The incidence of radiation-induced skin injury is high, and effective preventive measures are currently lacking. This study evaluates the role of the skin protective agent Pinoxin in preventing skin injury. Patients are randomly assigned into two prospective groups: treatment group and control group. In treatment group, patients will receive Pinoxin treatment. In control group，patients will receive placebo treatment. The rate of grade 2 or greater skin injury will be analyzed.

This study is a prospective, randomized controlled, multicenter phase II study, with a design of superior efficacy，to compare the efficacy of Pinoxin and placebo in protecting radiation induced skin injury. We will consecutively enrolled patients who were diagnosed with cancer，and will receive radiotherapy at the dose of 50Gy or higher and radiation field is near skin. A total of 202 patients will be Randomized 1:1 to the treatment group and control group. In treatment group, patients will be sprayed Pinoxin，four times daily (morning, noon, evening, bedtime) from radiotherapy start until 2 weeks post-radiotherapy (continuous, including weekends) .In control group, patiants will received vitamin B12 as placebo. The dosing frequency is the same as that in the treatment group. Unblinding will be triggered if Grade 3 or higher reactions occur. If participants in the placebo control group develop Grade 3 or higher skin injury, they are permitted to use Pinoxin or opt for other appropriate symptomatic treatments.

Inclusion Criteria:

1. Age ≥ 18 years, regardless of gender.
2. Pathologically diagnosed with a malignant tumor.
3. Scheduled to receive long-course radiotherapy with a total dose of ≥50 Gy, in accordance with standard treatment guidelines.
4. No prior history of radiotherapy.
5. Has provided signed and dated informed consent, indicating that the patient has been informed of all relevant aspects of the study.
6. Patients who are willing and able to comply with scheduled visits, treatment plans, laboratory tests, and other study procedures.

Exclusion Criteria:

1. History of dermatologic conditions (e.g., vitiligo, psoriasis, etc.) or collagen vascular diseases.
2. Planned hypofractionated radiotherapy regimen.
3. Recent use (e.g., within 3 months) of similar topical protective agents.
4. Known hypersensitivity to any related components or materials.
5. Immunodeficiency disorders.
6. Women who are pregnant or lactating.
7. Any other condition that, in the investigator's judgment, may compromise patient safety or protocol compliance. This includes severe concomitant illnesses (including psychiatric disorders) requiring active treatment, significant laboratory abnormalities, or significant social/familial factors.