Adapting planning strategies for cervix brachytherapy to reduce the dose to the vagina

Abstract

Background: The implementation of Image-guided Brachytherapy (IGBT) to treat cervical cancer has improved delineation of the target structures and Organs At Risk (OARs) to provide a more conformal and individualised treatment for patients. A European study on MRI guided brachytherapy in locally advanced cervical cancer (EMBRACE) is assessing the impact of IGBT in a multi-institutional setting. Findings of the EMBRACE study demonstrate that vaginal morbidity is common and may e ect the patients' Quality Of Life (QOL). Vaginal dose parameters still need to be de ned; only few studies have looked at this in detail. Objectives: To recommend the most appropriate planning strategy for IGBT of the cervix that conforms to all current planning aims and provides the greatest vaginal dose sparing. Research Design: Fifteen patients that were previously treated for cervical carcinoma with a Computed Tomography (CT)/Magnetic Resonance Imaging (MRI) compatible tandem-ring applicator were chosen. Five patients were randomly selected from the aforementioned sample. Di erent methods were investigated on these ve patients to model appropriately the dose to the vagina. These methods include vaginal points and volumetric dose parameters. Di erent planning strategies such as the clinically delivered plan, standard Manchester plan, conformal plan with modi ed applicator dwell time and positions and the Inverse Planning Simulated Annealing (IPSA) algorithm were applied on the ve patients and the best treatment plan in reducing the dose to the vaginal wall was applied to the rest of patients. The best vaginal dose reporting method and planning strategy were implemented for the rest of the patients and the resulting dose parameters were compared to the ones resulting from the clinically delivered plan. Finally, an investigation was done to determine whether vaginal morbidity including mucositis, stenosis, dryness and bleeding can be correlated with vaginal dose. Results and Conclusions: From this study it was concluded that the vaginal Dose Volume Histogram (DVH) parameters for the vaginal wall are inaccurate due to contouring uncertainties. On the other hand the vaginal dose points presented in this study provide a good dose representation throughout the vagina and can easily be used clinically in the near future. The best planning strategy in reducing the vaginal dose whilst maintaining the current planning aims was found to be the manual conformal plan. It kept the target coverage and dose to the bladder, rectum sigmoid and small bowel within dose constraints while it reduced vaginal dose by 42.34 %, 30.28 %, 33.71 %, 28.00 % and 24.21 % at the vaginal ring surface, the transition zone between middle and upper vagina, the anatomical mid-vagina, the transition zone from the lower and middle part of vagina and the vaginal introitus respectively. No correlation could be demonstrated between brachytherapy vaginal dose and vaginal morbidity in this small sample of patients used in this study.