Intensity-Modulated Radiation Therapy (IMRT)

Additional Details

The Radiation Oncology Department at V.S.Hospital has been functional since March 2006. It is currently equipped with a Varian Medical Systems' High Energy Linear accelerator and Eclipse Treatment Planning system. Currently, VS Hospital uses three-dimensional conformal radiotherapy (3DCRT) to treat most of the Cancer patients.

Intensity-modulated radiation therapy is an advanced form of three-dimensional conformal radiotherapy (3DCRT). It uses sophisticated software and hardware to vary the shape and intensity of radiation delivered to different parts of the treatment area. 

It is one of the most precise forms of external beam radiation therapy currently available. Like conventional 3DCRT, IMRT links CT scans to treatment planning software that allows the cancerous area to be visualized in three dimensions. However, regular 3DCRT and IMRT differ in how the pattern and volume of radiation delivered to the tumor is determined. In conventional 3DCRT, clinicians input delivery patterns into the computer, which is called forward planning. In IMRT, the Oncologist designates specific doses of radiation (constraints) that the tumor and normal surrounding tissues should receive. The physics team then uses a sophisticated computer program to develop an individualized plan to meet these constraints. 

This process is termed "inverse treatment planning." Treatment with IMRT is slightly longer than that with 3DCRT, but generally produces fewer side effects and better results.. IMRT uses the same medical linear accelerators that deliver x-ray beams in conventional 3DCRT. As a unique feature, it also involves dynamic multi-leaf collimators (DMLCs), computer-controlled devices that use up to 120 movable "leaves" to conform the radiation beam to the shape of the tumor from any angle, while protecting normal adjacent tissue as much as possible. Also Step and Shoot IMRT is possible in which the radiation is delivered using multiple static MLC shaped beams. DMLCs allow the dose of radiation to vary within a single beam - in other words, to deliver higher radiation in some areas and lower radiation in others. 

Earlier technology could also shape radiation beams but could deliver them only at a single, constant dose. The ability to vary the radiation dose with DMLCs is accomplished by "sliding windows" of radiation beams across the target cancerous area. To more easily picture how DMLCs work, imagine a shower head with many nozzles, with the water representing radiation. Standard radiation techniques only allow a constant flow of water to be delivered through all nozzles. But with DMLCs, individual nozzles may be turned off and on, or set to deliver water at different intensities. 

In radiation therapy, the net effect is that radiation doses can be "wrapped" around tumors, or "painted" within tumors, far more precisely than was previously possible. Treatment process and side effects for IMRT are similar to those for 3DCRT. IMRT involves stringent QA process, both machine and patient related. Head & neck tumors especially Nasopharynx, sinus tumors, Prostatic tumors are the common indication for the IMRT. There are lots of trials which involve IMRT for other sites also.