Brachytherapy in Cervical Cancer: Accuracy in Point Dose Demarcation

Cervical cancer is one of the commonest gynecological cancers in Sri Lanka. Due to very limited high dose rate (HDR) after loader facility, conventional brachytherapy is practiced in government sectors in our country. The dose specification point A in brachytherapy is a geometrical concept which represents the anatomical position of uterine artery crosses the ureter. This study aimed to assess how the Manchester point A represents the true anatomical point A (APA). A total of 48 diagnostic contrast enhanced CT scans of carcinoma of the cervix/endometrium were reviewed retrospectively for this descriptive quantitative study. Manchester point A was established. The APA and high-risk clinical target volume (HRCTV) were marked and contoured on the CT data.The dimensions of HRCTV on AP projection and coordinates of APA were recorded. The relationship between the dimensions of HRCTV and the position of APA also was assessed to discuss the possibilities of individualizing the point-based brachytherapy. The mean APA of the sample was at a vertical level of 1.18±0.35 cm from the external-orifice along the uterine axis and 3.63±0.52 cm laterally to either side. A significant moderate positive correlation exists between HRCTV dimensions and APA position. An approximate individualized Point A is defined using this correlation as a function of HRCTV dimensions, which can easily be measured from radiotherapy planning CT scans. The geometric point A does not provide an accurate estimate of the APA that indicates there is a need for patient-based model. The developed model is useful in a 3D brachytherapy setup for individualized dose recording and can be used in a 2D brachytherapy setup to individualize dose prescription if the applicability is proven.