Question

Describe in brief the features of Intensity Modulated Radiation Therapy (IMRT). Include in your description:

Definitions of IMRT and inverse planning.

Tumour shapes for which IMRT shows an advantage over conformal radiotherapy.

Name the organs at risk spared in head and neck radiotherapy, also what is the nasty

side effect that is avoided?

Answer 1

Intensity-modulated radiation therapy (IMRT) is an advanced type of radiation therapy which is used to treat cancer and noncancerous tumors. In this therapy, advanced technology is used to manipulate photon and proton beams of radiation to conform to the shape of a tumor. This radiotherapy also uses computer-controlled linear accelerators to deliver precise radiation doses to a malignant tumor or specific areas within the tumor.

The inverse planning can be defined as a method of radiation treatment planning where one starts with the desired dose distribution, or clinical objectives, and then determines the treatment parameters that will achieve it.

Tumours are groups of abnormal cells that form lumps or growths.Non-cancerous tumours tend to have a regular and smooth shape and have a covering called a capsule whereas a malignant tumour is irregularly shaped, vascular, and it is invasive, crossing the basement membrane.  The shape of a cancer cell so important for predicting how the disease will behave. The radiation dose is designed to conform to the three-dimensional (3-D) shape of the tumor so that the cancerous cells or the tumor can be focussed by a higher radiation dose and the radiation dose can be minimized to healthy cells. In this way tumor shape is very important to protect the healthy cells from the exposure of the radiation that damages the healthy cells. Conformal radiation therapy is a cancer treatment that shapes the radiation beams to match the shape of the tumor. Intensity modulated radiotherapy (IMRT) uses multiple radiation beams of non-uniform intensities. The beams are modulated to the required intensity maps for delivering highly conformal doses of radiation to the treatment targets, while sparing the adjacent normal tissue structures.  It can potentially benefit the patient in. IMRT shows an advantage over conformal radiotherapy as it improve conformity with target dose. Not only this, it also reduces irradiation of normal tissue and in this way, it can minimise the degree of morbidity associated with treatment.

Name the organs at risk spared in head and neck radiotherapy: thyroid gland, mandible, brain stem, cerebellum, brain, salivary glands, spinal cord occipital bone and the neck at shallow depth under the skin, to spare the hair..

The nasty side effect that is avoided:

1. Nausea and vomiting.

2. Mouth, throat and stomach sores.

3. swelling of soft tissues.

4. Epilation (hair loss)

5. Dryness of the salivary glands and tear glands

6. Dry mouth (xerostomia) and dry eyes (xerophthalmia)