ESTRO 2024 - Abstract Book

S3476

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

needed, the impact of such a small dose reduction on the tumor control probability of subclinical disease is expected to be insignificant. In addition, beam-gated treatment using a gating margin of 2 mm could be a feasible option to reduce underdosing the edges of the prostate even further, while ensuring high GTV coverage.

Keywords: PTV margin, Prostate cancer, intra-fraction motion

References:

1. Holmann BG, Van Triest B, Ghobadi G, et al. Gross tumor volume and clinical target volume in prostate cancer: how do satellites relate to the index lesion. Radiotherapy and Oncology, 2015. 115(1): p. 96-100.

2. Ghobadi G, De Jong J, Hollmann BG, et al. Histopathology-derived modeling of prostate cancer tumor control probability: Implications for the dose to the tumor and the gland. Radiotherapy and Oncology, 2016. 119(1): p. 97 103.

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Poster Discussion

Robust optimization for dynamic mixed-beam radiotherapy (DYMBER)

Jenny Bertholet, Gian Guyer, Silvan Mueller, Hannes A Loebner, Daniel M Aebersold, Peter Manser, Micheal K Fix

Inselspital, Bern University Hospital, and University of Bern, Division of Medical Radiation Physics and Department of Radiation Oncology, Bern, Switzerland

Purpose/Objective:

Dynamic mixed-beam radiotherapy (DYMBER) combines non-coplanar photon trajectories and electron beams where intensity modulation of both particle types is achieved with the photon multi-leaf collimator (MLC) and optimized simultaneously using direct aperture optimization (DAO) [1,2]. Planning-target-volume (PTV) and planning-at-risk-volume (PRV) margins are conventionally used to mitigate uncertainties (e.g., set-up uncertainties) but margin concepts are ill-defined for electron beams and margins are often cropped close to the skin or to serial organs at risk (OARs).

This study presents the first application of robust optimization for DYMBER plans on clinically motivated cases.

Material/Methods:

DYMBER plans consist of two dynamic 6 MV photon trajectories using dynamic gantry, table, and collimator rotation and two non-isocentric electron arcs. The photon paths are optimized to minimize PTV/OAR overlap and minimize potential MLC travel [3]. Partial electron arcs for all available energies (6, 9, 12, 15, 18 and 22 MeV) with a manually determined gantry-angle range and a source to surface distance of 80 cm are initially considered. A first DAO simultaneously optimizing photon and electron contribution is performed, and only two electron arcs, those contributing most to the PTV dose, are selected for the final plan generation.