SAIP2026

Analysis of Inter-Fraction Setup Errors and Organ Motion Using Daily kV-CBCT in VMAT for Prostate Cancer

7 Jul 2026, 17:20

1h 20m

Great Hall (University of the Western Cape)

Poster Presentation Track F - Applied Physics Poster Session 1

Speaker

Mr Kgomotso Lefenya (University of Witwatersrand - Wits)

Description

Prostate cancer is the second most prevalent malignancy that affects men globally and one of the curative approaches requires high-precision radiotherapy techniques. One of these recent and advanced techniques is volumetric modulated arc therapy (VMAT). This ensures accurate dose delivery whilst minimizing toxicity to the organs in proximity to the prostate, such as the rectum and bladder. This study aims to investigate the inter-fraction setup errors and internal organ motion using daily kilovoltage cone beam computed tomography (kV-CBCT) imaging in prostate cancer patients treated at Charlotte Maxeke Johannesburg Academic Hospital.
This study is a retrospective analysis will be conducted from patients that were treated for prostate cancer from 2023 until the end of 2024 undergoing VMAT. Daily CBCT images taken prior to treatment delivery will be used to quantify translational setup deviations in the left–right (LR), superior–inferior (SI), and anterior–posterior (AP) directions in relation to the planning CT images. Systematic and random errors will be calculated, and planning target volume (PTV) margins will be estimated using established margin recipes such as the van Herk calculation. Volumetric changes in bladder and rectal filling will also be assessed to evaluate their influence on prostate displacement.
It is anticipated that measurable inter-fraction variability will be observed, with larger deviations expected to occur in the AP direction. This is because of the expected volumetric changes in rectal and bladder. The utilization of daily image guidance is expected to limit setup uncertainties and improve target localization whilst sparing toxic radiation to the surrounding organs. This also improves the maximum dose delivery to the prostate without underdosing it. The results of this study are expected to contribute to the optimization of PTV margin design and support the implementation of adaptive radiotherapy strategies.
This study will provide essential data, that has an immediate impact to the local people, and will improve geometric accuracy and treatment outcomes in prostate cancer radiotherapy.