Validation of the RayStation Monte Carlo dose calculation algorithm using realistic animal tissue phantoms

Abstract

Purpose Our purposes are to compare the accuracy of RaySearch's analytical pencil beam (APB) and Monte Carlo (MC) algorithms for clinical proton therapy and to present clinical validation data using a novel animal tissue lung phantom. Methods We constructed a realistic lung phantom composed of a rack of lamb resting on a stack of rectangular natural cork slabs simulating lung tissue. The tumor was simulated using 70% lean ground lamb meat inserted in a spherical hole with diameter 40 ± 5 mm carved into the cork slabs. A single‐field plan using an anterior beam and a two‐field plan using two anterior‐oblique beams were delivered to the phantom. Ion chamber array measurements were taken medial and distal to the tumor. Measured doses were compared with calculated RayStation APB and MC calculated doses. Results Our lung phantom enabled measurements with the MatriXX PT at multiple depths in the phantom. Using the MC calculations, the 3%/3 mm gamma index pass rates, comparing measured with calculated doses, for the distal planes were 74.5% and 85.3% for the APB and 99.1% and 92% for the MC algorithms. The measured data revealed up to 46% and 30% underdosing within the distal regions of the target volume for the single and the two field plans when APB calculations are used. These discrepancies reduced to less than 18% and 7% respectively using the MC calculations. Conclusions RaySearch Laboratories' Monte Carlo dose calculation algorithm is superior to the pencil‐beam algorithm for lung targets. Clinicians relying on the analytical pencil‐beam algorithm should be aware of its pitfalls for this site and verify dose prior to delivery. We conclude that the RayStation MC algorithm is reliable and more accurate than the APB algorithm for lung targets and therefore should be used to plan proton therapy for patients with lung cancer.

Validation of the RayStation Monte Carlo dose calculation algorithm using a realistic lung phantom

“…We interpret the systematic improved passing rate for a uniform scaling of the HU‐to‐MD curve as mainly being caused by the difference in interpreted and the real stopping power of cork. This assumption is supported by the results in the previous study where only animal tissues were used together with the original HU‐to‐MD curve . As mentioned earlier we recalculated all the beams with a modified HU‐to‐MD curve where the mass density was increased by 5% over the cork region only.…”

“…The 5% shift is within the uncertainty of 7% in the measured stopping power for cork, as detailed above. Because our work using animal neck phantoms and a water‐based breast phantom revealed that the HU‐to‐MD curve in the soft tissue, water and bone region is adequately accurate, we decided to leave that portion of the HU‐to‐MD curve unchanged …”

“…We explain in another study how the RaySearch APB and MC algorithms work . When the MC dose engine became available in RayStation 6 (RaySearch Laboratories AB, Stockholm, Sweden), we proposed to validate it using animal tissue and realistic phantoms, because the use of animal tissue phantoms in dose validation has seen useful results, similar to using wood or cork to approximate lung tissue .…”

“…When the MC dose engine became available in RayStation 6 (RaySearch Laboratories AB, Stockholm, Sweden), we proposed to validate it using animal tissue and realistic phantoms, because the use of animal tissue phantoms in dose validation has seen useful results, similar to using wood or cork to approximate lung tissue . Previously, we studied these algorithms applied to animal neck phantoms and a water‐based breast phantom . In this study, we focused on validating the MC algorithm for a more complex lung phantom made of a composite of lamb ribs, ground lamb meat and cork.…”

Producing a Beam Model of the Varian ProBeam Proton Therapy System using TOPAS Monte Carlo Toolkit

“…Proton pencil beam scanning (PBS) systems are increasingly being employed for radiation therapy due to greater control over homogeneity and conformality of the dose distribution without the use of patient‐specific compensators 1 . As clinics transitioned away from passive scattering proton therapy, studies showed that analytical algorithms were not adequate for beam modeling and dose calculation of PBS treatments 2–7 . Often, the analytical algorithm‐based treatment planning software (TPS) overestimated dose to the target, while underestimating dose to organs at risk 4 .…”