ESTRO 2024 - Abstract Book

S3640

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

ESTRO 2024

2210

Proffered Paper

Assessing the treatment plan robustness of dynamic trajectory radiotherapy for head and neck cancer

Hannes A Loebner 1 , Jenny Bertholet 1 , Paul-Henry Mackeprang 1 , Werner Volken 1 , Olgun Elicin 1 , Silvan Mueller 1 , Gian Guyer 1 , Daniel M Aebersold 1 , Marco FM Stampanoni 2 , Michael K Fix 1 , Peter Manser 1 1 Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Bern, Switzerland. 2 Institue for Biomedical Engineering, ETH Zürich and PSI, Villigen, Switzerland

Purpose/Objective:

By extending volumetric modulated arc therapy (VMAT) with dynamic table and collimator rotation during beam on, dynamic trajectory radiotherapy (DTRT, [1]) has shown improved organ at risk sparing compared to volumetric modulated arc therapy (VMAT). However, the influence of patient- or machine-related uncertainties on dosimetric plan quality is yet unknown. The aim of this work is to evaluate and compare the dosimetric robustness of DTRT and VMAT treatment plans for head and neck (H&N) cancer cases, to patient-setup and machine-positioning uncertainties.

Material/Methods:

DTRT and VMAT treatment plans for 46 H&N cancer cases, prescribing 50 Gy to elective volumes and 66-70 Gy to the boost volume using a sequential boost technique, were created following the planning protocol of Bertholet et al. [2]. The DTRT paths were determined using an in-house path-finding software and imported in a research version of the Eclipse treatment planning system via scripting. DTRT and VMAT plans were optimized in Eclipse with a research version of the photon optimizer, using the Analytical Anisotropic Algorithm for dose-calculation. The dose distributions for the summed plans were recalculated, for several patient-setup and machine positioning uncertainty scenarios (US) using Monte Carlo dose calculation. All patient-setup US combine the same 6 dimensional random uncertainties (sampled from a Gaussian distribution with a sigma of 2 mm for each translational axis and 0.5° for each rotational axis), with each of the following systematic set-up uncertainties: 0 mm, ±2 mm, ±3 mm, ±5 mm for translation and for rotation. Machine-positioning uncertainties were investigated separately for gantry, table and collimator angle (0°, ±1.0°, ±2.0°) and opening/closing of all multi leaf-collimator (MLC) leaves (0 mm, 0.2 mm, 0.5 mm, 1.0 mm, 2.0 mm, 3.0 mm, 5.0 mm) to simulate mis calibrations. DTRT and VMAT plan robustness was analysed by assessing the dosimetric impact of the uncertainties on dosimetric end-points, fulfilment of planning goals and normal tissue complication probability (NTCP) for dysphagia and xerostomia [3]. Differences between DTRT and VMAT plan robustness were compared using Wilcoxon matched-pair signed-rank tests (significance level α = 5%).

Results:

The investigated uncertainties lead to average dosimetric differences in target and organ at risk dosimetric end points of ≤ 3.5 Gy for rotational (≤ 3°) US and < 7 Gy for translational (≤ 5 mm) patient-setup US; differences are ≤