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SU‐F‐T‐60: A Quick Dose Calculation Check for Accuboost Breast Treatment
Author(s) -
Sen A
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4956195
Subject(s) - brachytherapy , nuclear medicine , dwell time , dosimetry , nomogram , radiation treatment planning , monte carlo method , breast tissue , medicine , biomedical engineering , physics , mathematics , radiation therapy , radiology , optics , breast cancer , clinical psychology , statistics , cancer
Purpose: Accuboost treatment planning uses dwell times from a nomogram designed with Monte Carlo calculations for round and D‐shaped applicators. A quick dose calculation method has been developed for verification of the HDR Brachytherapy dose as a second check. Methods: Accuboost breast treatment uses several round and D‐shaped applicators to be used non‐invasively with an Ir‐192 source from a HDR Brachytherapy afterloader after the breast is compressed in a mammographic unit for localization. The breast thickness, source activity, the prescription dose and the applicator size are entered into a nomogram spreadsheet which gives the dwell times to be manually entered into the delivery computer. Approximating the HDR Ir‐192 as a point source, and knowing the geometry of the round and D‐applicators, the distances from the source positions to the midpoint of the central plane are calculated. Using the exposure constant of Ir‐192 and medium as human tissue, the dose at a point is calculated as: D(cGy) = 1.254 × A × t/R2, where A is the activity in Ci, t is the dwell time in sec and R is the distance in cm. The dose from each dwell position is added to get the total dose. Results: Each fraction is delivered in two compressions: cranio‐caudally and medial‐laterally. A typical APBI treatment in 10 fractions requires 20 compressions. For a patient treated with D45 applicators and an average of 5.22 cm thickness, this calculation was 1.63 % higher than the prescription. For another patient using D53 applicators in the CC direction and 7 cm SDO applicators in the ML direction, this calculation was 1.31 % lower than the prescription. Conclusion: This is a simple and quick method to double check the dose on the central plane for Accuboost treatment.