basedata carbon Generic in detail

[Yuri-HubL]

Dear matRad administrators,

I am not sure about the entry of matRad basedata carbon_Generic data.

I'll list all the specific items and ask what they mean in detail (I'll use a question mark if I don't understand, hoping for an answer) :

• range: The range of the carbon ion beam of a specific energy
• energy: The energy of the monoenergetic carbon ion beam
• Depth: 135 points are taken at different depths in the beam direction
• z: (?) I don't understand the meaning of this data
• peakPos: The depth of the Bragg score
• sigma: (not sure) I think this is a record of the non-uniformity value of the beam at different depths in the beam direction
• alpha: (not sure) I see 135×2 data, which may correspond to the alpha values of tumor cells and normal tissues at different depths at different beam energies
• beta: (not sure) There are also 135×2 data, which may correspond to the beta values of tumor cells and normal tissues at different depths under different beam energies.
• offset: (?) I don't understand the meaning of this data
• initFocus: (?) I don't understand the meaning of this data
• alphaX: alpha values for normal cells and tumors under reference X-ray conditions
• betaX: beta values of normal cells and tumors under reference X-ray conditions
• alphaBetaRatio: is the ratio of alpha to beta of normal nuclear tumor cells under reference X-ray conditions
• LET: LET values at 135 different depths of the monoenergetic carbon ion beam

Looking forward to your reply.

your sincerely,
Yuri

[wahln]

Please check out our Wiki:
https://github.com/e0404/matRad/wiki/Dose-influence-matrix-calculation#particles
https://github.com/e0404/matRad/wiki/Particle-Base-Data-File
Also read the provided reference there on the pencil-beam dose calculation algorithm, Should clear up most of the stuff.

[saxu3829]

Thank you for your reply! I have another question regarding the base data that is unfortunately not covered by the wiki. Which unit is used for the LET in the base data?

[wahln]

The LET should be keV/micrometer. How you score it for the database is your choice (so you can store either track-averaged or dose-averaged, restricted or unrestricted), but beware that matRad will then use it to compute a dose-weighted LET distribution (more exactly, matRad will multiply LET * dose for each spot for each voxel, then accumulate LET * dose over all spots per voxel, and finally divide by the total dose in each voxel).

[saxu3829]

Thank you for your quick reply! I looked into the following paper to extract the Monte Carlo simulation settings for the creation of base data for a clinical particle therapy facility: K Parodi et al 2012 Phys. Med. Biol. 57 3759. It was cited by the matRad paper on the base data for protons and carbons as well.
If I understood the paper correctly, all simulations for the ddd were performed without the nozzle. For the matRad base data, my first suggestion would have been to include the nozzle in the ddd and fragmentation spectra simulations to match the data to the respective facility. Am I wrong for thinking that way?
Another thing that I did not understand was which type of geometry was used for the laterally integrated ddd. There were two geometries used, one cylinder with a diameter of 28 cm and one with a diameter of the active volume of an IC. Since the volume used to score the laterally integrated ddd plays an important role on the output dose, it would be nice if you could share your insights with me.

[wahln]

If I remember correctly, the work of K Parodi wanted to include nozzle composition but separate from the air. One of the reasons probably were similar nozzles in all rooms but different nozzle-to-isocenter distances (and, secondary, different patient geometries). So I think what was done is the paper is to simulate the nozzle geometry (there was some trickery with approximating the BAMS), but then assume vacuum.

matRad doesn't bind you to make the same decisions. You can just simulate with your nozzle configuration / your phase space behind the nozzle and then store the ddd. The few fields that steer corrections due to simulation differences (e.g., every field has an "offset" field that allows to describe a constant difference in WEPL for this entry) could then be set to not correct (e.g. offset = 0).

When we generate new ddds, we usually just create a "large enough" water cylinder binned in depth.
I think the two geometries were mainly used by Parodi et al. to compare measurements with simulations and check their consistency.

If you do some simulation now, store ouputs well. We are currently implementing/revising the storage of spectra etc. for more flexible biological modeling and forwarding to MC.

One thing already present on the "dev" branch is that you can store now a energy spectrum parameterization at nozzle exit in machine.data.energySpectrum (a struct with the fields "mean" for mean energy (in MeV/u for carbon) and "sigma" in % for energy spectrum width). Similarly, machine.data.initFocus can hold a struct array called "emittance" with fields sigmaX, divX, corrX (and Y) to store a bigaussian emittance parameterization for each focus).
When using a Monte Carlo dose calculation engine, matRad uses those for the simulations. if not present, it tries to reverse engineer the beam optics and energy. Check this dataset, for example, https://github.com/e0404/matRad/blob/dev/matRad/basedata/protons_generic_TOPAS.mat

This is also helpful for quick consistency checks between a pencil-beam dataset and Monte Carlo.

[Yuri-HubL]

Hi wahln，

I would like to ask, during simulation, are ### water phantoms used?
What kind of ripple filters used to broaden the Bragg peak of carbon ions beam?
Is there somewhere I can refer to?

have a nice day!
yuri