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Dosimetry of 108 Strut-Based Accelerated Partial Breast Irradiation (APBI) Treatments With Applicator Distance Less Than 7 Mm From Both the Skin and Ribs

J Reiff

J Reiff1*, D Scanderbeg2, S Morcovescu3, E Butler4, K Imhoff5, (1) Drexel Univ. College of Medicine, Philadelphia, PA, (2) UCSD Medical Center, La Jolla, CA, (3) Texas Oncology-Denton, Denton, TX, (4) Schiffler Cancer Center Wheeling Hospital, Wheeling, WV, (5) South Florida Radiation Oncology, Boynton Beach, FL

SU-D-108-6 Sunday 2:05PM - 3:00PM Room: 108

Purpose: To report on the dosimetry of 108 strut-based APBI treatments where the applicators were less than 7 mm from both the skin and the ribs

Methods: Data from 108 patients whose applicators were sandwiched between the skin and ribs were analyzed. The patients were divided into three cohorts: those where the applicator was less than 7 mm from the skin and ribs (n=67), those where the distance was less than 5 mm (n=33), and those with less than 3 mm between both the skin and ribs (n=8). Dosimetric parameters analyzed include PTV_EVAL volume (cm³), V90 (%), V95 (%), V100 (%), V150 (cm³), V200 (cm³), and the maximum doses to the skin and ribs.

Results: Over all three cohorts the PTV_EVAL volumes ranged from 20.5 cm³ to 125.7 cm³ with a median value of 55.5 cm³. In each of the three groups, the V90 averaged between 94% and 95%, the V95 averaged between 90% and 92%, and the V100 averaged between 85% and 87%. The average V150 ranged between 21.8 cm³ and 26.6 cm³, and the average V200 ranged from 10.9 cm³ to 13.1 cm³. Across the three cohorts, the maximum skin dose ranged from 8.4% of the prescription dose to 117% of the prescription dose (median values were between 85% and 87%) and the maximum rib dose fell between 1.8% of the prescription dose and 198% of the prescription dose with the median values falling between 100% and 107%.

Conclusion: This study demonstrates the dosimetric versatility of the strut-based brachytherapy device. It has been used in patients where the proximity of the skin and chest wall precludes the use of other types of single-entry brachytherapy devices. It allows for optimized dose coverage of the target while providing dose sparing to the adjacent critical structures.

Funding Support, Disclosures, and Conflict of Interest: This project was partially funded by Cianna Medical, Inc.

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