Fibrosis is a common and irreversible adverse effect of radiotherapy. Radiotherapy is used with curative intent in most individuals (\~70%) with head and neck cancer (HNC), often in combination with surgery and/or chemotherapy. It is estimated that up to 60% of these individuals will experience persistent fibrosis as a toxic effect of the radiotherapy including trismus and dysphagia. As 680,000 new HNC cases/year are diagnosed worldwide, it is estimated that approximately 270,000 individuals will develop persistent trismus and/or dysphagia, with consequent reduced quality of life (QoL) due to impaired talking, eating, chewing and swallowing. Malnutrition, psychological and social issues add further suffering to affected individuals. Mortality is also significantly increased due to aspiration pneumonia. In the UK there are \~10,000 new H\&N cancer cases/year, which translates into approximately 4,200 individuals experiencing radiotherapy-induced fibrosis (RIF) every year. Increasing incidence rates of H\&N cancer suggest that these figures will increase over the next few years. This group of cancer survivors represent a challenge for the NHS: they have a chronic condition reducing their quality of life and no realistic therapeutic option as no intervention has proven long-term effective. Current best NHS practice consists of rehabilitation therapy (exercises). Although available literature suggests potential efficacy, evidence is very weak: relevant benefits seem to be short-lived, the effect size is usually small, and compliance with treatment is often poor. As preparatory work for this proposal we have performed a systematic review of the literature, which shows that five prospective studies investigated rehabilitation exercises, pentoxifylline and botulinum A in the therapy of post-RT trismus. Four prospective studies investigated rehabilitation exercises and electrical stimulation in the therapy of post-RT dysphagia.

Overall studies were at high risk of bias, and there was very limited evidence supporting the efficacy of the above interventions in the post-RT setting.

There remains little ongoing clinical research in this field at the present moment (clinical trials databases searched in March 2018). Most ongoing recruiting studies focus on preventive strategies during HNC radiotherapy. In terms of trials aimed at reducing established post-RT fibrosis, we could only find one recruiting Canadian study on manual therapy and one American study on self-care program, with no UK study.

RIF has been traditionally considered an irreversible disorder characterised by the generation of reactive oxygen species, vascular damage, pro-fibrotic inflammation, promotion of collagen formation and the development of excessive fibrous tissue. However research during the last 15 years has shown that co-administration of pentoxifylline and tocopherol (vitamin E) can reduce and reverse the fibrotic process. Pentoxifylline is known to improve microcirculation, inhibit fibroblast proliferation, reduce extracellular matrix production, and increase collagenase activity. Tocopherol (Vitamin E) has antioxidant properties. The precise mechanisms by which the pentoxifylline/tocopherol (vitamin E) combination interacts with fibro-atrophic tissues and induces fibrotic process reversibility are still unclear. It has been suggested that the anti-fibrotic effects are consequence of the inhibition of fibroblast proliferation and extracellular matrix production, increased collagenase activity, as well as a reduction in reactive oxygen species. Clinical trials have indicated that the combination of pentoxifylline and tocopherol (vitamin E) can decrease and even reverse RIF in individuals irradiated to the breast, pelvis, lung, and prostate, leading to functional and aesthetic benefits. It is not known whether this therapy may have similar beneficial effects in HNC survivors with permanent RIF (trismus and/or dysphagia). Preliminary small-scale studies suggest that this may be the case, and support the notion that pentoxifylline and tocopherol (vitamin E) represent a promising treatment that is worth investigating in well-designed clinical trials. The best available evidence comes from a 2001 uncontrolled, small (16 subjects) pilot study that showed functional improvement in subjects with established post-radiotherapy trismus after an 8-week course of pentoxifylline as monotherapy. Other studies have reported the beneficial effects of pentoxyfilline monotherapy or in combination with tocopherol (vitamin E) in reducing and/or preventing RIF in HNC, but these focused on cutaneous/subcutaneous neck fibrosis and did not measure trismus/dysphagia. There is a clear need for better-designed clinical research as more robust evidence is required in order to influence changes in NHS practice and improve the quality of life of HNC survivors.

The main study will be a multicentre randomised controlled trial with two arms including the experimental intervention plus the current best standard treatment versus the current best treatment as comparator \[1:1\]. The main outcome will be anticipated to be patient-centred and measured via a validated instrument (QoL questionnaire), with secondary outcomes including other patient-centred measures (validated functional questionnaires) as well as clinician-rated and instrumental outcomes. However several aspects of the main trial remain unknown/unclear and would require clarification via a feasibility study.

PITSTOP is a feasibility 36-month randomised trial of the best standard therapy alone \[rehabilitation exercises\] vs treatment with pentoxifylline and tocopherol (vitamin E) in addition to best standard therapy (rehabilitation exercises) in 50 participants with radiotherapy-induced fibrosis of the head and neck. It is a two-centre study with a 1:1 randomisation into two study arms. At each site a blocked randomisation list will be used to ensure an approximate balance in numbers between the two groups. Allocation concealment will be ensured using an online randomisation service (Sealed Envelope).