Inter-fraction heart displacement during voluntary deep inspiration breath hold radiation therapy without visual feedback measured by daily CBCT

Abstract

Purpose/ObjectiveDeep Inspiration Breath Hold (DIBH) is now considered as the standard of care for many breast cancer patients. However, there are still uncertainties about the dose given to the heart, and it is unknown if patients may improve voluntary DIBH depth by gaining experience during treatment. In this study, we will examine the interfractional three-dimensional (3D) heart displacement throughout voluntary DIBH (vDIBH) radiotherapy by means of daily cone-beam computed tomography (CBCT).Material and methodsTwo hundred twenty-five unique CBCTs from 15 patients treated in 15 fractions were analyzed. During CBCT, a vDIBH was conducted without any visual feedback. Patients performed their DIBH freely after receiving explanations and training. After daily CBCT matching to the chest wall (CW), surface-guided radiation therapy (SGRT) tracked DIBH depth to ensure that the CW position was the same as the daily acquired CBCT. The CBCTs were retrospectively registered to the DIBH planning-CT to calculate daily changes in heart displacement relative to the CW.ResultsThe mean displacement of the heart during DIBH treatment relative to the DIBH planning-CT was as follows: 1.1 mm to the right, interquartile range (IQR) 8.0; 0.5 mm superiorly, IQR 4.8; and 0 mm posteriorly, IQR 6.4. The Spearman correlation coefficients (rs) were -0.15 (p=0.025), 0.04 (p=0.549), and 0.03 (p=0.612) for the X, Y, and Z directions, respectively. The differences in median heart displacement were significant: Friedmann rank sum test p=0.031 and pairwise comparison using the Wilcoxon rank-sum test were p=0.008 for X and Y; p=0.33 for X and Z; and p=0.07 for Y and Z. The total median heart motion was δtot median= 7.26 mm, IQR= 6.86 mm.ConclusionDuring DIBH, clinicians must be aware of the wide range of intra- and inter-individual heart position variations. The inter-individual heterogeneity shown in our study should be investigated further in order to avoid unexpected cardiac overexposure and to develop a more accurate heart dose-volume model.

Chest Wall to Heart Distance Reproducibility in Postoperative Deep Inspiration Breath-Hold Radiotherapy for Left-Sided Breast Cancer Using an Anzai Laser Sensor With Visual Feedback

“…In particular, our measured IQRs were 4 mm in X, 2 mm in Y, and 2 mm in Z directions for all 250 fractions, whereas the largest distance reductions relative to the plans were 5 mm toward the left, 5 mm toward the superior, and 6 mm toward the anterior directions. Our IQRs were two to three times smaller than those reported in a previous study without visual feedback [ 10 ]. More specifically, their IQRs were 8.0 mm in X, 4.8 mm in Y, and 6.4 mm in Z directions for 225 fractions (15 cases each with 15 fractions), while the largest distance reductions were 21 mm toward the left, 9 mm toward the superior, and 18 mm toward the anterior directions.…”

“…Dual registration using the daily CBCT and planning CT images showed that the medians of the changes in the chest wall to the heart distance among 25 fractions in each of the 10 cases ranged from -2 mm to 3 mm, -1 mm to 3 mm, and -2 mm to 1 mm in the X, Y, and Z directions, respectively. In addition, the reproducibility of the chest wall to the heart distance in our study is substantially better than previously reported two different studies where visual feedback was not employed [ 9 , 10 ]. In particular, our measured IQRs were 4 mm in X, 2 mm in Y, and 2 mm in Z directions for all 250 fractions, whereas the largest distance reductions relative to the plans were 5 mm toward the left, 5 mm toward the superior, and 6 mm toward the anterior directions.…”

“…In this retrospective study, the change in the chest wall to the heart distance relative to the plan was calculated similarly as Benkhaled et al reported previously [ 10 ]. We employed the Elekta X-ray Volume Imaging (XVI) dual registration [ 13 ] that allowed us to make corrections based on the tumor registration and the critical structure registration, where interpolation may be further performed between the two registration results by a clinical decision.…”

“…Van Haaren et al measured daily changes in the distance from the heart to the chest wall relative to the plans for 50 patients receiving vDIBH radiotherapy without visual feedback, showing a maximum distance reduction of 8.3 mm relative to the plan [ 9 ]. Benkhaled et al also reported the distance reproducibility for 15 patients receiving vDIBH without visual feedback, where cone-beam CT (CBCT)-based image registration was retrospectively performed twice, one for the chest wall and the other for the heart [ 10 ]. They calculated daily changes in the chest wall to heart distance relative to each plan by subtracting registration errors for the heart from those for the chest wall.…”

“…Beaton et al stated that the risk of radiation-induced cardiac death at 10 years appeared to be very low if the mean heart dose (MHD) and the heart V25Gy were below 3.3 Gy and 5%, respectively, based on their analysis including 2,644 left-sided breast cancer patients [3]. for the chest wall and the other for the heart [10]. They calculated daily changes in the chest wall to heart distance relative to each plan by subtracting registration errors for the heart from those for the chest wall.…”