Prostate cancer radiation therapy shape variation analysis

Prostate cancer is a common disease among men worldwide, and patients are frequently treated with external beam radiation therapy (EBRT). Precise radiation dosage planning is required for treatment application to minimise side effects. Identification of tissue boundaries is crucial for radiation therapy treatment planning by providing essential shape information to clinicians, allowing optimisation of treatment delivery while limiting damage to healthy tissues. In this study, two approaches incorporating Principal Component Analysis (PCA) were proposed to investigate patterns of shape variation during radiotherapy. Trajectory analysis utilized PCA to track the evolution of prostate shape throughout the course of treatment, while variation pattern analysis examined the overall range of changes in target tumor volume over the treatment period. The data used consisted of 261 mesh prostate surfaces generated from radiation oncologist manual contours from 33 patients across eight weeks of treatment. Trajectory analysis revealed significant shape variations in the left superior region and from the inferior to the posterior-right region of the prostate throughout the treatment period. Variation pattern analysis indicated an overall increase in target tumor volume during treatment, with the highest average variation observed in the anterior superior region. Notably, most shape variations occurred during the first week of treatment, suggesting that implementing a second set of updated contours after the initial week's scan could improve accuracy in defining target volumes for subsequent treatments.