ESTRO 2024 - Abstract Book

S3516

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

ESTRO 2024

[12] Bakx N, Sangen M Van Der, Theuws J, Bluemink J, Hurkmans C. Evaluation of a clinically introduced deep learning model for radiotherapy treatment planning of breast cancer. Phys Imaging Radiat Oncol 2023;28:100496. https://doi.org/10.1016/j.phro.2023.100496.

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Digital Poster

A comparative study of single-arc vs dual-arc VMAT techniques in Linac-based prostate cancer SBRT

Denis Panizza 1,2 , Valeria Faccenda 1 , Stefano Arcangeli 2,3 , Elena De Ponti 1,2

1 Fondazione IRCCS San Gerardo dei Tintori, Department of Medical Physics, Monza, Italy. 2 University of Milan Bicocca, School of Medicine and Surgery, Milan, Italy. 3 Fondazione IRCCS San Gerardo dei Tintori, Radiation Oncology Department, Monza, Italy

Purpose/Objective:

The optimal management of localized prostate cancer has remained a subject of controversy despite recent advances in early detection and treatment of localized forms. Stereotactic Body Radiotherapy (SBRT) is a highly conformal extreme hypofractionated radiation therapy technique that can be safely delivered with excellent outcomes in patients. As the intrafraction prostate motion was increasingly influenced by the prolongation of treatment time, it is possible to shorten SBRT delivery by making adjustments at the planning stage when no organ motion management strategies are used. The aim of this study is to investigate the dosimetric quality and the treatment efficiency of single-arc (SA) versus dual-arc (DA) volumetric modulated arc therapy (VMAT) plans in Linac-based SBRT of localized prostate cancers.

Material/Methods:

Twenty low to intermediate-risk prostate (36.25 Gy in 5 fractions) and twenty high-risk prostate (42.7 Gy in 7 fractions) SBRT plans treated during 2021 with dual-arc flattening filter-free (FFF) VMAT technique, were re optimized by two medical physicists. The same PTV margin expansion (5 mm isotropic except 3 mm posterior) was used. A single-arc approach was adopted and new optimization parameters based on the increased planning and clinical experience were incorporated in a new template. Dosimetric parameters of newly optimized SA plans were evaluated and compared with those from original DA plans. The analysis included target coverage, organs at risk (OARs) sparing, treatment delivery time, and accuracy (perpendicular diode matrix tool, gamma analysis passing ratio, PR). Paired t-test was used to assess the statistical significance level (alpha=0.05). The relationships of rectum and bladder volumes with the rectum and bladder dose metrics were also investigated. One senior radiation oncologist performed a blind choice between DA and SA plans for the clinical assessment.

Results:

In all cases, the SA optimization technique resulted in a better treatment plan than the original one (Figure 1). PTV Dmean was higher in SA plans (SA: 101.4%; DA: 101.1%; P<0.001), while PTV D95% and PTV D2% were comparable between the two techniques (SA: 96.7% and 104.1%; DA: 96.5% and 103.9%; P>0.05). A significantly increased OARs sparing was observed in SA plans, especially in rectum and bladder mean doses. The mean absolute dose difference was -3.7 Gy [range, -7.6 – -0.6] for rectum Dmean (P<0.001) and -1.2 Gy [range, -4.0 – 0.4] for bladder