Clinical Investigation
Cardiac Motion During Deep-Inspiration Breath-Hold: Implications for Breast Cancer Radiotherapy

https://doi.org/10.1016/j.ijrobp.2011.01.035Get rights and content

Purpose

Many patients with left-sided breast cancer receive adjuvant radiotherapy during deep-inspiration breath hold (DIBH) to minimize radiation exposure to the heart. We measured the displacement of the left anterior descending artery (LAD) and heart owing to cardiac motion during DIBH, relative to the standard tangential fields for left breast cancer radiotherapy.

Methods and Materials

A total of 20 patients who had undergone computed tomography-based coronary angiography with retrospective electrocardiographic gating were randomly selected for the present study. The patients underwent scanning during DIBH to control the influence of respiration on cardiac motion. Standard medial and lateral tangential fields were placed, and the LADs were contoured on the systolic- and diastolic-phase computed tomography data sets by the clinicians. Displacement of the LAD during cardiac contractions was calculated in three directions: toward the posterior edge of the treatment fields, left–right, and anteroposterior. Displacement of the entire heart was measured on the maximal and minimal intensity projection computed tomography images.

Results

The mean displacement of the LAD from cardiac contraction without the influence of respiration for 20 patients was 2.3 mm (range, 0.7–3.8) toward the posterior edge of the treatment fields, 2.6 mm (range, 1.0–6.8) in the left–right direction, and 2.3 mm (range, 0.6–6.5) in the anteroposterior direction. At least 30% of the LAD volume was displaced >5 mm in any direction in 2 patients (10%), and <10% of the LAD volume was displaced >5 mm in 10 patients (50%). The extent of displacement of the heart periphery during cardiac motion was negligible near the treatment fields.

Conclusions

Displacement of the heart periphery near the treatment fields was negligible during DIBH; however, displacement of the LAD from cardiac contraction varied substantially between and within patients. We recommend maintaining ≥5 mm of distance between the LAD and the field edge for patients undergoing breast cancer radiotherapy during DIBH.

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.

Section snippets

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.

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