Comprehensive strain analysis in oncological patients undergoing thoracic radiotherapy: 1-year follow-up of a prospective study comparing proton vs. photon beam therapy

Abstract

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. FUNDunding Acknowledgement Type of funding sources: None. Table 1

An overview of radiation-induced heart disease

“…A 2D-STE aims to analyze strain patterns in three different dimensions of contractility (longitudinal, circumferential, and radial) and measure strain rates (SR) during systole (SRs), early (SRe), and late (SRa) diastole. Its principal value is detecting systolic and diastolic myocardial dysfunction when EF remains normal [47,48].…”

Radiation-Induced Heart Disease

“…One systematic review that included 13 studies from 2002 to 2017 showed that proton therapy reduced the mean heart radiation dose by a factor of two- or three-fold in breast cancer patients when compared to traditional RT [ 40 ]. Another prospective study in breast patients, which evaluated the mechanical function of the LV by using 2D speckle tracking imaging, showed that the relaxation properties of the LV were compromised with photon but spared with proton therapy [ 44 ]. A systematic review including 14 studies in patients with Hodgkin lymphoma proved that proton therapy had a lower radiation weighted average when compared against traditional 3D RT (3.57 Gy less) and IMRT (2.24 Gy less) [ 45 ].…”

“…Finally, a study which compared proton vs. photon therapy in pediatric patients with medulloblastoma showed that the proton mean radiation heart dose was 0.2 Gy while photon was 10.4 Gy [ 46 ]. The adverse effects of proton beam therapy and its relationship with cardiotoxicity still require long-term follow-up in patients to be better defined, but, up to now, there is a definite decrease in the amount of radiation delivered to the heart [ 44 ].…”

“…Some studies have shown that 2D-STE may play an important role in detecting early diastolic dysfunction by measuring abnormalities in the early diastolic (SRe) and late diastolic strain rate (SRa) [ 39 , 44 , 75 ].…”

“…Another study, which included 50 patients with breast or other thoracic cancers, evaluated conventional echocardiographic parameters and 2D-STE to predict myocardial dysfunction in subjects who received either photon or proton RT. While normal echocardiographic parameters were not able to detect differences between the two therapies, 2D-STE global circumferential, longitudinal, and radial SRe was abnormal in patients who received photon vs. proton beam therapy which was present even after 1 year’s follow-up [ 44 ]. These studies prove that early diastolic dysfunction is present after RT and that 2D-STE is a good tool to evaluate it.…”