Hi,
I am trying to calculate radioactivity of organs after injecting radio-tracer into body by knowing injected radio-tracer activity and absorbed dose per unit activity. How can I calculate organ's radio activity.
For example : The injected radio activity of radio tracer that injected into human body is 80 MBq and absorbed dose of liver per unit administered(mGy/MBq) is 1.1E-03. How much will be the radio activity of of liver after injecting this radio-tracer? If it is time dependent, could you please explain by considering any time?
Thanks in advance,
Manu
The dose to the organ posed by internal exposure depends on physical half-life and biological half-time of radionuclides. The latter depends on biokinetic models considering age, organs, chemical forms, etc. The organ mass may also change significantly depending on the disease status (e.g., liver by diffuse parenchymal liver disease).
there is no linear relationship to calculate the absorbed dose in organ, thus you can calculate the activity by the non-linear relationship and that due the measurement of the waste by urine, sweet , and any body excretion.
Although, there is no linear relationship to calculate the absorbed dose in organ, you can use different Monte Carlo codes such as MCNP and then you can convert your obtained results using output data.
Nobuyuki Hamada Muntaser S. Ahmad Huseyin Ozan Tekin Thanks a lot for your valuable reply
Hi Manu Francis
The easiest way to do this is through an imaging study because you need to know how much of the initial activity is in the liver over time (the time activity curve). The shape of this curve is dependent on the kinetics of the tracer (as mentioned above), but you can even estimate it if you have some initial timepoint data.
In terms of the practical steps, you then need to calculate the "cumulated activity" in the liver (the integral of the TAC curve in units of MBq x hr), then divide by the initial activity to get the Normalized Cumulated Activity (NCA). You can then multiply this answer by the "s-value" for the MIRD phantom liver (or scale it to your patient). There are published S-values available, for example see MIRD Pamphlet number 5
Sometimes it is easier to find an already published biodistribution study for the tracer you are interested in!
Hope that helps,
Jim
Will you be so kind to provide more details about pathway of intake of an tracer? Usually, the ICRP provides dose coefficients for inhalation, injection and, in some cases, for injection. Your question conserns that the input data is an absorbed dose per unit activity. Absorbed dose could be defined only for certain organ and for certain period of time after uptake. Please, provide more details about that.
Absorbed Dose Calculation The amount of absorbed dose (D) is equal to the average energy E absorbed by the body mass of the body or organ mass.
Unit mass (dm = ρ · dV, ρ density, dV unit volume element).
E= of radiation source average energy
D=dE/dm Absorbed dose (gray)
1 Gy = 1 J·kg-1 Then you can convert the absorbed dose to the unit rad (radiation absorbed dose). 1 rad = 0.01 Gy 1 Gy = 100 rad
Thanks Vladimir Kutkov for your willingness to help me. I just want to know how much emissions will be occur from an organ after radio-tracer injection in MBq. For example if Tc99m-colloid of 800 MBq is injected into adult human, what will be the amount of radio-tracer that reaches to the liver(healthy liver) in MBq(disintegrations/second)?
I got the method to find absorbed dose of every organs from different publications, but I didn't get any publications regarding radio-tracer uptake of each organ.I am trying to simulate SPECT imaging setup and scanning object. For a proper scanning simulation, I need to know how much radiations will be emitted from each organs.
Could you please give a feedback on my question?
Dear All, the specifics how much and in what organ can only be answered by dynamic SPECT acquisitions of the corps over time, so (i know very cumbersome), ask a patient to be scanned (multi volume Spect) at t 0, t 2 hours, t 8 hours, T 24 hours (up to your wishes). The professional will say, well, guys it is 99mTc, nothing left , but still i have seen examples of this (with MDP Bone scan) which worked. The above scans should be calibrated as much as possible, and a dosimetry program with proper aligned segmentation should be used, than segmented volume information should be inputted in Olinda and voila, your organ info.From here you could be researching the dose from the specific organs to the others however in my opinion this dose is already shown in the SPECT's. Mind you that MIRD with Olinda will not split kidney info into left and right. Providers of the hardware would be the new Gammacamera's and their quantitative suites for reconstruction. Providers of the software would be my previous and current company, peter
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