Photobiomodulation in the Prevention and Management of Oral Mucositis in Children

Inclusion Criteria: Prevention Arm - Inclusion Criteria * Age 4 to 17 years * Histopathologic diagnosis of malignant neoplasm: leukemia, lymphoma, or solid tumor of the head and neck. * Within days 1-3 of the start of any chemotherapy cycle; for leukemia patients, in consolidation phase as defined by protocol. * No signs of oral mucositis at enrollment. * Availability and willingness to attend scheduled photobiomodulation (PBM) application sessions. * Parent/legal guardian signed informed consent and child assent when applicable (≥ 8 years). * No documented primary immunodeficiency. * No severe concomitant systemic infection or medical condition that, in the investigator's judgment, contraindicates participation. * No PBM treatment within 14 days prior to enrollment. * No history of adverse reactions to light therapies or known photosensitivity. * No history of seizure disorder or diagnosis of epilepsy. Treatment Arm - Inclusion Criteria * Age 4 to 17 years * Histopathologic diagnosis of malignant neoplasm: leukemia, lymphoma, or solid tumor of the head and neck. * Currently receiving chemotherapy (any cycle of the regimen). * Presence of oral mucositis of any grade during chemotherapy, identified within the first 3 days from onset of the mucositis episode. * Parent/legal guardian signed informed consent and child assent when applicable (≥ 8 years). * No documented primary immunodeficiency. * No severe concomitant systemic infection or medical condition that, in the investigator's judgment, contraindicates participation. * No photobiomodulation (PBM) treatment within 14 days prior to enrollment. * No history of adverse reactions to light therapies or known photosensitivity. * No history of seizure disorder or diagnosis of epilepsy. Exclusion Criteria: * Documented primary immunodeficiency. * Severe concomitant systemic infection or unstable medical condition. * PBM treatment within 14 days prior to enrollment. * Known photosensitivity or prior adverse reaction to light therapy. * History of seizures or epilepsy. * Any condition that, in the investigator's opinion, would interfere with study participation or safety. Participant Withdrawal Criteria * Attendance to fewer than 80% of scheduled treatment sessions. * Any adverse event or persistent discomfort attributed to PBM that leads the participant or guardian to decline further intervention. * Withdrawal of consent by parent/guardian or assent withdrawal by participant when applicable. * Development of a new medical condition that, per investigator judgment, contraindicates continuation.