ESTRO 2023 - Abstract Book

S1822

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ESTRO 2023

Fig 1. Static part of the plan irradiated on EBT3 film.

Results The film analysis from the chest phantom gave the gamma passing rate (3%, 3mm) of 100% and 54,9% - with lower results in the junction plane. The dose drop in the junction showed underdosing of around 4%. Dose distribution verification of junctions for static part of H-VMAT plan without jaws offset showed 3.7% relative dose difference to TPS, and for 2 mm offset in Y1 and Y2 - 40% (the summary of results is shown in Fig 2). Additional measurements of simple abutting fields showed an underdosage of 4% to 17% depending on a linac. The short-term reproducibility gave the mean underdosing of 10.9% ± 0.7% and 14.9% ± 0.7% for junctions in X and Y jaws direction, respectively. The long-term reproducibility gave slightly larger deviations of 12.0%±1.0% and 14.6%±1.1% for junctions shaped with X jaws and Y jaws, respectively.

Fig 2. Profiles passing through the field junction.

Conclusion The junction of the abutting fields is a critical parameter for the H-VMAT plans. The jaw settings must be regularly checked on every linac to verify that they are in the optimal range for hybrid plans performance. Jaw setting at max tolerance (2 mm) would increase dose drop to an unacceptable level. The underdosing measured for abutting fields was at the level which allows the introduction of hybrid plans for clinical treatments.

PO-2050 Chest wall pain in lung SBRT patients: dose-volume correlations

C. Muñoz-Montplet 1 , R. Fuentes-Raspall 2 , D. Jurado-Bruggeman 1 , B. Gómez-Horsfield 3 , O. Font-Planas 4 , D. Lambisto-Castro 1 , S. Agramunt-Chaler 1 , A. Onsès-Segarra 1 , I. Romera-Martínez 1 , E. Massana-Melchor 1 , A. Eraso-Urién 2 1 Institut Català d'Oncologia, Medical Physics and Radiation Protection, Girona, Spain; 2 Institut Català d'Oncologia, Radiation Oncology, Girona, Spain; 3 Institut Català d'Oncologia, Haematology, Girona, Spain; 4 Universitat Autònoma de Barcelona, Physics, Bellaterra, Spain

Purpose or Objective