By Raphael obu

1Intensity modulated radiation therapy (IMRT) is a new technology in radiation oncology that delivers radiation more precisely to the tumor while relatively sparing the surrounding normal tissues. ?The most unique thing about IMRT is that it uses advanced technology to manipulate beams of radiation to conform to the shape of a tumor.The goal of IMRT is to bend the radiation dose to avoid or reduce exposure of healthy tissue and limit the side effects of treatment.This advanced type of radiotherapy uses a computer-controlled device, called a linear accelerator, to deliver precise doses of radiation to tumors or specific areas within the tumors.

It also introduces new concepts of inverse planning and computer-controlled radiation deposition and normal tissue avoidance in contrast to the conventional trial-and-error approach. IMRT has wide application in most aspects of radiation oncology because of its ability to create multiple targets and multiple avoidance structures, to treat different targets simultaneously to different doses as well as to weight targets and avoidance structures according to their importance. By delivering radiation with greater precision, IMRT has been shown to minimize acute treatment-related morbidity, making dose escalation feasible which may ultimately improve local tumor control. IMRT has also introduced a new accelerated fractionation scheme known as SMART (simultaneous modulated accelerated radiation therapy) boost. By shortening the overall treatment time, SMART boost has the potential of improving tumor control in addition to offering patient convenience and cost savings.

Intensity-modulated radiation therapy (IMRT) 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 available.


How does IMRT work?

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. In IMRT, the physician 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 the constraints. This process is termed “inverse treatment planning.” Treatment with IMRT is slightly longer than with 3DCRT, but generally produces fewer side effects.

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.

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 appears a good option for Ghanaian men diagnosed with localized Prostate Cancer since it has minimal side effects.? The Advantage to Patients is: ?Higher and more effective radiation doses can safely be delivered to tumors with fewer side effects and also reduced treatment toxicity but however the disadvantages will be the cost of treatment and its availability in Ghana.


Raphael Obu

Msc Prostate Cancer

Sheffield HallamUniversity,UK




Intensity Modulated Radiation Therapy (IMRT)

Teh BS1, Woo SY, Butler EB(1999). Intensity modulated radiation therapy (IMRT)a new promising technology in radiation oncology.Oncologist .4(6):433-42.


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