Clinical Outcomes of Computed Tomography-Based Volumetric Brachytherapy Planning for Cervical Cancer

Abstract

A report of clinical outcomes of a computed tomography (CT)-based image-guided brachytherapy (IGBT) planning technique for the treatment of intact cervical cancer. We included all patients with intact cervical cancer treated with IGBT at UCSD between 2007 and 2014. The majority (93%) of patients were treated using intensity-modulated radiotherapy (IMRT), while the remaining patients were treated with a 4-field three-dimensional conformal technique. The majority (95%) of patients received concurrent chemotherapy. All patients were treated with high-dose rate (HDR) brachytherapy using a tandem-and-ovoid (T&O) intracavitary device with an Iridium-192 source. Four patients received a combination of intracavitary and interstitial brachytherapy due to areas of residual gross disease not covered by the T&O or difficult anatomy. Planning CT scan was obtained prior to the delivery of each fraction. The high-risk clinical target volume (HRCTV) and organs at risk (OARs) were contoured on the planning CT according to the GEC-ESTRO guidelines using BrachyVisionTM brachytherapy planning software (Varian Medical Systems). The HRCTV included the entire cervix as well as visible residual gross tumor. A magnetic resonance imaging scan (MRI) was planned for the second fraction with the intracavitary device in place, as scheduling the MRI for the first fraction was infeasible. The HRCTV was then contoured on the fused T2-weighted axial MRI. The brachytherapy dose was converted to the 2-Gy equivalent (EQD2) doses using the linear quadratic model. The total combined EBRT and brachytherapy EQD2s to points A, B, and DVH parameters for HRCTV, rectal, sigmoid, and bladder were calculated and recorded. We estimated overall survival (OS) and disease-free survival (DFS) using the Kaplan-Meier method. We estimated the incidence of local failure (LF), regional failure (RF), and distant failure (DF) using cumulative incidence functions. The patient and treatment characteristics are shown in Table 1. Sixty patients (79%) were treated with MRI-guidance, while 16 patients (21%) were treated with only CT-planning. The 2 year cumulative incidences of LF, RF, and DF were 4.2% (95% CI: 0.73-13.1%), 5.4% (95% CI: 0.71-17.8%) and 18.7% (95% CI: 8.6-31.9%), respectively. The 2 year OS and DFS rates were 75% (95% CI, 61-91%) and 73% (95% CI, 60-90%), respectively. Twenty-nine patients (38%) experienced grade ≥2 acute toxicity, with 5 cases of acute grade 3 toxicity and no grade ≥4 toxicities. One patient experienced grade 3 GI toxicity with a benign sigmoid stricture with telangiectasias which required laser coagulation. There was no other late grade ≥3 toxicity observed. This is one of the largest reports to date of CT/MRI-based IGBT for the treatment of cervical cancer. The results are promising with excellent local control and acceptable toxicity. Further investigation is needed to assess the long-term safety and efficacy of this treatment.Table 1Patient and Treatment Characteristicsn76Age [median (range)] (y)51 (24-83)Follow-up time [median (range)] (mo)17 (3-54)Histology [n (%)] Squamous cell carcinoma55 (72) Adenocarcinoma18 (24)FIGO Stage [n (%)] IB1-IIA27 (35) IIB-IVA49 (65)Treatment Duration [median (range)] (d)56 (39-152)EBRT Dose [median (range)] (Gy)45 (43.2-50.4)Brachytherapy Prescription Dose [median (range)] (Gy)29 (25-30)EBRT/IGBT EQD2 sum [mean (SD)] (Gy) HRCTV D9086.3 (8.1) Bladder D2cc75.3 (9.2) Rectum D2cc67.5 (6.8) Sigmoid Colon D2cc66.2 (7.9) Open table in a new tab