ESTRO 37 Abstract book

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ESTRO 37

bladder dose is -2,9±0,9%, -2,9±1,2% and -4,5±0,8% for D2cc, maximum and average dose respectively . For lung treatments ACE calculation in standard mode without heterogeneity density corrections shows a difference of 1,0±2,5%, 0,4±0,4%, 0,5±0,5%, -28,0±25,4% and -7,2±8,3% for CTV D 100 , D 90 , D 95, maximum and average dose respectively. The difference for lung dose is 0,1±0.1% and 1,1±0,6% for D2cc and maximum dose respectively. For the same treatments ACE calculation in standard mode with heterogeneity density corrections shows a difference of 0,7±3,4%, 0,2±0,8%, 0,2±1,1%, -28,0±25,4% and -7,4±8,3% for CTV D 100 , D 90 , D 95, maximum and average dose respectively. The difference for lung dose is -1,1±0.6% and 0,2±1,1% for D2cc and maximum dose respectively. Conclusion For the cervical treatments the ACE algorithm shows a good agreement between TG43 and the calculation without density correction, both for standard and high resolution mode. Taking into account the density of the applicator a slight overestimation of the dose for the TG43 algorithm both for CTV and OARs is seen. In the case of lung treatments the ACE algorithm shows the same differences respect to TG43 both for calculation in water and in the case of density correction. EP-1889 Benchmarking spot fluence profiles for four proton treatment planning systems against measured data J. Alshaikhi 1 , D. D’Souza 1 , C. G. Ainsley 2 , G. Royle 3 , R. A. Amos 3 1 UCLH, Radiotherapy Physics, LONDON, United Kingdom 2 UPenn, Roberts Proton Therapy Center- University of Pennsylvania, Philadelphia, USA 3 UCL, Department of Medical Physics and Biomedical Engineering- University College London, London, United Kingdom Purpose or Objective Accurate beam modelling is an essential function of a treatment planning system (TPS) to ensure that plans can be calculated that are deliverable within clinically acceptable tolerances. The purpose of this work is to evaluate computed in-air spot fluence lateral profiles and spot ellipticity of four commercially available proton TPSs, benchmarked against measured data. The four TPSs (Eclipse TM , XiO ® , Pinnacle 3 , RayStation ® ) were commissioned using pencil beam scanning data from the University of Pennsylvania (UPenn) facility. Material and Methods Individual “in-air” spot fluence profiles for 27 nominal energies, ranging from 100 to 226.7 MeV, were calculated at the surface of a water phantom in each TPS with a calculation grid size of 1mm. Profiles at five source-to- surface distances relative to isocentre (+20, +10, 0, -10, - 17cm) were calculated for all energies. These were all benchmarked against measured data from UPenn, comparing full-width-at-half-maximum (FWHM) and widths at 95, 20, and 10% maximum in both x and y directions. Lateral penumbrae (80-20%) were also compared. Gamma-index analysis with pass criteria of 1, 1.5, 2, and 3%/1, 1.5, 2, and 3 mm were used. Spot ellipticity agreement was calculated using equation 1: Results Mean percentage of spot fluence lateral profiles at the isocentre with >95% pass rate for 1 mm/1% criteria in x – direction were 97.6% (SD 2) for XiO ® , 93.1% (SD 10.4) for Eclipse TM , 93.5% (SD 3.1) for Pinnacle 3 , and 77.6% (SD 12.4) for RayStation ® . For Y – direction at the isocentre were 94.2% (SD 4.8) for XiO ® , 83.9% (SD 7.5) for Eclipse TM , 84.5% (SD 9) for Pinnacle 3 , and 94.5% (SD 6.2) for

Fig. 2. Averaged DVH comparison of PTV and OARs for standard HT and StatRT scheme. 3.Total treatment time for StatRT scheme: MV scanning on HT–5 minutes, planning–20 minutes, treating 5 minutes (unnecessary additional positioning of patient).Total treatment time for standard HT: CT scanning–5 minutes (several days before treatment), planning–2 hours, treating–20 minutes. Conclusion The difference between the standard HT procedure and StatRT scheme for 9 iterations for PTV and OAR doses was not statistically and clinically significant. In time sensitive cases standard HT may be replaced by StatRT scheme for patients with good prognosis. There were no statistically significant differences between the HT plan and StatRT plan for 9 iterations, moreover it provides significantly faster start of treatment. EP-1888 A retrospective comparison of the new commercial algorithm ACE and TG43 for brachytherapy treatments V. Ravaglia 1 , G. Mazzotti 1 , G. Feliciani 1 , E. Menghi 1 , A. Sarnelli 1 1 IRST - Istituto Tumori della Romagna, Medical Physicist, ForliMeldola FC, Italy Purpose or Objective To evaluate the dosimetric impact of the novel commercial algorithm ACE (Advanced Collapsed-cone Engine, Elekta) respect to the TG43 calculation. Material and Methods 20 patients and a total of 100 plans of cervical and lung brachytherapy treatments were retrospectively evaluated using the commercial algorithm ACE, using both water density and the TG186 heterogeneity corrections. The original TG43 calculated plans were recalculated using ACE algorithm with same dwell positions and times. We recalculated the plans using both standard (grid size 1 mm within 1 cm from the implant, 2 mm within 8 cm and 5 mm beyond) and high resolution mode (grid size 1 mm within 8 cm from the implant and 2 mm beyond). The difference between TG43 and TG186 with and without density correction were calculated in terms of mean and maximum organ dose and DVH values for CTV, rectum and bladder for cervical treatments and CTV and lung for lung treatment. Results For cervical treatments ACE calculation without heterogeneity density corrections in standard mode shows a difference of -0,4±3,0%, 0,7±0,2%, 0,7±0,2% for D 90 , D 100 and D 95 for CTV respectively. The difference for rectum dose is 0,3±0,5%, 0,8±0,3% and -0,7±1,1% for D2cc, maximum and average dose respectively and the difference for bladder dose is 0,7±0,5%, 0,8±0,6% and - 0,5±0,6% for D2cc, maximum and average dose respectively. The same plans with heterogeneity corrections in standard mode shows a difference of -5,9±2,8%, - 3,6±0,4%, -3,8±0,6% for D 90 , D 100 and D 95 for CTV respectively. The difference for rectum dose is - 4,2±1,2%, -2,4±1,5% and -5,6±1,6% for D2cc, maximum and average dose respectively and the difference for