Feasibility of applying a single treatment plan for fractions in HDR image guided brachytherapy in cervix cancer : dosimetric and biological considerations

Abstract

Carcinoma of the uterine cervix is the eighth most common cancer among women in Hong Kong. Intracavitary brachytherapy in combination with external beam radiotherapy (EBT) has been successfully used for the treatment of cervical cancer. Image-guided brachytherapy (IGBT) with three-dimensional (3D) treatment planning is widely applied. This retrospective study assesses the feasibility of applying the computed tomography-based (CT-based) plans optimized for the first treatment to subsequent sessions, without significant changes in dose distributions if same applicators are used throughout the course.

Sixteen patients (FIGO stages IB = 1, II = 7 and III = 8) who underwent CT-based brachytherapy between December 2013 and June 2015 for cervical cancer were reviewed. High-risk CTV (HR-CTV) and organs-at-risk (OARs) were delineated and analyzed. Data using the fully optimized approach were taken from the actual treatment plans. The ‘‘standard plan procedure’’ was simulated by matching the dose distribution of the first plan to the CT datasets of each subsequent fraction. Dosimetric and radiobiological parameters for the target and OARs from the subsequent sessions were retrospectively compared to those that would have been delivered using the initial plan.

The mean D90 for HR-CTV was 2.6 Gy higher in standard plan setting than in fully optimized plan setting. The dose increase to D2cc Bladder, D2cc Rectum, and D2cc Sigmoid was 3.10 Gy, 4.04 Gy and 3.74 Gy respectively. The application of treatment plan would have resulted in 4, 7 and 8 extra cases exceeding total D2cc constraints for the bladder (90 Gy), rectum (75 Gy) and sigmoid (75 Gy) respectively. However, the dose increase was not statistically significant. Besides, equivalent uniform dose-based normal tissue complication probability (EUD-based NTCP) values for bladder and rectum were 0.00% in standard plan setting.

This study showed the application of the first CT-image guided plan to the subsequent brachytherapy treatments did not lead to a significant difference in target dose or a significant increase in OARs dose except sigmoid. Our study indicated that the standard plan technique achieved acceptable dosimetry and radiobiological impacts in most patients.