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  4. Validation and Application of a Fast Monte Carlo Algorithm for Assessing the Clinical Impact of Approximations in Analytical Dose Calculations for Proton Therapy

Validation and Application of a Fast Monte Carlo Algorithm for Assessing the Clinical Impact of Approximations in Analytical Dose Calculations for Proton Therapy

S Huang1*, K Souris2 , S Li1 , M Kang3 , G Janssens4 , A Lin1 , E Garver1 , C Ainsley1 , Y Xiao1 , L Lin1 , (1) University of Pennsylvania, Philadelphia, PA, (2) UCL, Woluwe, Brussels, (3) Georgetown University Hospital, Washington, DC, (4) Ion Beam Applications SA, Louvain-la-neuve, Walloon Brabant,

Presentations

(Monday, 7/30/2018) 3:45 PM - 4:15 PM

Room: Exhibit Hall | Forum 3

Purpose: To validate an open-source and fast Monte Carlo code, MCsquare, and assess the accuracies of analytical dose calculation (ADC) for PBS proton therapy treatment plans for multiple disease sites.

Methods: First, MCsquare was commissioned and validated using water and tissue-mimicking IROC lung phantom measurements as well as benchmarked with the general purpose Monte Carlo TOPAS. Then a comparative analysis between MCsquare and ADC was performed for a total of 50 patients with 10 patients per disease site (including liver, pelvis, brain, head-and-neck, lung). Differences between MCsquare and ADC were evaluated using dosimetric indices (target Dmean, D95, D5-D95, V90) based on the dose-volume histogram, a 3D gamma-index (3%/3mm) analysis, and estimations of tumor control probability (TCP).

Results: MCsquare significantly reduced the calculation time from 2 hours for TOPAS to 1 min on average with 1E7 protons simulated. Comparison between MCsquare and TOPAS showed less than 1.7% difference for all the dosimetric indices/TCP values and larger than 99% for the 3D gamma-index passing rate of the target. However, the variances of the differences between MCsquare and ADC increase from liver to lung, as the degree of tissue heterogeneity increases. The median gamma-index passing rate for target volumes decreased from 99.3% for liver to 75.8% for lung. The D95 difference can be as large as 6.5%. Resulting TCP differences can be large for lung (≤10.5%) and head-and-neck (≤6.2%), while smaller for brain, pelvis and liver (≤1.5%).

Conclusion: Accurate dose calculation algorithms such as Monte Carlo simulations are needed for proton therapy, especially for disease sites with high heterogeneity, such as head-and-neck and lung. The establishment of MCsquare can facilitate patient plan reviews at any institution and can potentially provide unbiased comparison in clinical trials given its accuracy, speed and open source availability.

Keywords

Monte Carlo, Protons

Taxonomy

TH- External Beam- Particle therapy: Proton therapy - computational dosimetry-Monte Carlo

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