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Multi-Source Conformal Superficial Brachytherapy: A Dose Escalation Study

B Rogers1*, J Lawrence2, C Ferreira3, (1) University of Minnesota - Twin Cities, Minneapolis, MN, (2) University of Minnesota, Saint Paul, MN, (3) University of Minnesota, Minneapolis, MN


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: The purpose was to perform a radiation dose escalation study in a non-tumor murine model using the yttrium-90 (90Y)-based Conformal Superficial Brachytherapy Device (CSBT).

Methods: Each source was placed on the distal end of one of 10 tungsten carbide rods, held in place by a one of two types of custom 3D printed tips. One tip type (Tip-0.5mm) provided a nominal source-to-surface distance (SSD) of 0.5 mm and the other tip type (Tip-surface) provided an SSD of 0.0 mm. Sources were placed in a hexagonal pattern with a center-to-center distance of 4.5 mm. Hairless SKH 1 mice were immobilized and the skin of the left flank were irradiated with increasing radiation doses: 30 Gy (n=3; Tip-surface), 40 Gy (n=4; Tip-surface), 50 Gy (n=2; Tip-surface & n=2; Tip-0.5mm), or 60 Gy (n=4; Tip-0.5mm). Skin was monitored daily following irradiation and dermatitis was scored according to a modified radiation-induced skin toxicity grading scheme. Mice were euthanized at peak toxicity and skin samples were collected for histopathologic analysis.

Results: Skin toxicity was noted in all dose groups within 14 days but was limited to grade 1 toxicity in mice that received 30 Gy or 40 Gy. All mice that received 60 Gy developed grade 4 dermatitis. The dermatitis distribution was visibly different between groups, with focal regions of dermatitis developing in mice treated with Tip-surface versus uniform skin injury for mice treated with Tip-0.5mm. Further, for the same administered dose, dermatitis following irradiation with Tip-surface (maximum mean grade 2) was markedly less severe than with Tip-0.5mm (maximum mean grade 3.5).

Conclusions: Further studies evaluating the CSBT in tumor-bearing SKH-1 mice will utilize Tip-0.5mm and a prescription dose of 50 Gy, with early evaluation of radiation-induced dermatitis.

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