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If you assume a linear dose profile from periphery to center and calculate average value of this function over disc of ctdi phantom you get these 1/3 2/3 weights. Essentially they come from the linear dose assumption. See attached photo, I just</div>
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If you assume a linear dose profile from periphery to center and calculate average value of this function over disc of ctdi phantom you get these 1/3 2/3 weights. Essentially they come from the linear dose assumption. See attached photo, I just did the math.</div>
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Amazing this isn't in a paper I could ever find, nor Dixon's book (I waited for a bit before posting so he could respond... I think the last time I brought this up with him he said the math was too easy to include in a book ;) )</div>
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<b>Subject:</b> [Intl_DxMedPhys] CTDIw - why 2:1 periphery/center weighting?</font>
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Hi List, I was recently contemplating the definition of CTDIw, and wondered why weighting factors of 2/3 periphery to 1/3 center CTDI100 were chosen. Anyone know the history here? If CTDIw is meant to estimate the average dose in the axial slice,</div>
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Hi List,</div>
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I was recently contemplating the definition of CTDIw, and wondered why weighting factors of 2/3 periphery to 1/3 center CTDI100 were chosen. Anyone know the history here?</div>
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If CTDIw is meant to estimate the average dose in the axial slice, then of course the periphery must have a higher weighting than the center due to geometric arguments (the area of the "periphery " region is larger than the "center" region) but it seems rather
arbitrary and simplistic to pick a 2:1 ratio. In a CTDI phantom of radius R, if you consider the "center" region to have radius R/2, and thus the "periphery" to be an annulus of outer-inner radius R-R/2, then the areal ratio would be 3:1 (or ¾ to ¼ periphery
to center weighting). Is it one of those things where a 2:1 ratio is "close enough" to experimental measurements and MC simulation data, and easy to remember?</div>
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Curious to hear what people know!</div>
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