Abstract
The purpose of this study was to analyze motion of the left anterior descending coronary artery (LAD) and left ventricle during normal breathing and deep inspiration breath hold (DIBH). This is a dosimetric study utilizing free-breathing and static DIBH scans from eleven patients treated with radiotherapy for breast cancer. The anterior-posterior displacement along the length of the LAD was measured in each respiratory phase. Standard treatment plans targeting the whole breast without treatment of the internal mammary lymph nodes were generated and dose to the LAD and LV calculated. Non-uniform movement of the LAD during respiratory maneuvers with the proximal third exhibiting the greatest displacement was observed. In DIBH compared to end-expiration (EP), the mean posterior displacement of the proximal 1/3 of the LAD was 8.99 mm, the middle 1/3 of the artery was 6.37 mm, and the distal 1/3 was 3.27 mm. In end-inspiration (IP) compared to end-expiration the mean posterior displacements of the proximal 1/3 of the LAD was 2.08 mm, the middle 1/3 of the artery was 0.91 mm, and the distal 1/3 was 0.97 mm. Mean doses to the LAD using tangential treatment fields and a prescribed dose of 50.4 Gy were 11.32 Gy in EP, 8.98 Gy in IP, and 3.50 Gy in DIBH. Mean doses to the LV were 2.38 Gy in EP, 2.31 Gy in IP, and 1.24 Gy in DIBH. In conclusion, inspiration and especially DIBH, cause a displacement of the origin and proximal 2/3 of the LAD away from the chest wall, resulting in sparing of the most critical segment of the artery during tangential radiotherapy.
Highlights
Several prospective randomized trials have demonstrated a significant reduction in locoregional recurrence with the addition of radiotherapy after breast-conserving surgery for invasive or in-situ carcinoma or after mastectomy in select patients with invasive carcinoma [1]
Seven patients (64%) were treated with breast-conserving surgery followed by whole breast radiotherapy and 4 (36%) underwent mastectomy and chest wall and nodal radiotherapy that did not target the internal mammary nodes (IMN)
During deep inspiration breath hold (DIBH), the chest wall was much more during Radiotherapy for Left-Sided Breast Cancers dramatically expanded in comparison to both normal end-inspiration (10.0 mm +/– 4.9 mm) and normal end-expiration (9.9 mm +/– 4.4 mm)
Summary
Several prospective randomized trials have demonstrated a significant reduction in locoregional recurrence with the addition of radiotherapy after breast-conserving surgery for invasive or in-situ carcinoma or after mastectomy in select patients with invasive carcinoma [1] This improvement in local control results in improved breast cancer specific mortality and overall survival [2]. Newer radiotherapy treatment planning techniques have attempted to address this concern with modulation of dose to the heart using conformal radiotherapy or intensity-modulated radiotherapy, [5,6] placement of heart blocks, or These results from Denmark are striking when considering left-sided radiotherapy treatment fields that include the IMNs, which can substantially increase radiation dose to the lung and heart compared to fields that do JCT. There are no published data comparing the dosimetric impact of using DIBH versus end inspiration (IP) and end-expiration (EP) gated radiotherapy on the heart and the LAD for this treatment method
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