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Microdosimetric depth measurements in the Nice fast neutron therapeutic beam
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86
Parameterization of the headscatter correction factor Sc for rectangular photon beams
MICRODOSIMETRIC MEASUREMENTS INTHE WGH ENERGY PROTON CANCER THERAPY BEAMS AT CLATIERBRIDGE ANDORSAY.
Symmetrical andasymmetrical. open and wedged fields J1M vanGasteren I) andJLMVenselwr) I) ART!, Anthem. 2) Dr B Verbeeten Instituut, Tilburg, The Netherlands
In lbecalculation of monitor units and tteatment times of MY photoo beams the beadscatter factor S, accounts for the change in pboton nuence when lbe collimator setting andthus lbefield size is changed. S, can be measured witll a narrow beam-coaxial phantom [I) as a fimctioo of the settings of tileX and Ycollimator blocks. Allboogh S, is expected to have a symmetrical nature S, turns outto be anasymmetrical fimClioo of these settings. Eloogated fields in X and Ydirections can haveSevalues which differseveral per cent. In m1er to obtain sufficient accuracy usually Se is measured for a matrix of field sizes of for instance X=2up to 40 an and Y=2up to 40 an . The reason of thisasymmetry originates from the factthat the X and Y blocks are located indifferent planes. So the apenure - loolring upstreem from the measurement pointto lbeblocks - is an asymmetrical'function of lbecollimator setting. Our approach is to correct lbe asymmetry in S, by considering S, as a function of lbe corrected field dimensions either CrX and Y or X and Cry. Thefactor Crhasa valuebetween 0.0 and 1.0depending onlbe beam energy and the accelerator design. An iteration algorithm based OIl the Clarkson approach is used to calculate a bestfit Crvalue from Sevalues of square and some elongated fields. Effectively the Se matrix is reduced to a one dimensional fimClion Se(r). with r the average radius of fields wilb dimensions X=~ and Y=aor X=aand Y=~. The algorithm is applied to calculate Se of rectangular shaped fields. The accuracy of the method. based on one single . a priori • unknown. parameter Cr is well within measurement accuracy (0.5 %). Besides. a substantial reduction of the number of Se measurements. necessary to covertheclinically used fields. is achieved thisway. Themethod is validated for symmetrical beams with energies ranging from 6 to 25 MY of accelerators of several manufacturers and also for asymmetrical wedged fields of the 6 MY beams of a Philips SU5 and a SallIme-41 machine. [I)
V.P.Cosgrove, S. Green. M.e.Scon, A. Kacperek and A. Mazal. The University of Birmingham, Edgbaston, Birmingham, England.
Microdosimetric measurements have been made in the 62MeV proton beam in Clatterbridge, UK, and in the 73MeV beam in Orsay, France. Both beams are currently used for the treatment of ocular melanoma (eye tumours). Measurements were made using a planar, wall-less proportional counter. designed specifically for use in proton beams. Measured lineal energy spectra indicated a shift to higher lineal energies with depth of beam penetration, with the most significant increases occurring near the end of each beams range. This trend was observed in both unmodulated and range modulated beams. The measured spectra were used to calculate mean quality factors. Q.using the latest ICRP relationshipsbetween Q and LET•. For the Clatterbridge and Orsay full-range modulated beams, was i.07±O.06 and i.26±OJ, respectively. at beam entrance. These values increased to 5.33±O.4 and 4.42±O.4. respectively, at the end of the beams range. with the most significant increase in ~ occurring in the final 2-3mmof range. The effect the increases in<:! will have on dose distribution with depth of penetration of the proton beams will be discussed, as too the implicationsthis will have regardingthe planning of proton therapy.
15
Van Gasterenet aI. Radiotherapy & Oncology, 20,250-257,1991.
87
88
MICRODOSIMETRIC DEPTII MEASUREMENTS IN llffi NICE FAST NEUTRONTHERAPEUTICBEAM
Quality assurance in 3-D treatment planning systems
LA.D. Bruinvis(Amsterdam. The Netherlands) P.COLAUTIl'. N.BRASSARTA, V.CONTE'. A. COURDIA, j,HERAULT\ G.TORNIELU', P.CHAlNELA 'INFN-LNL viaRomea 4,1·35020 LEGNARO· ITAI.Y o INFN-P.dov a. vi. Marwlo8, 1·35100 PADOVA -ITALY "Centre Antoine-Lacassagne, Cyclotron Biomedical. F·ll6200 NICE· FRANCE
In Nice biomedicalcyclotron, proton beams of 65 MeV of energy are used since June 1991 to treat ocular tumours (mainly uveal melanomas); up today 550 patients have been treated. Another application of the facility is tumour treatment by using fast neutron beams. 'The neutron beams are produced by bombarding beryllium targets with 60 MeV protons.The treatment unit consist of a vertical beam completed with a multileafCOllimator. The maximum aperture of the collimator at the treatment distance, 20 em from the end of collimator. is 23x24.5 em', The depth dose characteristics arc similar to those ones of a 8 MeV Linac. For lOx10 cm2 field the maximum dose is at 2 cm and the 50% isodose at 17em. The penumbra(80% 20%) at 5 em depth for this field is about 8 mm. Neutronsinteractwith biologicaltargets giving rise to charge particle secondary spectra of protons, deuterons, alfa particlesand light ions. Since neutron energy spectrum changes with depth, charge particle energy spectra is expected to change as well as their LET spectra. On the other words, the quality of the neutron beam is expected to change with the depth. Dosimetric measurements performed with iorusauon chambersare not able to measure the variation of radiation quality. Microdosimetry is a well known scientific tool able to describe the radiation quality and 10 measureits variation. We have performed microdosimetric measurements in the Nice fast neulron. beam at different depths with a spherical tissue-equivalent proporuonal counter which simulates211m of thickness. E~perim~n~ da~ will be compared with the dose depth curve and with radiobiological experimentdata, Results and comparisons will be discussed.
Abstractnot received
86
Parameterization of the headscatter correction factor Sc for rectangular photon beams
MICRODOSIMETRIC MEASUREMENTS INTHE WGH ENERGY PROTON CANCER THERAPY BEAMS AT CLATIERBRIDGE ANDORSAY.
Symmetrical andasymmetrical. open and wedged fields J1M vanGasteren I) andJLMVenselwr) I) ART!, Anthem. 2) Dr B Verbeeten Instituut, Tilburg, The Netherlands
In lbecalculation of monitor units and tteatment times of MY photoo beams the beadscatter factor S, accounts for the change in pboton nuence when lbe collimator setting andthus lbefield size is changed. S, can be measured witll a narrow beam-coaxial phantom [I) as a fimctioo of the settings of tileX and Ycollimator blocks. Allboogh S, is expected to have a symmetrical nature S, turns outto be anasymmetrical fimClioo of these settings. Eloogated fields in X and Ydirections can haveSevalues which differseveral per cent. In m1er to obtain sufficient accuracy usually Se is measured for a matrix of field sizes of for instance X=2up to 40 an and Y=2up to 40 an . The reason of thisasymmetry originates from the factthat the X and Y blocks are located indifferent planes. So the apenure - loolring upstreem from the measurement pointto lbeblocks - is an asymmetrical'function of lbecollimator setting. Our approach is to correct lbe asymmetry in S, by considering S, as a function of lbe corrected field dimensions either CrX and Y or X and Cry. Thefactor Crhasa valuebetween 0.0 and 1.0depending onlbe beam energy and the accelerator design. An iteration algorithm based OIl the Clarkson approach is used to calculate a bestfit Crvalue from Sevalues of square and some elongated fields. Effectively the Se matrix is reduced to a one dimensional fimClion Se(r). with r the average radius of fields wilb dimensions X=~ and Y=aor X=aand Y=~. The algorithm is applied to calculate Se of rectangular shaped fields. The accuracy of the method. based on one single . a priori • unknown. parameter Cr is well within measurement accuracy (0.5 %). Besides. a substantial reduction of the number of Se measurements. necessary to covertheclinically used fields. is achieved thisway. Themethod is validated for symmetrical beams with energies ranging from 6 to 25 MY of accelerators of several manufacturers and also for asymmetrical wedged fields of the 6 MY beams of a Philips SU5 and a SallIme-41 machine. [I)
V.P.Cosgrove, S. Green. M.e.Scon, A. Kacperek and A. Mazal. The University of Birmingham, Edgbaston, Birmingham, England.
Microdosimetric measurements have been made in the 62MeV proton beam in Clatterbridge, UK, and in the 73MeV beam in Orsay, France. Both beams are currently used for the treatment of ocular melanoma (eye tumours). Measurements were made using a planar, wall-less proportional counter. designed specifically for use in proton beams. Measured lineal energy spectra indicated a shift to higher lineal energies with depth of beam penetration, with the most significant increases occurring near the end of each beams range. This trend was observed in both unmodulated and range modulated beams. The measured spectra were used to calculate mean quality factors. Q.using the latest ICRP relationshipsbetween Q and LET•. For the Clatterbridge and Orsay full-range modulated beams, was i.07±O.06 and i.26±OJ, respectively. at beam entrance. These values increased to 5.33±O.4 and 4.42±O.4. respectively, at the end of the beams range. with the most significant increase in ~ occurring in the final 2-3mmof range. The effect the increases in<:! will have on dose distribution with depth of penetration of the proton beams will be discussed, as too the implicationsthis will have regardingthe planning of proton therapy.
15
Van Gasterenet aI. Radiotherapy & Oncology, 20,250-257,1991.
87
88
MICRODOSIMETRIC DEPTII MEASUREMENTS IN llffi NICE FAST NEUTRONTHERAPEUTICBEAM
Quality assurance in 3-D treatment planning systems
LA.D. Bruinvis(Amsterdam. The Netherlands) P.COLAUTIl'. N.BRASSARTA, V.CONTE'. A. COURDIA, j,HERAULT\ G.TORNIELU', P.CHAlNELA 'INFN-LNL viaRomea 4,1·35020 LEGNARO· ITAI.Y o INFN-P.dov a. vi. Marwlo8, 1·35100 PADOVA -ITALY "Centre Antoine-Lacassagne, Cyclotron Biomedical. F·ll6200 NICE· FRANCE
In Nice biomedicalcyclotron, proton beams of 65 MeV of energy are used since June 1991 to treat ocular tumours (mainly uveal melanomas); up today 550 patients have been treated. Another application of the facility is tumour treatment by using fast neutron beams. 'The neutron beams are produced by bombarding beryllium targets with 60 MeV protons.The treatment unit consist of a vertical beam completed with a multileafCOllimator. The maximum aperture of the collimator at the treatment distance, 20 em from the end of collimator. is 23x24.5 em', The depth dose characteristics arc similar to those ones of a 8 MeV Linac. For lOx10 cm2 field the maximum dose is at 2 cm and the 50% isodose at 17em. The penumbra(80% 20%) at 5 em depth for this field is about 8 mm. Neutronsinteractwith biologicaltargets giving rise to charge particle secondary spectra of protons, deuterons, alfa particlesand light ions. Since neutron energy spectrum changes with depth, charge particle energy spectra is expected to change as well as their LET spectra. On the other words, the quality of the neutron beam is expected to change with the depth. Dosimetric measurements performed with iorusauon chambersare not able to measure the variation of radiation quality. Microdosimetry is a well known scientific tool able to describe the radiation quality and 10 measureits variation. We have performed microdosimetric measurements in the Nice fast neulron. beam at different depths with a spherical tissue-equivalent proporuonal counter which simulates211m of thickness. E~perim~n~ da~ will be compared with the dose depth curve and with radiobiological experimentdata, Results and comparisons will be discussed.
Abstractnot received