Reversing External-beam Radiotherapy-associated Fibrosis Syndrome: an Interventional Bayesian Adaptive Randomized-controlled Orphan Drug Platform Trial for Orodental Sequelae (Reverse-fibrose)

Primary Objectives 1. Determine the relative utility of candidate agents to reduce clinician-rated radiation lymphedema/fibrosis 1. Hyp 1: Participants receiving candidate agent(s) will exhibit a proportional lower rate of Common Toxicity Criteria- Adverse Event (CTC-AE v5.0) rating of Grade 2 or greater on either "Fibrosis deep connective tissue" or "Superficial soft tissue fibrosis" by formal clinician assessment at 12 months post-randomization. 2. Hyp 2: Participants receiving candidate agent(s) will exhibit a proportional lower rate of objective lymphedema/fibrosis rated as "moderate/severe" grade at any head and neck subsite as measured by the Head and Neck External Lymphedema and Fibrosis (HN-ELAF) Assessment Criteria by a certified lymphedema specialist at 12 months post-randomization. 2. Determine the relative effect size observed of candidate agent(s) to reduce objective imaging-derived measures of radiation lymphedema/fibrosis-related sequalae \[Primary\] 1. Hyp 3: Participants receiving candidate agent(s) will exhibit a proportionally lower rate of objective DIGEST-detected swallowing dysfunction 12 months post-randomization. 2. Hyp 4: Participants receiving candidate agent(s) will exhibit a proportional lower rate of objective MRI-detected difference between 6- and 18-month post-randomization quantitative T1 (T1 mapping) intensity for paired muscle swallowing/neck/masticator muscles receiving \>=40Gy post-randomization. Secondary Objectives 1. Determine the relative effect size observed of candidate agent(s) to reduce patient reported measures of toxicity associated with lymphedema/fibrosis-related sequalae \[Secondary\] 1. Hyp 5: Participants receiving candidate agent(s) will exhibit a proportionally lower rate of moderate-severe rated items "Fibrosis deep connective tissue" or "Superficial soft tissue fibrosis" by patient self-assessment using the Participant Reported Outcomes-CTCAE (PROCTCAE) Scale at 12-months post-randomization. 2. Hyp 6: Participants receiving candidate agent(s) will exhibit a proportionally lower rate of moderate-severe rated symptom items by participant self-assessment using the Head and Neck External Lymphedema and Fibrosis (HN-ELAF) Symptom Inventory Scale at 12-months post-randomization. 3. Hyp 7: Participants receiving candidate agent(s) will exhibit a proportionally lower rate of moderate-severe global symptom burden by participant self-assessment using the MD Anderson Symptom Inventory Scale at 12-months post-randomization. 4. Hyp 8: Participants receiving candidate agent(s) will exhibit a proportionally improved global quality of life as denoted by patient self-assessment using the EQ-5D Visual analogue Scale at 12-months post-randomization. .