High-Dose Dosimetry Uncertainty Tables

The high-dose dosimetry program supports radiation-processing applications by assuring that the absorbed dose to the product, often prescribed or limited by regulatory agencies, is traceable to NIST standards. In addition, our most accurate measurements using small alanine-pellet dosimeters for these high-dose processes show promise to provide traceability to national measurement standards in clinical applications for the small-field radiation beams increasingly being used in radiation therapy.

High-dose dosimetry service descriptions can be found in Procedures 11 and 12 of the RBPD Quality System.

The tables below are the uncertainty budgets for the high-dose dosimetry services.  Alanine transfer dosimetry uncertainties are for pellet dosimeters only. While these uncertainty budgets support the majority of the high-dose dosimetry services other uncertainties have been characterized and may be reported for source-specific irradiation geometries.

Gammacell™ Calibration Geometry Dose Rate
Uncertainty Source	Type A (%)	Type B (%)
Water Calorimetry in Vertical Beam	0.16	0.51
Gammacell/Pool Source Ratio Data	0.10
Pool/B036 Source Ratio Data	0.17
Geometry Correction Factor	0.11
Field Uniformity		0.01
Source Timer (irrad time > 8min)		0.20
Co-60 Decay Correction		0.02
sqrt(sum)	0.28	0.55
combined in quadrature		0.60
t-factor for 19 d.f at 95.45%		2.14
Expanded Uncertainty at 95.45% conf.		1.3

High-Dose Alanine Response
Uncertainty Source	Type A (%)	Type B (%)
Repeatability and Reproducibility	0.30
Mass Determination	0.20
Interspecimen Contamination		0.10
Ruby Correction		0.05
System Drift		0.10
sqrt(sum)	0.36	0.15

Alanine Transfer - Photons >100 Gy
Uncertainty Source	Type A (%)	Type B (%)
Alanine Dose Rate	0.25	0.55
Alanine Response	0.36	0.15
Dose Rate Effect		0.10
Temperature Correction		0.10
Calibration Curve	0.50	0.10
sqrt(sum)	0.66	0.59
combined in quadrature		0.89
t-factor for 45 d.f at 95.45%		2.06
Expanded Uncertainty at 95.45% conf.		1.8

Alanine Transfer - Photons <=100 Gy
Uncertainty Source	Type A (%)	Type B (%)
Alanine Dose Rate	0.25	0.55
Alanine Response	0.36	0.15
Dose Rate Effect		0.10
Temperature Correction		0.10
Calibration Curve	0.50	0.10
Check Dose c.f.	0.44	0.10
sqrt(sum)	0.80	0.60
combined in quadrature		1.00
t-factor for 45 d.f at 95.45%		2.06
Expanded Uncertainty at 95.45% conf.		2.1

Alanine Transfer - Dose(Silicon)
Uncertainty Source	Type A (%)	Type B (%)
Alanine Dose Rate	0.25	0.55
Alanine Response	0.36	0.15
Dose Rate Effect		0.10
Temperature Correction		0.10
Calibration Curve	0.50	0.10
Uen Ratio Water to Silicon		1.80
sqrt(sum)	0.66	1.90
combined in quadrature		2.01
t-factor for 45 d.f at 95.45%		2.06
Expanded Uncertainty at 95.45% conf.		4.1

Alanine Transfer - E-Beam
Uncertainty Source	Type A (%)	Type B (%)
Alanine Dose Rate	0.25	0.55
Alanine Response	0.36	0.15
Dose Rate Effect		0.10
Temperature Correction		0.10
Calibration Curve	0.50	0.10
Electron Energy Dependence		0.10
sqrt(sum)	0.66	0.60
combined in quadrature		0.90
t-factor for 50 d.f at 95.45%		2.06
Expanded Uncertainty at 95.45% conf.		1.8

Alanine Transfer - CS-137
Uncertainty Source	Type A (%)	Type B (%)
Alanine Dose Rate	0.25	0.55
Alanine Response	0.36	0.15
Dose Rate Effect		0.10
Temperature Correction		0.10
Calibration Curve	0.50	0.10
Cs-Co Correction	1.00	0.10
sqrt(sum)	1.20	0.60
combined in quadrature		1.34
t-factor for 18 d.f at 95.45%		2.14
Expanded Uncertainty at 95.45% conf.		2.9

 

Revisions History	Date
Calibration Geometry Dose Rate changed: 1) GC207 to Gammacell; 2) GC/Pool Ratio from 0.08 to 0.10; 3) Added Geometry Correction Factor term of 0.11 to budget; 4) df/t-factor changed from 16/2.17 to 19/2.14. Changes allow budget to represent the largest uncertainty expected for the majority of geometries available.	Dec 13,2010