Difference between the D&S H+(10) and D&S++ for dose calculations?

June 26th, 2017
by Joseph Magill

Qu. I have difficulties to understand the differences between D&S++ and D&S H*(10). I read the wiki, but still find myself wondering what causes the difference in calculation.
Ans. The main differences between D&S++ and D&S H*(10) are the following:
1. Short-lived daughters are included automatically in H*(10) version but not the ++ version.
2. Buildup calculations are now more accurate in H*(10) than in the ++.
Most importantly:
3. Internationally standardised H*(10) is calculated rather than the Htis in the ++ version. The difference between H*(10) and Htis is that Htis just calculates the dose absorbed in a thin layer near the surface. In the H*(10) the dose is calculated at a distance of 10 mm inside the surface and also takes account of backscattering from behind the point in question. i.e. H*(10) makes two additional calculations (1) the attenuation over a distance 10mm is calculated and (2) backscattering from deeper tissue to the surface. See image below.H10doserate

Qu.:It’s still confusing for me. What I am not understanding: what is the difference in the calculation, between what was done before, and what is done now. Is it just a coefficient which change in the formula? Which one? Or the whole principle which change? The definition of H*(10) and Htis is understood, but not the way it is computed, I think this is the main problem.
Ans.:It is not just a change in a coefficient. Its really a different principle.
To calculate H*(10), one first calculates the kerma rate at the surface Kair.  The kerma is similar to the exposure or the dose rate in air at the surface (approximately!).
Knowing the kerma rate at the surface one then calculates H*(10) inside the body using H*(10) = Kair * (H*(10)/Kair). The quantity in brackets in a function of energy and has to be calculated for every gamma energy by Monte Carlo. 
This function evaluated using Monte Carlo and is shown here..
This section gives a detailed description of how H*(10) is calculated in Nucleonica. Its all a bit mathematical but at the end of the day, it gives values which are about 10-20% higher than those calculated using D&S++ (i.e. Htis).

Qu. You state that H*(10) should give results 10-20% higher – can you expand?
Ans.: Consider Co-60: H*(10) = 0.3539 µSv/h using D&S H*(10) no shielding. Htis = 0.337 µSv/h using D&S++ no shielding. So for Co-60 the H*(10) values is about 5% higher than the Htis value. The reason why the H*(10) is higher than Htis is due to scattering of radiation from deeper inside the bode back to the surface. This is neglected in the calculation for Htis.

We have introduced this H*(10) on the request of some users. For official declarations, only the H*(10) is acceptable and not the Htis as calculated in D&S++.

More info…
Nucleonica Support

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