Chemotherapy-induced oropharyngeal mucositis (OM) negatively impacts the quality of life of adult and pediatric patients by causing pain, dysphagia, dysgeusia and dysphonia.

Photobiomodulation (PBM) by low level laser therapy (LLLT), light therapy of low level of red and infrared wavelengths (630-1000 nm) has been recommended since 2014 in patients treated with high-dose chemotherapy for bone marrow transplantation. Available pediatric studies highlighted positive/promising results of PBM with excellent safety and no adverse effects. Nevertheless, a wide variety of application parameters is described in the literature, with no consensus guidelines.

Considering the lack of standardized protocol of photobiomodulation in the pediatric population as well as the burden and cost of a daily application, investigators have decided to conduct, for the first time in children of 3 years of age or older, a multicenter, randomized, double-blind, non-inferiority clinical trial to compare two PBM protocols with same PBM parameters, combining red and infrared wavelengths, but with different frequencies of laser application (daily versus every other day), in the treatment of chemotherapy-induced OM of WHO grade 2 or higher.

Inclusion Criteria:

1. Male or female children aged ≥ 3 years and < 18 years.
2. Hospitalization in an oncology or hematology department in the participating centres.
3. Patients with oropharyngeal mucositis of grade 2 or higher (WHO grading system) related to cancer chemotherapy, including conditioning for Hematopoietic Stem Cell Transplantation (HSCT).
4. Written informed consent of both patient's holders of parental authority, and patient's assent when applicable.
5. Patients affiliated to a French Social Security insurance or equivalent social protection.
6. Absence of any physical or psychological disability that may interfere with the LLLT application.

Exclusion Criteria:

1. Patients with a solid cancer lesion in the area of low-level laser application.
2. History of cervicofacial radiotherapy.
3. Application of low-level laser therapy for oral mucositis within 2 weeks prior to randomization.
4. Hyperthyroidism defined by TSH < 0.4 IU/mL at inclusion.
5. Patients susceptible to epilepsy seizure.
6. Patients with pacemaker.
7. Patients refusing to wear retinal goggles during low-level laser 1. Patients with a solid cancer lesion in the area of low-level laser application.
8. Patients protected by law (guardianship and safeguarding of justice).
9. Pregnant female patients as determined by positive serum pregnancy test at screening.
10. Lactating female patients who are actively breast feeding.
11. Participation in another clinical trial involving oral care.