Author: Dylan Richeson, Dorin A. Todor 👨🔬
Affiliation: Inova Schar Cancer Institute, Virginia Commonwealth University 🌍
Purpose: High dose-rate (HDR) brachytherapy is prone to errors that can lead to incorrect dose delivery and potential medical events. One common issue is applicator length discrepancies, either due to incorrect entry in the treatment planning system (TPS) or inter-fractional catheter length changes. This study quantifies the dosimetric impact of unaccounted catheter lengthening and its clinical implications in accelerated partial breast irradiation (APBI) using multi-catheter HDR.
Methods: A retrospective analysis of 14 breast cancer patients treated with multi-catheter HDR brachytherapy was performed. Catheter length changes were measured using Varian’s Bravos remote afterloader and correlated with changes in dosimetric parameters, including CTV coverage (V95%, V90%) and skin dose (D0.1cc). Treatment plans were recreated to simulate scenarios where length adjustments were or were not applied. Patients were categorized based on target location (distal, medial, proximal) and breast size to assess dose distribution variations.
Results: Average catheter lengthening between fractions was 1.95 ± 0.97 mm, peaking at 6 mm. This resulted in reductions in V95% (up to 6.8%) and V90% (up to 5.5%), particularly in proximal targets, leading to potential target underdosing. Skin dose (D0.1cc) increased by up to 136 cGy, particularly in cases where targets were closer to the skin surface. Distal targets showed a clinically significant reduction in skin dose, whereas medial targets had minimal impact.
Conclusion: Unaccounted catheter lengthening can significantly affect target coverage and skin dose, particularly for proximal targets. Routine pre-treatment length verification is recommended, especially for cases where the target is close to the skin. Further studies should refine guidelines for applicator-specific QA to enhance treatment accuracy and patient safety