Predicting which patients may benefit from the hybrid intracavitary+interstitial needle (IC/IS) applicator for advanced cervical cancer: A dosimetric comparison and toxicity benefit analysis

Abstract

The purpose of this study is to compare the predicted rate of local control and bladder and rectum toxicity rates for image-guided adaptive brachytherapy plans using a tandem and ovoid (T/O) applicator versus using a simulated hybrid intracavitary/interstitial tandem and ring applicator with needles (T/R þ N) for patients with locally advanced cervical cancer (LACC). METHODS AND MATERIALS: Patients with $ FIGO Stage IIB locally advanced cervical cancer treated with T/O from a single institution were included. Simulated treatment plans were created with a T/R þ N applicator for the best high-risk clinical target volume (CTV) coverage and minimal dose to organs at risk. Three-year local control rate was estimated using published dose-volume effect relationships. Next, the high-risk CTV EQD2 D90 of T/R þ N plans were calculated, and bladder and rectum toxicity rates were estimated. Analysis was performed in subpatient groups defined based on tumor volume and ratio of maximal and minimal tumor radii (RR) that reflects tumor shape asymmetry. RESULTS: Improvements in predicted local control rate for the T/R þ N were 0.8, 4.1, 1.6, and 3.9% for groups with tumor volume !35 cc, $35 cc, RR ! 2.0, and $2.0, respectively, with the latter three being statistically significant. Predicted reductions in Grade 2e4 toxicity rates of bladder and rectum were significant in all groups except bladder toxicity in tumor volume ! 35 cc, when T/R þ N plans were normalized to the same CTV coverage as the T/O plans. Comparing unnormalized T/R þ N plans and T/O plans, predicted toxicity reductions were significant in all groups except rectum toxicity in RR $ 2.0. Predicted reduction of toxicity rate was larger for patients with large tumor or large tumor RR, although some reductions were relatively small.

An Asian multi-national multi-institutional retrospective study comparing intracavitary versus the hybrid of intracavitary and interstitial brachytherapy for locally advanced uterine cervical carcinoma

“…[ 15 ] showed that HR-CTV size between 4 × 3 × 3 cm and 5 × 4 × 4 cm could be better treated by HBT, and Gonzalez et al. [ 20 ] found that tumor volume ≥ 35 cc or significant tumor asymmetry would benefit more from HBT. Despite the fact that the HBT group had more patients with advanced stage, uterine body invasion and parametrium invasion ( Table 1 ) and rectum D 2cc was higher in HBT patients, bladder D 2cc was comparable between the two groups, suggesting that HBT is better than ICBT at delivering a higher dose to the target volume while sparing organs at risk (OAR).…”

Japanese Society for Radiation Oncology Consensus Guidelines of combined intracavitary and interstitial brachytherapy for gynecological cancers

“…IC/IS should be adopted for uterine or vaginal tumors in which an adequate dose cannot be delivered to the entire high-risk CTV (CTV HR ) and/or dose constraints for surrounding OARs cannot be observed by the conventional ICBT. In particular, CTV HR > 30 cm 3 , the maximum diameter of CTV HR > 4 cm, irregularly or asymmetrically shaped tumors, or thickness of vaginal wall extension >5 mm are good candidates for IC/IS [ 8 , 14 ].…”

Evolution of brachytherapy applicators for the treatment of cervical cancer

“…[ 73 74 ] Patients with large or asymmetric tumor can be treated effectively with this hybrid applicator. [ 75 ]…”