Effect of different definitions of prescription point "A" in high dose rate brachytherapy for cervical cancer.

Aim: 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.Background: 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).Materials and Methods: 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.Results: 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.Conclusion: 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.