Validation of bladder preparation in prostate radiotherapy

Abstract

Purpose: Tomotherapy relies heavily on consistent patient preparation to ensure accurate treatment delivery. This study assesses the effectiveness of a preparation protocol by analyzing variations in bladder and evaluating impact of poor preparations among patients undergoing tomotherapy. Methods: This study involved two study cases focused on prostate tomotherapy. The first case included 10 patients who received hypofractionated treatment whose dose volumes were computed for each fraction by experienced physicists using the TomoTherapy planning system. Bladder contours and dose computations were performed by supervised medical physicist students which involved contouring the bladder across multiple MegaVoltage Computed Tomography (MVCT) scans, yielding over 200 bladder contours using RayStation™ and Planned Adaptive™. The second case surveyed 24 patients on treatment preparation. Computed Tomography (CT) images from treatment sessions were registered with planning CT. Bladder contours were contoured and were used to calculate verification doses in Planned Adaptive™. Summation doses were assessed and compared to planning doses using Dose-volume histograms (DVHs). Exported summation doses, planning doses, CT images, and contours were analyzed using Python. The analysis included computing bladder volumes, constructing DVHs, and performing regression analyses to explore correlations among parameters. Results: All patients, except one, exhibited significant dose volume inter-fraction differences between initial planning and poor preparation, both in low and high dose regions. Re-preparations significantly reduced these differences. Some planning preparations could have matched the optimal preparations. Dose volume metrics showed an average inter-fraction difference, with bladder volume increases of 18.48% at 2.04 Gy, 13.68% at 2.43 Gy, and 1.2% at 3 Gy. Comparing bladder volumes, there was a 53.5% decrease between planning and poor preparations, and re-preparations increased bladder volume by 8.09%, while optimal preparations increased it by 30.39%. An exponential regression model given by the expression D mean = 2.09e explained 77.33% of the variance in the mean bladder dose. Summation dose indicated six patients with DVH metrics exceeding planning, with two exceeding constraints, while three had met the constraints. One patient had alternating DVH metrics, and one of the patients benefited from re-preparations that lowered metrics below constraints. A linear increase in the number of acceptable poor preparations was observed with increasing planning bladder volume, becoming fully acceptable at 398.61 −0.005V cubic centimeters (cc). Due to missing bladder volume data in the second study case, the sample size was smaller than expected, with only 2 out of 28 samples having complete data. High variance in bladder filling patterns was observed, with an R2 score of 0.1724, not aligning with the expected pattern. Conclusion: The results demonstrated that all well-prepared patients met the treatment constraints. Other findings showed that thorough bladder preparation before planning is crucial, as it significantly impacts the effectiveness and accuracy of subsequent treatments.