Improving dose delivery by adding interstitial catheters to fixed geometry applicators in high-dose-rate brachytherapy for cervical cancer.

PURPOSE: Image-guided brachytherapy (IGBT) is an essential component of the treatment of locally advanced cervical cancer. Interstitial (IS) catheters are being increasingly used for bulkier tumors. We have retrospectively assessed the dosimetric impact of IS catheters.

METHODS AND MATERIALS: All patients who received IGBT for cervical cancer between August 2014 and February 2017 were identified. Clinical and dosimetric data were collected. Patients were grouped into the intracavitary (IC) cohort or the IC and IS implant (IC/IS) cohort. Ten patients who had been treated with IS catheters (IC/IS plan) had their brachytherapy replanned without IS catheters (IC plan). The total D90 % received by the high-risk clinical target volume (CTVHR ) and the D2 cm3 (minimum dose received by the most irradiated 2 cm3 ) to the bladder, bowel, sigmoid, and rectum were compared.

RESULTS: Forty-two patients received IGBT in this period. Seventy-four percent of patients were treated with IS catheters. Sixty-one percent of patients in the IC/IS cohort had CTVHR volumes ≥30 cm3  at Fraction 1 compared to 18% in the IC cohort (p = 0.014). There was no difference in cumulative D90 % to CTVHR between the IC/IS cohort and the IC cohort. The replanned brachytherapy showed that the cumulative CTVHR D90 % was on average 5.8 Gy higher when IS catheters were used (mean CTVHR D90 % 86.1 compared to 80.3 Gy, p < 0.001). The D2 cm3 to the organs at risk was not significantly increased.

CONCLUSIONS: IS catheters allow the dose to the CTVHR to be escalated significantly without increasing the dose to the bladder, bowel, sigmoid, and rectum in patients with bulky tumors.