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Comparison of Breast V105% Between Pre- and Post-Merged Subfields in Field-In-Field Hypofractioanted Breast Radiation Treatment Plans

A Dwivedi1, T McGarry2 , L Bond3 , J Braver4 , N Biswal5* , (1) Robert Wood Johnson University Hospital Somerset, Steeplechase Cancer Center, Somerville, NJ, (2) Robert Wood Johnson University Hospital Somerset, Steeplechase Cancer Center, Somerville, NJ, (3) Robert Wood Johnson University Hospital Somerset,Steeplechase Cancer Center, Somerville, NJ, (4) Robert Wood Johnson University Hospital Somerset,Steeplechase Cancer Center, Somerville, NJ, (5) Rutgers- Cancer Institute of New Jersey, New Brunswick, NJ

Presentations

(Sunday, 7/14/2019)  

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.

Keywords

Breast, Volume Effects

Taxonomy

Not Applicable / None Entered.

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