Dear @dengtiantian22
I am not familiar with the S-value, however from the K. Khamwan, A. Krisanachinda, P. Pasawang paper, if my understanding is correct, the S-value is used to convert the Activity (Bq) to Dose (Gy), such as D = A \times S
using an approximate formula to calculate the S from the decays, and the fraction that is absorbed per organ (Eq, 1.,2,3).
If so, FLUKA can simulate for you the decays, their absorption, so you don’t need any approximation.
You could do a simulation:
- using as geometry the CT scan converted to voxel (as you already did)
- convert the F-18 PET activity as a USRBIN. In flair select the CT scan and click on the Export dropdown menu and select USRBIN
- Add a SPECSOUR card with Type: BIN-SOUR and select the PET USRBIN you created before (Using also an OPEN card to load the file).
- In the BEAM card select ISOTOPE and with HI-PROPE card select the decaying F-18 isotope
- WIth a USRBIN matching the VOXEL (From flair DICOM, select the CT and add USRBIN card) score DOSE
If you divide the simulated DOSE with the USRBIN activity of F-18 you should get the S-value per voxel. You could even sum it up to get it per organ, maybe using the RTSTRUCT information.