Abstract
Volume not the defining metric: Dosimetric benefits of adding supplemental interstitial needles for small volume cervical tumors
Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, USA
J Contemp Brachytherapy 2026; 18, 2: 147–153
Purpose
In brachytherapy for cervical cancer, previous data have demonstrated improved local control with adding supplementary interstitial needles for cervical tumors > 30 cm3 and increased D90 to high-risk clinical target volume (HR-CTV) without increasing dose to adjacent normal tissues. Therefore, needles are more routinely added for larger volume tumors. At our institution, supplemental interstitial needles have routinely been used for all cervix cancer brachytherapy cases, even smaller volume tumors. This study aimed to identify the dosimetric advantages of supplementary interstitial needles for small volume cervix tumors.
Material and methods
Fifty-seven intracavity/interstitial (IC/IS) patients treated from November 2019 through November 2023 with HR-CTV < 30 cm3 at the first brachytherapy fraction were included. High-dose-rate (HDR) brachytherapy plans were re-optimized using an intracavitary applicator only, without needles, to improve coverage while maintaining similar minimum doses to the clinical plan for the most irradiated 2 cm3 of bladder, rectum, and bowel.
Results
The median HR-CTV was 19.3 cm3 (range, 4.38-29.95 cm3). For a single-brachytherapy fraction per patient, the average volume of HR-CTV receiving 100% of the prescription dose (V100) was 92.9% vs. 79.8% for IC/IS vs. no-needle plans, respectively (p < 0.0001). Normal tissue metrics for the rectum, bowel, and bladder showed no statistically significant difference between the two plans. Combining the external beam and extrapolated brachytherapy doses, the average HR-CTV dose received by 90% of the volume (D90) was 90.1 Gy for IC/IS vs. 81.1 Gy for no-needle plans (p < 0.0001). Even for volumes < 20 cm3 (n = 32) and < 15 cm3 (n = 16), HR-CTV V100 and D90 were significantly improved with needles added (p < 0.0001).
Conclusions
These results suggest a significant dosimetric benefit of adding supplementary interstitial needles even for small volume cervical tumors, allowing enhanced dose shaping to improve HR-CTV coverage and achieving EMBRACE II target dosing goals, while maintaining normal tissue sparing.
Keywords
brachytherapy, interstitial needles, image-guided radiotherapy, cervical cancer, hybrid applicator
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