2255 - Dual Port Tissue Expander Displacement in Post Mastectomy Radiotherapy: Dosimetric Challenges

K. Dibs¹, J. Eckstein², T. Andraos³, R. Young⁴, K. Lindsey², C. Huelskamp², K. Tedrick², K. Fernando⁵, D. Roesener², E. Cochran⁶, R. Skoracki⁷, S. Morelli², M. J. Cho², R. Farhadi², K. Kuhn², M. Shupe², J. Barrus², S. Beyer⁶, and S. R. Jhawar³; ¹The Ohio State University Wexner Medical Center, Columbus, OH, ²Ohio state university, Columbus, OH, ³Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, OH, ⁴The Ohio State University Wexner Medical Center, Department of Radiation Oncology, Columbus, OH, ⁵department of radiation oncology, The James Cancer Center, Ohio State University Wexner Medical Center, Columbus, OH, ⁶Department of Radiation Oncology, The James Cancer Center, Ohio State University Wexner Medical Center, Columbus, OH, ⁷The Ohio State University Wexner School of Medicine; Dept of Plastic and Reconstructive Surgery, Columbus, OH

Purpose/Objective(s): The effectiveness of radiation relies on the precise delivery of the prescribed dose, with many treatment outcomes requiring accuracy within a range of 3% to 4%. Achieving this level of precision is challenging due to treatment setup uncertainty and the body’s inhomogeneities such as difference in tissue density. The presence of man-made materials such as tissue expanders (TE) can add to these challenges. Here we focus on the dosimetric challenges faced in treating breast cancer patients who undergo mastectomy followed by immediate smooth (the surface of the device is not textured) dual-port TE placement. Such patients are prone to the risk of TE displacement during radiotherapy and pose increased dosimetry complexity due to the second port, leading to changes in coverage and doses to organs at risk (OARs). Materials/

Methods: A retrospective analysis was performed on 10 node-positive breast cancer patients who underwent mastectomy with immediate dual-port TE placement. These patients received adjuvant radiation to the chest wall and regional lymph nodes. TE position was monitored throughout treatment, and in the event of TE displacement, verification planning and replanning were initiated at the discretion of the treating physician. Treatment metrics including prescribed dose, max dose, mean dose, homogeneity index (HI), PTV coverage, lung V20, lung mean dose, and heart mean dose were recorded at the time of CT simulation and at the verification planning in cases of TE displacement.
Results: The median prescribed dose was 50 Gy (42.56-66.00). The median Dmax was 113 % (109% - 136%). The median mean dose was 50.79 Gy (45.62-57.37). The median HI was 1.11 (1.08-1.32). All patients had PTV 95% covering at least 95% of the prescribed volume except one patient had 90% to meet lung constraint. Median lung V20 was 14.86% (11.50%-18.80%) with median mean lung dose of 8.70 Gy (6.69-10.18). The median mean heart dose was 2.30 Gy (0.71-4.99). Two patients experienced TE displacement during treatment that led to dosimetric changes. The first patient had a single instance of TE displacement, which caused the PTV 95% coverage to decrease from 95% to 89%, necessitating a treatment replan. The second patient encountered TE displacement twice without notable alteration in OAR or coverage metrics. However, this did lead to an increase in the Dmax from 110% to 116%. Despite this, her treatment was considered acceptable to continue as planned.
Conclusion: TEs are susceptible to movement during radiotherapy, which could potentially alter the dose distribution within the tissue, affect radiotherapy coverage, or even lead to increased hotspots that increase toxicity. These changes are particularly problematic with dual port expanders which have additional metal and challenges caused by the relative geometry of the two ports. It is recommended to consider additional caution when reviewing cone-beam CT scan and to obtain verification plans to confirm safe dosimetry when TE movement is noted.