Doses to pelvic bone marrow from intracavitary brachytherapy in carcinoma cervix: A dosimetric study

Current dose-volume constraints for pelvic bone marrow (PBM) sparing in radiotherapy for locally advanced cervical carcinoma (LACC) typically do not account for the dose contribution from intracavitary brachytherapy (ICBT). This study aimed to quantify the radiation dose received by PBM during ICBT.Materials and Methods: This dosimetric analysis utilized computed tomography (CT) data from 15 patients with LACC treated with ICBT. Each patient received 3 weekly fractions of 7 Gy. PBM was delineated from the sacrum to the ischial tuberosities across all 45 CT sessions (three per patient). Two treatment plans were generated-Plan A (high-risk clinical target volume [HR-CTV]-based) and Plan B (Point A-based)-yielding 90 plans in total. PBM volumes receiving ≥1.5 Gy (V1.5), 1 Gy (V1), 0.75 Gy (V0.75), and 0.5 Gy (V0.5) were recorded.

Out of 15 patients, 9 were diagnosed with stage IIB and 6 with stage IIIB (FIGO 2018). The median HR-CTV volume was 19.2 cc (range: 17-35.8 cc), with a median D90 per fraction of 6.9 Gy. The median PBM volume was 927.5 cc (range: 620.8-999.3 cc). For Plan A, the median V1.5, V1, V0.75, and V0.5 were 2.7%, 13%, 24.98%, and 53.69%, respectively, compared to 3.89%, 21.82%, 40.3%, and 67.36% for Plan B. Mean values for Plan A vs. Plan B were as follows: V1.5 (2.89% ±2.6% vs. 5.15% ± 3.57%, P = 0.058), V1 (14.14% ±9.67% vs. 20.6% ±7.82%, P = 0.054), V0.75 (29.22% ±14.99% vs. 39.47% ±11.36%, P = 0.045), and V0.5 (53.2% ±17.1% vs. 64.39% ±12.33%, P = 0.049).

ICBT contributes a measurable dose to the PBM, with approximately 15-20% of PBM receiving around 1 Gy per 7 Gy fraction.