A comparative study of Manchester system and ABS system in intracavitary brachytherapy dose calculations

The success of brachytherapy in the treatment of cancer of cervix depends on the delivery of high radiation dose to the tumour in the cervix, sparing the critical organs rectum and bladder. Ideally, the dose should be prescribed to the individual patient's target volume. But almost all the institutions follow the dose prescription at a point instead of target volume, since tumour localization is not possible in radiograph. There are different systems of dose specifications for Ca. cervix treatment: -Manchester system and American Brachytherapy Society system. In Manchester system, Point A and Point B were defined. Point A was defined to be 2 cm superior to the external cervical os (or cervical end of the tandem) and 2 cm lateral to the cervical canal, which represents the location where the uterine vessels cross the ureter. Point B was defined 3 cm lateral to point A, which represents the lymph nodes. The American Board of Brachytherapy (ABs) recommends prescribing the dose to the new point called point H and pelvic wall points. Point H is based on the mid-dwell position of the vaginal ovoids. Finding Point H begins with drawing a line connecting the mid-dwell positions of the ovoids. From the intersection of this line with the tandem, move superiorly along the tandem 2 cm plus the radius of the ovoids, and then 2 cm perpendicular to the tandem in the lateral direction. In selectron LDR machine, instead of the mid-dwell position, the center of the ovoid source is taken. The pelvic wall points are located at the intersection of a horizontal tangent to superior aspect of the acetabulum on the AP radiograph