Heterogeneity Corrections

What TG covers heterogeneity corrections

TG-65

ICF = Inhomogeneity Correction Factor general formula definition

Dose in medium/Dose in homogenous medium

Effective attenuation coefficient method

ICF = exp(mu(d-d’))

where d’ is the equivalent depth weighted by relative electron densities

Ratio of Tissue-Air Ratios (RTAR) method

ICF = TAR(d’,W)/TAR(d,W)

where W is the field size

Power Law (Batho)

1. 

   .

2. Rho1 = the relative electron density of the medium in which the point of calculation lies.

3.  Rho2 = the relative electron density of the overlying material.

4.  d1 = the depth within this medium.

5. d2  = the distance to the upper surface of the overlying inhomogeneity slab.

6. Note that the TAR ratios can be replaced by TMR or TPR.

convolution superposition method

1. This method consists of two parts: a TERMA part which describes the distribution of the energy that is released at a primary interaction site and is available for consumption in the medium and a kernel part that describes the distribution of the scatter from a primary interaction (that is, the kernel dictates how the TERMA is going to be distributed in the medium).

issue with switching heterogeneity correction methods

physician’s clinical results and prescribing history have been based on a non-corrected calculation.  The physician does not have an accurate knowledge of how much dose he was actually giving.  If he prescribes the same doses he has always given under the new algorithm, there is the potential for large changes in dose to the patient which may affect clinical outcome.