ESTRO 37 Abstract book

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ESTRO 37

summary of the current status of dose-painting using PET and then focus on integrating the upcoming field of Radiomics. References: [1] Everitt S, Ball D, Hicks RJ, et al. Int J Radiat Oncol Biol Phys 2017;99:947-955. [2] Grootjans W, de Geus-Oei LF, Troost EG, Visser EP, Oyen WJ Bussink J. Nat Rev Clin Oncol 2015;12:395-407 [3] Hoeben BA, Troost EG, Span PN, et al. J Nucl Med 2013;54:532-540. [4] Ling CC, Humm J, Larson S, et al. Int J Radiat Oncol Biol Phys 2000;47:551-560. [5] Lock S, Perrin R, Seidlitz A, et al. Radiother Oncol 2017;124:533-540. [6] Madani I, Duprez F, Boterberg T, et al. Radiother Oncol 2011;101:351-355. [7] Nehmeh SA, Lee NY, Schroder H, et al. Int J Radiat Oncol Biol Phys 2008;70:235-242. [8] Peeters SG, Zegers CM, Lieuwes NG, et al. Int J Radiat Oncol Biol Phys 2015;91:351-359. [9] Servagi-Vernat S, Differding S, Hanin FX, et al. Eur J Nucl Med Mol Imaging 2014;41:1544-1552. [10] Troost EG, Schinagl DA, Bussink J, Oyen WJ Kaanders JH. Radiother Oncol 2010;96:328-334. [11] van Elmpt W, De Ruysscher D, van der Salm A, et al. Radiother Oncol 2012;104:67-71. [12] Wanet M, Delor A, Hanin FX, et al. Strahlenther Onkol 2017;193:812-822. [13] Welz S, Monnich D, Pfannenberg C, et al. Radiother Oncol 2017. [14] Zegers CM, van Elmpt W, Reymen B, et al. Clin Cancer Res 2014;20:6389-6397. [15] Zegers CM, van Elmpt W, Wierts R, et al. Radiother Oncol 2013;109:58-64. [16] Zips D, Zophel K, Abolmaali N, et al. Radiother Oncol 2012;105:21-28. [17] Zschaeck S, Haase R, Abolmaali N, et al. Acta Oncol 2015;54:1355-1363. SP-0030 Dose calculation accuracy for lung proton therapy in clinical practice D. Followill 1 , P. Taylor 1 , D. Branco 1 , S. Kry 1 1 MD Anderson Cancer Center, IROC Houston QA Center, Houston, USA Abstract text Purpose : To compare analytic and Monte Carlo-based algorithms for proton dose calculations in the lung, benchmarked against static geometrical and moving anthropomorphic lung phantom measurements. Methods : Heterogeneous static geometrical and anthropomorphic moving lung phantoms (figure 1) have been irradiated at numerous proton therapy centers. At multiple centers, the treatment plan could be calculated with both an analytic and Monte Carlo algorithm. The doses calculated in the treatment plans were compared with the doses delivered to the phantoms, which were measured using thermoluminescent dosimeters and film. Point doses were compared, as were planar doses using a gamma analysis. Results : The analytic algorithms overestimated the dose to the center of the target by an average of 7.2%, whereas the Monte Carlo algorithms were within 1.6% of the physical measurements on average. In some regions of the target volume, the analytic algorithm calculations differed from the measurement by up to 31% in the iGTV (46% in the PTV), over-predicting the dose. SP-0029 Abstract not received Symposium: Is dose calculation in proton therapy clinical practice a solved problem?

All comparisons showed a region of at least 15% dose discrepancy within the iGTV between the analytic calculation and the measured dose. Some analytical algorithms appear to agree better with Monte Carlo calculations than other algorithms. The Monte Carlo algorithm recalculations showed excellent agreement with the measured doses, showing mean agreement within 4% for all cases, and a maximum difference of 12% within the iGTV. Conclusions : Analytic algorithms often do a poorer job predicting proton dose in lung tumors but there varying levels of accuracy. Monte Carlo algorithms showed excellent agreement with physical measurements. Analytic algorithms for treatment of lung targets should not be used unless extensive validation counters the consistent results of the current study. The use of Monte Carlo algorithms for proton therapy in the lung is expected to improve clinical outcomes.

SP-0031 Impact of beam modifiers and heterogeneities in dose calculation accuracy F. Fracchiolla 1 1 Centro di Protonterapia, Protonterapia ospedale di Trento, Trento, Italy Abstract text I’ll discuss about pencil beam scanning proton therapy delivery techniques and the impact of any passive hardware and heterogeneities in patient’s anatomy on the dose calculation accuracy. For both of these points I will show a complete bibliography review on how those issues are treated all around the world and what is my experience, in particular in our proton therapy center. The discussion on beam modifiers can be limited to the pre-absorber (also known as Range Shifter) and collimators for pencil beam scanning delivery technique. The Range Shifter is a plastic block mounted at the very end of the beamline to let the treatment of shallow lesions. Usually the lowest energy available in a cyclotron based facility is around 60-70MeV that, in terms of range in water, is around 3.1-4.0 cm. In order to treat tumors shallower than these we need to pull back the Bragg peak with an energy degrader just before the patient surface: this is the role of the Range Shifter. Different centers use it in different configurations. It can be used attached to