Determining the Correlation and Effect of Rectal and Bladder Volume Change in Shift of Planning Target Volume and Calculating Planning Target Volume Margin With Van Herk Formula in Prostate Cancer Tomotherapy Publisher

Summary: Can bladder and rectal changes affect prostate radiotherapy? In 20 patients, both tracked tumor-target shifts, informing treatment margins. #Radiotherapy #ProstateCancer

Shabaninejad V ; Shanei A ; Roayaei M ; Akhavan A ; Saeb M ; Hadinezhad S
Source: Journal of Biomedical Physics and Engineering Published:2026

Abstract

Background: Movement of the Planning Target Volume (PTV) is considered one of the main challenges in radiotherapy for prostate cancer. Objective: The current study aimed to assess the correlation and impact of rectal and bladder volume changes on PTV shift during tomotherapy for prostate cancer, calculate PTV margins using the Van Herk formula to optimize treatment accuracy, and reduce healthy tissue irradiation. Material and Methods: This prospective study investigates PTV displacement and calculates PTV margin considering changes in rectum, bladder, and prostate volumes in 20 prostate cancer patients undergoing tomotherapy. PTV contouring, including prostate and seminal vesicles was performed on patient CT images. Systematic and random PTV motion errors were measured on Mega Voltage Computed Tomography (MVCT) images relative to the reference CT. PTV margin for 95% prescription dose coverage was calculated using the van Herk formula. The correlation between PTV displacement and prostate volume, rectum volume changes, bladder volume changes, age, and patient weight was investigated. Results: Linear regression analysis showed that changes in rectum and bladder volumes were significantly correlated with PTV displacement. The PTV margin was calculated using the van Herk formula, effectively achieving 95% prescription dose coverage. The largest PTV displacement range was in the anterior direction and related to the seminal vesicles. Conclusion: Significant PTV displacements were observed in prostate cancer patients undergoing tomotherapy. Rectum and bladder volume changes are key parameters associated with PTV displacement. Clinical Target Volume (CTV) to PTV margin for delivery of 95% of the prescribed dose is different and non-homogeneous in different parts of the target volume. © Journal of Biomedical Physics and.