Evaluation of Dosimetric Impact of Systematic Source Position Uncertainty during MRI-Guided Gynecological HDR Interstitial Brachytherapy
Abstract
Purpose
To assess the dosimetric impact of systematic source position uncertainty along the source path during MRI-guided gynecological high-dose-rate (HDR) interstitial brachytherapy (ISBT) treatment planning.
Methods
Treatment plans from 11 cervical cancer patients treated using interstitial brachytherapy were retrospectively analyzed. Uncertainty in source position along the source path was modeled by systematically shifting the source position at the increment of 1 mm in the -5 mm to +5 mm range along the source path in original treatment plans. Dosimetric parameters, including HRCTV_D90 and D2cc for organs at risk (OARs), were computed for each source position. Statistical significance was evaluated using the Wilcoxon signed-rank test.
Results
Dosimetric changes were significant for all OARs (all shift positions; p≤0.003). HRCTV_D90 was also significantly affected at all source position shifts (p≤0.033) except −1 and −2 mm. HRCTV_D90 decreased by up to 11.9%, and the OARs D2cc increased by up to 17.2%, 3.0%, 7.6%, and 13.8% for the bladder, bowel, rectum, and sigmoid, respectively.
Conclusion
Systematic source position shift can significantly influence dosimetry in MR-guided gynecological HDR interstitial brachytherapy. This indicates that treatment plan re-optimization strategies may be necessary to minimize this effect.