Magnetic resonance image-based 3D volume interstitial brachytherapy using polyether ether ketone catheters in advanced cervical cancer - a feasibility study.

Purpose: A feasibility study of 3D volume-based interstitial brachytherapy using thermoplastic polyether ether ketone (PEEK) catheters in advanced cervical cancer MR-based brachytherapy, when MR-compatible applicators are not available. Material and methods: Five cervical cancer patients received EBRT dose of 50 Gy in 25 fractions to whole pelvis using 3D conformal radiotherapy after standard pre-treatment evaluation. In our institute, interstitial brachytherapy (ISBT) is planned in BrachyVision TPS and routinely performed using stainless steel needles with Syed-Neblett template. Standard MR-compatible ISBT applicators were not available; therefore, the implant was carried out using PEEK catheters and Syed-Neblett template. The T1 and T2 MR and CT images of patients were acquired for treatment planning. Gross tumor volume (GTV), high-risk clinical target volume (HR-CTV), intermediate-risk clinical target volume (IR-CTV), and organs at risk (OARs) were delineated with the use of MR T2 weighted images, following GEC-ESTRO guidelines. Volumetric optimization was used for planning, and the treatment plan was executed with high-dose-rate (HDR) Ir-192 Gammamed Plus device. Results: The dose prescribed to HR-CTV was 30 Gy low-dose-rate (LDR) equivalent (5 Gy x 4 fractions). Doses to target volume and OARs were analyzed using dose volume histogram (DVH). Dose values were biologically normalized to equivalent doses of 2 Gy fractions (EQD(2)). The average tumor volume was 67 cc and the average D-90 of HR-CTV was 29 Gy (5.7 Gy/fraction) EQD(2). D-100 of HR-CTV volume was 18 Gy (3.8 Gy/fraction) EQD(2). The total doses of 2 cc of rectum and bladder were 70 Gy and 76 Gy EQD(2) (3.71 Gy and 4.04 Gy dose/fraction), respectively. Conclusions: When the facilities for MR-compatible applicators are not available, MR-based ISBT is feasible with PEEK catheters using available resources for advanced cervical cancer. Doses to HR-CTV and IR-CTV were achieved, restricting doses to OARs as per GEC-ESTRO guidelines.