Dosimetry of very-small (5-10 mm) and small (12.5-40 mm) diameter cones and dose verification for radiosurgery with 6-MV X-ray beams.
The dosimetry and dose verification for 6-MV X-rays were performed for radiosurgery cones of 5- to 40-mm diameter. The total scatter factors decrease slowly from 0.936 (40-mm cone) to 0.893 (10-mm cone; a variation of 5%), but they fall to 0.83 (7.5-mm cone) and 0.67 (5-mm cone). The dmax increases from about 12.9 (5-mm cone) to 16.3 mm (40-mm cone). The full width half maximum (FWHMs) of the beam profiles, measured at 5 cm depth, agree with the cone diameters within 1 mm. The 10-90% beam penumbra/FWHM ratio is 0.23 +/- 0.03 (> or = 20-mm cones); for the smaller-diameter cones this ratio increases reaching 0.84 (5-mm cone). New tissue maximum ratios (TMRs) are reported for the 5-, 7.5-, 32.5-, and 37.5-mm-diameter cones. TMRs for the other diameter cones are consistent with published data. The measured doses in two verification studies using the 12 cones with diameters > or = 12.5 mm with a single 360 degrees arc agreed to 2% with the planned doses, and to about 10% for the three smaller cones. In a simulated treatment neglecting tissue heterogeneties (skull bone), the measured doses for two five arc studies (22.5-mm cone) were within 4% of the calculated dose to isocenter.
Fan
C J
CJ
Department of Neurological Surgery, Stritch School of Medicine, Loyola University Chicago, Maywood, Ill 60153, USA.
Devanna
W G
WG
Leybovich
L B
LB
Kurup
R G
RG
Hopkins
B J
BJ
Melian
E
E
Anderson
D
D
Glasgow
G P
GP
D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008954:Models, Biological; D010315:Particle Accelerators; D017785:Photons; D016634:Radiosurgery; D012542:Scattering, Radiation; D012886:Skull / Q000528:radiation effects; D014965:X-Rays