this present describes about the project done my self at Aga Khan university Hospital Karachi for checking the validity of AAA Algorithm

1. A Comparative Study of
AAA Vs PBC Treatment Planning
Algorithms
Rahim Gohar
Medical Physicist
Radiation Oncology,
Dr Ziauddin University Hospital

2. Study objectives
 Introduction to PBC and AAA
 Inhomogeneity
 comparison
 Non-clinical
 Water phantom
 Clinical cases
 Head and neck
 Importance of body editing
 Effects on dose distribution
 Limitations of PBC
 Validation of AAA and PBC using measurement
 OSL, Film Dosimetry, point dose measurement

4. Dose Calculation Algorithms
 Broad-beam, Semi-empirical or
Correction-based algorithms
 MU Calc. (AKUH)
 Model- or kernel-based
algorithms; also referred to as
“Fluence-to-dose modeling”
 PBC, AAA
 Direct Monte Carlo
 Near future, I hope

5. Algorithm
“A procedure for solving a mathematical problem in
a finite number of steps that frequently involves
repetition of an operation”
OR
“step-by-step procedure for solving a problem or
accomplishing some end especially by a computer”

6. Convolution
 A coil or twist, esp. one of many
 A thing that is complex and difficult to follow
“Mathematical operation on two functions f and g,
producing a third function that is typically viewed
as a modified version of one of the original
functions”

7. Where, in the planning system, do
we find algorithms?
 MU calculations
 Isodose distributions
 DVH generation
 IMRT optimization
 DRR generation
 Brachytherapy calculations

8. PBC
 Dose calculation model
 pencil-beam kernels
Convolve
AAA
 The AAA is a 3D pencil-beam convolution
superposition algorithm
 it is modeling for
 primary photons, scattered
extra focal photons, and electrons
scattered from the beam-limiting
devices.

10. Inhomogeneity Correction
 Differ in density than H2O
 This results in
 Dose distribution different from that in water
 Change in absorbed dose
 Changes in electron Fluence
 Put limits on location of plan normalization

11. inhomogeneity correction
Med. Phys., 27, 1266-1274 (2000)
Solid squares: PDD in homogeneous medium
Solid triangles: Calculated using equivalent path length
Solid Line: Measured PDD

12. inhomogeneity correction
Med. Phys., 27, 1266-1274 (2000)
Solid squares: PDD in homogeneous medium
Solid triangles: Calculated using equivalent path length
Solid Line: Measured PDD

13. Comparison of PBC and AAA

14. Experimental validation of AAA and PBC

15. Comparison of PBC and AAA
PBC over doses, in lower dense medium?????

16. PBC limitation

17. Comparison of PBC and AAA

18. Non-Clinical cases
 Beam profile using PBC in heterogeneous medium(air)

19. Non-Clinical cases
 Beam profile using AAA in heterogeneous medium(air)

20. Non-Clinical cases
 Beam profile using PBC in heterogeneous medium(bone)

21. Non-Clinical cases
 Beam profile using AAA in heterogeneous medium(bone)

22. Wedge profile comparison
 PBC is not reliable for planning a treatment
when using a 60-degree EDW for large field sizes
 Importance of wedge profile(EDW)
 Measured VS calculated

23. Wedge profile comparison
(From Eclipse(PBC))

24. Wedge profile comparison
(From Eclipse(AAA)

25. Clinical Cases(PBC)
MR # (246-66-61)
 Slice#0(with body editing) (without body editing)
Huge difference in iso dose distribution i.e. PBC is not able to model the beam
At interface where there is gradient in terms of tissue density(here bolus and air)

26. Clinical Cases(PBC)
Maxi. Dose=4918 Maxi. Dose=4801
(with body editing) (without body editing)
Huge difference in iso dose distribution i.e. PBC is not able to model the beam
At interface where there is gradient in terms of tissue density(here bolus and air)

27. Clinical Cases(PBC)
(with body editing) (without body editing)
Huge difference in iso dose distribution i.e. PBC is not able to model the beam
At interface where there is gradient in terms of tissue density(here bolus and air)

28. Clinical case(AAA)
(with body editing) (without body editing)
Note: as the air gap is not too much so no any major difference
In iso dose distribution as AAA is taking care of the inhomogeneity
In between bolus and body.

29. Clinical Cases
 MR # (241-16-35)

30. Clinical Cases
 MR # (246-26-94)

31. Clinical Cases
MR#(239-90-25)

32. Testing of treatment Algorithms
 Films dosimetry
 Point dose measurements

33. Conclusion
 The implementation of AAA represents an
improvement for the Eclipse TPS at the level of dose
accuracy
 Dose calculation in heterogeneous medium
 Taking into account the electron contamination
 PBC is very weak algorithm for dose calculation
where there is sharp gradient in terms of medium
density
 Mask making and bolus placement are considerable
clinical issues
 Never place plan normalization at the region of
interface
 Heterogeneities pose the greatest challenge to
predicting accurate dose distributions in patients

34. Discussion
34
For coplanar beams in transverse plane tissue
heterogeneity usually does not change abruptly
from a given slice to an adjacent slice; for non-
coplanar beams this may not be the case
Thank you for listening me
The whole credit goes to TPS
staff
Questions or
comments????