International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationCardiac Motion During Deep-Inspiration Breath-Hold: Implications for Breast Cancer Radiotherapy
Introduction
Radiotherapy (RT) is an effective treatment of breast cancer, reducing the risk of both local cancer recurrence and breast cancer death 1, 2. However, several studies have demonstrated increased risks of mortality from ischemic heart disease among patients undergoing RT for breast cancer 3, 4, 5, 6. Once the adverse effects of RT on the heart were recognized, several groups evaluated the radiation dose to the heart during RT for breast cancer, especially for tumors of the left breast 7, 8, 9, 10, 11. The RT guidelines have since been modified to minimize cardiac exposure using various methods, including placement of radiation fields to avoid cardiac exposure. Intensity modulation and various respiratory motion control techniques were also developed to reduce the dose received by the heart during breast RT.
Effective treatment techniques in terms of reducing the heart dose depend on understanding the cardiac motion, both intrinsic motion, independent of respiration, and motion resulting from respiration. The deep-inspiration breath-hold (DIBH) technique (i.e., the patient takes a deep inspiration and holds her breath during RT, which could move the heart away from the chest wall) has been used to minimize the dose to the heart during RT for cancer of the left breast 12, 13, 14, 15. However, its use requires accurate information about the cardiac motion such that the safe proximity of the treatment field edge to the displaced heart can be determined and the treatment plans can be optimized to minimize cardiac toxicity, particularly that arising from exposure of the left anterior descending artery (LAD). Although many studies have evaluated cardiac displacement during respiration (16), few studies have addressed the extent of displacement arising from intrinsic cardiac motion (i.e., movement from cardiac contraction that is independent of respiration). The purpose of the present study was to determine the extent of displacement of the entire heart and the LAD resulting from the intrinsic motion of the heart, during DIBH, relative to the typical tangential fields for left-sided breast cancer RT. We believe the information obtained will be useful for additional sparing of the heart from radiation exposure during DIBH and to accurately estimate the cardiac doses delivered during breast RT using advanced techniques such as three-dimensional conformal RT, gated irradiation, and others.
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Methods and Materials
The computed tomography (CT) data used for the present study were obtained from 20 randomly selected patients who had undergone CT-based coronary angiography with retrospective electrocardiographic gating at the M.D. Anderson Cancer Center. The institutional review board at the M.D. Anderson Cancer Center approved the study. Two sets of CT scans from a GE LightSpeed 64-slice CT scanner (GE Healthcare, Waukesha, WI) were obtained for each patient according to our standard of care procedure for
Results
The extent of heart displacement in the SI and LR directions, calculated from the MIP and mIP CT images from all the patients, is listed in Table 1. The mean displacement in the SI direction was 6.4 mm (range, 3.0–10.9), and the mean displacement in the LR direction was 2.5 mm (range, 0–4.6). The heart moved >5 mm in the SI direction in 16 of 20 patients, and the movement in the LR direction tended to be less (none of the patients had movement that >5 mm in the LR direction).
To further observe
Discussion
Deep-inspiration breath hold is an effective method for limiting the motion of the heart caused by respiration and also for maximizing the distance between the LAD and the treatment fields for RT of the left breast. Several studies have demonstrated that DIBH can displace the heart posterior from the chest wall and reduce the heart dose without compromising the dose to the target 12, 13, 14, 15. However, little information is available about the extent of heart movement, particularly of the
Conclusions
The most substantial displacement of the heart periphery during cardiac motion was at the posterior part of the heart, far from the radiation fields and unlikely to be affected by RT. Displacement of the LAD owing to cardiac motion during DIBH varied substantially both between and within patients, which could significantly affect the dose received by the LAD from breast RT. When the posterior edge of the treatment fields must be positioned close to the LAD, we recommend maintaining a distance
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Conflict of interest: none.