Age or size?

In order for us to get the most accurate dose estimate using NCIRF, do you think its more important for us to match the patient's age, or weight, based on the backend calculation? For example, the 5 year old patient mode

In order for us to get the most accurate dose estimate using NCIRF, do you think its more important for us to match the patient's age, or weight, based on the backend calculation?

For example, the 5 year old patient model in NCIRF has a weight of 19 kg, while the 15 year old model has a weight of 52 kg. If we have a 15 year old patient that's 21 kg, would you advise us to use the 5 year old model (since that more closely matches weight), or 15 year old model (since that matches age), to get the most accurate effective dose estimate?

I'd assume weight (so the 5 year old model in the example presented above) since that's more indicative of patient girth/size, but just wanted to confirm.

NCI Dose Team response

The weight of the NCIRF phantoms follow the ICRP reference data from Publication 89 so that “normal” patients would follow the trend but obvious variation from the reference data actually happens in patients. Your question is tricky to answer. First, bodyweight does not fully reflect the patient circumference which is directly related to attenuation of x-ray entering patient anatomy. Second, by using bodyweight, we don’t take into account patient height which is related to the field height. Again the best solution would be having the full library of body size-dependent phantoms (see attached) which we're currently working on. The feature should be available in NCIRF3.0 maybe this summer. For the time being, we would recommend matching body weight which may give fewer dosimetric errors than matching age.