ESTRO 2020 Abstract Book

S305 ESTRO 2020

Results The three systems use different approaches and customized alert indices, based on institutional preferences. For VMAT treatments T% mean values were 11.8 and 18.0% for DC, 16.0% for PF systems, and up to 8.9% for SD system. Errors due to “anatomical variations” for Head and Neck treatments were up to 9.0% for SD, 9.0% for DC and 8.0% for PF systems, while for Abdomen Pelvis/Prostate treatments were up to 9.0% for SD, up to 17.1 for DC and up to 9.0% for PF. Comparison among various techniques can be obtained analyzing mean SD results: 1.5% (range 0-3.0%) for SBRT; 7.0% (range 4.7 – 8.9%) for VMAT; 10.4% (range 7.0 - 12.2%) for IMRT; 13.2% (range 8.8 – 21.0%) for the 3D CRT.

Conclusion Assessment of whole volume concordance with JCI does not reliably distinguish between acceptable and unacceptable variations in the iITV. This was not improved by increasing of JCI to 0.8. The addition of GMI may aid analysis but there is no agreed significant value. Further work is needed to explore whether slice-by-slice analysis would lead to better discrimination and provide automated decision making. However, the qualitative review with clinician feedback remains an essential component of a RTQA programme. It can lead to improved clinician skills, delineation and identification of ambiguities in the protocol. PD-0549 Improving radiotherapy accuracy with EPID in- vivo dosimetry: results from a multicentric study. M. Esposito 1 , A. Piermattei 2 , S. Bresciani 3 , L.C. Orlandini 4 , M.D. Falco 5 , S. Giancaterino 5 , C. Savino 6 , A. Ianiro 6 , R. Nigro 7 , L. Botez 3 , S. Riccardi 7 , A. Fidanzio 2 , F. Greco 2 , E. Villaggi 8 , S. Russo 9 , M. Stasi 3 1 USL CENTRO TOSCANA, S.C. Fisica Sanitaria, Bagno a Ripoli, Italy ; 2 Radioterapia Oncologica ed Ematologia- Fondazione Policlinico Universitario “A. Gemelli” IRCCS, UOC di Fisica Sanitaria-, Roma, Italy ; 3 Candiolo Cancer Institute – FPO IRCCS, Medical Physics, Candiolo, Italy ; 4 Sichuan Cancer Hospital, Department of Radiation Oncology, Chengdu, China ; 5 Università di Chieti, Dipartimento di Radioterapia, Chieti, Italy ; 6 Fondazione di ricerca e cura “Giovanni Paolo II”, Medical Physics Unit, Campobasso, Italy ; 7 OGP S. Camillo de Lellis, Medical Physics Unit, Rieti, Italy ; 8 AUSL Piacenza, Medical Physics Unit, Piacenza, Italy ; 9 USL Toscana Centro, S.C. Fisica Sanitaria, Bagno a Ripoli, Italy Purpose or Objective The Working Group of Associazione Italiana di Fisica Medica on in-vivo dosimetry (IVD) carried out a program to investigate critical aspects and effectiveness of IVD obtained by electronic portal imaging device (EPID). Material and Methods 8 Centers, equipped with three commercial systems (SOFTDISO (SD), Dosimetry Check (DC), and PerFRACTION (PF)), collected IVD results for a total of 2010 patients and 32516 tests. In the table, data are summarized for IVD software, radiotherapy technique and treated anatomical site. Every Center reported the number of patients and tests carried out and the percentage of tests out of the tolerance level (T%). T% was categorized as due to: incorrect setup, incorrect use of immobilization devices, incorrect computation, anatomical variations and unknown causes.

Table: Number of patient (P), test (T), and percentage of tests out of the tolerance level (T%), divided for source of error, Center, and EPID dosimetry software. Conclusion The implementation of IVD improved dosimetric accuracy and treatment reproducibility in all Centers participating to this study.

PD-0550 Esophageal tumor identification by deep learning on treatment planning CT images

Abstract withdrawn

PD-0551 Experimental investigation of magnetically focused proton minibeams A. Teran 1 , G. McAuley 1 , J. Slater 1 , A. Wroe 1 1 Loma Linda University, Department of Radiation Medicine, Loma Linda, USA Purpose or Objective Proton minibeam radiation therapy (pMBRT) potentially allows for dose escalation at the target through normal tissue sparing via spatial fractionation. Proton minibeams are typically generated via collimation, however Monte Carlo studies have demonstrated that magnetic focusing of proton beams can produce minibeam dose distributions with enhanced delivery efficiency and less primary beam