COQ10 and Vitamin E for Off-Target Radiation Toxicity

Inclusion Criteria: 1. Pathologically confirmed post-prostatectomy prostate, uterine (endometrial and cervical), or anal cancer. 2. Scheduled for curative-intent, multi-fraction (at least 15 fractions) external-beam radiotherapy +/- chemotherapy at the study site which does not involve re-irradiation to the same field. 3. Age ≥ 19 years at the time of consent. 4. Eastern Cooperative Oncology Group Performance Status ≤ 2. 5. Life expectancy ≥ 6 months at the time of consent as determined by the participant's treating physician. 6. Participants must be able to swallow soft-gel capsules. 7. Participants must not have a disease significantly affecting drug absorption (e.g., resection of the stomach or small bowel, symptomatic inflammatory bowel disease, partial or complete bowel obstruction). 8. Participants must agree to limit alcohol consumption to ≤ 2 standard drinks (14 g of pure ethanol) within 6 hours before and 6 hours after vitamin administration. 9. Participants must agree to discontinue current vitamin/mineral supplements, including multivitamins, that contain Vitamin E (α-tocopherol) or CoQ10 (ubidecarenone) and abstain from taking these supplements while on study, including during the follow-up period. Participants must also agree to discontinue and abstain from high-dose vitamin/mineral supplementation while on-study and during the study follow-up period. NOTE: Participants for whom high-dose vitamin/mineral supplementation is medically necessary are eligible if the principal investigator determines that continuing treatment will not impact safety or study outcomes. 10. Women of childbearing potential and male participants with partners of childbearing potential must agree to use two forms of medically effective contraception (at least one of which must be a barrier method) while on study until one month following the last dose of vitamin supplements. 11. As determined by the enrolling physician, the participant must be able to understand and comply with study procedures for the entire length of the study. There must not be psychological, familial, sociological, or geographical conditions potentially hampering protocol compliance, including alcohol dependence or drug abuse. 12. The participant or the participant's legally authorized representative must provide documented informed consent after being informed of the procedures to be followed, the experimental nature of the therapy, alternatives, potential benefits, side effects, risks, and discomforts. 13. Participant must have adequate hematological, organ, and clotting function as defined below. Screening labs must be obtained prior to the end of radiation therapy. * Absolute Neutrophil Count (ANC) ≥ 500/mm3 * Platelets ≥ 50,000/mm3 • Hemoglobin ≥ 8.0 g/dL. The use of transfusion or other intervention to achieve Hgb ≥ 8.0 g/dL is acceptable. * Calculated creatinine clearance (CrCl (mL/min); Cockcroft-Gault formula) ≥ 30 mL/min. * Total bilirubin ≤ 1.5X institutional upper limit of normal (ULN) or ≤3 X ULN for patients with known Gilbert's syndrome * AST (SGOT) and ALT (SGPT) ≤ 3X institutional ULN * PT/INR and PTT (in the absence of lupus anticoagulant) ≤ 2X institutional ULN. Exclusion Criteria: 1. Participants who do not receive ≥ 80% of the planned total radiation. 2. Participants who are scheduled to receive SBRT/SRS 3. Participant's treatment plan must not include anti-cancer pharmaceutical therapies during the period of vitamin administration (\~3 months after completion of radiation therapy). 4. Participants must not receive any other investigational agents while on study. 5. Participants must not have contraindications to Vitamin E or CoQ10 supplementation, including: 1. Anticoagulation or antiplatelet therapy that cannot be stopped. NOTE: To be eligible, participants must be able to discontinue contraindicated medications at least 2 weeks prior to the initiation of study treatment. These medications may be resumed 1 month after completing study treatment. 2. Underlying bleeding conditions (e.g., hemophilia or von Willebrand disease) 3. Retinitis pigmentosa 4. Hepatobiliary dysfunction 5. Vitamin K deficiency 6. Preexisting severe fibrosis 7. History of significant cerebrovascular disease/event, including stroke or intracranial hemorrhage. 8. Uncontrolled Grade 2 hypertension defined as ≥ 140 mm Hg systolic blood pressure or ≥ 90 mm Hg diastolic blood pressure. 9. Uncontrolled AIHA (autoimmune hemolytic anemia) or ITP (idiopathic thrombocytopenia purpura). 10. Uncontrolled systemic bacterial, fungal, parasitic, mycobacterial, viral, or other infections, despite appropriate antibiotics or other treatments. 11. Any other uncontrolled comorbidities that, in the opinion of the treating investigator, would compromise subject safety or study outcomes. 6. Participant must not have a history of allergic reactions to Vitamin E or CoQ10 or any of the vitamin excipients (soybean oil, soy lecithin, gelatin, glycerin). 7. Not pregnant or lactating. A negative pregnancy test (serum hCG) is required for participants of childbearing potential. Female participants who are permanently sterilized (hysterectomy/bilateral oophorectomy) or postmenopausal (12 months of consecutive amenorrhea, \> 45 years-of-age in the absence of other biological or physiological causes; females \< 55 years-of-age with serum FSH level \> 40 mIU/mL) are exempt