1. CALCULATION OF A SINGLE PENCIL BEAM KERNEL FROM MEASURED PHOTON BEAM DATA
Pascal Storchi
Daniel den Hoed Cancer Center
University Hospital Rotterdam

2. Calculation of irregular photon fields by pencil beam convolution

3. Pencil beam model

4. Calculation of the pencil beam kernel "theoretical" approach
Pencil beam kernel computed by Monte Carlo techniques:
Energy spectrum must be known:
for the pencil beam kernel
for the primary photon fluence
Results must be fitted to specific linac.

5. Calculation of the pencil beam kernel "empirical" approach
Is it possible to extract the pencil beam kernel from measured data ?

6. Is it possible to extract the pencil beam kernel from measured data ?

7. Is it possible to extract the pencil beam kernel from measured data ?

8. Present model

9. Pencil beam model

10. Phantom Scatter Factor

11. Calculation of the scatter kernel Ks(R,z)

12. Fluence of primary photons first guess: intensity profile Pi = envelope profile Pc
only "scatter"
measured profile

13. Fluence of primary photons deconvolution of scatter kernel Ks from envelope profile Pc => intensity profile Pi

14. Boundary kernel Kb

17. Results: square field (20x20 cm2)

18. Results: asymmetric square field (20x20 cm2)

19. Results: rectangular field (30x5 cm2)

21. Conclusions
It is possible to use the PSF and the penumbra region of measured square fields for the derivation of the pencil beam kernel.
Measurement of the penumbra region must be done with a small detector (diode).