ESTRO 2024 - Abstract Book

S4332

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

2384

Digital Poster

Improvement of treatment delivery efficiency for prostate SBRT using single arc VMAT

Edoardo Mastella 1 , Joel Eduardo Epile 2 , Antonio Malorgio 3 , Antonio Stefanelli 3 , Alessandro Turra 1

1 Azienda Ospedaliero-Universitaria di Ferrara, Department of Medical Physics, Ferrara, Italy. 2 International Centre for Theoretical Physics, Master of Advanced Studies in Medical Physics, Trieste, Italy. 3 Azienda Ospedaliero-Universitaria di Ferrara, Department of Radiation Oncology, Ferrara, Italy

Purpose/Objective:

In the last decade, SBRT for localized prostate cancer significantly increased its popularity. In ultra-hypofractionated regimens, intra-fraction prostate motion is an important source of treatment uncertainty and is generally complex to take into account. As prostate displacements increase with time, a straightforward solution to manage intra-fraction motion is to minimize delivery time. Nowadays, prostate SBRT delivered with traditional linacs is commonly planned with multiple arcs, generally two, using flattening filter free (FFF) beams. In this work, double and single arc arrangements were compared for VMAT of low- and intermediate-risk prostate cancer in order to minimize beam delivery time and so to reduce treatment uncertainties. To the best of our knowledge, this is the first study which compares different beam geometries and qualities for prostate SBRT delivered on a C-arm linac. Planning comparisons and experimental results are presented to highlight the feasibility of the proposed single arc VMAT strategy for prostate SBRT. A retrospective dataset of 10 low- and intermediate-risk patients was used. Before treatment simulation, patients were asked to follow a preparation regimen to achieve anatomical reproducibility (full bladder, empty rectum). CT scans were registered with multiparametric MRI for accurate contouring. The PTV was defined with an isotropic 6 mm expansion (except 3 mm posterior) from the CTV. Three VMAT beam arrangements were compared on VersaHD linac (Elekta) equipped with a standard Agility 120 MLC: two full arcs 6 MV FFF; one full arc 6 MV FFF; one full arc 10 MV FFF. A total of 30 treatment plans were optimized using Philips Pinnacle TPS and starting from the same protocol, i.e. the same stored settings of objectives, weights and optimization parameters. The prescription dose was 40 Gy in 5 fractions. The plan were normalized to ensure at least 99% of the CTV received the prescription dose. Target and OARs dose constraints were selected for treatment planning comparison. A plan quality index (PQI) was defined to compare achievement of the planning goals among the arrangements. Higher PQI value corresponded to a better plan quality, i.e. more homogenous target dose and/or lower dose to the OARs. The modulation factor (MU/Gy) was chosen to compare plan complexity. Statistical significance of the dosimetric differences was evaluated with the non-parameter Wilcoxon signed-rank test. Patient specific quality assurance (PSQA) plans were delivered to the PTW Octavius 4D phantom coupled with the 1500 Detector to evaluate delivery accuracy. The delivered and recalculated 3D dose distributions were compared with the gamma analysis method following the AAPM Task Group 218 guidelines. The beam on time (BOT) was compared to evaluate treatment delivery efficiency. Material/Methods: