Verif dose-msmt-2-signed
•
0 likes•44 views
compare TPS vs measured dose using 2 calculation methods fore measured dose. Demonstrate validity of both.
![3/23/2016
Absolute Dose Analysis: E2E First Step - Verification of dose; comp msmt vs calc
Phantom: Standard Imaging Stereotactic Dose phantom with insert for Exradin A16 microchamber
Geometry: 100 SAD, 95 SSD, 10x10 FS, d=5 , Max4000 electrometer
Dose plan: deliver 200 cGy to active volume of A16, actual TPS mean dose = 200.1 cGy [ADAC]
Note: msmt bias was -300V
Reported data assumes accurate contouring of active volume, biggest error source;
careful expert review of contour is required, and may need adjustment more than once.
Msmt calc method 1 Msmt calc method 2
from ADCL & pub values from Manuf spec's, density calc & const's
Temp 23.7 C
Pressure 761.4 mmHg Chg-raw 4.950E-10 C
Ct,p 0.9961 Ct,p 0.9961
Chg-corr 0.4931 nC Chg-corr 4.931E-10 C
Nd,w 4.0650 Gy/nC Vol 0.0069 cc
EF 1.0000 dens[air] 0.001196 g/cc
kQ 0.9970 mass[air] 8.2524E-06 g
Pion 1.0000 mass[kg] 8.252E-09 kg
Ppol 1.0088 Exp 0.05975 C/kg
W/e 33.70 J/C
Dose-msd 2.0080 Gy Dose-msd 2.0135 Gy
Dose-TPS 2.0010 Gy Dose-TPS 2.001 Gy
% diff -0.3505 % diff -0.6222
Cal factor notes:
Nd,w (ADCL) Nd,w-eff (1st principles)
4.065 Gy/nC 4.084 Gy/nC
0.470 % diff between methods for Nd,w
The above difference of ~ 0.5% shows the validity
of the non TG-51 calculation for results within 0.5%
Conclusion - both methods of determining measured dose are valid,
although TG-51 style calc is 0.27% closer to TPS value in this test
This is well within the expected margin of error due to contouring, msmt & extrapolation.
So this 'first principles' method relies on accurate knowledge of location & size of Act Vol.
Most manuf's have measured the active volume accurately, but you must call & speak
with their expert - DO NOT use values from brochures! Contouring this vol can be
challenging, but companies will often provide tech drawings helping define the Act Vol
Note: it's vital to get the correct air density, less vital is to use W/e for 20-80% humidity.
Mark Colgan, MS, DABR](https://image.slidesharecdn.com/verif-dose-msmt-2-signed-160728003853/85/Verif-dose-msmt-2-signed-1-320.jpg)
Recommended
Recommended
More Related Content
Similar to Verif dose-msmt-2-signed
Similar to Verif dose-msmt-2-signed (20)
Recently uploaded
Recently uploaded (20)
Verif dose-msmt-2-signed
- 1. 3/23/2016 Absolute Dose Analysis: E2E First Step - Verification of dose; comp msmt vs calc Phantom: Standard Imaging Stereotactic Dose phantom with insert for Exradin A16 microchamber Geometry: 100 SAD, 95 SSD, 10x10 FS, d=5 , Max4000 electrometer Dose plan: deliver 200 cGy to active volume of A16, actual TPS mean dose = 200.1 cGy [ADAC] Note: msmt bias was -300V Reported data assumes accurate contouring of active volume, biggest error source; careful expert review of contour is required, and may need adjustment more than once. Msmt calc method 1 Msmt calc method 2 from ADCL & pub values from Manuf spec's, density calc & const's Temp 23.7 C Pressure 761.4 mmHg Chg-raw 4.950E-10 C Ct,p 0.9961 Ct,p 0.9961 Chg-corr 0.4931 nC Chg-corr 4.931E-10 C Nd,w 4.0650 Gy/nC Vol 0.0069 cc EF 1.0000 dens[air] 0.001196 g/cc kQ 0.9970 mass[air] 8.2524E-06 g Pion 1.0000 mass[kg] 8.252E-09 kg Ppol 1.0088 Exp 0.05975 C/kg W/e 33.70 J/C Dose-msd 2.0080 Gy Dose-msd 2.0135 Gy Dose-TPS 2.0010 Gy Dose-TPS 2.001 Gy % diff -0.3505 % diff -0.6222 Cal factor notes: Nd,w (ADCL) Nd,w-eff (1st principles) 4.065 Gy/nC 4.084 Gy/nC 0.470 % diff between methods for Nd,w The above difference of ~ 0.5% shows the validity of the non TG-51 calculation for results within 0.5% Conclusion - both methods of determining measured dose are valid, although TG-51 style calc is 0.27% closer to TPS value in this test This is well within the expected margin of error due to contouring, msmt & extrapolation. So this 'first principles' method relies on accurate knowledge of location & size of Act Vol. Most manuf's have measured the active volume accurately, but you must call & speak with their expert - DO NOT use values from brochures! Contouring this vol can be challenging, but companies will often provide tech drawings helping define the Act Vol Note: it's vital to get the correct air density, less vital is to use W/e for 20-80% humidity. Mark Colgan, MS, DABR