Radiation Oncology/Head & Neck/Nasopharynx/Ho's Technique

• Patients immobilized in flexed head position in the initial phase (dose: 40 Gy / 20 fx)

• Three field arrangement:

(1) Opposed lateral fields: irradiate the upper cervical lymphatics (up to level III) en bloc

(2) Anterior field: irradiate the lower field

• Shielding of the lateral fields to adjust for the beam overlap with the anterior field

• Midline shield placed in the lower anterior field throughout the treatment

• Brainstem shielded with 5 HVL block (0.5 cm behind the upper edge of the clivus and 1 cm below the lower edge)

• Eye with 5 HVL shield placed 1.5 cm behind the lateral canthus

• Posterior tongue shielded with standard block

• Upper half of the pituitary Foss shielded

• Three field arrangement used in the boost phase (dose prescribed: 22.5 / 9 fx):

(1) Replanned in the extended head position with oral stent

(2) Anterior cervical-facial field used in all patients

(3) Lower border of the lateral fields reduced down to the level of angle of mandible

(4) Dose reduction allowed for TM joints, ears, parotids, and pinnae

• Posterior oblique boost given after the second phase in patients with parapharyngeal disease (dose prescribed: 20 Gy / 10 fx)

(1) Field usually 5.5 cm * 8 cm in size

(2) Ascending ramus of the mandible shielded in this phase