PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s): Reduction in left ventricular global and segmental myocardial strain following tangential radiotherapy (RT) for left sided breast cancer treatment has been demonstrated using advanced echocardiographic techniques. This study aimed to determine if cardiac MRI (CMR), a more sensitive and precise imaging modality, could detect similar changes in segmental myocardial strain as per the American Heart Association(AHA) 16 segment model of the left ventricle in left sided breast cancer patients, and correlate this to RT dose.
Materials/Methods: For 21 patients receiving left-sided breast RT, two serial CMR scans were obtained; immediately prior, and 4-6 weeks following RT. Single breath-hold Steady-State Free Precession (SSFP) Cine 2, 3, 4 chamber and short axis views were acquired, and using cvi42 tissue tracking software, two independent readings of 2D and 3D strain values were obtained, with the average being used for analysis. A linear mixed effects model was used to account for potential clustering of values between patients and segments. Multiple RT dosimetric values (including mean, max, V25) of each segment were calculated and their relationship with delta 2D/3D strain values explored.
Results: Median age was 59 years (range 38-76 years). Comprehensive nodal treatment using modified wide tangents using a deep inspiration breath hold technique (n=1) and the remainder received tangential breast radiation alone (n=20). No patient received chemotherapy. Two patients received 50Gy in 25 fractions, with 19/21 receiving 42.4Gy in 16 fractions. Median mean heart dose was 2.6Gy (1.5-3.9Gy). No difference was found between any pre and post RT strain parameters. These results are summarised in the table below.
|Strain Parameter||Pre-RT Mean||Post-RT Mean||Difference||95% CI|
|Radial 2D (Short Axis)||54.59||50.23||-3.43||[-8.8, 1.9]|
|Circumference 2D (Short Axis)||-23.11||-22.15||0.73||[-0.51, 2.0]|
|Radial 2D (Long Axis)||48.56||47.46||0.07||[-3.7, 3.8]|
|Longitudinal 2D (Long Axis)||-22.45||-22.27||-0.08||[-0.80, 0.63]|
|Radial 3D||40.77||37.85||-2.17||[-7.4, 3.1]|
|Circumference 3D||-20.05||-19.20||0.72||[-0.62, 2.1]|
|Longitudinal 3D||-19.49||-18.92||0.47||[-0.79, 1.7]|
Conclusion: No differences in left ventricular segmental strain were detected using CMR 4-6 weeks following left-sided breast radiotherapy, nor was there a clear relationship between RT dose and delta strain. Changes below the threshold of CMR detection given the lower temporal scanning resolution of CMR cannot be excluded. Longer term follow-up of this cohort will help determine if more delayed effects of radiation on LV function become manifest.
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