ESTRO 2024 - Abstract Book

S3581

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

ESTRO 2024

Keywords: KB, Benchmark, WBI

References:

The current study was performed within the MIKAPOCo (Multi-Institutional Knowledge-based Approach for Plan Optimization for the Community) project, supported by AIRC grant (IG23150, 248/2021)

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Comparing Partial- and Full-arcs VMAT for Prostate SIBs: Impact on OAR, PTV, Duration and Modulation

Lauri J Koivula 1,2 , Johannes A.E. Ahlnäs 1 , Arthur Sinimyrsky 1

1 Kymenlaakso Central hospital, Radiation oncology, Kotka, Finland. 2 University of Helsinki, Doctoral Programme in Materials Research and Nanoscience, Helsinki, Finland

Purpose/Objective:

This study aimed to compare partial-arcs and full-arcs 6 MV photon VMAT treatment for prostate cancer radiotherapy (RT). The objective was to evaluate the reduction of the treatment time and beam modulation in the context of inherent prostate motion caused by rectum, bladder, and pelvic muscles during RT treatment [1]. These physiological motions present a known challenge in radiotherapy, necessitating techniques like gold seed kV imaging, implanted radiofrequency seeds or surface-guided RT to mitigate their effects [2][3]. We studied the possibility to shorten the treatment time and reduce the beam modulation associated with partial-arcs, which may aid in addressing the effect of inherent anatomical motion [4]. The study also aimed to compare the dose to organs at risk (OARs) and planning target volume (PTV), and to demonstrate a noninferiority between full-arcs and partial-arcs.

Material/Methods:

A cohort of 14 prostate cancer patients underwent a retrospective comparative dosimetric analysis. These patients received treatment using a simultaneous-integrated-boost (SIB) approach, with a prescribed dose of 60 Gy delivered in 3 Gy fractions to the prostate and 50 Gy delivered in 2.5 Gy fractions to the seminal vesicles. In the clinical setting, the patients received a treatment with two partial-arcs (with case-specific posterior and anterior avoidance sectors) 6 MV flattening-filter-free (FFF) VMAT plans (max dose-rate: 1400 MU/min). For the purpose of comparison, retrospective plans were generated with two full-arcs (with case-specific posterior avoidance) 6 MV flattened-field (FF) VMAT plans (max dose-rate: 600 MU/min) with Eclipse software for TrueBeam (v.16.1, Varian). We collected the monitor unit data and treatment durations for both plans. Treatment durations for the clinical plans were obtained from the patients' clinical treatment records. For the retrospective plans, we irradiated them with the linac to determine the actual treatment duration, considering any potential mechanical limitations of the treatment machine. We compared the arc length between full- and partial-arc plans. Additionally, the study