An adjustable collimator for stereotactic radiosurgery.
Stereotactic radiosurgery utilizing a linear accelerator is now carried out using small non-coplanar beams to produce a high-dose volume that is approximately spherical in shape. It is desirable to shape the high-dose region so that it is similar to the target volume thereby reducing the amount of healthy tissue irradiated by a high dose. An adjustable collimator has been developed that can be employed to control the target volume height and diameter. Based on film dosimetry and measurements made with a small parallel-plate ionization chamber it was determined that the beams produced by the collimator have properties that make them suitable for radiosurgery. The basic dosimetry parameters (output factors and tissue maximum ratios, TMR) needed for patient treatment were evaluated. It was found that the diameter and length of the high-dose region produced by the patient rotation method are related to the light-field size at 100 cm from the x-ray target. A more favourable dose distribution was found for the adjustable collimator as compared to treating the same volume by use of the two-target method.
McGinley
P H
PH
Emory Clinic, Division of Radiation Oncology, Atlanta, GA 30322.
Butker
E K
EK
Crocker
I R
IR
Aiken
R
R
D006801:Humans; D010315:Particle Accelerators; D016634:Radiosurgery / Q000295:instrumentation*; D011879:Radiotherapy Dosage