T3: Tumour causes fixation of the vocal cords, with or without invasion of neighbouring areas. T4:

T4A – Tumour invades at least one of the following: the outer cortex of the thyroid cartilage, extra-laryngeal tissue
T4B – Tumour invades at least one of the following: the pre-vertebral space, any structures of the mediastinum, the carotid sheath, or the structures within the carotid sheath. Glottis
T1: Tumour only involves the vocal cords. Vocal cords have normal mobility.
WHO recommended schedule, which is universally recommended is as follows:

Infants 6–12 months old and any older children weighing less than 8 kg – 100,000 IU orally every 3–6 months
Children over 1 year and under 6 years of age – 200,000 IU orally every 6 months
Infants less than 6 months old, who are not being breastfed – 50,000 IU orally should be given before they attain the age of 6 months

Treatment
Treatment can occur in two ways: treating symptoms and treating the deficiency. Treatment of symptoms usually includes the use of artificial tears in the form of eye drops, increasing the humidity of the environment with humidifiers, and wearing wraparound glasses when outdoors. Treatment of the deficiency can be accomplished with a Vitamin A or multivitamin supplement or by eating foods rich in Vitamin A. Treatment with supplements and/or diet can be successful until the disease progresses as far as corneal ulceration, at which point only an extreme surgery can offer a chance of returning sight. Epidemiology
Throughout southeast Asia, estimates are that more than half of children under the age of six years have subclinical vitamin A deficiency and night blindness, with progression to  xerophthalmia being the leading cause of preventable childhood blindness. Estimates are that each year there are 350,000 cases of childhood blindness due to vitamin A deficiency. The causes are vitamin A deficiency during pregnancy, followed by low transfer of vitamin A during lactation and infant/child diets low in vitamin A or beta-carotene.