Key result
Proton beam therapy resulted in a lower mean heart dose than photon therapy (79 vs 829 cGy, P<0.001) and, unlike photon therapy, did not compromise left ventricular relaxation properties at 1 year.
Why the study?
Proton beam therapy may reduce radiation dose to non-target normal tissues compared with conventional photon treatment, but its impact on left ventricular mechanical function needed evaluation.
Does proton beam therapy compared to photon beam therapy preserve left ventricular mechanical function in patients with breast or thoracic cancer undergoing thoracic radiotherapy?
Cohort (n=58)
Does proton beam therapy compared to photon beam therapy preserve left ventricular mechanical function in patients with breast or thoracic cancer undergoing thoracic radiotherapy?
Proton beam therapy, unlike photon beam therapy, preserves left ventricular relaxation properties (early diastolic strain rate) up to one year in patients undergoing thoracic radiotherapy.
Proton beam therapy may preserve LV diastolic function versus photon therapy in thoracic radiotherapy; hypothesis-generating, needs randomized confirmation before practice change.
Background Proton beam therapy (PBT) is a promising radiotherapeutic method by which the proton Bragg peak may be exploited to reduce the dose to non-target normal tissues, when compared with the conventional photon treatment (PhT). Purpose To evaluate the mechanical function of the left ventricle by endocardial longitudinal (GLS-basic strain), circumferential (GCS) and radial strain (GRS) and systolic (SRs) and early diastolic (SRe) strain rate following thoracic radiotherapy. Methods Between March 2016 and March 2017, 58 patients with breast or thoracic cancer scheduled to receive radiotherapy were enrolled prospectively and, underwent 2D-STE echocardiography with basic (GLS) and comprehensive (GCS, GRS,GLSRs, GCSRs, GRSRs, GLSRe, GCSRe, GRSRe parameters) analysis at pre-treatment, mid-treatment, end of treatment, 3 month and 1 year follow-up. LVEF was calculated by the biplane Simpson technique. Shapiro-Wilk's test was performed to evaluate the normal distribution of the data. Comparison between groups was performed with Student's t-test or Wilcoxon test for quantitative variables and with Chi-Square test or Fisher's exact test for qualitative variables. Tukey-Kramer method was used to compare means during follow up. A p-value <0.05 was assumed as the level of statistical significance. Results Mean age was 53.3±10.9 years and 91.3% were women. PBT was used to treat 38 patients; PhT in 20. The median of the mean heart dose was lower with PBT than PhT (79±92 vs 829±1121 cGy, respectively [P<.001]). No significant changes in LVEF or GLS for PBT or PhT were seen. Comprehensive strain analysis showed changes in endocardial longitudinal, radial, and circumferential early diastolic strain rate (SRe) in patients undergoing photon beam (PhT) up to one year of follow up (Table 1). No changes were detected in the PBT group. All other variables were non-significant (Not shown). Conclusion This is the first longitudinal study, with a one-year follow-up, that shows the relaxation properties of LV are compromised during PhT but not PBT. These findings should be followed in time to evaluate their influence on overall heart function.
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Cordova-Madera et al. (2021) conducted a cohort in breast or thoracic cancer (n=58). Proton beam therapy vs. Photon beam therapy was evaluated on mechanical function of the left ventricle by strain and strain rate. Proton beam therapy resulted in a lower mean heart dose than photon therapy (79 vs 829 cGy, P<0.001) and, unlike photon therapy, did not compromise left ventricular relaxation properties at 1 year.
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