Is On Line Dose Calculation Accurate
Name Answer
Santam I am not a physicist but from what i have read it seems that dose calculations on megavoltage CTimages can be theoretically more accurate dosimetrically than the corresponding KV images.
Andrew I agree, whether kV or MV, the CBCT images provide accurate e/g measures for accurate planning. The vendors then seem to say 'voila, adaptive radiotherapy', but this question hangs in my brain - 'adapting TO WHAT??'
Indranil The vendors will find a way to sell you anything. Its probably accurate enough mathematically
Santam One additional pertinent issue with the dose calculation in online treatments is what kind of image fusion are we using ? Rigid or deformable. This question is important as if rigid registration is being utilized then voxel based dose summation will not be possible. Superimposing intensity maps over fused images which have been fused using rigid registration will not give a true dosimetric/ biological estimate of the dose deposited in the tissue. Another issue of note is what metric do you use in such a situation. Assume that voxel A of CTV was receiving dose x during planning and during subsequent replanning the dose shown is a fraction x. However at the same time voxel A has shifted position due to alteration in tissue geometry with the result that what is being shown as voxel A dose after rigid registration is actually voxel B dose. Besides just summing the physical dose is of little relevance unless we know what the biological dose equivalent will be. Any thoughts on this issue?
Andrew Fortunately, dose summation is a separate issue from dose deposition on today's contours. We have all this data and we will be looking at dose summation. Once again, I think that anatomy rules the day. I think the issue is to map the CT onto a malleable pixel size and then assign a dose and enlarge/compress pixels without letting the dose 'slide' on to nearby neighbours, and then summing the dose per pixel. But we have a researcher starting on this issue soon anyway, so you can ask again in 12 months and I might have an answer.
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