Analysis of outcomes after non-contour-based dose painting of dominant intra-epithelial lesion in intra-operative low-dose rate brachytherapy

Abstract

To compare the outcomes of patients with intermediate risk prostate cancer (IR-PCa) treated with lowdose rate I-125 seed brachytherapy (LDR-BT) and targeted dose painting of a histologic dominant intra-epithelial lesion (DIL) to those without a DIL. Methods: 455 patients with IR-PCa were treated at a single center with intra-operatively planned LDR-BT, each following the same in-house dose constraints. Patients with a DIL on pathology had hot spots localized to that region but no specific contouring during the procedure. Results: 396 (87%) patients had a DIL. Baseline tumor characteristics and overall prostate dosimetry were similar between patients with and without DIL except the median number of biopsy cores taken: 10 (10-12) vs 12 (10-12) (p ¼ 0.002). 19 (5%) and 18 (5%) of patients with and 1 (2%) and 0 (0%) of those without DIL experienced CTCAE grade 2 and 3 toxicity respectively. Overall, toxicity grade did not significantly correlate with presence of DIL (p ¼ 0.10). Estimated 7-year freedom from biochemical failure (FFBF) was 84% (95% confidence interval: 79-89) and 70% (54-89) in patients with and without a DIL (log-rank p ¼ 0.315). In DIL patients, cox regression revealed location of DIL ("Base" vs "Apex" HR: 1.03; 1.00-1.06; p ¼ 0.03) and older age (70 vs 60 HR: 1.62; 1.06-2.49; p ¼ 0.03) was associated with poor FFBF. Conclusions: Targeting DIL through dose painting during intraoperatively planned LDR-BT provided no statistically significant change in FFBF. Patients with DILs in the prostate base had slightly lower FFBF despite DIL boost.

A machine-learning approach based on 409 treatments to predict optimal number of iodine-125 seeds in low-dose-rate prostate brachytherapy

“…Low-dose-rate brachytherapy (LDR-BT) is a treatment recommended for patients suffering from low-risk or favorable intermediate-risk prostate cancer [1][2][3]. For this purpose, specific radioactive seeds (typically, iodine-125 [ 125 I] or palladium-103 [ 103 Pd]) are inserted permanently inside the prostate using dedicated transperineal needles, which are manually or semi-automatically introduced [4,5].…”

“…Considering seed strength, there were two main strategies, one advocating the same activity for all patients, the other adapting activity to the expected prostate volume V pi [10,11,14]. We have chosen the latter approach with the following activities: 0.398 mCi for V pi < 25 cm 3 , 0.460 mCi for V pi < 40 cm 3 , 0.498 mCi for V pi < 50 cm 3 , 0.543 mCi for V pi < 60 cm 3 , and 0.585 mCi for V pi = 60 cm 3 (1 mCi = 1.27 U = 1.27 cGy cm 2 /h for 125 I). Prostates with a volume less than 25 cm 3 are generally considered very small, and dosimetric planning becomes more challenging in such cases, especially with regard to the risk of hot spots for urethra and rectum.…”

“…For the sake of simplicity, the algorithm, which obtained the best score in predicting the number of seeds, was also used in successful prediction of each feature of the dataset for a given V pi . Hence, the artificial dataset consisted of one series of individually predicted feature values for each V pi from 20 cm 3 to 60 cm 3 . In the last step, for each V pi and its own set of predicted features, the prediction of number of seeds St was obtained by applying a trained algorithm.…”

“…Also, there is a noticeable difference when comparing with mean number of seeds. In particular, SVR model tends to predict more seeds than the mean value for V pi < 40 cm3 , and less seeds than the mean value for V pi > 40 cm3 . B) Corresponding total implanted activity according to the abacus (grey disks) and from experimental mean values (black squares).…”