## 2 Materials and Methods
### Assessment of OM  
For the PG, the oral examination and OM evaluation were performed for all patients before the start of each session by the same oral medicine clinical personnel. A custom-made clinical chart was used to register all patients' findings including OM grade, pain score, and the site of the OM. The OM evaluation was performed five times a week (Monday to Friday) from one day before the conditioning regimen until the 10 th day after transplantation (D+10) or continued until the complete resolution of OM.  
The evaluation of the OM grade was performed using the World Health Organization (WHO) grading scale. Grade 0 was considered in case of the absence of signs and symptoms; grade I, in case of the presence of localized or diffused erythema; grade II, in case of the presence of ulcers that did not hinder eating solid food; grade III, in case of the presence of ulcers that hindered eating solid food but the patient was able to swallow liquids; and grade IV, in case where the ulcers impair eating or swallowing liquids [31]. The assessment of pain was performed using the Numeric Rating Scale (NRS).  
For the retrospective CG, OM evaluation was provided as part of routine patient care at the Haematology Department, using the WHO grading scale on a daily base. The OM site and grade were collected from the Department database and registered using the same schedule as the PG (i.e., 5 days a week starting from one day before the start of the conditioning regimen until the complete OM resolution).  
The total duration of OM and the duration of each grade were calculated for both groups. The maximum OM score was recorded. To evaluate the impact of PBM on the severity of OM, patients with maximum OM grade \(\leq\)I were grouped and called \"non-ulcerative OM\", and patients with maximum OM grade \(\geq\)II were grouped and called \"ulcerative OM\".  
To evaluate the impact of PBM on the incidence of OM, patients were grouped into two groups with the first group, called \"no OM\", including patients with grade 0 as a maximum score of OM and the second group, called \"with OM\", including patients with \(\geq\)grade I OM.  
To evaluate the impact of PBM on the OM pattern and course, OM grades were registered for all the patients at six evaluation time points (Monday to Friday). The evaluation time points (E) were fixed to better compare analyzed patients: E0 was the day of transplantation (D0); E1 was the OM value  
\begin{table}
\begin{tabular}{l l} \hline Manufacturer & FISIOLINE \\ \hline Model identifier & Lumix2® (Double diode laser) \\ \hline Number and type of emitters & Two wavelengths, visible GaAs and infrared GaAs \\ \hline Wavelength and bandwidth & 650 nm, and 904–910 nm \\ \hline Pulse mode & For visible 650 nm: continuous mode and for \\  & 904–910 nm: 13 kHz \\ \hline Beam spot size at target & \(\sim\)0.5 cm\({}^{2}\) \\ \hline Exposure duration & 45 s per point \\ \hline Number of points irradiated & 10 points intraorally including buccal mucosa, tip, \\  & ventral and marginal surface of the tongue, floor of \\  & the mouth, soft palate, and inner surfaces of the lip. \\ \hline Area irradiated & \(\sim\)5 cm\({}^{2}\) \\ \hline Application technique & Point by point in a defocused mode \\ \hline Total irradiation energy per session & 40 J \\ \hline Number and frequency of treatment sessions & 5 sessions per week (Monday to Friday) starting one \\  & day before the conditioning regimen and continued \\  & till the 10 th day after transplantation (D+10) \\ \hline \end{tabular}
\end{table}
Table 2: Irradiation and photo-biomodulation parameters.  
during D+1 to D+3, E2 was the OM value during D+4 to D+6, E3 was the OM value during D+7 to D+9, E4 was the OM value during D+10 to D+12, and E5 was the OM value during D+13 to D+15 [1].