ESTRO 2023 - Abstract Book

S1469

Digital Posters

ESTRO 2023

pattern, horizontal orientation, 90% infill and 0.2mm layer thickness was the most similar to plastic water with dose difference less than 3%. The 3D printed bolus on STEEV phantom showed good treatment result with an average dose of 200.6 cGy on the surface, which was much better compared to the phantom without bolus (161.0 cGy). The average doses on the surface of the wax bolus and the standard bolus were below expectation (193.0 cGy and 188.0 cGy respectively) Conclusion The optimal printing parameters were defined for patient-specific 3D-printed bolus with PLA-Pro material and the M300 Dual printer. Grid pattern, 0.2 mm layer thickness and 90% infill density were chosen for further use. The 3D printed bolus showed good agreement between calculated and measured dose. The clinical use is thus promising for 3D printed bolus. 1 Queen's Hospital, Radiotherapy Physics, Romford, United Kingdom; 2 Queen's Hospital, Radiotherapy Physics, Romford, United Kingdom Purpose or Objective The aim of this study is to determine and validate the local pass rates criteria for pre-treatment patient plan specific QA using commercial PerFRACTION software (Sun Nuclear Corporation, Melbourne, FL) for Halcyon treatment plans. Halcyon v2.0 (Varian Medical Systems, USA) uses a pre-configured beam model and produces IMRT/VMAT plans. Halcyon treatment plans’ use of dynamic modulation of dose rate, field aperture and gantry speed demands diligent pre-treatment verification. The centre currently verifies all treatment plans with Varian’s Portal Dosimetry (PD), which uses Anisotropic Analytical Algorithm (AAA) to predict the fluence pattern; this is the same algorithm used to generate clinical plans. The main disadvantage of PD is the lack of projecting delivered dose distribution onto a 3D patient dataset. PD uses an integrated measurement of 2D fluence in which the verification is done by field-by-field basis and composite plan. Dose reconstruction using information from the delivery trajectory log files of Halcyon could be more useful to verify the deliverability of the plan. Recently, Sun Nuclear has released the PerFRACTION software module to analyse trajectory log files, to provide a 3D dose distribution on a 3D patient CT dataset and compare with DICOM RT Dose input of the Halcyon plan. The centre also performs plan-of-the-month phantom-based PSQA on selected plans using ArcCHECK (Sun Nuclear Corporation) to complement PD. Materials and Methods Ten Halcyon patient treatment plans were produced in Eclipse v15.6 (Varian Medical System), using AAA algorithm. The tested plans cover treatment sites including head & neck, lung, prostate, bladder, rectum and breast. When the delivery log file is captured by PerFRACTION, the dose calculation is performed using a Collapsed Cone Convolution Superposition Algorithm. PD and ArcCHECK phantom measurements were performed at the planned gantry and collimator angles. A composite dose image of all treatment fields was created for the PD measurements. Gamma analysis was performed for the PerFRACTION, PD and ArcCHECK measurements. The correlation between the gamma passing rates of composite PD (Gamma 2%-2mm) and ArcCHECK (Gamma 3%-2mm) and PerFRACTION (Gamma 2%-2mm) was evaluated using the Bland Altman method. Results The mean pass rates were: PerFRACTION - 97.2% (SD ± 2.0%); PD - 98.3% (SD ± 1.8%); and ArcCHECK - 98.7% (SD ± 1.4%). Bland-Altman analysis indicates a good correlation between both PD and ArcCHECK versus PerFRACTION. Among the data plotted, only one datum was found to be an outlier in both correlation analysis. Conclusion This study confirms suitability of using PerFRACTION as a log file-based plan verification system for Halcyon with a pass rate criterion of 97% for 2%-2mm Gamma analysis (global). It is independent from the vendor’s PD and will be more efficient than using phantom-based ArcCHECK PSQA (which will be used at a lower frequency). 1 CIEMAT, Technology Department, Madrid, Spain; 2 CIEMAT, Unidad de Innovación Biomédica, Madrid, Spain; 3 CIEMAT, Technology Department , Madrid, Spain Purpose or Objective Some RX-tubes used in radiobiology studies has not monitor chamber to control the output X-ray dose. In this case the dose delivery to culture cells is based on the irradiation time controller. This could be a problem for a correct dose assignment to cell cultures and would implicate an important variation in radiobiological studies results because of X-ray tube output beam stability. To solve this, we propose the use of a conventional Ionization Chamber (IC) used for dosimetry as a pseudo Monitor Chamber (pMC) in a reference point which is placed off axis. Materials and Methods The RX-tube used was a MCN321 Philips model with a MG323 control system. The dosimetry equipment was a Farmer IC (Nuclear Enterprise; model NE-2571). The IC calibration was done based on the TRS-398 protocol supported by a secondary PO-1749 Validation of local tolerances for Halcyon pre-treatment plan verification using PerFRACTION V. Ganesan 1 , A. Ifthaker 2 , G. Kidane 2 , D. Withers 2 PO-1750 RX tube without monitoring chamber, dose corrections and implications in radiobiology results J.I. Lagares 1 , M. Ibáñez 1 , M. Oteo 1 , M.Á. Martín 2 , N. Chamorro 3 , P. Arce 3 , J.M. Pérez 3 , M.Á. Morcillo 3