 12-bit, 4096 gray-scale mode. Special software routines have been implemented for evaluating the film data. The film were positioned in a solid water phantom perpendicular to the beam axis and irradiated at 10 cm depth using two different Linac. Two-dimensional dose distributions were measured in two different standard geometries. The goat of the first geometry was to verify the EBT response outside field edge comparing absolute doses with cylindrical ionizing chamber; in the second geometry Gafchromic EBT film will also be used to measure variations in dose outside edge of a MLC beam caused by interleaf leakage. Results: No significance differences between Gafchromic EBT and ionization chamber was observed in the first geometry while TPS seems to overestimate doses in condition of large scattered radiation. A comparison for the same MLC field (Flekta Precise) between low energy (6 MV) and high energy (25 MV) photon shows that Dlo(%) (dose at 10 cm depth normalized to the beam axes) at 3 cm from the field edge is about 7.5% for 6 MV and 4.8% for 25 MV. For two different MLC (Elekta Precise and Varian Clinac 2300 c/d) at the same nominal energy (6 MV) photon, D~0(%) at 3 cm from the field edge is about 7.5% for Elekta and 6.6% for Varian. Conclusions: Gafchromic EBT film produces a high dose r e s p o n s e with a relatively unaffected e n e r g y response, in fact, at clinical relevant conditions (10 cm depth outside field edg e), no meaningful differences (about 1%) were obse rve d c o m p a r e d with ionization chamber. Therefore, EBT film, is found to be an excellent two-dimensional d o s i m e t e r for verification of d ose outside a multileaf collimated be a m showing th at s c a t t e r e d radiation d e c r e a s e with the increase of nominal e n e r g y and that, at the s a m e nominal ene rgy, changing of primary and s c a t t e r radiation c o m p o n e n t s ma y be related to specific LINAC mechanical feature such as source-collimator-distance. 463 The application of Co-60 calibrated chambers in electron dosimetry
plane-parallel
R. Kapsch 1, G. Bruggmoser2, G. Christ 3, O. Dohm 3, G. Hartmann 4, E. SchiJle 5 ~Physikalisch- Technische Bundesanstalt, Braunschweig, Germany 2Universit~tsklinikum Freiburg, Freiburg, Germany 3Universit~tsklinikum TiJbingen, TiJbingen, Germany 4German Cancer Research Center, Heidelberg, Germany Sphysikalisch-Technische Werkst~tten Dr. Pychlau GmbH, Freiburg, Germany For plane-parallel chambers used in electron dosimetry, modern dosimetry protocols (e.g. IAEA TRS-398) recommend a cross-calibration against a calibrated cylindrical chamber. The rationale for this is the assumed chamber-to-chamber variation of the correction factors (Pwa~l)co for plane-parallel chambers which may be unacceptably high (variations of up to 3% have been reported). In recent studies, however, much smaller chamber-to-chamber variations of (Pwali)co (less than 0.5%) were found for chambers of modern designs such as the PTW Roos M34001 or the similar Wellh0fer PPC-35. In our study we determined the overall perturbation factors
Pco (which are usually a s s u m e d to be equal to (Pwall)co) for a total of 28 c h a m b e r s of the Rods type (25 PTW 34001, 3 Wellh6fer PPC40), 15 c h a m b e r s of the Markus t ype (PTW 23343) and 10 c h a m b e r s of t he Advanced Markus type (PTW 34045). These c h a m b e r s were cross-calibrated a g a i n s t reference cylindrical c h a m b e r s of the type PTW 30006 (waterproof Farmer) in the hi gh-e ne rgy electron b e a m s available at PTB Braunschweig, the universities of TObingen and Freiburg, and t he German Cancer Research Center (DKFZ) in Heidelberg. All c h a m b e r s were furnished with an absorbed dose to w a t e r calibration factor for 6°Co from PTWFreiburg, which is directly t ra c e a bl e to PTB Braunschweig. The m e a s u r e m e n t s were performed in accordance with the revised version of the German dosimetry protocol DIN 68002 (to be published next year), which will be very similar to IAEA TRS-398. The a v e r a g e va l ue s for Pco obtained from all m e a s u r e m e n t s and t he relative e x p e r i m e n t a l s t a n d a r d deviations are shown in the following table: chamber type
Rods (PTW M34001, Wellhofer PPC40/ Markus (PTW M23343) Advanced Markus (PTW M34045)
1.020 1.018 1.016
experimental standard deviation 0.26% 0.19% 0.24%
The relative combined standard uncertainty of the Pco values determined here is 1.05% (including the uncertainties associated with the perturbation factors needed for the evaluation of P c o - cf. IAEA TRS-398). This should be compared with the uncertainty value of 1.5% stated in IAFA TRS-398. Our investigations confirm the results of other authors that chamber-to-chamber variations of Pco values for planeparallel chambers of the Rods, Markus and Advanced Markus types are less than 0.5%. This allows the specification of type-specific Pco values for these chambers in the revised version of the German dosimetry protocol DIN 6800-2, with the aim of making cross-calibrations for these types of planeparallel chambers unnecessary. 464 First results of t h e M O P I pixel ionization c h a m b e r used as beam m o n i t o r at t h e I n s t i t u t Curie - Centre de Protonthbrapie d'Orsay ( I C P O ) .
A. La Rosa 1,2 F. Bourhaleb s, R. Cirio 2, M. Donetti 23, M. A. Garella 2, S. Giordanengo 2, N. Givehchi x,2, S. Iliescu 2, B. Le Gall4, F. Marchetto 2, F. Martin 4, S. Meyroneinc 4, C. Peroni ~'2, G. Pitt~ s SExperimental Physics Department of Turin University, Turin, Italy 2INFN, Turin, Italy 3CNAO Foundation, Milan, Italy 4Curie Institute - Proton therapy Center (ICPO), Orsay, France STERA Foundation, Novara, Italy In a proton therapy center, one of the main issues is to assure a correct delivery of the dose to the patient. The beam has to be monitored in a non-invasive way downstream of the spreading system and its position, shape and intensity have to be measured just upstream the target. This in order to feedback the upstream elements of the beam line or to prevent against any possible failure. There are many requirements for a successful treatment, for example the accuracy in the spatial distribution of the dose delivered to the patient and the stability and reproducibility of the beam. For this reason real-time monitors placed along the beam line are recommended. The Orsay Proton therapy Center (ICPO) has been operating since 1990 for the ophthalmologic and intracranial treatments. The proton energy delivered by a synchrocyclotron is 200 MeV and the dose delivery system operates with passive scattering. Turin University and INFN, in collaboration with the ICPO,
$200 water phantom at clinical relevant condition using a new type of gafchromic film. Materials and m e t h o d : Recently the Gafchromic EBT has been introduced commercially in film dosimetry for external beam therapy including IMRT. The high spatial resolution, weak energy dependence and near tissue-equivalence of EBT films make them suitable for measurement of dose distributions in radiation outside a multileaf collimated beam. In this work, an Fpson GT 12000, flatbed scanner has been used to study the FBT response in a dose interval of 0-8 Gy. A 36-bit colour-scale mode along with colour image splitting into its red, green and blue components (RGB) is suggested as an improvement over formerly employed 12-bit, 4096 gray-scale mode. Special software routines have been implemented for evaluating the film data. The film were positioned in a solid water phantom perpendicular to the beam axis and irradiated at 10 cm depth using two different Linac. Two-dimensional dose distributions were measured in two different standard geometries. The goat of the first geometry was to verify the EBT response outside field edge comparing absolute doses with cylindrical ionizing chamber; in the second geometry Gafchromic EBT film will also be used to measure variations in dose outside edge of a MLC beam caused by interleaf leakage. Results: No significance differences between Gafchromic EBT and ionization chamber was observed in the first geometry while TPS seems to overestimate doses in condition of large scattered radiation. A comparison for the same MLC field (Flekta Precise) between low energy (6 MV) and high energy (25 MV) photon shows that Dlo(%) (dose at 10 cm depth normalized to the beam axes) at 3 cm from the field edge is about 7.5% for 6 MV and 4.8% for 25 MV. For two different MLC (Elekta Precise and Varian Clinac 2300 c/d) at the same nominal energy (6 MV) photon, D~0(%) at 3 cm from the field edge is about 7.5% for Elekta and 6.6% for Varian. Conclusions: Gafchromic EBT film produces a high dose r e s p o n s e with a relatively unaffected e n e r g y response, in fact, at clinical relevant conditions (10 cm depth outside field edg e), no meaningful differences (about 1%) were obse rve d c o m p a r e d with ionization chamber. Therefore, EBT film, is found to be an excellent two-dimensional d o s i m e t e r for verification of d ose outside a multileaf collimated be a m showing th at s c a t t e r e d radiation d e c r e a s e with the increase of nominal e n e r g y and that, at the s a m e nominal ene rgy, changing of primary and s c a t t e r radiation c o m p o n e n t s ma y be related to specific LINAC mechanical feature such as source-collimator-distance. 463 The application of Co-60 calibrated chambers in electron dosimetry
plane-parallel
R. Kapsch 1, G. Bruggmoser2, G. Christ 3, O. Dohm 3, G. Hartmann 4, E. SchiJle 5 ~Physikalisch- Technische Bundesanstalt, Braunschweig, Germany 2Universit~tsklinikum Freiburg, Freiburg, Germany 3Universit~tsklinikum TiJbingen, TiJbingen, Germany 4German Cancer Research Center, Heidelberg, Germany Sphysikalisch-Technische Werkst~tten Dr. Pychlau GmbH, Freiburg, Germany For plane-parallel chambers used in electron dosimetry, modern dosimetry protocols (e.g. IAEA TRS-398) recommend a cross-calibration against a calibrated cylindrical chamber. The rationale for this is the assumed chamber-to-chamber variation of the correction factors (Pwa~l)co for plane-parallel chambers which may be unacceptably high (variations of up to 3% have been reported). In recent studies, however, much smaller chamber-to-chamber variations of (Pwali)co (less than 0.5%) were found for chambers of modern designs such as the PTW Roos M34001 or the similar Wellh0fer PPC-35. In our study we determined the overall perturbation factors
Pco (which are usually a s s u m e d to be equal to (Pwall)co) for a total of 28 c h a m b e r s of the Rods type (25 PTW 34001, 3 Wellh6fer PPC40), 15 c h a m b e r s of the Markus t ype (PTW 23343) and 10 c h a m b e r s of t he Advanced Markus type (PTW 34045). These c h a m b e r s were cross-calibrated a g a i n s t reference cylindrical c h a m b e r s of the type PTW 30006 (waterproof Farmer) in the hi gh-e ne rgy electron b e a m s available at PTB Braunschweig, the universities of TObingen and Freiburg, and t he German Cancer Research Center (DKFZ) in Heidelberg. All c h a m b e r s were furnished with an absorbed dose to w a t e r calibration factor for 6°Co from PTWFreiburg, which is directly t ra c e a bl e to PTB Braunschweig. The m e a s u r e m e n t s were performed in accordance with the revised version of the German dosimetry protocol DIN 68002 (to be published next year), which will be very similar to IAEA TRS-398. The a v e r a g e va l ue s for Pco obtained from all m e a s u r e m e n t s and t he relative e x p e r i m e n t a l s t a n d a r d deviations are shown in the following table: chamber type
Rods (PTW M34001, Wellhofer PPC40/ Markus (PTW M23343) Advanced Markus (PTW M34045)
1.020 1.018 1.016
experimental standard deviation 0.26% 0.19% 0.24%
The relative combined standard uncertainty of the Pco values determined here is 1.05% (including the uncertainties associated with the perturbation factors needed for the evaluation of P c o - cf. IAEA TRS-398). This should be compared with the uncertainty value of 1.5% stated in IAFA TRS-398. Our investigations confirm the results of other authors that chamber-to-chamber variations of Pco values for planeparallel chambers of the Rods, Markus and Advanced Markus types are less than 0.5%. This allows the specification of type-specific Pco values for these chambers in the revised version of the German dosimetry protocol DIN 6800-2, with the aim of making cross-calibrations for these types of planeparallel chambers unnecessary. 464 First results of t h e M O P I pixel ionization c h a m b e r used as beam m o n i t o r at t h e I n s t i t u t Curie - Centre de Protonthbrapie d'Orsay ( I C P O ) .
A. La Rosa 1,2 F. Bourhaleb s, R. Cirio 2, M. Donetti 23, M. A. Garella 2, S. Giordanengo 2, N. Givehchi x,2, S. Iliescu 2, B. Le Gall4, F. Marchetto 2, F. Martin 4, S. Meyroneinc 4, C. Peroni ~'2, G. Pitt~ s SExperimental Physics Department of Turin University, Turin, Italy 2INFN, Turin, Italy 3CNAO Foundation, Milan, Italy 4Curie Institute - Proton therapy Center (ICPO), Orsay, France STERA Foundation, Novara, Italy In a proton therapy center, one of the main issues is to assure a correct delivery of the dose to the patient. The beam has to be monitored in a non-invasive way downstream of the spreading system and its position, shape and intensity have to be measured just upstream the target. This in order to feedback the upstream elements of the beam line or to prevent against any possible failure. There are many requirements for a successful treatment, for example the accuracy in the spatial distribution of the dose delivered to the patient and the stability and reproducibility of the beam. For this reason real-time monitors placed along the beam line are recommended. The Orsay Proton therapy Center (ICPO) has been operating since 1990 for the ophthalmologic and intracranial treatments. The proton energy delivered by a synchrocyclotron is 200 MeV and the dose delivery system operates with passive scattering. Turin University and INFN, in collaboration with the ICPO,