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) ¹⁹²Ir Gammamed Plus device.

Results
The dose prescribed to HR-CTV was 30 Gy low-dose-rate (LDR) equivalent (5 Gy × 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 (EQD₂). The average tumor volume was 67 cc and the average D₉₀ of HR-CTV was 29 Gy (5.7 Gy/fraction) EQD₂. D₁₀₀ of HR-CTV volume was 18 Gy (3.8 Gy/fraction) EQD₂. The total doses of 2 cc of rectum and bladder were 70 Gy and 76 Gy EQD₂ (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.