Inversely and adaptively planned interstitial brachytherapy: A single implant approach.

Objective: To evaluate the efficacy, feasibility and safety of image-based, inversely and adaptively planned high-dose rate interstitial brachytherapy (HDR-ISBT) to treat advanced primary or recurrent gynecologic malignancy in a single implant, three-consecutive-day regimen.

Methods: Clinical demographics and outcome data were abstracted from all patients with primary and recurrent gynecologic malignancies who received HDR-ISBT boost from 2014 to 2017. Treatment consisted of a single implant (~7 Gy × 4 fractions) of interstitial needles using the Syed-Neblett template over a three-day hospital admission. CT-based (3D) simulation with inverse and adaptive planning was utilized for each fraction. MR prior to and MR immediately after external beam therapy were fused for HDR-ISBT target delineation.

Results: Forty women with an overall median follow-up of 18 months (range: 6-54 months) received an HDR-ISBT boost. Of the 30 primary cases (83% cervix, 10% vaginal, 7% uterine), 44% had organ invasion (bladder, rectal or both) on MRI. Median coverage and dose are reported (V: 98%, HR-CTV EQD: 85.1 Gy, D: 92 Gy). A significant association existed between rectal doses exceeding GEC-ESTRO recommendations (D < 75 Gy) and the development of grade 3 gastrointestinal toxicity with a relative risk of 1.4 [1.1-1.8] (p = .046). Actuarial two-year overall survival (OS), local control (LC) and progression-free survival (PFS) were 81%, 81% and 64%, respectively.

Conclusions: A four fraction, inversely and adaptively planned, single-implant approach of image-based HDR-ISBT provides excellent coverage, minimal toxicity and effective local control in patients with advanced and recurrent disease.