The Role of Computed Tomography Based Treatment Planning in High Dose Rate (hdr) Brachytherapy in Carcinoma of the Cervix

Aim: To compare the high dose rate (HDR) brachytherapy treatment planning using standard orthogonal radiography and computerized tomography (CT) for carcinoma of the cervix. Methods: Forty applications with orthogonal planning using the Brachy Vision treatment planning system version 7.3.10 were performed. Orthogonal and CT based planning in these applications were compared; the doses to point A, rectum and bladder were defined according to the American Brachytherapy Society (ABS) recommendation. Using CT planning, we calculated the dose volume histogram (DVH) for the CTV, rectum and bladder. Results: Using orthogonal films to prescribe to point A, only 63.5% of CTV received the prescribed dose. The mean dose to the bladder point is 2.9 Gy and 17% of the bladder volume was encompassed by 2.9 Gy isodose line. The mean dose at the rectum point is 3.4 Gy and 21% of the rectum volume was encompassed by 3.4 Gy isodose line. The maximum dose to the rectum and the bladder derived from the CT is 1.7 and 2.6 times higher than the orthogonal reference points. Conclusions: CT based treatment planning for HDR brachytherapy of cancer cervix is reliable and more accurate in definition and calculation of the dose to the target as well as the critical organs. It allows dose calculation based on the actual volume rather than points or bony landmarks.