ESTRO 2024 - Abstract Book

S4319

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

ESTRO 2024

1. US National Institutes of Health. Clinical Trial NCT04748094: Quantification of Abdominal Organ Motion Using MRI (QUANTUM) [Internet]. [cited 2023 May 24]. Available from: https://clinicaltrials.gov/study/NCT04748094

2221

Digital Poster

Quantifying dose errors in prostate radiotherapy due to 6DoF prostate and pelvic lymph node motion

Karolina Alexandra Klucznik 1 , Thomas Ravkilde 2 , Simon Skouboe 3 , Ditte Møller 2 , Steffen Hokland 2 , Paul Keall 4 , Simon Buus 2 , Lise Bentzen 5 , Per Poulsen 1,2 1 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark. 2 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark. 3 Aarhus University Hospital, Danish Centre for Particle, Aarhus, Denmark. 4 University of Sydney, Image X Institute, Sydney, Australia. 5 Vejle Hospital, Department of Oncology, Vejle, Denmark

Purpose/Objective:

Radiotherapy of the prostate and the pelvic lymph nodes (LN) is the standard of care for high-risk prostate cancer patients [1]. Differential translational and rotational prostate and LN motion (i.e., six degrees-of-freedom, 6DoF, motion) can perturb the target doses. In this study, we developed a framework for monitoring the dose perturbation caused by differential 6DoF motion during high-risk prostate radiotherapy and investigated its dose calculation accuracy and real-time capabilities for prostate and LN dose reconstruction.

Material/Methods:

The study includes 20 patients treated with 39 or 23 fractions delivering either 78Gy to the prostate CTV and 56Gy to the LN CTV or 46Gy to both targets using a 3-arc VMAT-technique. A pre-treatment CBCT matched on 3-4 implanted prostate fiducial markers was used for patient setup. Triggered kV-images were acquired every 3s during treatment along with a post-treatment CBCT for 7-10 fractions per patient. The time-resolved 6DoF prostate position was extracted based on the marker positions in the CBCT projections and kV-images using the formalism of kilovoltage intrafraction monitoring (KIM). The LN were assumed static during treatment with a 6DoF positioning error obtained from a 6DoF bone match between planning CT and post-treatment CBCT. The in-house developed software DoseTracker [2] was used to calculate the 6DoF motion-including dose distributions for both target volumes. Real time dose reconstruction was simulated retrospectively by broadcasting the target positions and machine state parameters to DoseTracker once per 2deg of gantry rotation and additionally whenever triggered kV imaging resulted in an updated prostate position. DoseTracker was deemed sufficiently fast for online real-time application during actual treatments if it could finish the dose calculation for one parameter set before the arrival of the next one. Motion-including DICOM-RT dose files from DoseTracker were imported into the TPS for each fraction. The difference between the planned and motion-including dose distributions in D 99.5% (ΔD 99.5% ) for the prostate CTV and in D 98% (ΔD 98% ) for the LN CTV were extracted for each fraction and for the average over all fractions. The accuracy of the dose calculation by DoseTracker was assessed by comparing dose calculations including only translational motion with