Impact of 3D image-based PDR brachytherapy on outcome of patients treated for cervix carcinoma in France: results of the French STIC prospective study

Abstract

Purpose: In 2005 a French multicentric non randomized prospective study was initiated to compare two groups of patients treated for cervix carcinoma according to brachytherapy (BT) method: 2D vs 3D dosimetry. The BT dosimetric planning method was chosen for each patient in each center according to the availability of the technique. This study describes the results for 705 out of 801 patients available for analysis.

Patients and methods: For the 2D arm, dosimetry was planned on orthogonal X-Rays using low dose rate (LDR) or pulsed dose rate (PDR) BT. For the 3D arm, dosimetry was planned on 3D imaging (mainly CT) and performed with PDR BT. Each center could follow the dosimetric method they were used to, according to the chosen radioelement and applicator. Manual or graphical optimization was allowed.

Patients and methods: Three treatment regimens were defined: Group 1: BT followed by surgery; 165 patients (2D arm: 76; 3D arm: 89); Group 2: EBRT (+chemotherapy), BT, then surgery; 305 patients (2D arm: 142; 3D arm: 163); Group 3: EBRT (+chemotherapy), then BT; 235 patients, (2D arm: 118; 3D arm: 117).

Patients and methods: The DVH parameters for CTVs (High Risk CTV and Intermediate Risk CTV) and organs at risk (OARs) were computed as recommended by GYN GEC ESTRO guidelines. Total doses were converted to equivalent doses in 2Gy fractions (EQD2). Side effects were prospectively assessed using the CTCAEv3.0.

Results: The 2D and 3D arms were well balanced with regard to age, FIGO stage, histology, EBRT dose and chemotherapy. For each treatment regimen, BT doses and volumes were comparable between the 2D and 3D arms in terms of dose to point A, isodose 60 Gy volume, dose to ICRU rectal points, and TRAK.

Results: Dosimetric data in the 3D arm showed that the dose delivered to 90% of the High Risk CTV (HR CTV D90) was respectively, 81.2Gy(α/β10), 63.2Gy(α/β10) and 73.1Gy(α/β10) for groups 1, 2 and 3. The Intermediate Risk (IR) CTV D90 was respectively, 58.5Gy(α/β10), 57.3Gy(α/β10) and 61.7Gy(α/β10) for groups 1, 2 and 3. For the OARs, doses delivered to D2cc ranged 60-70Gy(α/β3) for the bladder, 33-61Gy(α/β3) for the rectum, and 44-58Gy(α/β3) for the sigmoid according to the regimen.

Results: At 24 months, local relapse-free survival was 91.9% and 100% in group 1, 84.7% and 93% in group 2, 73.9% and 78.5% in group 3; grade 3-4 toxicity rate was 14.6% and 8.9% in group 1, 12.5% and 8.8% in group 2, and 22.7% and 2.6% in group 3 for 2D and 3D arm.

Conclusion: This multicentric study has shown that 3D BT is feasible and safe in routine practice. It has improved local control with half the toxicity observed with 2D dosimetry. The combined treatment with radiotherapy and surgery was more toxic than definitive radiotherapy. For patients with advanced tumors, it is necessary to improve coverage of target volumes without raising toxicity.