THE USE OF A TRANSVERSE CT IMAGE FOR THE ESTIMATION OF THE DOSE GIVENTO THE RECTUM IN INTRACAVITARY BRACHYTHERAPY FOR CARCINOMA OF THE CERVIX

Background and purpose: The three-dimensional (3D) dose distribution i n combination with 3D anatomy of 13 patients treated for cervical carc inoma with intracavitary brachytherapy was analyzed. The aim of this s tudy was to determine the correlation between a dose value obtained fr om the integral dose volume histogram (DVH) of the rectum and (a) the Nederlands Kanker Instituut (NKI) point of reference for the rectum do se (R) and (b) the highest dose to the frontal rectum wall in the tran sverse CT slice near the top of the vagina through point R. Results: T he correlation between the DVH rectum dose value for 2 cm(3) in the hi ghest dose region and the rectum dose at point R was poor (regression coefficient 0.50). On the contrary, however, the correlation between t he DVH rectum dose value for 2 cm(3) in the highest dose region and th e maximum rectum dose value in a transverse CT slice through point R w as good (regression coefficient 0.90). Conclusions: The maximal rectum dose value obtained from a transverse CT slice near the top of the va gina through point R was found to be a more representative point for t he rectal dose burden and might therefore show a good correlation with complications. The point of reference for the rectal dose (R) was fou nd not to be a reliable estimation of the maximal dose in the rectum. (C) 1998 Elsevier Science Ireland Ltd.