Effect of different definitions of prescription point “A” in high dose rate brachytherapy for cervical cancer

Abstract

This study intended to compare the dosimetric parameters using different definitions of prescription point A in high dose rate (HDR) brachytherapy of cervical cancer patients. Manchester point A has been widely used for prescribing dose in brachytherapy. However, due to certain limitations of this point, a new definition of point A has been recommended by the American Brachytherapy Society (ABS). We retrospectively investigated 55 computed tomography-based plans of 20 cervical cancer patients treated with Ir-192-based intracavitary HDR brachytherapy. The dose of 7 Gy in 3 fractions each was prescribed to point A using revised Manchester definition of point A (AMAN) and ABS guideline definition (AABS). The effect of both definitions on various parameters including dose to point A and 90% of tumor volume (D90), dose received by 2cc volume of bladder, rectum and small bowel and treatment volume receiving 100% of prescription dose (V100) was analyzed. Mean percentage difference of point AMAN dose and AABS dose with respect to prescription dose was 1.25% ± 1.43% and 1.21% ± 1.01%, respectively. Mean V100 was 80.4 ± 20.45cc and 88.47 ± 16.78cc for AMAN and AABS plans, respectively, while mean percentage difference between prescribed dose and D90 was found to be -37.90% ± 25.06% and -30.47% ± 25.50% respectively for both the definitions. Doses to both Manchester point A and ABS point A may be recorded during the transition period. However, ABS point A can be preferred over the Manchester point A as it conforms better with the desired dosimetric outcome and is found to be more static.