Experimentally determined three-dimensional dose distributions in small complex targets.
OBJECTIVE
The purpose of the paper is to describe a workable three-dimensional dosimetry system for use in quality assurance programs of departments in which radiosurgery is performed.


METHODS
A system was developed on the basis of radiochromatic films. The experimental findings of the measured dose distributions for small complex-shaped targets, within a specially designed phantom, are described and compared with the same parameters calculated from the corresponding dose plan. The following parameters were determined for 83 patients with irregularly shaped targets who underwent gamma knife radiosurgery (GKS): target volume; dose-volume histograms of the target; 12-Gy, 15-Gy, and 18-Gy volumes; dose plan conformity; dose fall profiles in all dimensions to 50% of the prescription dose; and a quality factor (QF) to evaluate the adequacy of a GKS plan or treatment. The precise function and accuracy of the developed measuring device is shown and it demonstrated the expected steep dose falloff outside the irregularly shaped targets in all directions. The dose falloff was of the order of > 3 Gy/mm and the values of the QF were in the range between 0.5 and 0.9.


CONCLUSIONS
A comparison with data from the literature shows that at least for small targets (< 2 cm3 and < 2.5 cm3) simulated within a head phantom, the dose gradient is significantly steeper in all directions than when using alternative treatment devices in radiosurgery and the overall QF is superior in most of the cases.
Mack
Andreas
A
Gamma Knife Centre, Frankfurt, Germany. a.mack@gkfrankfurt.de
Wolff
Robert
R
Weltz
Dirk
D
Mack
Gunther
G
Jess
Anja
A
Heck
Bernd
B
Czempiel
Heinz
H
Kreiner
Hans-Jürg
HJ
Wowra
Berndt
B
Böttcher
Heinz
H
Seiffert
Volker
V
D000236:Adenoma / Q000601:surgery; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000601:surgery; D008577:Meningeal Neoplasms / Q000601:surgery*; D008579:Meningioma / Q000601:surgery*; D009464:Neuroma, Acoustic / Q000601:surgery; D019047:Phantoms, Imaging; D010911:Pituitary Neoplasms / Q000601:surgery; D011829:Radiation Dosage; D016634:Radiosurgery / Q000379:methods*