Dose perturbation in the radiotherapy of breast cancer patients implanted with the Magna‐Site: a Monte Carlo study

Christos Chatzigiannis,Panagiotis Sandilos,Georgia Lymperopoulou,Constantinos Dardoufas,Evaggelos Georgiou,Emmanouil Yakoumakis,Pantelis Karaiskos

doi:10.1120/jacmp.v12i2.3295

Abstract

External beam radiation therapy (RT) is often offered to breast cancer patients after surgical mastectomy followed by breast reconstruction with silicone implants. In some cases, the RT is administered while the patient is still implanted with a temporary tissue expander including a high‐density metallic port, which is expected to affect the planned dose distribution.This work uses Monte Carlo (MC) simulation in order to evaluate the aforementioned effect when the McGhan Style 133 Tissue Expander with the Magna‐Site injection port is used. Simulations have been performed on a patient model built using the actual CT images of the patient for two irradiation schemes, involving two tangential photon beams of 6 MV and 18 MV respectively. MC results show that the presence of the Magna‐Site within the two irradiation fields leads to an overall reduction of absorbed dose for points lying in the shadow of the metallic port (relative to each of the opposing beams). The relative reduction compared to dose results without the expander in place ranges from 7% to 13% for the 6 MV beam and is around 6% for the 18 MV photon beam. However, in the close vicinity of the metallic port, increased absorbed doses are observed, due to the increase of secondary electrons emerging from the metallic part of the insert.PACS numbers: 87.53.Bn, 87.55.K‐, 29.20.‐c, 87.56.bd, 75.50.‐y

Highlights

Reconstruction of the breast is the usual choice of breast cancer patients that undergo surgical mastectomy
Since many of the clinically used tissue expanders contain high-Z metallic ports with complicated apertures which usually lie within the treatment fields, questions have arisen about the dosimetric effect on the planned dose distribution of the RT scheme
We evaluate the dose perturbation of the McGhan Style 133 Tissue Expander in a radiotherapy treatment of the breast, with the aid of Monte Carlo simulation of an actual breast patient implanted with the expander

Summary

Introduction

Reconstruction of the breast is the usual choice of breast cancer patients that undergo surgical mastectomy. The first stage involves the subcutaneous or submuscular implanting of a tissue expander at the site of the mastectomy, which is gradually filled with dilute saline solution injections through an injection port to the desired volume. High-risk breast cancer patients, as well as intermediate risk patients, are often referred for adjuvant radiation therapy, since this is shown to increase long-term survival, on the condition that appropriate radiotherapy techniques are being used.[1] Many of these patients undergo RT before the second phase of breast reconstruction with the expander in place. Since many of the clinically used tissue expanders contain high-Z metallic ports with complicated apertures which usually lie within the treatment fields, questions have arisen about the dosimetric effect on the planned dose distribution of the RT scheme. One of the major concerns is whether the high-density material perturbs the photon RT fields in such a way that small areas in the chest wall region can undergo a dose reduction, appearing in the chest wall region, with a potential impact on the RT outcome

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