Int J Radiat Oncol Biol Phys. 2020 Aug 14:S0360-3016(20)34123-7. doi: 10.1016/j.ijrobp.2020.08.033. Online ahead of print.
PURPOSE: To examine dose-volume effect relationships for anorectal morbidity in children treated with image-guided brachytherapy for pelvic tumors.
METHODS AND MATERIALS: Medical records of all consecutive children with pelvic tumors treated in our center and receiving image-guided pulsed-dose-rate (PDR) brachytherapy with or without external beam radiation therapy (EBRT) between 2005 and 2019 were reviewed. The impact of the minimal doses to the most exposed 0.5 cm3, 1 cm3 and 2 cm3 of the anorectum (respectively: D0.5cm3, D1cm3 and D2cm3), total reference air kerma (TRAK) and volume of 100% isodose was examined for anorectal toxicities.
RESULTS: 78 consecutive children were included. Median age was 2.9 years (range: 0.8-14.9 years). Most of the tumors were bladder/prostate (67%) or vaginal (22%) rhabdomyosarcoma. Six patients received EBRT in addition to brachytherapy. Median follow-up was 21.3 months. At last follow-up, 30 children (38%) had experienced CTCAEv5 grade ≥ 1 acute or late anorectal events: 24% had grade 1 events, 7.7% had grade 2 and 6.4% had grade 3. No grade >3 toxicity was observed (e.g. fistula or stricture). In univariate analysis, the D0.5cm3 and D1cm3 were significant for probability of grade 1-3 (p=0.009 and p=0.017, respectively) and grade 2-3 anorectal morbidity (p=0.007 and p=0.049, respectively). There was no significant correlation for D2cm3 (p=0.057 for grade 1-3 and p=0.407 for grade 2-3). A 10% probability (95% CI: 4-20%) for grade ≥ 2 anorectal toxicity was reached for a D0.5cm3 = 52 Gy. The age, EBRT use, TRAK, and treated volume were not significant.
CONCLUSIONS: This is the first study showing significant dose/volume effect relationships for anorectal morbidity in children treated with brachytherapy. Integrating these data into brachytherapy treatment planning may help to optimize the therapeutic index in these very young patients.