Radiotherapy and the Heart: Damage, Protection, or Treatment?

Radiotherapy is a primary modality in cancer treatment, employed in more than 50% of all oncological patients.¹ While effective against malignancies, ionising radiation can cause damage to adjacent healthy tissues, resulting in acute and chronic complications.¹ The heart is among the organs susceptible to such injury, alongside the skin, mucosa, lungs, bones, and gastrointestinal tract.¹ These radiation-induced injuries significantly diminish patients' quality of life and can restrict the maximum therapeutic radiation doses that can be administered.¹ Managing these complications represents a major unmet clinical challenge.¹

The clinical manifestations of radiation-induced heart disease (RIHD) are diverse and can include pericarditis, myocarditis, coronary artery disease, valvular heart disease, and conduction abnormalities. These complications often develop years or even decades after initial radiation exposure, posing a long-term burden on survivors. The incidence and severity of RIHD depend on several factors, including the total radiation dose, fractionation schedule, irradiated heart volume, and individual patient susceptibilities. For instance, patients treated for left-sided breast cancer or mediastinal lymphomas are at higher risk due to the proximity of the heart to the radiation field. The increasing survival rates for many cancers mean that a growing number of patients will live long enough to experience these late cardiac toxicities, underscoring the critical need for effective cardioprotective strategies.

Novel Strategies for Cardioprotection

Hydrogels have emerged as promising biomaterials for addressing radiation-induced damage.¹ Their utility stems from their high water content, tunable mechanical properties, and ability to mimic the extracellular matrix.¹ Recent innovations in hydrogel technology include stimuli-responsive, injectable, and bioactive systems.¹ These advanced hydrogels are capable of delivering therapeutic agents such as antioxidants, growth factors, or living cells.¹ A novel classification framework for hydrogels has been proposed, based on their mechanism of action within the pathophysiology of radiation injury.¹ This framework evaluates how specific designs, including reactive oxygen species (ROS)-scavenging matrices, barrier-forming injectable shields, and bioactive delivery vehicles, can target distinct phases of inflammation and fibrosis.¹ This approach aims to protect healthy tissues, suppress chronic inflammation, and promote effective tissue regeneration.¹

The proposed hydrogel classification framework delineates three primary mechanisms of action. First, ROS-scavenging hydrogels are designed to mitigate the initial oxidative stress induced by radiation, which is a key trigger for cellular damage and inflammation. These hydrogels often incorporate antioxidant compounds or enzymes. Second, barrier-forming injectable shields physically protect healthy tissues by creating a temporary, biocompatible barrier between the radiation source and vulnerable organs like the heart. This physical separation can reduce the absorbed dose to critical structures. Third, bioactive delivery vehicles are engineered to release therapeutic agents in a controlled and sustained manner. These agents may include anti-inflammatory drugs, growth factors to promote tissue repair, or stem cells for regeneration. The precise targeting of these distinct phases of radiation injury—initial damage, chronic inflammation, and impaired regeneration—represents a sophisticated approach to cardioprotection.

The impact of adjuvant radiotherapy, particularly when combined with targeted or immunotherapy, on the heart in breast cancer patients is a specific area of concern.³ The European Association of Cardiovascular Imaging (EACVI), the European Association of Percutaneous Cardiovascular Interventions (EAPCI), the Heart Failure Association (HFA), and the Association for Acute CardioVascular Care (ACVC) of the ESC have issued a clinical consensus statement regarding women's heart centres.² While the abstract provided for this consensus statement reiterates the general challenges of radiotherapy-induced damage and the potential of hydrogels, it underscores the broader recognition within cardiology of the need for specialised care and research into cardiac complications arising from cancer treatments.²

The ongoing development of hydrogel-based strategies for both prevention and therapy highlights the potential of these mechanistically aligned systems.¹ By targeting the specific phases of radiation injury, these systems may offer a pathway to protect healthy tissues, mitigate chronic inflammation, and facilitate tissue repair.¹ Further research is required to translate these preclinical insights into clinical applications, particularly in the context of specific organ systems like the heart and in patient populations receiving complex multimodal cancer therapies. The limitations of current preclinical models often include their inability to fully replicate the long-term, multifactorial nature of RIHD in humans. Future studies must focus on larger animal models and ultimately human trials to validate the safety and efficacy of these novel hydrogel systems, ensuring their integration into clinical practice for improved patient outcomes.