IMRT is an advanced form of providing External Beam radiotherapy to target lesion with very little or minimal radiation to organ at risk. By this technique we can modify the intensity of beam to deliver precise dose to planned target volume. In head and neck area it is used (i) As radical radiotherapy for carcinoma nasopharynx, thyroid, Para nasal sinuses, larynx, hypopharynx (ii) In re-irradiation (iii) For parotid sparing to prevent xerostomia and in boost. Head and neck is regarded as highly attractive site for IMRT because these cancers are radio sensitive, immobilization of the patient is easy, most are squamous cell carcinoma an location of various organs at risk (e.g. Optic chiasm, brain stem, spinal cord, parotid gland) are easy to identify.

The technique for IMRT in head and neck cancers is

1.Patient Immobilization
2.Taking of multiple CT slices through the region of interest
3.Tumour plotting on each slice
4.Delineation of sensitive structures on each slice
5.3- D reconstruction of all structures
6.Fixing of dose restrictions for individual sensitive structures.
7.Prescription of tumor dose.
8.Evaluation of computer generated plan.
9.Treatment of the patient

The main components of planning are nodal outlining and primary tumor outlining. The nodal stations are defined as: Level l (a) Submental triangle: Level I (b) Submandibular triangle: Level II: Upper jugular Level III Mid jugular: level IV lower jugular: Level V Posterior Cervical triangle: Level VI Anterior Neck.

The main problem comes in altered anatomy as in postoperative neck, node positive neck and in deciding which nodal group are to be included in the target volume. There are no accepted guidelines for primary tumor outlining. All available information such as tumor size/stage, tumor natural history, anatomical descriptions, and surgeons experience is used for outlining. The primary tumor has gross target volume (GTV) +1-2 cm margin and PTV CTV +3 mm margin. The organs at risk in head and neck are spinal cord, parotid, brain stem, optic nerve, lens, retina, oesophagus, larynx and trachea.

Before IMRT is delivered rigorous Quality assurance is done by dosimetry and phantom check. Phantom check is done by Ion chamber dosimetry for Point dose and Film Dosimetry for fluence. There are various phase II trials which have shown a lower incidence of Xerostomia with IMRT. Various studies have shown that 50- 60% of salivary functions recover after 6 months with IMRT.

To conclude IMRT in head and neck cancer represents an excellent model. It allows treatment of concave tumours and in conformal avoidance of normal tissues. There are certain clinical trials in progress which will further defuse the benefit and toxicity of these new approaches. IMRT is an advanced mode of high precision external radiotherapy utilizing non uniform intensity patterns to deliver high doses of radiation to tumours while providing a sharp fall off of dose to normal and critical organs around the tumor.

The procedure of IMRT is a very complex one. It requires a gamut of sophisticated equipments for planning, verification and treatment delivery in addition to a team of dedicated, highly trained and skilled radiation oncologists, physicist, dosimeterists and technicians. Meticulous treatment planning and dose verification is required before treatment is delivered. It was concluded that for better cure rates, improved quality of life and no side effects IMRT should be the first choice of radiation therapy in selected cases. Till date, it is available only at few cancer centres in India, including Dharamshila Cancer Hospital And Research Centre, Delhi (India)

For more information on Cancer Plaese visit http://www.dhrc.in