The study will be a randomized double blind prospective placebo controlled clinical study and aims to determine the therapeutic efficacy of Probiotics in Oral Mucositis pathogenesis in patients undergoing head and neck radiotherapy.

The study will be a randomized double blind prospective placebo controlled clinical study (Clinical Trial phase II) of 50 patients (25 in LR group, 25 in placebo group) with a confirmed cancer diagnosis requiring head and neck radiotherapy with a minimum dose of 6000cGy.

Patients will be randomly assigned to either of the treatment arms in a 1:1 ratio. The active agent; Lactobacillus reuteri Prodentis (Biogaia ®) will be supplied in droplet form by Pharma forte Singapore Pte Ltd and dosage used will be as recommended by manufacturer (5 drops/time twice a day which is equivalent to 4 X 108 CFU of live bacteria). The control agent will be identical in physical appearance and color to the study agent and will be made by the manufacturer.

Patients assigned to either LR group or placebo group will start from the first day of radiotherapy and continued until 2-week post radiation (approximately 8-9 weeks). Patients will be instructed to use the LR droplets twice a day according to manufacturer's instructions; once in the morning after breakfast and the other just before bedtime and to avoid any food/drinks 30 minutes before and after usage. Compliance with treatment will be elicited and recorded.

The dose selection is based on manufacturer's recommendations and is safe for use during pregnancy and breastfeeding. However, this is not an issue in this population as none of the patients should be pregnant or breastfeeding while receiving radiation and anti-neoplastic chemotherapy.

The PI will serve as the auditor for data quality assurance on a quarterly basis.Data collected on paper will be stored in the principal investigator's locked cabinet. Data will be entered into Microsoft Excel™ (2007) and double entered for accuracy. Data will be kept in a password secured portable computer and backed up to dedicated local back-up drive every week. Only group statistics will be reported. The database will only be accessible to investigators involved in and approved for the study. All data will be kept for 6 years after study completion to access data for publication of the work done, after which data will be destroyed.

Inclusion Criteria:

1. patients who are 21 years of age or older
2. histological diagnosis of head and neck carcinoma available
3. undergoing head and neck radiotherapy of at least 6000cGY
4. Eastern Cooperative Oncology Group (ECOG) performance status 0 to 2
5. no known allergy to Biogaia
6. able to give written informed consent, or have written consent given on their behalf.

Exclusion Criteria:

1. patients who cannot use the products or have it administered to them
2. patients with existing conditions predisposing to oral ulcer formation
3. patients with mucositis at baseline (prior to initiation of treatment)
4. previous radiotherapy to the head and neck region
5. female patients who are pregnant or breastfeeding
6. patients who have central venous catheters
7. patients who have impaired intestinal epithelial barrier
8. patients who have cardiac valvular disease
9. unable to give written informed consent, or are unable to have written consent given on their behalf.
10. inability to converse in English or Mandarin
11. severe immunosuppression (Absolute Neutrophil Count of less than 1500 cells/µL)