Improving prostate brachytherapy outcomes through MRI-Assisted dominant lesion dose painting.

Abstract

Background: The aim of this study was to assess the feasibility of using magnetic resonance (MR) images to implement a dose painting (DP) approach in prostate high-dose-rate brachytherapy.

Methods: The study included 45 patients with prostate tumors of varying grades, with the tumors (DILs) manually segmented with a 0.5 cm margin on T2W MR Images. The bladder, rectum, and urethra were considered as organs at risk (OARs) and treated using LLA300-KB plastic needles and the HDRplus treatment planning system. The patients received an external dose of 45 Gy and a boost dose based on the tumor's malignancy, with the dosimetric evaluations and radiobiological analysis performed according to the RTOG protocol and using the equivalent dose in 2 Gy fractions (EQD2).

Results: Our study found no statistically significant differences in dose values for the rectum between the DP methods and conventional treatment planning for tumor grades 2 to 5 (p > 0.05). However, two patients with grade 5 tumors showed rectal V75cc values exceeding the limit with the DP method and a 43 Gy boost dose, although the average V75 remained below 1 cc. The analysis revealed no significant differences in bladder dose values between conventional treatment planning and DP methods for tumor grades 2 to 4 (p > 0.05). However, the mean V75cc of the bladder in grade 5 patients with a 43 Gy boost dose exceeded the permissible limit at 1.09. There was no significant difference in urethral V125cc values for patients with tumor grades 2 and 3 between both DP methods and conventional planning (p > 0.05). However, a significant difference was observed for patients with tumor grades 4 and 5. The average V125% and V150% of the whole prostate remained within the standard range of 50-65% and 20-35% respectively for all tumor grades, and both DP methods and conventional treatment planning were within acceptable limits. However, the average V125 and V150 DILs for all tumor grades exceeded the standard limits and showed a significant difference from conventional treatment planning (p < 0.05). Our results showed a significant difference in EQD2 values for the whole prostate and DIL in the DP method for all tumor grades (P < 0.05).

Conclusion: The DP approach offers individualized doses but may be limited by the proximity of DILs to OARs.