Room: ePoster Forums
Purpose: In the FIF forward planning technique, a merged plan with 2-4 segmental fields is the final plan delivered to the machine. As per the ASTRO guidelines for the hypofractionation regimen, V105% < 200cc. This study compares the V105% of 29 breast plans before and after merging the subfields.
Methods: We retrospectively collected dosimetry data on a total of 29 breast patients who were treated in 2018 with a dose of 4256 cGy in 16 fractions at our institution using FIF tangents. After the plans were reviewed by the physician, the subfields were merged and a final deliverable plan was approved for treatment. The variables included in this study are; patient orientation, number of fields and sum of monitor units (MUs) before and after merge and V105% (cc) of pre- and post-merge plans.
Results: In the 29 plans, the numbers of subfields in each plan ranged from 5 to 12, which merged into 2-4 fields in the final plan. Due to the rounding of MUs, there was often a change in sum of MUs in the pre- and post-merged plans. Owing to the creation of segmental fields, there is a miniscule change in leakage and scatter dose, which is reflected by the modification of isodose lines coverage. The sum of MUs of all the fields and subfields between un-merged and merged plans were unchanged in 13 plans, increased by 1 MU in 9 plans, decreased by 1 MU in 3 plans, decreased by 2 MUs in 3 plans and increased by 2 MUs in 1 plan. This resulted a appreciable change in V105% ranged between -55 cc to + 47.1 cc for 29 patients.
Conclusion: The plans should be reviewed by the MD and V105% should be re-measured after merging the sub-fields in a FIF breast forward planning.
Not Applicable / None Entered.