# Three-Dimensional Gel Dosimetry in a Simulated Postmastectomy with Expandable Prosthesis Radiotherapy

## TL;DR

This study investigates how a metal port in breast implants affects radiation therapy using a 3D gel dosimeter, finding a small but notable dose reduction near the metal.

## Contribution

The study introduces a realistic phantom and gel dosimetry to evaluate dose alterations caused by metallic implants in postmastectomy radiation therapy.

## Key findings

- A dose reduction of approximately 5% was observed near the metal port.
- Gamma analysis revealed significant gamma fail regions near the metal port.
- The underdose is within ICRU tolerance thresholds but should be considered in treatment planning.

## Abstract

Postmastectomy radiation therapy (PMRT) is an adjuvant treatment for breast cancer. Some mastectomized women undergoing PMRT can have breast reconstruction with expander implant reconstruction. However, the expander implant contains a magnetic metal port for its inflation, and in patients with a high risk of recurrence, the PMRT is performed before the expander replacement. The difficulties in radiation treatment near high-Z metals are mainly due to dose alterations around them. Therefore, this study proposes using a realistic breast phantom and gel dosimetry to investigate the effects of the metallic parts of the expandable prosthesis on the 3D delivery of the treatment. A conformal radiation treatment was planned and delivered to the gel phantom with the metal port. MAGIC-f gel was used with magnetic resonance imaging for dose assessment. The treatment plan dose distribution was compared to the measured dose distribution by gamma analysis (3%/3 mm/15% threshold). A significant gamma fail region was found near the metal port, corresponding to a dose reduction of approximately 5%. This underdose is within the tolerance threshold for dose heterogeneity established by the International Commission on Radiation Units (ICRU), but should be considered when treating these patients.