Green Nuclear Medicine and Radiotheranostics

Use More Environment-Friendly Techniques to Diagnose Patients

When acceptable, transitioning to other techniques, that is, non–GHG-emitting examinations such as blood tests (which partly still need to be developed), could potentially enable initiation of treatment. As an example, when a patient with a chronic cardiac ischemic condition is triaged, a complete history and physical examination with an abnormal electrocardiogram and elevated cardiac enzymes can often guide patient management without the need for perfusion imaging. In another currently well-established example, most patients with a history of differentiated thyroid cancer are monitored using serum thyroglobulin without a need for periodic radioiodine scans or CT for their surveillance follow-up (15).

Do More Nuclear Medicine Studies

Increasing the ratio of (adequate) nuclear medicine techniques—for instance, instead of MRI—saves GHG emissions. Obviously, this is a somewhat oversimplistic view since many clinical indications are specific to MRI. Additionally, the generalization of hybrid imaging, that is, SPECT/CT and PET/CT, partly mitigates the benefit due to the higher footprint of CT, especially when underused.

Increase the Use of PET and SPECT Devices

Going from 8 to 12 scans per workday could decrease the environmental impact of SPECT by approximately 66% (12). This stems from the impact generated by assembly, transport, end of life, and, more importantly, stand-by electricity such as that consumed during nonoperational hours. Additionally, technologies such as full-ring cadmium-zinc-telluride (for SPECT) and silicon photomultipliers, and scanners with a long axial field of view (for PET), are much faster, allowing an increased use rate. This also includes artificial intelligence–based methods to denoise the images and provide equivalent diagnostic quality with significantly shorter acquisition times or lower injected doses (16). This partly allows older systems to be used longer and may have secondary positive consequences in terms of production, transport, and waste management.

Foster Frugal Innovation (Maybe Even Outside Nuclear Medicine)

Essential health care services are available to a maximum of half the world’s population (17). Frugal innovation fosters the development of “low-cost and efficacious, new or adapted products (or services), mostly emerging from contexts of institutional voids and resource constraints, involving the creative use of existing resources” (17). The main benefit is the trickling-up effect, or reverse innovation—that is, innovations initially developed toward low- and moderate-income countries felt efficient enough to be used in high-income countries at a lower cost. Examples exist in radiology, notably in the development of U.S. devices (18).

Another hospital-based aspect again relates to waste management. It is estimated to be responsible for approximately 3% of the total health care carbon footprint (19). Therapeutic radioisotopes such as ¹³¹I, ¹⁷⁷Lu, and ⁹⁰Y have longer half-lives, and subsequently, waste management becomes complex. Nuclear medicine departments that are treating inpatients have to deal with contaminated body fluids, the injection material, disposable clothing, plastic films that cover part of the hospital room, etc., and possibly even food. This waste may require storage for extended periods, often in low-temperature rooms, and hence, radiation protection requirements may contradict sustainability efforts. Countries that allow outpatient therapies with the current or upcoming modern radiotheranostic agents (i.e., ¹⁷⁷Lu-PSMA) are therefore balancing radiation protection and cost with the secondary benefit (probably beyond the original goal) of promoting sustainability in the practice of nuclear medicine. Also, the next generation of radiotheranostics may be partly geared more toward ²¹²Pb or ²¹¹At, which have short half-lives.

Hospital heating, ventilation, and air conditioning systems generate the highest consumption of energy and CO₂ emissions (20). Considering that SPECT and PET devices, as well as the abovementioned waste storage rooms, are required to be maintained at specific cool temperatures, smart heating and cooling systems (available already for home use) can support the sustainability efforts. Vendors will need to develop energy-saving states in which the imaging system can remain when not in use without impacting the required temperature.

Also, turning off workstations after core working hours could reduce total energy consumption by approximately one third, resulting in an extrapolated saving of more than 22 tons in CO₂ emissions per year in a single-center experience (21,22). Lastly, using highly efficient lighting and energy-friendly bulbs (e.g., motion-detector lights) in the department can create significant annual energy savings.

Reducing the Environmental Impact of the Increasing Use

It is expected that the large number of patients on whom radiopharmaceuticals are used will grow. If addressing only 5% of cancer patients (global prevalence of 44 million (23)), this would mean that more than 8 million doses of radiopharmaceuticals will have to be produced yearly. Thus, increased radioactive waste will have to be taken care of, but additionally, the amount of radioactivity to be released in water 10 y from now, without protective measures, will be substantial. With long-half-life radionuclides such as ¹⁷⁷Lu (6.7 d) and ²²⁵Ac (9.9 d), the water contamination may reach a level that raises serious concerns. In some U.S. centers, patients are requested to wear diapers during the first days at home and to keep them in a safe container until full decay (respectively, 2 and 3 mo). Thus again, shorter-half-life radionuclides without long-half-life contaminants may have a competitive advantage in this scenario.

²²⁵Ac- and ¹⁷⁷Lu-labeled drugs appear to be on their way to becoming the future blockbusters of nuclear medicine and possibly will generate significant revenues for the industry during the next 15 y. Although currently in development with somewhat uncertain market and distribution uptake, an equivalent efficient drug labeled with a shorter-half-life radionuclide, such as ²¹¹At or ²¹²Pb, has, however, a great chance to claim a significant market share over the long term, if showing at least equal efficacy.

Reducing the Impact of Transport and Travel

When considering radionuclides with shorter half-lives, the number of production sites needs to be increased, and the balance between investment in new sites and transportation costs must be evaluated carefully. However, the example of the production of ¹⁸F (900 cyclotrons among the 1,500 operating cyclotrons in the world in good-manufacturing-practice condition (24)) shows that the industry is actually able to develop large networks of production tools. Although this corresponded to over 25 y and a $4 billion investment, a network of about 30 ²¹¹At production units that could easily cover the 3 major markets would correspond to not more than a $600 million investment, less than what is now spent to develop the ²²⁵Ac production network and far above what will be required to achieve worldwide access to ²¹²Pb.

Lastly, providing remote access, such as through telereporting, can help reduce the carbon footprint by decreasing pollution and energy use related to transportation. This is also implied in research programs and scientific events. If open-access cloud-based databases become available for radiopharmaceutical purposes, they will obviously decrease the need for the same research studies to be initiated in other jurisdictions. International scientific events can have a significant carbon footprint, which should be considered. It was calculated that attending the Radiological Society of North American annual meeting generates a carbon footprint equal to the average annual footprint of 3,689 people living in high-income countries, 10,560 people living in middle-income countries, or 123,072 people living in low-income countries (25).

Using the Current Long-Half-Life Therapeutics Equitably

Although long-half-life therapeutics can be more impactful on the environment, some measures can be taken to limit their adverse effects. For example, adapted radionuclide therapy, instead of a fixed-dosing approach, will help to optimize dosage and radiopharmaceutical waste. Dosimetry can maximize the benefit-to-risk ratio for patients by calculating the maximum tolerated activity in a personalized manner. SPECT serves as the primary posttreatment quantification modality for dosimetry, and with current cadmium-zinc-telluride technology and artificial intelligence–based image reconstruction techniques, scanning time can be reduced and multiple sessions of dosimetry after therapy can be omitted (26). Also, there are novel artificial intelligence–based methods, such as digital twins, that can provide a precise virtual analog of each individual patient before administration of radiopharmaceutical therapy (27).