Improving plan quality in cervical brachytherapy using a simple knowledge-based prediction tool for OAR dose (D2cm3).

PURPOSE: Toxicity from cervical brachytherapy has been demonstrated to correlate with the D2cm3 of the bladder, rectum, and bowel. This suggests a simplified version of knowledge-based planning investigating the relationship of the overlap distance for 2cm3 and the D2cm3 from planning may be possible. This work demonstrates the feasibility of simple knowledge-based planning to predict the D2cm3, detect suboptimal plans, and improve plan quality. METHODS AND MATERIALS: The overlap volume histogram (OVH) method was used to determine the distance for 2cm3 of overlap between the OAR and CTV_HR. Linear plots modeled the OAR D2cm3 and 2cm3 overlap distance. Two datasets of 20 patients (plans from 43 insertions in each dataset) were used to create two independent models, and the performance of each model was compared using cross-validation. Doses were scaled to ensure consistent CTV_HR D90 values. The predicted D2cm3 is entered as the maximum constraint in the inverse planning algorithm. RESULTS: Mean bladder D2cm3 decreased by 2.9% for the models from each dataset, mean rectal D2cm3 decreased 14.9% for the model from dataset 1 and 6.0% for the model from dataset 2, mean sigmoid D2cm3 decreased 10.7% for the model from dataset 1 and 6.1% for the model from dataset 2, mean bowel D2cm3 decreased 4.1% for the model from dataset 1 but no statistically significant difference was observed for the model from dataset 2. CONCLUSIONS: A simplified knowledge-based planning method was used to predict D2cm3 and was able to automate optimization of brachytherapy plans for locally advanced cervical cancer.

A single-institution review of image-guided brachytherapy for vaginal malignancies using customized molded applicators and interstitial needles.

PURPOSE: To review a single-institution's pattern of practice, dosimetry results, and clinical outcomes for patients with unresectable malignancies of vagina, vulva, or urethra, receiving brachytherapy using customized vaginal moulds with or without interstitial needles. MATERIAL AND METHODS: Twenty-one consecutive patients were reviewed. Patients were treated using customized moulds with or without interstitial needles, implanted with a free-hand technique. Technical implementation, such as type of implant and imaging used were recorded. D90 and D98 of clinical target volume (CTV), D0.1cc of urethra, and D2cc and D0.1cc of bladder and rectum were analyzed. Any adverse clinical outcomes were reported. RESULTS: Eleven patients experienced endometrial cancer recurrences, one a cervical cancer recurrence and nine vaginal or peri-urethral primary disease. After a median follow-up of 3.5 years, local control was achieved in 14 patients (67%). Median D98 and D90 to CTV was 73.7 Gy and 78.3 Gy, respectively. One patient died from disease progression, one developed distant metastasis, and seven failed locally. Median D2cc to bladder was 64.8 Gy, with low-grade toxicity reported. Median D2cc to rectum was 62.9 Gy, with low-grade toxicity and one case of rectal proctitis was observed. Median urethral D0.1cc was 66 Gy, with no toxicity reported. One patient suffered from a sacral insufficiency fracture. It was presumed that vaginal mucosa proximal to CTV received the total dose, with two patients developing vaginal ulcers, which both resolved; 10 patients reported mild telangiectasia, fibrosis, or stenosis. CONCLUSIONS: A review of patients treated with a customized vaginal mould and interstitial needles showed acceptable doses to CTV, with local control achieved in 67% of patients, and reasonable doses to organs at risk (OARs) and acceptable toxicity.