Assessing PTV margins in prostate cancer tomotherapy; a comprehensive analysis of interfractional motion and factors affecting prostate and OAR displacement type of study

Abstract

Introduction: Patient adherence to preparation protocols in tomotherapy for prostate cancer is crucial for treatment accuracy. Objectives: This study aimed to analyze factors affecting prostate displacement, evaluate the required clinical target volume (CTV) to planning target volume (PTV) margins, and assess the impact of patient adherence on treatment precision. Materials and Methods: This cross-sectional analytical study included 20 prostate cancer patients who underwent tomotherapy from February 2021 to July 2023. Prostate-specific antigen (PSA) levels were measured before treatment, and prostate volume was determined via ultrasound (US). Bladder volume and intestinal cross-sectional area were calculated from megavoltage computed tomography (MVCT) images and compared with CT simulation images. PTV displacement in the anterior-posterior direction was measured, and safety margins were calculated using the formula 2SD +/- m. Statistical analyses, including the independent T-test and linear regression were conducted to examine correlations between prostate displacement and changes in rectal and bladder volumes. Results: A heterogeneous safety margin was determined for three PTVs in the posterior-anterior direction. Bladder and rectal volume changes were significantly associated with prostate displacement. Patient adherence to preparation instructions declined during the second 5-day treatment period, affecting treatment accuracy. Conclusion: Volumetric changes in the bladder and rectum influence prostate displacement, necessitating the application of heterogeneous safety margins. Ensuring consistent patient adherence, especially in later treatment stages, is essential for maintaining treatment precision. Continuous education and reinforcement of preparation protocols can help mitigate setup uncertainties and improve treatment outcomes.