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

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.

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 (CTV_HR) and the D₂cm³ (minimum dose received by the most irradiated 2 cm³) to the bladder, bowel, sigmoid, and rectum were compared.

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 CTV_HR volumes ≥30 cm³ at Fraction 1 compared to 18% in the IC cohort (p = 0.014). There was no difference in cumulative D₉₀% to CTV_HR between the IC/IS cohort and the IC cohort. The replanned brachytherapy showed that the cumulative CTV_HRD₉₀% was on average 5.8 Gy higher when IS catheters were used (mean CTV_HRD₉₀% 86.1 compared to 80.3 Gy, p < 0.001). The D₂cm³ to the organs at risk was not significantly increased.

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