ESTRO 2024 - Abstract Book

S3424

Physics - Dose calculation algorithms

ESTRO 2024

Belosi MF, van der Meer R, Garcia de Acilu Laa P, Bolsi A, Weber DC, Lomax AJ. Treatment log files as a tool to identify treatment plan sensitivity to inaccuracies in scanned proton beam delivery . Radiother Oncol. 2017.

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Impact of VOLO TM Ultra optimizer for Radixact system on treatment plan quality and efficiency

Patrizia Urso, Nathan A Corradini, Cristina Vite, Giorgio Ballerini, Laura Negretti, Alessandra Franzetti-Pellanda

Gruppo Ospedaliero Moncucco, Radiotherapy, Lugano, Switzerland

Purpose/Objective:

With the last upgrade of treatment planning system (TPS) for Radixact and TomoTherapy from Precision v.2 to Precision v.3, the new VOLO TM Ultra optimizer substituted Volo Classic. It is based on the estimation to the inverse Hessian matrix with a different management of the leaf open time (LOT), resulting in very different approach in the planning processes. The effects of its new features were however not widely investigated. This pilot study has the aim to evaluate the different performances compared with the previous optimizer.

Material/Methods:

In order to investigate the new algorithm without confounding factors linked to the different treatment regions, only left breast treatments of 20 patients were randomly selected. A total of 10 direct (TD) and 10 helical (TH) treatment plans, having the same dose fractionation (50Gy/25 fx), that were planned with Volo Classic were replanned with VOLO TM Ultra. Geometrical aspects were mantained, as the patient position with respect to isocenter (green laser setup) and, for the TD re-planning, the previous beam angles. Also the field width (FW) and the beam intersection was mantained. At the end of the optimization process, the dose was rescaled requiring the same percentage volume covered by prescription dose in the original plan. The different features of VOLO TM Ultra required specific settings, described as follow: ▪ in Normal Tissue Objective the VOI was the Body, with weight 1, and the Distance from Target (mm)/Dose (%): (5/100;20/50;100/20); ▪ LOT cut-off was set to 20 ms; ▪ the number of interaction rounds was set at 3, accelerate optimization was 1; ▪ the ‘accelerate treatment’ was fixed at its minimum; ▪ medium and high resolution was set for ‘optimization’ and ‘final dose’ steps, respectively. Then, replanning was performed chosing optimization parameters aimed to obtain the best dosimetric plan, using a script and applying possible variation to it, if necessary, in order to accomplish to the international and internal planning guidelines (D 95% > 95% of volume, 99% < D prescr < 101% of target volume, V 107% < 0.1cc, dosimetric constraints to organ at risk (OAR)).