Comparative Evaluation of Two-dimensional Radiography and Three Dimensional Computed Tomography Based Dose-volume Parameters for High-dose-rate Intracavitary Brachytherapy of Cervical Cancer: A Prospective Study

Background: Dosimetric comparison of two dimensional (2D) radiography and three-dimensional computedtomography (3D-CT) based dose distributions with high-dose-rate (HDR) intracavitry radiotherapy (ICRT) forcarcinoma cervix, in terms of target coverage and doses to bladder and rectum. Materials and
Methods: Sixtyfour sessions of HDR ICRT were performed in 22 patients. External beam radiotherapy to pelvis at a dose of 50Gray in 27 fractions followed by HDR ICRT, 21 Grays to point A in 3 sessions, one week apart was planned . Allpatients underwent 2D-orthogonal and 3D-CT simulation for each session. Treatment plans were generated using2D-orthogonal images and dose prescription was made at point A. 3D plans were generated using 3D-CT imagesafter delineating target volume and organs at risk. Comparative evaluation of 2D and 3D treatment planning wasmade for each session in terms of target coverage (dose received by 90%, 95% and 100% of the target volume:D90, D95 and D100 respectively) and doses to bladder and rectum: ICRU-38 bladder and rectum point dose in2D planning and dose to 0.1cc, 1cc, 2cc, 5cc, and 10cc of bladder and rectum in 3D planning.
Results: Mean dosesreceived by 100% and 90% of the target volume were 4.24±0.63 and 4.9±0.56 Gy respectively. Doses received by0.1cc, 1cc and 2cc volume of bladder were 2.88±0.72, 2.5±0.65 and 2.2±0.57 times more than the ICRU bladderreference point. Similarly, doses received by 0.1cc, 1cc and 2cc of rectum were 1.80±0.5, 1.48±0.41 and 1.35±0.37times higher than ICRU rectal reference point.
Conclusions: Dosimetric comparative evaluation of 2D and 3DCT based treatment planning for the same brachytherapy session demonstrates underestimation of OAR dosesand overestimation of target coverage in 2D treatment planning.