Technology: 3D & IMRT Treatment Planning

At FLROC most patients are treated using radiation beams from several different directions, which makes it possible to deliver high doses of radiation to the cancer while avoiding excessive radiation to normal structures. To plan these complex treatments, CT images are transmitted to our planning computer. The radiation oncologist then outlines the structures which need to be treated or protected on the computer screen.

We use the Prowess 3D planning system (www.prowess.com) for most of our patients. 3D planning is a major improvement over older methods because:

1. the target volumes and normal structures are identified on CT slices 5mm (about ¼ inch) apart, allowing for greater precision
2. the dose calculations for any point in the patient’s body reflect the radiation given to every other point being treated
3. 3D software corrects for differences between radiation absorption in structures such as bone, muscle, and lung tissue
4. 3D planning allows the use of beams which come in directions other than front/back and side to side, such as beams coming at an angle from the head to the foot
5. 3D images make it easier for the radiation oncologist, physicist, and dosimetrist to decide whether a plan is satisfactory
6. tables and graphs accurately describe the radiation doses to both the tumor and normal structures.

3D planning does share some of the limitations of older planning systems. The dosimetrist develops a plan using a limited number of radiation beams and makes adjustments as necessary to achieve the desired dose distribution. We might be able to develop a better plan if it was possible to evaluate a hundred beam arrangements rather than four or six or a dozen. It might be better if we could use a hundred beams rather than 4 or 6 or 8.

The Intensity Modulated Radiation Therapy (IMRT) system we installed in October 2000 achieves these goals. The system comprises the Corvus planning software and Multileaf Intensity Modulating Collimator (MIMiC) by the Nomos Corporation (www.nomos.com). The MIMiC is a computer controlled device which turns portions of the treatment beam on and off thousands of times during each treatment as the machine rotates around the patient. The Corvus software uses what is called inverse planning. In this approach the radiation oncologist prescribes the dose desired to the tumor and normal structures and the computer sifts through many combinations of beam sizes, directions, and intensity to develop a plan which matches the prescription as closely as possible.

IMRT makes it possible to deliver a high dose of radiation to the tumor while sparing normal tissues. FLROC was the first in the area to install this technology. Currently we are the first center in the country to install nomosSTAT Encore serial tomotherapy system (see the news and events section for a full write up of this advancement).

"I can’t believe how quickly the time has gone… I am so thankful for the many wonderful people here at the center and the great work they all do."