​​​Should UK photon radiotherapy centres be moving to a flattening filter free only service? An economic, clinical and environmental evaluation of a FFF only radiotherapy department

Clinical radiotherapy megavoltage photons (x-ray) beams are generated in linear accelerators through the interaction of high energy electrons with a high atomic number material target. The resulting bremsstrahlung x-rays are in a forward peaked direction and have historically been ‘flattened’ using a conical-shaped filter to achieve a uniform dose profile at depth in a material, primarily for ease of treatment planning.

Modern treatment planning techniques employ moving gantry and multi-leaf collimators and variable doserates and are calculated using treatment planning computers. These do not rely on flattened beams (cFF) and a generation of linear accelerators are now available that can deliver flattening filter free (FFF) photon beam radiotherapy. Removing the filter reduces the amount of radiation scattered in the head of the linac and therefore the out of field dose received by patients. Loss of low energy x-ray absorption in the target material reduces the beam-hardening effect changing the beam energy and enabling considerably higher doserate, faster treatment deliveries.

Despite this, roll-out of FFF modalities across the UK is inconsistent. The impact of perceived benefits such as efficiency savings may vary between disease sites and treatment regimens and must be balanced alongside the requirement to develop alternative work practices, quality assurance programs and expert knowledge. The move to FFF must be carefully considered from a clinical perspective on a site-by-site basis and requires time and staff resources.

Some centres have implemented FFF delivery for the majority of their patients; others limit use to high dose per fraction stereotactic treatments. Providing FFF and cFF treatments in a single centre is commonplace.

Whilst a large body of published work exists describing the technical aspects of FFF radiotherapy there is little evidence of a comprehensive review of the benefits or otherwise offered by a move to FFF only delivery. Dated publications may lack validity in the context of advances in technology and technique. Evidence from countries outside of the UK offer useful insight but cannot represent an accurate picture without taking local patient populations and the restrictions and opportunities experienced in the NHS into account.

The research aims to fully evaluate the benefit to patients, the environment and the NHS from implementation of FFF delivery to support informed decision making in individual UK radiotherapy centres. It could serve to highlight where the most significant gains can be made and discover barriers to implementation. If appropriate, a simple model of implementation taking into consideration all relevant stakeholders could be proposed for adoption locally.

Outputs

None. Started September 2025.