Room: Exhibit Hall
Purpose: To develop a method to evaluate the cumulative dose when using Multi-Lumen Cylinder (MLC) applicator in vaginal cuff brachytherapy.
Methods: A retrospective analysis of 11 patients treated in 2017 with the MLC applicator 3 cm diameter, were considered for this study. All patients received 5 fractions with 5 Gy each delivered twice a week and prescribed to the applicatorâ€™s surface for 2/3 of the vaginal length. The CT scans of these patients, taken for treatment plan were separately imported into the treatment planning system and paired with the initial CT scan after completing the contouring. Two sets of CT images were fused at a time together with respect to the applicator, using mutual registration.The maximum doses received by the rectum wall, bladder wall, bowels and PTV on were analyzed and traced over the five fractions to determine the total dose distribution over the entire prescribed treatment.
Results: No contour of any of the OAR was exactly similar when the CT images were fused each other. Depending on the depth of the insertion the PTV varied minimally.There is a difference between the doses received by the OARs between treatments and between the points of maximum dose. The maximum dose varied between 15% and 25% in rectum wall and bladder neck. The minimum dose varied between 3% and 6% in rectum wall and bladder neck. The average dose varied between 10% and 22% in rectum and bladder. The cumulative treatment does do not indicate a total maximum dose exceeding the tolerances for the rectum and bladder.
Conclusion: The variations in volumes of the PTVs and isodoses are minor, indicating that the desired area receives the entire prescribed treatment. Rectum wall will not exceed 85% of the prescribed cumulative dose and the bladder neck will not exceed 75% of the prescribed dose.