Data abstraction and analysis

From the 16 studies, characteristics of patients (e.g. age, gender), cancer (e.g. disease site, stage), treatment (e.g. RT doses, chemotherapy), dietary intervention (e.g. vitamins, supplements), patient-reported outcomes (PROs), toxicity, and other outcomes were coded. Dietary interventions in a clinical setting sit within a comprehensive, individualized nutritional consultation which encompasses nutritional screening, anthropometry and review of the clinical picture and medical history. The key dietary interventions used are: dietary counselling (diet modification/fortification techniques/eating strategies), oral nutritional supplementation, and reactive nutritional support in the form of nasoenteric feeding, gastrostomy or jejunostomy tube feeding or total parenteral nutrition for cases where oral intake is not possible. Dietary interventions that involved a single supplement, such as amino acids or antioxidants, were coded as “micronutrient” interventions, while interventions changing the content of an entire meal, such as low fiber or fat, were coded as “macronutrient” interventions.

For objective 1, acceptability was defined as: (the number of patients agreeing to perform the dietary intervention + RT)/(the number of eligible participants). Feasibility was defined as: (number of patients who completed the dietary intervention + RT)/(number agreeing to perform the dietary intervention + RT). There were four papers that did not report adherence [9], [10], [21], [24]. Four papers reported a feasibility rate for those who completed the study, with compliance ranging from 9% to 93% [12], [18], [20], [22]. The remaining studies only included data for participants who maintained a particular level of compliance, ranging from 33% to 100% [11], [19], [16], [17]. For reference, all values are listed in Table 1.

Summary of studies evaluating RT +/− dietary interventions.

For objective 2, we assessed patient reported outcomes, toxicities, and survival per the primary endpoint listed in each study (listed in Table 1). Toxicities were recorded using the Common Terminology Criteria for Adverse Events (CTCAE) scale, attributable to the addition of the dietary modification, per the assessment of the authors of the primary study. QOL was most commonly measured pre- and post-treatment by the European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire- C30 (QLQ-C30) and QLQ-PR25. Adverse effects of RT were reported with Radiation Therapy Oncology Group (RTOG) Acute Radiation Morbidity Scale and CTCAE questionnaires. Gastrointestinal (GI) adverse events were reported most commonly using the GI Side Effects Questionnaire [24], Inflammatory Bowel Disease-Questionnaire (IBD-Q) [25], and Vaizey Incontinence Questionnaire [26].