Investigation of radiation dose to heart tissue and associated risks from radiological imaging in heart transplant patients

The purpose of this project is to determine typical heart doses from Computed Tomography Coronary Angiography (CTCA) and invasive coronary angiography (ICA), and hence the doses to coronary vessels. Once the typical doses have been determined, to then apply the latest risk information.

All exposures to ionising radiation carry some risk, including stochastic risks (cancer induction) and tissue effects. The risks arising from a single radiation exposure are small and are outweighed by the clinical benefit to the patient. The risks increase with dose and stochastic risks can be considered cumulative while tissue effects can be considered cumulative over specific timeframes determined by the specific tissue. Therefore, patients who receive multiple imaging exposures over a clinical pathway, such as heart transplant recipients, are likely to be subject to increased risks from the ionising radiation.

Recent literature suggests that the risk of cardiovascular tissue effects is greater than previously thought. It is important for patients, clinicians and scientists to understand the risks as far as possible to ensure that clinical pathways are optimised and patients can make the most well informed decisions possible.

In 2024, 44 heart transplants were carried out at Harefield Hospital and approximately 200 heart transplants for adult patients were performed in England [2].

Existing techniques for calculating radiation dose and risk are available for cancer risk. This project will consider the risk of damage to coronary vessels, which the literature suggests could be greater than the cancer risk. Consequently, we have few tools in routine use for estimating risk to coronary vessels. My project will use a dose calculation tool (NCIDose) to assess heart dose from existing cardiac CT scans and cardiac catheter laboratory studies. NCIDose can provide estimates of dose to the heart wall, which can be used as a surrogate for dose to coronary vessels.

Additionally, the techniques available to estimate organ and effective doses from interventional radiological procedures, such as coronary angiography, are limited. NCIDose includes a module for fluoroscopy to allow for more realistic dose estimations. Many current dose estimation techniques include application of conversion factors determined by previous studies based on outdated data sets using imaging technology no longer in clinical use and less well optimised protocols, or using dose estimation software that is based on crude mathematical virtual phantoms that are poor representations of human anatomy and cannot be varied in shape and size. NCIDose contains a virtual phantom library including the ability to change the shape and size of the phantom allowing for more accurate estimations of patient doses.

The aims of my project are to:

• determine typical doses to the heart, and therefore, coronary arteries, for cardiac catheter laboratory procedures and cardiac CT
• audit the imaging received by the heart transplant patients over the whole pathway
• use the published literature to estimate the magnitude of the risk for cancer induction and cardiovascular disease from radiation exposures
• develop a simple predictive calculator tool and/or determine some heart dose per Dose Length Product (DLP) and /Dose Area Product (DAP) conversion factors that will enable cardiologists and clinical scientists to estimate the risks from imaging to specific patients to inform justification and optimisation of the pathway

[2] https://www.gov.uk/government/publications/cardiothoracic-information-collation-exercise-additional-survey-analysis/cardiothoracic-heart-and-lung-information-collation-exercise-additional-analysis-of-patient-and-staff-survey

Outputs

Poster presentation for HSST research day 2025.
More is planned.