Evaluation of Volumetric Doses of Organs at Risk in Carcinoma Cervix Patients with HDR Intracavitary Brachytherapy and Comparison of CTbased and Conventional Plans

Brachytherapy treatment planning in cervix carcinoma patients using two dimensional (2D) orthogonal images provides only point dose estimates while CT-based planning provides volumetric dose assessment helping in understanding the correlation between morbidity and the dose to organs at risk (OARs) and treatment volume.

Aim of present study is to compare International Commission on Radiation Units and Measurements Report 38 (ICRU 38) reference point doses to OARs with volumetric doses using 2D images and CT images in patients with cervical cancer.

In this prospective study, 20 patients with cervical cancer stages (IIB-IIIB) were planned for a brachytherapy dose of 7Gy per fraction for three fractions using 2D image-based treatment plan and CT-based plan. ICRU 38 points for bladder and rectum were identified on both 2D image-based plan and CT-based plan and doses (DICRU) at these points were compared to the minimum dose to 2cc volume (D2cc) of bladder and rectum receiving the highest dose.

D2cc bladder dose was 1.60 (±0.67) times more than DICRUb bladder dose whereas D2cc rectum dose was 1.13±0.40 times DICRUr. Significant difference was found between DICRUb and D2cc dose for bladder (p=.0.016) while no significant difference was seen between DICRUr and D2cc dose for rectum (p=0.964).

The study suggests that ICRU 38 point doses are not the true representation of maximum doses to OARs. CT-based treatment planning is more a reliable tool for OAR dose assessment than the conventional 2D radiograph-based plan.