- Email: [email protected]
211. CyberKnife SBRT: Monte Carlo (MC) vs. Ray Tracing (RT) in retrorbital and subcutaneous tumors.
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Abstracts / Physica Medica 56 (2018) 133–278
radiation to be correlated with iViewGT pixel reading (R). For open and modulated fields, comparison to TPS dose maps (MonacoXVMonteCarlo) was assessed through profiles and gamma analysis. Results. For a given beam, the response of iViewGT was confirmed to be linear (D(Gy) = m ⁄ R + q), as already established for Varian EPIDs. Similarly, the variable slope response to primary radiation was modelled according to the following empirical algorithm: mpr(OF) = aOF + b; OF (EwwF) = [c + d ln(EwwF)] 1 where EwwF is the equivalent field size of each segment based on IC data and OF is the EPID reading measured output factor. For transmitted radiation the relation mtr = k mpr was adopted. Conclusions. The extension of GLAaS to iViewGT offers the opportunity to easily set-up flexible and reliable verification, also in highly demanding conditions as for SRS and SBRT treatments; the compatibility with different technologies could encourage multi-centers studies concerning treatment delivery and dose calculation problematics.
Reference 1. Nicolini G. Evaluation of an aSi-EPID with FFF beams: applicability to the GLAaS algorithm for portal dosimetry and first experience for pretreatment QA of RapidArc. Med Phys 2013; 40(11):111719/1–9/9. https://doi.org/10.1016/j.ejmp.2018.04.221
211. CyberKnife SBRT: Monte Carlo (MC) vs. Ray Tracing (RT) in retrorbital and subcutaneous tumors A. Micali, F. Midili, A. Brogna, A. Di Pasquale, V. Mongelli, C. Siragusa, M.C. Angiocchi, P. Inferrera, S. Lanzafame, I. Ielo U.O.C. di Fisica Sanitaria – A.O.U. Policlinico ‘‘G. Martino”, Messina, Italy Purpose. Monte Carlo (MC) is indicated as the ‘‘gold standard” of dose calculation algorithms. MC predicts the absorbed dose by simulating electron and photon transport and takes into account the electronic disequilibrium due to tissues heterogeneity. In this study, MC algorithm was used first to re-calculate and then to re-optimize RT plans of retrorbital and subcutaneous tumors in order to investigate differences in the dose distribution and PTVcoverage. Methods. Firstly, 10 retrorbital and 10 subcutaneous RT and MC re-calculated plans were generated with the aim of evaluate the PTVcoverage. Then, in the ‘‘Sequential” workspace, the RT plans were optimized using the MC algorithm, setting medium resolution and 1% statistical uncertainty, leaving the other optimization parameters (collimators size, max Monitor Units (MU) per beam and per node, constraints and objectives) unchanged. In the ‘‘Evaluate” workspace, MC plans were calculated in high resolution and were prescribed at the same isodose of the RT ones and compared. The same process was repeated setting 0.5% statistical uncertainty. Results. For the retrorbital tumors, the comparison between RT and only re-calculated MC plans did not show significant differences in the PTVcoverage and in the dose distributions. Instead, MC optimized plans with 1% statistical uncertainty always showed a PTVcoverage lower than RT one (Fig. 1): V100 RT [95.4–99.08]% vs. V100 MC [78.7–80.1]%. When MC plans were optimized with 0.5%
Fig.1: An example of retrorbital MC optimized plan with 1% statistical uncertainty (Active) compared with RT one (Ref). MC plan showed a PTVcoverage [78.7%] lower than RT one [95.0%].
Abstracts / Physica Medica 56 (2018) 133–278
191
Fig.2: An example of retrorbital MC optimized plan with 0,5% statistical uncertainty (Active) compared with RT one (Ref). MC plan showed a PTVcoverage [97.3 %] comparable with RT one [95.0 %]. statistical uncertainty, the PTVcoverage was similar to the RT one (Fig. 2). Furthermore, RT and MC plans had comparable beams number and total MU. For the subcutaneous tumors, in all the comparison performed, no significant differences were registered. Conclusion. For retrorbital and subcutaneous tumors, the negligible difference between the optimized MC plans with 0.5% statistical uncertainty and the RT ones, justified the use of the RT algorithm, involving a corrected prescription isodose choice and a right DVH evaluation. https://doi.org/10.1016/j.ejmp.2018.04.222
212. RapidArc versus IMRT for postoperative irradiation of a case of recurrent breast cancer with internal mammary lymph node involvement P. Tamborra a, M. Bettiol a, R. Carbonara b, A. Di Rito a, M. Lioce a, A. Milella a, A. Nardone a, R. Necchia a, V. Didonna a, R. Massafra a a b
time. Target coverage and dose-sparing for OARs were not acceptable with 3DCRT because of chest’s anatomical conformation. Conclusion. Our dosimetric results confirmed that RapidArc allows to obtain optimal target-coverage and adequate dose-sparing for OARs as reported in literature [1]. It could be appropriate to reduce the respiration-induced intra-fraction target motion using breathhold techniques. Reference 1. Zhang Q, Yu XL, et al.. Dosimetric comparison for volumetric modulated arc therapy and intensity-modulated radiotherapy on the left-sided chest wall and internal mammary nodes irradiation in treating post-mastectomy breast cancer. Rad Oncol 2015; 49(1):91–8.
https://doi.org/10.1016/j.ejmp.2018.04.223
I.R.C.C.S. ‘‘Giovanni Paolo II”, National Cancer Centre, Bari, Italy University of Bari ‘‘Aldo Moro”, Bari, Italy
Purpose. The aim of this case-report is a dosimetric comparison between RapidArc and IMRT treatment plans for a recurrent breast cancer with internal mammary chain (IMC) involvement. Methods. A 46 years old woman with peri-prosthetic recurrent breast cancer was evaluated for postoperative left chest wall and homolateral periclavicular and IMC irradiation, with the inclusion of internal mammary lymph node (IMN) that uptaked fluorodeoxyglucose at postoperative PET. Prescription dose (PD) to PTV (left chest wall and homolateral IMC) was 50 Gy(2 Gy/die); PD to left periclavicular region was 46,8 Gy (1,87 Gy/die); the PET-positive IMN received a simultaneous integrated boost up to 59,25 Gy (2,37 Gy/die; EQD2 of 64 Gy with estimated a/ b3). A 1 cm-tissue equivalent bolus was used on the skin. We compared RapidArc with 5-beams step-and-shot IMRT plans according to target coverage, conformity and dose-homogeneity index, Organs at Risk (OARs) sparing (heart, lungs, spinal cord). Controlateral breast was not evaluated because of a previously implanted prosthesis. Number of monitor units (MU) and treatment delivery time were also considered. Daily image-guided radiotherapy was performed in order to reduce inter fraction organ motion. Results. RapidArc achieves better PTV and boost dose coverage and dose-homogeneity compared to IMRT. RapidArc also allows a better normal OARs sparing, with fewer monitor units and shorter delivery
213. Pre-treatment verification of stereotactic plans using a bi-dimensional diamond detector C. Talamonti a,b, A. Bartoli b, M. Scaringella c, A. Baldi d, L. Masi e, S. Pallotta a,b, M. Bruzzi b,f a University of Florence, Dept Biomedical Experimental Clinical Science ‘‘Mario Serio”, Florence, Italy b Istituto Nazionale di Fisica Nucleare, Florence Unit, Florence, Italy c University of Florence, Dept. Information Engineering, Florence, Italy d University of Florence, Dept. Industrial Engineering, Florence, Italy e IFCA, Dept. Medical Physics and Radiation Oncology, Florence, Italy f Dept. Physics and Astronomy, University of Florence, Florence, Italy
Purpose. The aim of this study is to test the performance of a new bi-dimensional diamond dosimeter, manufactured within the DIAPIX and IRTP Italian INFN projects, in pre-treatment verification of high conformal plans. Methods. DIAPIX dosimeter consists of two pCVD diamond matrices (12 12 pixels, 2 mm pitch) coupled together covering a total area 2.5 4.8 cm2 with 1 mm dead space between matrices [1]. Dosimetric verifications of lung plans delivered with Cyberknife (CK) and 6 MV photon Elekta Synergy BM (EBM) were compared with the plans calculated with Multiplan Cyberknife and Monaco Elekta TPS. Since some pixels, mainly concentrated in a single matrix, were not fully operational, two measurements in gun-
Abstracts / Physica Medica 56 (2018) 133–278
radiation to be correlated with iViewGT pixel reading (R). For open and modulated fields, comparison to TPS dose maps (MonacoXVMonteCarlo) was assessed through profiles and gamma analysis. Results. For a given beam, the response of iViewGT was confirmed to be linear (D(Gy) = m ⁄ R + q), as already established for Varian EPIDs. Similarly, the variable slope response to primary radiation was modelled according to the following empirical algorithm: mpr(OF) = aOF + b; OF (EwwF) = [c + d ln(EwwF)] 1 where EwwF is the equivalent field size of each segment based on IC data and OF is the EPID reading measured output factor. For transmitted radiation the relation mtr = k mpr was adopted. Conclusions. The extension of GLAaS to iViewGT offers the opportunity to easily set-up flexible and reliable verification, also in highly demanding conditions as for SRS and SBRT treatments; the compatibility with different technologies could encourage multi-centers studies concerning treatment delivery and dose calculation problematics.
Reference 1. Nicolini G. Evaluation of an aSi-EPID with FFF beams: applicability to the GLAaS algorithm for portal dosimetry and first experience for pretreatment QA of RapidArc. Med Phys 2013; 40(11):111719/1–9/9. https://doi.org/10.1016/j.ejmp.2018.04.221
211. CyberKnife SBRT: Monte Carlo (MC) vs. Ray Tracing (RT) in retrorbital and subcutaneous tumors A. Micali, F. Midili, A. Brogna, A. Di Pasquale, V. Mongelli, C. Siragusa, M.C. Angiocchi, P. Inferrera, S. Lanzafame, I. Ielo U.O.C. di Fisica Sanitaria – A.O.U. Policlinico ‘‘G. Martino”, Messina, Italy Purpose. Monte Carlo (MC) is indicated as the ‘‘gold standard” of dose calculation algorithms. MC predicts the absorbed dose by simulating electron and photon transport and takes into account the electronic disequilibrium due to tissues heterogeneity. In this study, MC algorithm was used first to re-calculate and then to re-optimize RT plans of retrorbital and subcutaneous tumors in order to investigate differences in the dose distribution and PTVcoverage. Methods. Firstly, 10 retrorbital and 10 subcutaneous RT and MC re-calculated plans were generated with the aim of evaluate the PTVcoverage. Then, in the ‘‘Sequential” workspace, the RT plans were optimized using the MC algorithm, setting medium resolution and 1% statistical uncertainty, leaving the other optimization parameters (collimators size, max Monitor Units (MU) per beam and per node, constraints and objectives) unchanged. In the ‘‘Evaluate” workspace, MC plans were calculated in high resolution and were prescribed at the same isodose of the RT ones and compared. The same process was repeated setting 0.5% statistical uncertainty. Results. For the retrorbital tumors, the comparison between RT and only re-calculated MC plans did not show significant differences in the PTVcoverage and in the dose distributions. Instead, MC optimized plans with 1% statistical uncertainty always showed a PTVcoverage lower than RT one (Fig. 1): V100 RT [95.4–99.08]% vs. V100 MC [78.7–80.1]%. When MC plans were optimized with 0.5%
Fig.1: An example of retrorbital MC optimized plan with 1% statistical uncertainty (Active) compared with RT one (Ref). MC plan showed a PTVcoverage [78.7%] lower than RT one [95.0%].
Abstracts / Physica Medica 56 (2018) 133–278
191
Fig.2: An example of retrorbital MC optimized plan with 0,5% statistical uncertainty (Active) compared with RT one (Ref). MC plan showed a PTVcoverage [97.3 %] comparable with RT one [95.0 %]. statistical uncertainty, the PTVcoverage was similar to the RT one (Fig. 2). Furthermore, RT and MC plans had comparable beams number and total MU. For the subcutaneous tumors, in all the comparison performed, no significant differences were registered. Conclusion. For retrorbital and subcutaneous tumors, the negligible difference between the optimized MC plans with 0.5% statistical uncertainty and the RT ones, justified the use of the RT algorithm, involving a corrected prescription isodose choice and a right DVH evaluation. https://doi.org/10.1016/j.ejmp.2018.04.222
212. RapidArc versus IMRT for postoperative irradiation of a case of recurrent breast cancer with internal mammary lymph node involvement P. Tamborra a, M. Bettiol a, R. Carbonara b, A. Di Rito a, M. Lioce a, A. Milella a, A. Nardone a, R. Necchia a, V. Didonna a, R. Massafra a a b
time. Target coverage and dose-sparing for OARs were not acceptable with 3DCRT because of chest’s anatomical conformation. Conclusion. Our dosimetric results confirmed that RapidArc allows to obtain optimal target-coverage and adequate dose-sparing for OARs as reported in literature [1]. It could be appropriate to reduce the respiration-induced intra-fraction target motion using breathhold techniques. Reference 1. Zhang Q, Yu XL, et al.. Dosimetric comparison for volumetric modulated arc therapy and intensity-modulated radiotherapy on the left-sided chest wall and internal mammary nodes irradiation in treating post-mastectomy breast cancer. Rad Oncol 2015; 49(1):91–8.
https://doi.org/10.1016/j.ejmp.2018.04.223
I.R.C.C.S. ‘‘Giovanni Paolo II”, National Cancer Centre, Bari, Italy University of Bari ‘‘Aldo Moro”, Bari, Italy
Purpose. The aim of this case-report is a dosimetric comparison between RapidArc and IMRT treatment plans for a recurrent breast cancer with internal mammary chain (IMC) involvement. Methods. A 46 years old woman with peri-prosthetic recurrent breast cancer was evaluated for postoperative left chest wall and homolateral periclavicular and IMC irradiation, with the inclusion of internal mammary lymph node (IMN) that uptaked fluorodeoxyglucose at postoperative PET. Prescription dose (PD) to PTV (left chest wall and homolateral IMC) was 50 Gy(2 Gy/die); PD to left periclavicular region was 46,8 Gy (1,87 Gy/die); the PET-positive IMN received a simultaneous integrated boost up to 59,25 Gy (2,37 Gy/die; EQD2 of 64 Gy with estimated a/ b3). A 1 cm-tissue equivalent bolus was used on the skin. We compared RapidArc with 5-beams step-and-shot IMRT plans according to target coverage, conformity and dose-homogeneity index, Organs at Risk (OARs) sparing (heart, lungs, spinal cord). Controlateral breast was not evaluated because of a previously implanted prosthesis. Number of monitor units (MU) and treatment delivery time were also considered. Daily image-guided radiotherapy was performed in order to reduce inter fraction organ motion. Results. RapidArc achieves better PTV and boost dose coverage and dose-homogeneity compared to IMRT. RapidArc also allows a better normal OARs sparing, with fewer monitor units and shorter delivery
213. Pre-treatment verification of stereotactic plans using a bi-dimensional diamond detector C. Talamonti a,b, A. Bartoli b, M. Scaringella c, A. Baldi d, L. Masi e, S. Pallotta a,b, M. Bruzzi b,f a University of Florence, Dept Biomedical Experimental Clinical Science ‘‘Mario Serio”, Florence, Italy b Istituto Nazionale di Fisica Nucleare, Florence Unit, Florence, Italy c University of Florence, Dept. Information Engineering, Florence, Italy d University of Florence, Dept. Industrial Engineering, Florence, Italy e IFCA, Dept. Medical Physics and Radiation Oncology, Florence, Italy f Dept. Physics and Astronomy, University of Florence, Florence, Italy
Purpose. The aim of this study is to test the performance of a new bi-dimensional diamond dosimeter, manufactured within the DIAPIX and IRTP Italian INFN projects, in pre-treatment verification of high conformal plans. Methods. DIAPIX dosimeter consists of two pCVD diamond matrices (12 12 pixels, 2 mm pitch) coupled together covering a total area 2.5 4.8 cm2 with 1 mm dead space between matrices [1]. Dosimetric verifications of lung plans delivered with Cyberknife (CK) and 6 MV photon Elekta Synergy BM (EBM) were compared with the plans calculated with Multiplan Cyberknife and Monaco Elekta TPS. Since some pixels, mainly concentrated in a single matrix, were not fully operational, two measurements in gun-