Description of IROC Houston’s Measurement and Calculation Procedures

 

M/U	=	Meter reading, corrected to 22 degrees Celsius and 760 mm Hg, per monitor unit (or minute), uncorrected for timer error or monitor end effect.
Î	=	The monitor end effect, timer or shutter error.  See Refs. 1 and 4. It is usually applied to photon beams, but not to electron beams as the latter are commonly calibrated with the clinically-used number of monitor units.  The IROC Houston uses the symbol Î for this term so it is not confused with the symbol "a" in TG-21 Figs. 1 and 7. Refs.1 and 4 use "a".
NX	=	Exposure calibration factor in R per scale division (SD) or reading (rdg.) (includes electrometer correction factor).
NK	=	Air kerma calibration factor in Gy per scale division.  This term is also used as the brachytherapy dosimeter calibration factor.  See Section II E of this Appendix for values of NK/NX.
ND,W	=	Absorbed dose to water calibration factor in cGy per reading (rdg.) ( includes electrometer correction factors)
KQ	=	Quality conversion factors for photons
KR50,Kecal	=	Quality conversion factors for electrons
(L/ρ)waterair	=	Mean restricted collision mass stopping power ratio,  from TG-21, Fig. 2, using ionization ratio (TMR10 / TMR20), not NAP, as the independent variable.
Ppol	=	Polarity correction factor
Pion	=	Ion recombination correction factor, from TG-21, Fig. 4.
Prepl	=	Gradient correction factor for photon beams and fluence correction for electron beams, from TG-21, Fig. 5 or Table VIII.
PQgr	=	Gradient correction factors for electrons.
ddf	=	The depth-dose factor (fractional depth dose, tissue-air ratio, etc.) used to convert dose at the calibration depth to dose at the reference depth (usually dmax).
(µen/ρ)musclewater	=	Ratio of mean mass energy absorption coefficients, used with photons to convert from dose-to-water to dose-to-muscle.  The IROC Houston uses a value of 0.99 for all of the megavoltage beams it calibrates.  See Ref. 10 and Ref. 1, eq. 39.
(S/ρ)musclewater	=	Ratio of mean unrestricted collision mass stopping power coefficients, used with electron beams to convert dose-to-water to dose-to-muscle.  The IROC Houston uses a value of 0.99 for all the beams it calibrates.  See Ref. 11 or 12.