Patients receiving radiotherapy for head and neck cancer often develop oral mucositis, a painful condition that causes redness and sores in the mouth. Oral mucositis can make it difficult to eat, drink, and speak, and may interfere with cancer treatment. Some viruses from the herpesvirus family, which commonly remain inactive in the body, may become active during cancer treatment and worsen mouth sores. However, the role of these viruses in oral mucositis is not fully understood.

This study aims to understand whether herpesviruses present in the mouth are associated with the development and severity of oral mucositis in adults receiving radiotherapy for head and neck cancer. The study also evaluates whether taking an antiviral medication (valacyclovir) can reduce viral activity and improve mouth symptoms during treatment.

Participants are randomly assigned to receive either valacyclovir or a placebo while undergoing radiotherapy. Samples from the mouth and saliva are collected at different time points before, during, and after radiotherapy to detect herpesviruses. Mouth sores are regularly examined, and pain levels are recorded throughout treatment.

The results of this study may help clarify the role of herpesviruses in oral mucositis and support better strategies to prevent or manage this condition in patients receiving radiotherapy for head and neck cancer.

Oral mucositis is a frequent and clinically significant side effect of radiotherapy for head and neck cancer. While mucosal injury is primarily related to radiation exposure, additional biological factors may influence the onset and severity of this condition. Reactivation of viruses from the Herpesviridae family has been suggested as a potential contributing factor, but existing evidence is limited and inconsistent. There is currently no standard preventive antiviral strategy for oral mucositis in this population.

This study is designed to characterize the presence and changes of herpesviruses in the oral cavity of adults undergoing radiotherapy for head and neck cancer and to evaluate whether prophylactic antiviral treatment affects viral detection and clinical outcomes related to oral mucositis. The trial uses a randomized, double-blind, placebo-controlled design to reduce bias and allow for an objective assessment of antiviral prophylaxis.

Participants receive either oral valacyclovir or matching placebo during the course of radiotherapy. Oral and saliva samples are collected at predefined time points before the start of radiotherapy, during treatment, and after completion of radiotherapy. These samples are analyzed to detect and quantify human herpesviruses using molecular methods. Clinical assessments of the oral cavity are performed regularly to evaluate the presence and severity of oral mucositis, and patient-reported pain is monitored throughout treatment.

The study aims to describe the pattern of herpesvirus detection in the oral cavity over time and to explore associations between viral presence, mucositis severity, and pain. In addition, the study evaluates whether antiviral prophylaxis influences these outcomes when compared with placebo.

By improving the understanding of the relationship between herpesvirus activity and oral mucositis, this study may inform future preventive or supportive care strategies for patients receiving radiotherapy for head and neck cancer.

Inclusion Criteria:

• Adults aged 18 years or older.
• Diagnosis of head and neck cancer.
• Planned to receive curative or definitive radiotherapy to the head and neck region.
• Ability to swallow oral medication.
• Adequate clinical condition to participate in study procedures.
• Ability to provide written informed consent.

Exclusion Criteria:

• Known hypersensitivity or contraindication to valacyclovir or related antiviral agents.
• Current or recent use of systemic antiviral therapy.
• Severe renal impairment requiring dose adjustment or contraindicating valacyclovir use.
• Active oral infection requiring systemic antimicrobial treatment at baseline.
• Pregnant or breastfeeding individuals.
• Participation in another interventional clinical trial that may interfere with study outcomes.

De-identified individual participant data underlying the results of this study will be made available upon reasonable request. Requests will be reviewed by the study investigators and subject to institutional approvals and data sharing agreements, in accordance with ethical and regulatory requirements.

De-identified individual participant data and the study protocol will be available beginning after publication of the primary study results and will remain available for up to 5 years following publication.

Access to de-identified individual participant data and the study protocol will be provided to qualified researchers upon reasonable request. Requests will be reviewed by the study investigators and subject to approval by the sponsoring institution, execution of a data use agreement, and compliance with ethical and regulatory requirements. Only data necessary to achieve the approved research objectives will be shared.

Participants, healthcare providers, investigators, and outcome assessors are blinded to treatment allocation. Valacyclovir and placebo are identical in appearance and administration, and treatment assignment is concealed until completion of data analysis or in the event of a medical emergency requiring unblinding.