FLASH Proton Radiation Therapy Mitigates Inflammatory and Fibrotic Pathways and Preserves Cardiac Function in a Preclinical Mouse Model of Radiation-Induced Heart Disease

PURPOSE

Studies during the past 9 years suggest that delivering radiation at dose rates exceeding 40 Gy/s, known as "FLASH" radiation therapy, enhances the therapeutic index of radiation therapy (RT) by decreasing normal tissue damage while maintaining tumor response compared with conventional (or standard) RT. This study demonstrates the cardioprotective benefits of FLASH proton RT (F-PRT) compared with standard (conventional) proton RT (S-PRT), as evidenced by reduced acute and chronic cardiac toxicities.

METHODS AND MATERIALS

Mice were imaged using cone beam computed tomography to precisely determine the heart's apex as the beam isocenter. Irradiation was conducted using a shoot-through technique with a 5-mm diameter circular collimator. Bulk RNA-sequencing was performed on nonirradiated samples, as well as apexes treated with F-PRT or S-PRT, at 2 weeks after a single 40 Gy dose. Inflammatory responses were assessed through multiplex cytokine/chemokine microbead assay and immunofluorescence analyses. Levels of perivascular fibrosis were quantified using Masson's Trichrome and Picrosirius red staining. Additionally, cardiac tissue functionality was evaluated by 2-dimensional echocardiograms at 8- and 30-weeks post-PRT.

RESULTS

Radiation damage was specifically localized to the heart's apex. RNA profiling of cardiac tissues treated with PRT revealed that S-PRT uniquely upregulated pathways associated with DNA damage response, induction of tumor necrosis factor superfamily, and inflammatory response, and F-PRT primarily affected cytoplasmic translation, mitochondrion organization, and adenosine triphosphate synthesis. Notably, F-PRT led to a milder inflammatory response, accompanied by significantly attenuated changes in transforming growth factor β1 and α smooth muscle actin levels. Critically, F-PRT decreased collagen deposition and better preserved cardiac functionality compared with S-PRT.

CONCLUSIONS

This study demonstrated that F-PRT reduces the induction of an inflammatory environment with lower expression of inflammatory cytokines and profibrotic factors. Importantly, the results indicate that F-PRT better preserves cardiac functionality, as confirmed by echocardiography analysis, while also mitigating the development of long-term fibrosis.

Myocardial microvascular function assessed by CMR first-pass perfusion in patients treated with chemotherapy for gynecologic malignancies

OBJECTIVES

Cancer chemotherapy potentially increases the risk of myocardial ischemia. This study assessed myocardial microvascular function by cardiac magnetic resonance (CMR) first-pass perfusion in patients treated with chemotherapy for gynecologic malignancies.

METHODS

A total of 81 patients treated with chemotherapy for gynecologic malignancies and 39 healthy volunteers were prospectively enrolled and underwent CMR imaging. Among the patients, 32 completed CMR follow-up, with a median interval of 6 months. The CMR sequences comprised cardiac cine, rest first-pass perfusion, and late gadolinium enhancement.

RESULTS

There were no significant differences in the baseline characteristics between the patients and normal controls (all p > 0.05). Compared with the normal controls, the patients had a lower myocardial perfusion index (PI) (13.62 ± 2.01% vs. 12% (11 to 14%), p = 0.001) but demonstrated no significant variation with an increase in the number of chemotherapy cycles at follow-up (11.79 ± 2.36% vs. 11.19 ± 2.19%, p = 0.234). In multivariate analysis with adjustments for clinical confounders, a decrease in the PI was independently associated with chemotherapy treatment (β = - 0.362, p = 0.002) but had no correlation with the number of chemotherapy cycles (r = - 0.177, p = 0.053).

CONCLUSION

Myocardial microvascular dysfunction was associated with chemotherapy treatment in patients with gynecologic malignancies, and can be assessed and monitored by rest CMR first-pass perfusion.

KEY POINTS

• Chemotherapy was associated with but did not aggravate myocardial microvascular dysfunction in patients with gynecologic malignancies. • Rest CMR first-pass perfusion is an ideal modality for assessing and monitoring alterations in myocardial microcirculation during chemotherapy treatment.

Nuclear medicine imaging methods of radiation-induced cardiotoxicity

Breast cancer survival is significantly improved over the past decades due to major improvements in anti-tumor therapies and the implementation of regular screening, which leads to early detection of breast cancer. Therefore, it is of utmost importance to prevent patients from long-term side effects, including radiotherapy-induced cardiotoxicity. Radiotherapy may contribute to damage of myocardial structures on the cellular level, which eventually could result in various types of cardiovascular problems, including coronary artery disease and (non-)ischemic cardiomyopathy, leading to heart failure. These cardiac complications of radiotherapy are preceded by alterations in myocardial perfusion and blood flow. Therefore, early detection of these alterations is important to prevent the progression of these pathophysiological processes. Several radionuclide imaging techniques may contribute to the early detection of these changes. Single-Photon Emission Computed Tomography (SPECT) cameras can be used to create Multigated Acquisition scans in order to assess the left ventricular systolic and diastolic function. Furthermore, SPECT cameras are used for myocardial perfusion imaging with radiopharmaceuticals such as ^99mTc-sestamibi and ^99mTc-tetrofosmin. Accurate quantitative measurement of myocardial blood flow (MBF), can be performed by Positron Emission Tomography (PET), as the uptake of some of the tracers used for PET-based MBF measurement almost creates a linear relationship with MBF, resulting in very accurate blood flow quantification. Furthermore, there are PET and SPECT tracers that can assess inflammation and denervation of the cardiac sympathetic nervous system. Research over the past decades has mainly focused on the long-term development of left ventricular impairment and perfusion defects. Considering laterality of the breast cancer, some early studies have shown that women irradiated for left-sided breast cancer are more prone to cardiotoxic side effects than women irradiated for right-sided breast cancer. The left-sided radiation field in these trials, which predominantly used older radiotherapy techniques without heart-sparing techniques, included a larger volume of the heart and left ventricle, leading to increased unavoidable radiation exposure to the heart due to the close proximity of the radiation treatment volume. Although radiotherapy for breast cancer exposes the heart to incidental radiation, several improvements and technical developments over the last decades resulted in continuous reduction of radiation dose and volume exposure to the heart. In addition, radiotherapy reduces loco-regional tumor recurrences and death from breast cancer and improves survival. Therefore, in the majority of patients, the benefits of radiotherapy outweigh the potential very low risk of cardiovascular adverse events after radiotherapy. This review addresses existing nuclear imaging techniques, which can be used to evaluate (long-term) effects of radiotherapy-induced mechanical cardiac dysfunction and discusses the potential use of more novel nuclear imaging techniques, which are promising in the assessment of early signs of cardiac dysfunction in selected irradiated breast cancer patients.

Impact of stent types on in-hospital outcomes of patients with cancer undergoing percutaneous coronary intervention: A nationwide analysis

BACKGROUND

Cardiovascular disease and cancer frequently coexist, and patients with cancer are at increased risk of cardiovascular events, including myocardial infarction and stroke. However, the impact of stent types on in-hospital outcomes of patients with malignancy is largely unknown.

METHODS

Patients with concomitant diagnosis of cancer undergoing PCI between January 2005 and December 2014 were identified in the National Inpatient Sample. They were then categorized into those who have undergone coronary stenting with bare-metal stent (BMS) or drug-eluting stent (DES). Primary outcomes were in-hospital mortality and stent thrombosis. Adjusted and unadjusted analysis was employed on appropriate variables of interest.

RESULTS

8755 patients were included in the BMS group and 11,611 patients in the DES group. Following propensity matching, 4313 patients were randomly selected in both groups using a 1:1 ratio. There was high use of BMS stent in cancer patient (BMS 43.0%, DES 57.0%) compared to general population (BMS 23.2%, DES 76.8%). When comparing BMS to DES group, there was no statistically significant difference in mortality (4.7% vs. 3.8%, p = 0.097), acute kidney injury (11.3% vs. 10.6%, p = 0.425), bleeding complications (3.50% vs. 3.45%, p = 0.914), and length of hospital stay (5.4% vs. 5.2%, p = 0.119). However, an increased incidence of stent thrombosis was observed in the DES group (4.26% vs. 3.01%, p = 0.002).

CONCLUSION

A higher incidence of BMS placement was noted in patients with cancer than in the general population. Paradoxically there was a high incidence of stent thrombosis in the DES group without increasing mortality.

Quantification of intramyocardial blood volume with 99mTc-RBC SPECT-CT imaging: A preclinical study

BACKGROUND

Currently, there is no established non-invasive imaging approach to directly evaluate myocardial microcirculatory function in order to diagnose microvascular disease independent of co-existing epicardial disease. In this work, we developed a methodological framework for quantification of intramyocardial blood volume (IMBV) as a novel index of microcirculatory function with SPECT/CT imaging of 99mTc-labeled red blood cells (RBCs).

METHODS

Dual-gated myocardial SPECT/CT equilibrium imaging of 99mTc-RBCs was performed on twelve canines under resting conditions. Five correction schemes were studied: cardiac gating with no other corrections (CG), CG with attenuation correction (CG + AC), CG + AC with scatter correction (CG + AC + SC), dual cardiorespiratory gating with AC + SC (DG + AC + SC), and DG + AC + SC with partial volume correction (DG + AC + SC + PVC). Quantification of IMBV using each approach was evaluated in comparison to those obtained from all corrections. The in vivo SPECT estimates of IMBV values were validated against those obtained from ex vivo microCT imaging of the casted hearts.

RESULTS

The estimated IMBV with all corrections was 0.15 ± 0.03 for the end-diastolic phase and 0.11 ± 0.03 for the end-systolic phase. The cycle-dependent change in IMBV (ΔIMBV) with all corrections was 23.9 ± 8.6%. Schemes that applied no correction or partial correction resulted in significant over-estimation of IMBV and significant under-underestimation of ΔIMBV. Estimates of IMBV and ΔIMBV using all corrections were consistent with values reported in the literature using invasive techniques. In vivo SPECT estimates of IMBV strongly correlated (R2 ≥ 0.70) with ex vivo measures for the various correction schemes, while the fully corrected scheme yielded the smallest bias.

CONCLUSIONS

Non-invasive quantification of IMBV is feasible using 99mTc-RBCs SPECT/CT imaging, however, requires full compensation of physical degradation factors.

Symptomatic cardiac toxicity is predicted by dosimetric and patient factors rather than changes in 18F-FDG PET determination of myocardial activity after chemoradiotherapy for esophageal cancer

PURPOSE

To determine factors associated with symptomatic cardiac toxicity in patients with esophageal cancer treated with chemoradiotherapy.

MATERIAL AND METHODS

We retrospectively evaluated 102 patients treated with chemoradiotherapy for locally advanced esophageal cancer. Our primary endpoint was symptomatic cardiac toxicity. Radiation dosimetry, patient demographic factors, and myocardial changes seen on (18)F-FDG PET were correlated with subsequent cardiac toxicity. Cardiac toxicity measured by RTOG and CTCAE v3.0 criteria was identified by chart review.

RESULTS

During the follow up period, 12 patients were identified with treatment related cardiac toxicity, 6 of which were symptomatic. The mean heart V20 (79.7% vs. 67.2%, p=0.05), V30 (75.8% vs. 61.9%, p=0.04), and V40 (69.2% vs. 53.8%, p=0.03) were significantly higher in patients with symptomatic cardiac toxicity than those without. We found the threshold for symptomatic cardiac toxicity to be a V20, V30 and V40 above 70%, 65% and 60%, respectively. There was no correlation between change myocardial SUV on PET and cardiac toxicity, however, a greater proportion of women suffered symptomatic cardiac toxicity compared to men (p=0.005).

CONCLUSIONS

A correlation did not exist between percent change in myocardial SUV and cardiac toxicity. Patients with symptomatic cardiac toxicity received significantly greater mean V20, 30 and 40 values to the heart compared to asymptomatic patients. These data need validation in a larger independent data set.

Risk of coronary heart disease in patients with cancer: a nationwide follow-up study from Sweden

BACKGROUND

Risk of coronary heart disease (CHD) in cancer patients has not been thoroughly investigated. The aim of the present study was to examine whether there is an association between cancer and first hospitalisation for CHD.

METHODS

All individuals in Sweden with a diagnosis of cancer between 1st January 1987 and 31st December 2008 were followed for first hospitalisation for CHD. The reference population was the total population of Sweden without cancer. Standardised incidence ratios (SIRs) for CHD were calculated.

RESULTS

The overall CHD risk during the first 6 months after diagnosis of cancer was 1.70 (95% confidence interval (95% CI) 1.66-1.75). For 26 of the 34 cancers studied, the risk of CHD was increased during the first 6 months after diagnosis of cancer. The overall CHD risk decreased rapidly, but remained slightly elevated, even 10+years after diagnosis of cancer (SIR 1.07; 95% CI 1.04-1.11). The cancer sites/types for which risk of CHD was highest during the first 6 months were small intestine (SIR 2.88; 95% CI 2.02-3.99), leukaemia (SIR 2.84; 95% CI 2.37-3.37), kidney (SIR 2.65; 95% CI 2.30-3.04), lung (SIR 2.56; 95% CI 2.35-2.80) and liver (SIR 2.28; 95% CI 1.91-2.71). Metastases were associated with an increased risk of CHD (SIR 1.46; 95% CI 1.28-1.65).

INTERPRETATION

Most cancers were associated with an increased risk of CHD during the first 6 months after diagnosis. CHD risk was related to the presence of metastates. Cancer patients may need a more aggressive treatment of classical CHD risk factors.

Managing coronary artery disease in the cancer patient

The cancer patient with coronary disease presents particular challenges that directly impact on the management of coronary disease, both stable and acute. The frequent need for surgery in the cancer patient is an important consideration in avoiding a coronary artery stent or any percutaneous coronary intervention for management of chronic stable angina, which will delay surgery or pose of risk of stent thrombosis during surgery. Cancer surgery is considered low or intermediate cardiac risk so revascularization before surgery is needed only in exceptional circumstances. Medical treatment in most patients or coronary artery bypass graft in high risk situations may be preferable if the cancer is being actively treated. The likelihood of thrombocytopenia, either primary from bone marrow disease, or secondarily during chemotherapy causes concern about the need for continuous use of platelet suppressing agents, aspirin for all patients, or double antiplatelet therapy in all patients after receiving a coronary artery stent. Drug-eluting stents pose special problems and should be avoided. Even bare metal stents may have a higher long-term risk of stent thrombosis in the cancer patient. The increase in propensity for venous clotting, either as a result of the cancer itself, or especially with selected chemotherapeutic agents may be an issue after stenting and certainly early after coronary bypass surgery. Aggressive medical treatment to reduce risk factors, especially with statins is essential to stabilize the underlying coronary disease.