Obioma Nwankwo, Gerhard Glatting, Frederik Wenz, Jens Fleckenstein |

- 2020-07-14

- 8 M

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A PSF of a 6 MV photon beam was generated by simulating the interactions of

primary electrons with the relevant geometries of a Synergy linear accelerator

(Elekta AB, Stockholm, Sweden) and recording the particles that reach a plane 16

cm downstream the electron source. Probability distribution functions (PDFs) for

particle positions and energies were derived from the analysis of the PSF. These

PDFs were implemented in the VSM using inverse transform sampling. To model

particle directions, the phase space plane was divided into a regular square grid.

Each element of the grid corresponds to an area of 1 mm2 in the phase space

plane. The average direction cosines, Pearson correlation coefficient (PCC) between

photon energies and their direction cosines, as well as the PCC between the

direction cosines were calculated for each grid element. Weighted polynomial

surfaces were then fitted to these 2D data. The weights are used to correct for

heteroscedasticity across the phase space bins. The directions of the particles

created by the VSM were calculated from these fitted functions. The VSM was

validated against the PSF by comparing the doses calculated by the two methods

for different square field sizes. The comparisons were performed with profile and

gamma analyses.

1 : SIMULINK ⺻

1.1 SIMULINK 1

5

Ķ 7

ùķ̼ Ķ (Configuration Parameters) 8

ùķ̼ 9

Ķ ǥ 9

ǥ 11

2.2 ùķ̼ 13

̺й 17

º 23

DC ùķ̼ 24

Լ 29

й(difference equation) 34

Subsystem(νý) 37

2 :

A single-source photon source model of a linear accelerator for Monte

Carlo dose calculation

1. Introduction 42

2. Materials and methods 43

3. Results 48

4. Discussion 53

5. Conclusion 54

6. References 55