MEDIRAD has conducted research on five key elements for further optimisation of radiation-based medical protocols for diagnostics or therapy. The related results have led to the elaboration of novel practical recommendations in the following fields.
Computed Tomography (CT) is the largest contributor to the European population’s collective exposure from medical uses of ionising radiation, and poses a potential health risk to patients. It is thus critical to employ the principle of optimisation in radiological protection to ensure doses are as low as reasonably achievable (ACLARA), unproductive exposure is avoided, and the benefit to risk ratio is maximised for all CT examinations. This is of particular importance for the paediatric population as a result of their higher radiosensitivity and prolonged life expectancy. While dose reduction inherently reduces the risk of potential harmful radiation effects, the extent to which doses can be reduced is constrained by image quality, which in turn is dependent on clinical needs. Therefore, to effectively optimise exposure to ionising radiation from CT examinations and multimodality imaging, optimisation strategies should be based upon patient and organ dosimetry, image quality, patient characteristics, and clinical indications. The development of robust optimisation tools that account for each of these contributing factors, along with further advancements in personalised medicine, are therefore needed.
Patient-specific dosimetry to assess the radiation absorbed doses in target volumes and organs at risk is important to understand and improve the safety and efficacy of both existing and new radiopharmaceuticals. The planning and confirmation of absorbed doses is required under Council Directive 2013/59/Euratom for molecular radiotherapy (MRT) as well as for external beam radiotherapy (EBRT). The evaluation of patient dosimetry on an individual basis can help to highlight the range of absorbed doses delivered from empirically-based fixed administrations of activity and the consequent range of likely outcomes, including long-term risks of secondary malignancies.
Multi-centre studies are required to develop personalised treatments with radiotherapeutics due to the limited numbers of patients treated at single centres. Individualised biokinetics should be considered rather than models and values established for a healthy population, and biomarkers of radiosensitivity can inform further levels of personalisation. While the clinical studies performed within MEDIRAD focused on radioiodine therapy for thyroid cancer, the methodologies developed for harmonised data collection and analysis are widely applicable to existing, and novel, radiotherapeutics as MRT experiences rapid expansion.
Breast cancer (BC) is among the most commonly diagnosed cancers in women. Around 21% of BC cases occur in women younger than 50-64 years of age and 35% occur in those aged 50-64. Radiotherapy plays a pivotal role in the treatment of breast cancer BC patients, but may induce cardiac damage and subsequent major cardiac events like acute coronary events, which may occur relatively early or up to decades after completion of radiation treatment. As overall survival of BC patients has significantly improved, the prevalence of BC survivors at risk of developing cardiac toxicity is increasing. This is relevant at the individual level, as cardiac toxicity has a major impact on quality of life and leads to increased morbidity and mortality, but also at the societal level, as it leads to secondary health costs and may interfere with daily functioning and subsequent labour participation. Therefore, identification of BC patients at high risk for cardiac toxicity is crucial for developing effective strategies for individualised primary and/or secondary prevention of cardiac toxicity.
The radiation dose to the heart is an important risk factor for radiation-induced cardiac toxicity and it has been generally acknowledged that there is no threshold dose below which no toxicity will occur. Therefore, cardiac dose should be kept as low as reasonably achievable (ALARA) to prevent radiation-induced cardiac events.
There are several options to lower the dose to the heart, e.g., by means of reducing the radiation target volume (e.g., partial breast irradiation) and/or using more advanced radiation techniques (e.g., breath hold techniques and proton therapy). However, not all patients are suitable candidates for reducing the target volume. In addition, applying more advanced radiation techniques generally requires more resources, is more expensive, and may be more burdensome to patients.
Although there is an increasing awareness among radiation oncologists that sparing the heart is essential to broaden the therapeutic ratio in BC patients, the currently available options are not always applied in routine clinical practice.
Patient dosimetry is an essential part of ensuring quality and safety both in radiotherapy and diagnostic imaging. In radiotherapy, the determination of the radiation doses has to be improved, especially in nuclear medicine therapy. In external radiotherapy, knowledge about radiation dose, especially outside the planning target volume, also has to be improved. It is therefore necessary to move from planned dose distribution to delivered dose distribution in order to improve the quality of care, including person-centred care, and the radiological protection of the patient. In diagnostic imaging, where the radiation dose is not planned for individual patients, better knowledge about the radiation dose to organs is needed to improve optimisation in general and for individualisation of imaging processes.
Today, to a great extent, only radiation dose indices are used to document patient doses. This lack of information hinders real optimisation and can also conceal radiation-related risks to specific organs also in the field of diagnostic imaging.
Recent advances in computer science will facilitate progress in this field, since the specific constitution of the patient, as well as technical parameters specifying the exposure, are now available and usable for dose estimation. Internal dosimetry can also include information from molecular imaging to advance the knowledge about patient-specific biokinetic data. The MEDIRAD project has made several contributions to this end.
The following science-based policy recommendations have been produced in an effort to advocate and facilitate the further development of tools and techniques to optimise both image quality and patient exposures to ionising radiation. They are addressed to different stakeholders in an effort to disseminate and implement the project’s key findings and learnings.