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Depth dose characteristics of 24‐MV x‐ray beams at extended SSD
Author(s) -
Jani Shirish K.,
Pennington Edward C.
Publication year - 1991
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.596673
Subject(s) - collimator , percentage depth dose curve , field size , dosimetry , linear particle accelerator , nuclear medicine , optics , diode , beam (structure) , ionization chamber , x ray , detector , materials science , physics , ionization , medicine , optoelectronics , ion , quantum mechanics
Depth dose characteristics of 24‐MV beams from a medical linear accelerator at various SSDs have been measured. The dose buildup, percent depth dose (PDD), and output were measured using ionization chambers and a diode detector under full scatter. Surface dose ranged from 8% to 51% depending upon the collimator setting at 100‐cm SSD. It decreased by 10%–15% as distance was increased to 200 cm, but remained unchanged beyond this distance. The d max migrated rapidly toward the surface with increasing field size at 100‐cm SSD. At extended SSD, the d max occurred at greater depths and shifted a little toward the shallow depths with increasing field size. Large field PDDs measured at extended SSD agreed well with those predicted from 100‐cm data. The output followed the 1/(distance) 2 relationship quite well. The extended SSD beam data are clinically useful when treating hemibody or performing total body irradiation (TBI) procedures.