Scoring quantities

Several quantities can be scored inside the defined regions, e.g. dose, LETd. Present implementation of scores in Fred is restricted to voxel-based scorers defined on the same grid of the referenced region. For instance, when scoring the dose on the phantom region, Fred accumulates the energy deposited in each voxel of the phantom during particle tracking. At the end of the run, the deposited energy is divided by the mass of the voxel and the dose map is saved to disk in mhd format.

Scorers are actived within the definition of each region, as reported here.

An example of requiring dose and LETd scoring on a CTscan phantom is here below:

region: phantom ; CTscan = MrHead ; score = [dose,LETd]

Scorers

Edep

total energy deposited in a voxel

$E_{dep} = \sum_{events} \Delta E$

for each energy deposition event the voxel scorer is incremented by the $\Delta E$ energy released in the voxel. This energy is typically due to the collisional stopping power $\frac{dE}{dx}$ of the particle in the medium. It also can have contributions from heavy fragments produced in nuclear interactions which, due to very short range, are deposited locally at the production site.

Scoring units = MeV

dose

total energy deposited in a voxel divided by the mass of the voxel

$\mathrm{Dose} = D = \frac{E_{dep}}{m} = \frac{E_{dep}}{\rho\;V}$

This is equivalent to dose-to-medium in dosimetry jargon.

Scoring units = Gy

dose-to-water

equivalent dose to water obtained from stopping power conversion

$D_{w} = D \cdot \frac{\rho}{\rho_w} \cdot \frac{\left(\frac{dE}{dx}\right)_w}{\frac{dE}{dx}} = D \cdot \frac{\left(\frac{dE}{ds}\right)_w}{\frac{dE}{ds}} = D / RMSP$

where the dose-to-medium $D$ is converted into dose-to-water $D_{w}$ using the density ratio and the stopping power ratio. It is equivalent to divide the dose $D$ by the relative mass stopping power RMSP.

Scoring units = Gy

LETd

dose-averaged LET according to Eq. 14 in Polster et al, PMB 2015

$\mathrm{LET}_d = \frac{\sum_{events} \frac{dE}{dx} \frac{1}{\rho}\;\Delta E} {\sum_{events} \Delta E} = \frac{\sum_{events} \frac{dE}{ds} \;\Delta E} {\sum_{events} \Delta E}$

Scoring units = $\mathrm{\frac{MeV\,cm^2}{g}}$