ESTRO 2024 - Abstract Book

S3548

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

Feasibility of using VMAT and 3D-RT for left breast with a cardiac implanted electronic device

Tiziana Malatesta 1 , Lucia Clara Orlandini 2 , Xin Xin 2 , Antonella Bufacchi 1 , Alessio Bonanni 1 , Yanqun Zhao 2 , Feng Yang 2 , Francesco Miccichè 1 1 Isola Tiberina - Gemelli Isola Hospital, Radiation Oncology, Rome, Italy. 2 Sichuan Cancer Hospital & Institute, Radiation Oncology, Chengdu, China

Purpose/Objective:

Left-sided breast radiotherapy for patients with a cardiac implanted electronic device (CIED) is challenging as the achievement of an appropriate dose coverage must be combined with the lowest possible dose to the implant itself to avoid malfunction. Although the 3D technique, in principle, is the priority choice to minimize the scattered dose, this study verifies the feasibility of using the VMAT technique taking the 3D technique as benchmark. This study compares the dosimetry of VMAT and 3D-tangential field in field (TFiF) for left-sided breast treatment plans optimised in the presence of CIED.

Material/Methods:

Twenty-six patients with early stage left-sided breast cancer who underwent external beam radiotherapy (50Gy, 25 x 2Gy) were included in this retrospective study. For each patient, a VMAT and a TFiF treatment plan (TP) were optimized with 6MV photon beams of Elekta Infinity linac and Pinnacle TP system version 9.5 (16 patients), and of a Varian True Beam linac and Eclipse TP system version 15.5 (14 patients). The plans were optimised to achieve at least 95% of the target covered by 95% of the dose prescribed while keeping the dose to the CIED below 2 Gy [1,2,3]. Target and OARs contours of the delivered clinical plans were used while the region of interest representing the CIED was artificially added in each simulation CT imaging dataset and its position was adjusted by an experienced radiation oncologist under the supervision of the interventional cardiologist. Specifically, CIED model used in this study and imported in each CT imaging data is an ICD System from Boston Scientific with a volume of 30 cc. The minimum distance between the CIED and the target was registered; the minimum distance was measured as the distance from the point of the CIED nearest to the border of the field (Figure 1). Planning target volume (PTV), left lung, heart, and CIED dosimetry were assessed. Statistical analysis was performed with SPSS software; a p value less than 0.05 was considered statistically significant. Twenty out of twenty-six (76.9%) patients analysed met clinical requirements for target coverage and OARs limits. For these patients, a mean CIED-target distance of 2.5 cm range (1.8-4.3) cm was found; for the six remaining patients, the mean CIED-target distance of 0.9 cm range (0.3; 1.6) cm did not allow TFiF and VMAT plans to comply with clinical requirements without compromising CIED dose. A minimum distance of 2.5 cm from the CIED and the edge of the target was found beyond which 100% of patients achieved adequate dose coverage and met the CIED dose limit with both the 3D TFiF and VMAT techniques. The CIED and PTV contours and isodoses of a representative patient are shown in Figure 1. For the group of twenty patients, no significant (p > 0.05) differences between VMAT and TFiF were found for the target coverage and the mean dose to the heart; expected differences were observed for the dosimetry of the lung as also confirmed in the bibliography by other studies [4,5]. The results are shown in Table 1. Results:

Table 1: VMAT and TFiF dosimetry for the twenty patients complying with the treatment plan clinical requirements