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Computer‐controlled direct TMR measurement
Author(s) -
Reinstein Lawrence E.,
McShan Daniel L.
Publication year - 1982
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 - 10.1118/1.595204
Subject(s) - isocenter , ionization chamber , imaging phantom , linear particle accelerator , dosimetry , monitor unit , percentage depth dose curve , optics , ionization , computer science , physics , medical physics , nuclear medicine , beam (structure) , medicine , ion , quantum mechanics
It is common practice to derive tissue maximum ratios (TMRs) indirectly by calculation from percent depth doses (PDD) data which are more convenient to measure using currently available automated scanners. A system has been developed, however, for the completely automatic direct measurement of TMR, using an ionization chamber which is rigidly supported at the isocenter of a teletherapy machine. The chamber is immersed in a water phantom which is moved up and down by computer control of the motorized treatment couch. Ionization current is sampled by the computer which simultaneously regulates both the radiation field size and chamber depth. This system provides a means of rapidly measuring and processing complete sets of TMR and output factor values for both square and elongated field shapes. The results of such measurements performed on the Clinac 18 accelerator are described in this paper.