• Mucositis scale - World Health Organization (WHO) [ Time Frame: after delivering a dose of 2 J/cm2/d ] [ Designated as safety issue: Yes ]
  

• Mucositis period [ Time Frame: after delivering a dose of 8 J/cm2/d ] [ Designated as safety issue: Yes ]
  
• Mucositis free survival [ Time Frame: after delivering a dose of 8 J/cm2/d ] [ Designated as safety issue: Yes ]
  
• Pain intensity [ Time Frame: after delivering a dose of 8 J/cm2/d ] [ Designated as safety issue: Yes ]
  
• Morphinic administration [ Time Frame: after delivering a dose of 8 J/cm2/d ] [ Designated as safety issue: Yes ]
  
• Duration of hospitalisation [ Time Frame: after delivering a dose of 8 J/cm2/d ] [ Designated as safety issue: Yes ]
  
• Febrile neutropenia [ Time Frame: after delivering a dose of 8 J/cm2/d ] [ Designated as safety issue: Yes ]
  
• Duration of parenteral nutrition [ Time Frame: after delivering a dose of 8 J/cm2/d ] [ Designated as safety issue: Yes ]
  
• Psychological impact [ Time Frame: after delivering a dose of 8 J/cm2/d ] [ Designated as safety issue: Yes ]
  

Device: LLLT :low level laser therapy

The patients will be randomized in 2 groups according to the delivered dose: 2 J/cm2/d or 8 J/cm2/d.

Main evaluation criteria: mucositis maximal intensity (WHO scale).

Secondary evaluation criteria: mucositis duration, mucositis survival free, pain, opioid treatment, hospitalization, fever and infection, nutrition.

Mucositis is one of the main complications of cytotoxic chemotherapy and total body irradiation in children cancers. Local and systemic treatments are not efficiency or limited by side effects, (particularly for opioid). Two randomized recent studies in adult have showed the efficiency of LPLT (wavelength 650nm at the intensity of 4J/cm²) in prevention of severe mucositis. In pediatrics patient, only one randomized study was performed to the same intensity of 4J/cm² but with a wavelength of 732nm, and did not show the evidence of profit. In theory, tissues absorption level of laser is similar at 650 and 900nm but lower around 700nm. Procedure was very well tolerated by children; the main limiting factor is the deadline directly proportional to intensity delivered.

The aim of our study is to compare two preventives energies (2J/cm² or 8 J/cm²) daily delivered of LPLT to oral mucosa in decreasing the severity of mucositis in children. Placebo study was not possible to our opinion and we preferred to compare two intensity of LPLT for three reasons : being given the sensation of heat generated by the treatment, a true placebo is difficult to obtain; considering the difficulties proceeding to large-sized clinical trials in this population, it seems to us necessary to end quickly in an optimal protocol; the main inconvenience of LPLT is the duration of the sessions, so in case of negative result, our study will generate data allowing not to realize useless too long sessions.

It's a prospective controlled study, randomized in double blind phase II, in one center. All the patients will receive LPLT (GaAlAs, wavelength 980nm) daily of the 1st in the 5th day of cytotoxic treatment. The patients will be randomized in 2 groups according to the delivered dose: 2 J/cm2/d or 8 J/cm2/d.

Main evaluation criteria: mucositis maximal intensity (WHO scale) Secondary evaluation criteria: mucositis duration, mucositis survival free, pain, opioid treatment, hospitalization, fever and infection, nutrition.

Expected clinical effects: improvement of the children's comfort; dissemination of the technique in the other oncology pediatric centers