Evaluation of target motion and determination optional treatment margins for prostate cancer treated with external beam radiotherapy on Halcyon

Background External beam radiotherapy (EBRT) is an important part of the treatment for prostate cancer. To account for organ motion and set-up error, margins are used in radiotherapy planning. These are essential for the delivery of safe and effective treatment. Aim and Setting To measure prostate motion during the course of EBRT on the HalcyonTM at Groote Schuur Hospital. Using published margin recipes, the minimum clinical target volume (CTV)-planning target volume (PTV) expansion margin was calculated. Patients and Methods Prostate motion was evaluated by comparing prostate position on the planning CT to cone-beam CT (CBCT) scans. Prostate position error in the medio-lateral (ML), antero-posterior (AP) and superoinferior (SI) directions was measured for each CBCT. The systematic (Σ) and random (σ) error of prostate motion was calculated. The minimum CTV-PTV margin was determined. Results The mean position error of the prostate was -0.04mm (95% CI -0.14, 0.10), -0.30mm (95% CI -0.70, 0.15) and -0.40mm (95% CI -0.89, 0.00) in the ML, AP and SI directions, respectively. Using Van Herk's margin formula (2.5Σ +0.7σ), the following minimum CTV-PTV margins for the ML, AP and SI directions were calculated: 1.9mm, 6.9mm and 7.8mm, respectively. Using Stroom's margin formula (2Σ +0.7σ), the following minimum CTV-PTV margins for the ML, AP and SI directions were calculated: 1.6mm, 5.8mm and 6.6mm, respectively. Conclusion Based on prostate motion, our institution's current margins are sufficient. However, further studies are necessary to measure other factors that influence the CTV-PTV margin before considering reducing this margin.

Grantor

Division of Radiology

Year dc:date.issued

2023

Author dc:creator

• Algar, Marion

Advisor dc:contributor.advisor

• Punt, Lydia

• Radiation Oncology

Handle dc:identifier.uri

http://hdl.handle.net/11427/39261

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/39261