Evaluation of plan quality, safety, and toxicity of brachytherapy for locally advanced cervical cancer in an Australian setting following changes in prescription and applicator design.

Introduction: Chemoradiotherapy with MRI-guided brachytherapy boosts is the standard of care for locally advanced cervical cancer. Data from the RetroEMBRACE and EMBRACE I trials provide dose-response curves for target volumes and OAR. This study evaluated plan quality, safety and toxicity following escalation of the CTV_HR D90 prescription from 80-90 Gy to 85-95 Gy for two different applicator designs.

Methods: A retrospective dosimetric plan quality review was undertaken for consecutively treated locally advanced cervical cancer brachytherapy boosts between 2017 and 2022, and the relationships between implant total reference air kerma (TRAK), CTV_HR volume and vaginal dose were investigated. Safety and ≤grade 3 toxicity results were evaluated.

Results: Seventy patients were identified. All patients received a CTV_HR D90 dose >85 Gy and rectum D2cm³ of <75 Gy, while 88.6% of patients received a bladder D2cm³ <90 Gy. Needles were used in 48.6% of patients, and the mean percentage needle TRAK was 38.2%. Increasing the percentage of needle TRAK decreased vaginal TRAK. Sixty-three patients had more than 12 months of follow-up (median 27 months). From this cohort, grade 3 or higher toxicity for vaginal, genitourinary, gastrointestinal and fistula events were seen in 3.2%, 1.6%, 0% and 3.2% of patients, respectively.

Conclusion: Increased dose prescriptions and a change of applicator design were successfully adopted into an Australian practice. Applicator design and interstitial needle use affect the plan quality and ability to meet OAR dose constraints following target dose escalation. No safety concerns with needle use or dose escalation were identified.