Developing an action plan for patient radiation safety in adult cardiovascular medicine. Proceedings from the Duke University Clinical Research Institute/American College of Cardiology Foundation/American Heart Association Think Tank Held on February 28, 2011

Long-term prognostic value of low-dose normal stress-only myocardial perfusion imaging by wide beam reconstruction: A competing risk analysis

BACKGROUND

A normal stress myocardial perfusion single-photon emission computed tomography (MPS) is associated with a good clinical outcome. New iterative algorithms, such as wide beam reconstruction (WBR), which improve image interpretation with half-dose or half-time acquisition, have been proposed for cardiac MPS. The aim of this study was to assess the long-term predictive value of a low-dose normal stress-only MPS with WBR using conventional Anger camera in patients with known or suspected coronary artery disease (CAD).

METHODS AND RESULTS

A total of 2106 patients with known or suspected CAD and normal perfusion at half-dose stress-only MPS protocol were followed for a mean of 6.6 ± 2.7 years. MPS data were reconstructed with WBR iterative algorithm. End-point events were cardiac death or nonfatal myocardial infarction. Noncardiac death was considered the competing event. During follow-up, 149 cardiac events occurred with an annualized event rate of 1.2%. Independent predictors of cardiac events at Cox analysis were age, male gender, diabetes mellitus, previous myocardial infarction and the need for pharmacologic stress testing. At Fine-Gray analysis the cumulative incidence of cardiac events progressively increases with age and in the presence of diabetes for any combination of gender and stress type. Survival tree analysis confirmed that long-term prognosis considerably varies according of risk factors profile.

CONCLUSIONS

Low-dose normal stress-only WBR MPS has a reliable long-term prognostic value in patients with suspected or known CAD. This finding supports the introduction of such a method into clinical practice with a consistent dose optimization in the interest of patients and exposed staff.

Monitoring Ionizing Radiation Exposure for Cardiotoxic Effects of Breast Cancer Treatment

Serial assessments of left ventricular ejection fraction (LVEF) are customary in patients with breast cancer receiving trastuzumab. Radionuclide angiography (RNA) is often used; however, a typical monitoring schedule could include 5 scans in a year. We evaluated the proportion of imaging-related ionizing radiation attributable to RNA in 115 patients with breast cancer, from 3 medical centers in the United States, Ireland, and Japan, who completed 12 months of trastuzumab treatment. Estimated radiation dose (ERD) was used to calculate exposure associated with imaging procedures spanning the 18 months before and after trastuzumab therapy. In addition, 20 cardiologists and oncologists from participating centers were surveyed for their opinions regarding the contribution of RNA to overall radiation exposure during trastuzumab treatment. When RNA was used to monitor LVEF, the mean ERD from imaging was substantial (34 ± 24.3 mSv), with the majority attributable solely to RNA (24.7 ± 14.8 mSv, 72.6%). Actual ERD associated with RNA in this population differed significantly from the perception in surveyed cardiologists and oncologists; 70% of respondents believed that RNA typically accounted for 0% to 20% of overall radiation exposure from imaging; RNA actually accounted for more than 70% of ERD. In conclusion, RNA was used to monitor LVEF in most patients in this cohort during and after trastuzumab therapy. This significantly increased ERD and accounted for a greater proportion of radiation than that perceived by surveyed physicians. ERD should be taken into account when choosing a method of LVEF surveillance. Alternative techniques that do not use radiation should be strongly considered.

Anthracycline or trastuzumab-related cardiotoxicity: do we have a predictive biomarker?

Chemotherapy-induced cardiotoxicity, is a well-known and potentially serious complication strongly impacting the quality of life and overall survival of breast cancer patients. The current diagnostic approach to detect cardiac damage is the estimation of left ventricular ejection fraction by echocardiography. However, this approach exhibits less sensitivity toward early prediction of cardiomyopathy, not allowing for preventive strategies. Measurement of serum cardiac-specific biomarkers can be a valid diagnostic tool for identifying patients prone to developing cardiotoxocity and in whom closer cardiac monitoring and preventive strategies are pivotal. In this article, we review work done on biomarkers in recent years, with an emphasis on troponin and B-type natriuretic peptide, which are currently the most studied in this field. We also briefly discuss current and emerging imaging techniques for early detection of cardiomyopathy.

A quality improvement project for reducing cardiac computed tomography radiation dose in a community-based, multihospital setting

Radiation associated with computed tomography coronary angiography (CTCA) is a persistent concern. Strategies for reducing radiation exposure have been described, primarily in academic settings. We developed a standard protocol for CTCA acquisition focused on radiation reduction strategies in a community-based, multihospital setting and hypothesized that the protocol would be effective at reducing radiation in this setting. The protocol included the use of body mass index based tube voltage adjustment and routine use of prospective electrocardiographic gating with either dose modulation or step-and-shoot acquisition. Data on radiation exposure were collected retrospectively and compared by nonparametric testing. Some hospitals failed to routinely record radiation exposure data; only 2 facilities had data available from both before and after the intervention for direct comparison. Data were acquired from 124 subjects, 41 from the standard of care group and 83 scanned under the new protocol. In hospital A, radiation was significantly reduced by 61% from 20.5 ± 4.6 millisieverts (mSv) to 7.9 ± 4.8 mSv (P < 0.001). Within the new protocol group for hospital A, radiation was lower with step-and-shoot (4.0 ± 1.5 mSv) as compared to dose modulation (10.2 ± 4.2 mSv, P < 0.001). In hospital B, which already employed step-and-shoot acquisition, radiation dose was reduced 16% from 9.3 ± 3.0 mSv to 7.9 ± 2.2 mSv (P < 0.017) by applying body mass index-based tube voltage adjustment alone. In conclusion, a minimal investment in institutional resources can result in a reduction in radiation exposure from CTCA, even in a community-based, multihospital setting. Some facilities do not routinely record radiation exposure data.

Temporal evolution of administered activity in cardiac gated SPECT and patients' effective dose: analysis of an historical series

PURPOSE

Myocardial perfusion imaging contributes >20 % of the average medical radiation exposure to the population in the USA. Imaging protocols able to achieve a radiation exposure ≤9 mSv in 50 % of the studies by 2014 have been recommended. The aim of this study was to analyse the temporal evolution of administered activities in patients scheduled for dual-day (99m)Tc tracer gated single photon emission computed tomography (SPECT) and to compare different dose administration protocols in terms of patients' effective dose.

METHODS

Patients evaluated from 1 July 2002 to 31 January 2012 were allocated according to the protocol adopted: group 1: fixed activity according to diagnostic reference level: 740 MBq up to 80 kg (adapted for weight <60 kg); 900 MBq 80-100 kg, 1,110 MBq >100 kg, standard filtered back-projection (FBP) reconstruction; group 2: weight-adjusted activity: 8 MBq/kg up to 1,110 MBq, standard FBP reconstruction; and group 3: 4 MBq/kg, UltraSPECT wide beam reconstruction (WBR) reconstruction. A dual-head Anger camera (GE Helix) was used.

RESULTS

A total of 9,060 patients were allocated to different groups: 4,751 in group 1, 2,844 in group 2 and 1,465 in group 3. The stress + rest administered activity was 1,617 ± 180 in group 1, 1,136 ± 260 in group 2 and 682 ± 164 MBq in group 3 (all p < 0.001). Patients' effective dose was 13.7 ± 3 in group 1, 9.5 ± 2.8 in group 2 and 5.7 ± 1.6 mSv in group 3 (all p < 0.001). The 50th percentile was 12.6 in group 1, 9.1 in group 2 and 5.3 mSv in group 3. The effective dose received by the dedicated cardiologists was 2.1, 1.5 and 1.0 μSv/exam in group 1, group 2 and group 3 periods, respectively (all p < 0.001).

CONCLUSION

A significant reduction over time in the administered activity for gated SPECT was achieved; accordingly, a significant reduction in patients' exposure was obtained. A simple weight-adjusted strategy with 8 MBq/kg immediately fulfils the recommendations to limit exposure. In selected group 3 patients, a stress-only strategy allows for studies with <3 mSv exposure. Thus, at least the adoption of a new reconstruction algorithm is strongly encouraged, and suggested tracer activities for cardiac gated SPECT are to be revised.