Publication: Evaluation of source loading position in HDR brachytherapy dose calculation for patients with oral tongue cancer
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Date
2025-06
Authors
Britonathan, Mathilda Roshini
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Abstract
The dosimetric impact of six different dwell activation strategies in high-dose-rate (HDR) interstitial brachytherapy for oral tongue squamous cell carcinoma (OTSCC) was retrospectively investigated in twenty patients. Treatment plans were generated using Oncentra Treatment Planning System (TPS) with varying source loading configurations: Initial activation (uniform 0.25 cm spacing), system-optimized Autoactivation, fixed spacings of 0.50 cm, 0.75 cm, and 1.00 cm, and an alternating Zig-zag pattern. Dosimetric parameters assessed included D90, V100%, and V200% for target volume coverage, and D0.2cc and D2cc for organs at risk (OARs), specifically the mandible, pharyngeal constrictor muscles (PCM), and right and left submandibular glands (SMGs). Surface dose was also evaluated to estimate mucosal toxicity risk. All data were analyzed using SPSS version 29. Normality tests were followed by Friedman and Wilcoxon signed-rank tests, as well as repeated measures ANOVA where appropriate. The 0.50 cm dwell activation strategy demonstrated the most favorable dosimetric profile, yielding the lowest mean surface dose (0.59 Gy) and mandible D0.2cc (1.56 Gy), while maintaining adequate tumor coverage (mean D90: 5.17 Gy; V100%: 99.64%). Although the Initial plan resulted in the highest D90 (5.82 Gy), it was associated with elevated surface and OAR doses. The Zig-zag pattern achieved comparable OAR sparing to the 0.50 cm configuration but exhibited higher inter-patient variability. Wider activation intervals (0.75 cm and 1.00 cm) did not improve tumor coverage and were linked to increased dose exposure to adjacent healthy structures. Statistically significant dose reductions were observed for the mandible and PCM using tighter dwell configurations (p < 0.05). Dwell position selection significantly influenced dose distribution in HDR tongue brachytherapy. Among the strategies evaluated, the 0.50 cm dwell spacing provided the most favorable balance between target coverage and OAR sparing, supporting its consideration as an optimal source loading pattern in clinical planning.
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