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.

[wahln]

The dist value is relative to the (virtual) scanning source, so having a value at 0 would not make too much sense. That's also why the values are all relatively large. Subtract the SAD to make them relative to the isocenter, for example. To make them relative to the nozzle, use BAMStoIsoDist (strictly speaking that is the distance from the Monitoring System to the IsoCenter, but we use it as the nozzle position).

[saxu3829]

Thank you for your quick reply! If I understand correctly, you could for example say if the sigma at the end of the beam nozzle is X, then dist = SAD-BAMStoIsoDist, right? And we then could approximate all values before this point with the same sigma, so that sigma[0, SAD-BAMStoIsoDist] = X? Or is it also correct if you don't define a sigma value between zero and SAD-BAMStoIsoDist?

[wahln]

you don't need to define a sigma before the nozzle. What matRad is doing with this data is to interpolate the initial width of the beam when impinging on the patient: we compute the SSD, which should always be > BAMStoIsoDist, and then interpolate at the SSD value in dist & sigma to get the initial beam sigma used to convolve the lateral kernel with.

[ni484call5]

Hello!

I notice that multi gaussian seems supported in the code
https://github.com/e0404/matRad/blob/ca05aed22762deed3b0d54289bda5c2ab8d96660/matRad/doseCalc/%2BDoseEngines/matRad_ParticlePencilBeamEngineAbstract.m#L224C1-L237C16

I'm wonder is triple gaussian supported or not in carbon? If so, what's the format should be in carbon_Generic for baseData.weightMulti and baseData.sigmaMulti?

Sincerely,
Nicholas

[wahln]

@ni484call5 yes, in the new version you can have a triple-gaussian model using these entreis (they are not present in the carbon_Generic data, though).

• sigmaMulti: needs to be a d x n matrix where d is the length of the depths vector and n is the number of Gaussian components. Thus each kernel component is tabulated in depth at the same points, with components' data stacked in columns
• weightMulti: needs to be a d x (n-1) matrix representing the weights in depth of the 2nd to last component per column. The weight of the first component will be calculated from the condition that all components weights must sum up to 1.