What question did this study set out to answer?

This research aims to understand how BMI influences dosimetric outcomes in CT-based interstitial brachytherapy for gynecological cancers.

May 29, 2026F1000Research0 citationsOpen Access

Influence of Body Mass Index on Dosimetric Outcomes in CT-Based Interstitial Brachytherapy for Gynecological Malignancies

SSSahana Srinivasan JSJohan Sunny DLDilson Lobo

Key Points

This research aims to understand how BMI influences dosimetric outcomes in CT-based interstitial brachytherapy for gynecological cancers.
Retrospectively analyzed data from 55 patients treated between 2019 and 2023.
Evaluated dosimetric parameters using ANOVA across different BMI groups.
Calculated biologically effective doses and converted doses to equivalent dose in 2-Gy fractions.
BMI had no effect on implant quality or tumor coverage, with a mean tumor EQD2 of 88.99 ± 4.52 Gy10.
Rectal BED was significantly lower in obese patients (p = 0.014) compared to normal and underweight patients.
Sigmoid BED and EQD2 showed significant variability by BMI (p = 0.024), particularly lower doses in obese individuals.

Abstract

Abstract Background Body mass index (BMI) may influence dosimetric outcomes in interstitial brachytherapy (ISBT), but its impact on CT-based ISBT is not well established. Unlike intracavitary brachytherapy, ISBT is strongly dependent on applicator geometry, needle placement, and patient-specific anatomy. These factors suggest that body habitus could affect both target coverage and organ-at-risk (OAR) doses, with meaningful clinical implications. Methods We retrospectively analyzed 55 patients with cervical, vaginal, or vault cancers treated between 2019 and 2023 with definitive external beam radiotherapy (EBRT) followed by high-dose-rate (HDR) ISBT using a cobalt-60 source. All patients underwent CT-based planning with Syed–Neblett templates. Dose–volume histogram parameters and implant quality indices—coverage index (CI), dose homogeneity index (DHI), overdose index (OI), dose non-uniformity ratio (DNR), and conformity index (COIN)—were assessed. Tumor and OAR doses were converted to biologically effective dose (BED) and equivalent dose in 2-Gy fractions (EQD 2 ). Patients were grouped according to WHO BMI categories, and differences were evaluated using ANOVA. Results Cervical cancer accounted for 94.5% of cases. BMI distribution was 45.5% normal, 20% underweight, 16.4% overweight, and 18.2% obese. High-risk CTV volumes ranged from 25 to 54 cm 3 . Implant quality indices and tumor dose coverage were consistent across all BMI categories, with a mean tumor EQD 2 of 88.99 ± 4.52 Gy 10 . In contrast, gastrointestinal OAR doses showed a significant association with BMI. Rectal BED was significantly lower in obese patients compared with normal and underweight patients (p = 0.014). Sigmoid BED and EQD 2 also varied significantly by BMI (p = 0.024), with the lowest doses observed in obese patients. Bladder doses were unaffected by BMI. Conclusion BMI did not influence implant quality or tumor coverage in HDR ISBT but significantly affected rectal and sigmoid doses. Underweight patients may be more vulnerable to higher gastrointestinal OAR exposure and may benefit from stricter dose optimization.

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