Monte Carlo Techniques in radiation therapy - mcneg

Monte Carlo Techniques
in radiation therapy
Henry Lawrence
Ipswich Hospital

History of M/C
Calculate π using method of Buffon and Laplace
Throw a stick of length L onto a surface ruled with parallel
lines d apart.
Buffon (1777) suggested that the probability of the stick crossing the line
p=2L/(π *d)
Laplace (1886) suggested calculate π.
Lawrence (2013) gave it a go, and got to
~ 2 % after 3000 ‘throws’

Development of EGS/MCNP
1949 von Neumann and Ulam
1960 Etran and ITS
1978 EGS3
Step size artifacts in e- transport
1985 EGS4
PRESTA (Bielajew) solved step size problem
2000 EGSnrc

Splitting
Variance reduction
– Uniform,dir. brems…
Russian Roulette
Range rejection
Interaction forcing

Dosimetry applications
Stopping power ratios
– Calculate fluence using m/c
Detector response
– Subtract components
(4.4.1)
– Positioning uncertainty
(4.4.4)

Modelling external photon beams
1978 Patau
– Target, flattening filter
1981 Nilson and Brahme
– Transparent components
1988 Udale
– Modular Philips linac
1995 Rogers et al (BEAM)
– General purpose code

Where do the photons come from?
Chaney et al (1994)
Centre of mass 6cm

Details of linac components
Flattening filter
– Different material

Multileaf collimator model
Tongue and groove
– [a] &[c] use ray trace
– [c] includes t & g
Intensity map
M/C

kV cone beam CT
Calibrating M/C calculated dose (Ding, 2008)
– Wrt chamber in phantom ,then apply to image.

MatrixX
– Chamber array
– Limited resolution
EPID
– portal imager dose
TPS
– Analytical model
IMRT verification

Tomotherapy
Rotating source
Sterpin(2008)
– TomoPen
– PENELOPE code
3 phase spaces
– Each jaw setting
Weight PSF
– For each angle
– Interpolate angles

Conclusion
Excellent overview of M/C in
radiotherapy
Helpful summary of computational
issues
Radiation physics concisely described

Thank you for your attention