RESUMO
Image-guided radiotherapy (IGRT) systems using ionizing radiation may increase the risk of secondary cancer and normal tissue toxicity due to additional radiation exposure caused by large field sizes or repeated scans during X-ray imaging. As an alternative to these modalities, surface-guided radiotherapy (SGRT) systems which do not employ ionizing radiation have been developed. This study presents a comprehensive performance evaluation of the Varian Identify SGRT system by using an anthropomorphic Alderson Rando phantom in three different aspects: (a) the accuracy and reproducibility of the system in different regions of interest (ROI) for varying couch displacements, (b) the setup accuracy of the system for patient positioning based on different computed tomography (CT) slice thicknesses, and (c) the potential influence of obstructing SGRT cameras by the gantry on the system's overall accuracy and reproducibility. The accuracy and reproducibility of the SGRT system fell within 1 mm and 1°. Nevertheless, in certain situations, these values were observed to exceed prescribed limits. Consequently, concerning SGRT tolerance limits for treatment applications, careful consideration of ROIs and offset values of the system is crucial. We also recommend that patients should ideally be set up during 0° gantry rotation, and the on-board imaging (OBI) system should be retracted to prevent obstruction of the cameras. Additionally, reference CT images with a slice thickness of under 3 mm are recommended for this purpose.
RESUMO
OBJECTIVE: The liver is a critical organ at risk during right breast radiotherapy (RT). Liver function tests (LFTs) such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyl transferase (GGT) serve as biochemical markers for hepatobiliary damage. In this multicenter cross-sectional study, the effects of liver dose-volume on changes in LFTs pre- and post-RT in patients treated for right breast cancer were evaluated. MATERIALS AND METHODS: Between January 2019 and November 2022, data from 100 patients who underwent adjuvant right breast RT across three centers were retrospectively assessed. Target volumes and normal structures were contoured per the RTOG atlas. Patients were treated with a total dose of 50 Gy in 25 fractions to the CTV, followed by a boost to the tumor bed where indicated. The percentage change in LFT values in the first two weeks post-RT was calculated. Statistics were analyzed with SPSS version 22 software, with significance set at p < 0.05. Statistical correlation between liver doses (in cGy) and the volume receiving specific doses (Vx in cc) on the change in LFTs were analyzed using Kolmogorov-Smirnov, Mann-Whitney U test. RESULTS: The median age among the 100 patients was 56 (range: 29-79). Breast-conserving surgery was performed on 75% of the patients. The most common T and N stages were T1 (53%) and N0 (53%), respectively. None of the patients had distant metastasis or simultaneous systemic treatment with RT. A total of 67% of the treatments utilized the IMRT technique and 33% VMAT. The median CTV volume was 802 cc (range: 214-2724 cc). A median boost dose of 10 Gy (range: 10-16 Gy) was applied to 28% of the patients with electrons and 51% with IMRT/VMAT. The median liver volume was 1423 cc (range: 825-2312 cc). Statistical analyses were conducted on a subset of 57 patients for whom all three LFT values were available both pre- and post-RT. In this group, the median values for AST, ALT, and GGT increased up to 15% post-RT compared to pre-RT, and a median liver Dmean below 208 cGy was found significant. While many factors can influence LFT values, during RT planning, attention to liver doses and subsequent regular LFT checks are crucial. CONCLUSION: Due to factors such as anatomical positioning, planning technique, and breast posture, the liver can receive varying doses during right breast irradiation. Protecting patients from liver toxicity secondary to RT is valuable, especially in breast cancer patients with a long-life expectancy. Our study found that, even in the absence of any systemic treatment or risk factors, there was an average increase of nearly 15% in enzymes, indicating acute liver damage post-RT compared with pre-RT. Attention to liver doses during RT planning and regular follow-up with LFTs is essential.