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

Abstract

PurposeOur 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.MethodsWe 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.ResultsOur 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.ConclusionsRaySearch 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.

Retrospective Planning Study of Patients with Superior Sulcus Tumours Comparing Pencil Beam Scanning Protons to Volumetric-Modulated Arc Therapy

“…The Monte Carlo calculation algorithm is considered to be more accurate in heterogeneous environments, like the lung cohort [ 72 ]. As expected, Monte Carlo calculations had little effect on the OARs, but showed an approximate 5% reduction in mean CTV D95 compared with the clinical algorithm utilised, which is in agreement with other reports [ 73 , 74 ]. Unfortunately, Monte Carlo-based optimisation is not currently available within the Eclipse treatment planning system but follow-up studies utilising this are warranted.…”

Impact of errors in spot size and spot position in robustly optimized pencil beam scanning proton‐based stereotactic body radiation therapy (SBRT) lung plans

“…The results reported in the current study complement previous findings 1,5,7,8 by adding the impact of variations in spot sizes and positions in robustly optimized PBS lung plans. Due to the availability of the Monte Carlo algorithm in commercially available TPS, researchers are recommending the Monte Carlo algorithm for the optimization and dose calculations in the proton lung plans 14–17 . The current study provides additional information regarding the impact of spot size and position errors on the dose distributions of the lung plans, which were robustly optimized (SFO technique) and calculated using the Monte Carlo algorithm.…”

“…In commercial proton treatment planning systems (TPS), Monte Carlo algorithms have been shown to be more accurate in estimating spot sizes than analytical pencil beam algorithms. 12,13 A growing number of publications [14][15][16][17] have now recommended using the Monte Carlo algorithm for the dose calculations in PBS lung cancer. Recently, robust optimization 14,18 feature has been made available in the clinical environment, whereas previous studies 1,[5][6][7][8] did not address the impact of variation in spot size on robustly optimized clinical plans.…”

FRoG dose computation meets Monte Carlo accuracy for proton therapy dose calculation in lung

“…Despite being subject to scrutiny, the pencil beam algorithm (PBA) in PT provides fast speeds at the potential sacrifice of accuracy in complex tissue inhomogeneities. The gold standard for accuracy is the MC simulation and related codes are only recently introduced to the clinics, fostered by past and on-going efforts to develop clinical dose engines [11,12].…”

“…Most notably, investigations with anthropomorphic lung phantoms suggest that application of commercial TPSs using analytical algorithms for the treatment of lung tumors should be deemed unfit for clinical use or used with extreme caution [15]. The lateral dose distribution computed by PBA in the lung and in bone interfaces may reach a level of inaccuracy around 30% [16,17], while commercial MC-based TPSs can improve the accuracy of dose calculation in the lung/bone interfaces or through inhomogeneities within ~5% [12,17]. Despite being considered clinically tolerable, another source of uncertainty in proton therapy of lung originates from the heterogeneous structure of the lung itself, which leads to a degradation of the Bragg peak and a wider distal fall-off [18].…”