Feasibility and Dosimetric Evaluation of Beta-Emitting Sources in Surface Mold Brachytherapy for Oral Rhabdomyosarcoma: A Monte Carlo Study Publisher

Summary: Can beta radiation treat superficial oral tumors? A simulation found limited penetration and uneven doses with two brachytherapy designs, indicating key constraints. #Radiotherapy #MedicalPhysics

Seraj S ; Yazdi S R ; Sarvestani S N ; Zare M H ; Hajihosseini S
Source: Iranian Journal of Pediatric Hematology and Oncology Published:2026

Abstract

Background: This study aimed to evaluate the feasibility and dosimetric characteristics of 90Sr/90Y and 188Re sources for treating superficial oral rhabdomyosarcoma (RMS) using a surface mold brachytherapy approach. Materials and Methods: In this Monte Carlo simulation study, TG-149 dosimetric parameters were calculated to validate the source models. A patient-specific surface mold was then simulated for a 2.0-cm superficial tongue RMS lesion in a 5-year-old child anatomical model based on International Commission on Radiological Protection Publication 156. The effects of radionuclide type, number of active sources per catheter, catheter arrangement, and total number of catheters on dose rate, treatment time, and dosimetric characteristics were evaluated. Also, cylindrical 188Re plaques with a 3.0-cm diameter and thicknesses of 0.1 and 0.2 cm were investigated. Results: Reference dose rates were 0.54 ± 0.00 Gy.min-1.mCi-1 for 90Sr/90Y and 7.24 ± 0.01 cGy.μCi-1.h-1 for 188Re. In the catheter-based design, increasing the number of loaded sources increased dose rate and reduced the flatness (F), while central catheter placement provided the highest dose rate together with lower symmetry (S) and penumbra (P). Increasing the number of catheters from 3 to 20 reduced the treatment time from 2307.4 to 413.7 min for 90Sr/90Y and from 268.5 to 52.4 min for 188Re. For 90Sr/90Y, F ranged from 16.0% to 19.5%, S reached 1.06, and P reached 1.09 cm; corresponding values for 188Re were 15.4%-18.3%, 1.10, and 1.13 cm, respectively. The 0.2-cm-thick 188Re plaque achieved a dose rate of 433.4 cGy.min-1 and reduced treatment time to less than 1 min, but showed F = 22.3% and S = 1.36. Conclusion: Catheter- and plaque-based beta-emitting brachytherapy geometries showed limitations for treating superficial oral RMS at a 0.5-cm prescription depth. These limitations were primarily related to restricted beta-particle penetration and nonuniform lateral dose distribution. © This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License.