Monte Carlo simulations of a nozzle for the treatment of ocular tumours with high-energy proton beams

Abstract

By the end of 2002, 33 398 patients worldwide had been treated with proton radiotherapy, 10 829 for eye diseases. The dose prediction algorithms used today for ocular proton therapy treatment planning rely on parameterizations of measured proton dose distributions, i.e., broad-beam and pencil-beam techniques, whose predictive capabilities are inherently limited by severe approximations and simplifications in modelling the radiation transport physics. In contrast, the Monte Carlo radiation transport technique can, in principle, provide accurate predictions of the proton treatment beams by taking into account all the physical processes involved, including coulombic energy loss, energy straggling, multiple Coulomb scattering, elastic and nonelastic nuclear interactions, and the transport of secondary particles. It has not been shown, however, whether it is possible to commission a proton treatment planning system by using data exclusively from Monte Carlo simulations of the treatment apparatus and a phantom. In this work, we made benchmark comparisons between Monte Carlo predictions and measurements of an ocular proton treatment beamline. The maximum differences between absorbed dose profiles from simulations and measurements were 6% and 0.6 mm, while typical differences were less than 2% and 0.2 mm. The computation time for the entire virtual commissioning process is less than one day. The study revealed that, after a significant development effort, a Monte Carlo model of a proton therapy apparatus is sufficiently accurate and fast for commissioning a treatment planning system.

Monte Carlo simulation of a proton therapy beamline for intracranial treatments

“…Finally, it should be mentioned that the differences found between calculated and measured proton depth dose distributions and lateral profiles are comparable with the results published in similar studies (Paganetti et al, 2004;Hérault et al, 2005;Newhauser et al, 2005;Polf et al, 2007;Koch et al, 2008;Martinetti et al, 2009;Stankovskiy et al, 2009;etc.). Indeed, the MC model presented by Paganetti et al (2004) accurately reproduced measured dose distributions in range and modulation width, in the case of a spread-out Bragg peak (SOBP), with an agreement of 1 mm.…”

“…Different types of particles can be transported, including protons and neutrons. Proton absorbed doses calculated with MCNPX have been validated with measurements in different studies (Herault et al, 2005;Newhauser et al, 2005;Polf et al, 2007;Martinetti et al, 2009). …”

“…Every non-modulated distribution was normalised at the depth of the maximum dose, as usually done in previous studies (Paganetti et al, 2004; Newhauser et al, 2005;Koch et al, 2008;Martinetti et al, 2009). The simulations were compared with the measurements using several characteristics of the beam profiles: -the range, which was chosen as the distal (d) depth of 90% of the maximum dose (Z d90 ), -two field widths chosen as the distance between the proximal (p) and distal depths of 90% and 50% of the maximum dose (Z p90 -Z d90 and Z p50 -Z d50 ), and -the penumbra width, the distance between the distal depths of 80% and 20% of the maximum dose (Z d80 -Z d20 ).…”

“…MCNPX does not simulate variable geometries in time; therefore, an alternative method should be used to calculate modulated distributions. As previously adopted by some authors (Hérault et al, 2005;Newhauser et al, 2005), we performed several simulations, each one corresponding to each of the crossed steps in order to reproduce the modulation. In every simulation the modulator was modelled by two superimposed cylinders with each having the exact thickness of lead and lexan as the simulated step.…”

“…In proton therapy, it has been validated by several published studies. With an accurate Monte Carlo simulation of the beamline, authors have reported a good agreement between calculated and measured proton dose distributions (Paganetti et al, 2004;Hérault et al, 2005;Newhauser et al, 2005;Polf et al, 2007;Martinetti et al, 2009;Stankovskiy et al, 2009). Recent literature even suggests using Monte Carlo methods in clinical proton therapy applications (Hérault et al, 2007;Paganetti et al, 2008).…”