Study On the Possibility of An Intensity Modulation Technique Using a Scanning X-Ray Pencil Beam Based On Monte Carlo Simulation
C Guo*, K Men, Y Hu, Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, BeijingCN,
Presentations
PO-GePV-T-353 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Nowadays MLC-based intensity-modulation technique has gained much progress in radiotherapy, yet facing high costs of purchasing (including software and hardware) and heavy maintaining for daily use. The purpose of this study is to explore the possibility of using a scanning X-ray Pencil Beam to achieve intensity modulation based on Monte Carlo simulation.
Methods: A 22MeV electron beam was ejected with coordinates described as [(0, 0, 0), (θφ)], where (θφ) is the bending angle by quadrupoles magnet. Then incident electron beam was guided into one hole of a honeycomb-like multi-holes collimator array. The multi-holes collimator array was constructed by upper (primary) and lower (secondary) layers, with the corresponding holes radically lined-up. X-ray targets were put inside each primary collimator’s hole. The time electron hitting target was defined as Tₓ, proportioned to X-ray pencil beam intensity planned by Treatment Planning System. To obtain an optimum square photon pencil beam with FWHM of 5mm at SAD = 102cm, based on Monte Carlo simulation results, we determined primary and secondary collimator’s hole diameters were 1mm and 3.5mm, the hole’s wall thicknesses were 0.5mm and 0.3mm, and heights of two-layer collimators were 9.7cm and 4cm, respectively.
Results: X-ray pencil beam was scanned along ±5cm in X- & Y-direction at SAD = 102cm to get a composite 10x10cm field size, with deviation of off-axis ratio less than ±3%. By adjusting the delivered time TX, wedge-shaped and various composite treatment fields can be achieved. Monte Carlo simulation was tested on a Varian accelerator-based TPS and the accuracy of calculation results were verified.
Conclusion: The results of this study based on Monte Carlo Simulation have shown that the scanning X-ray pencil beam intensity modulation technique could potentially be an alternative of MLC based intensity modulation with much low cost, faster delivery, and more reliable for clinical use.
Keywords
Pencil Beam Algorithms, Intensity Modulation, Monte Carlo
Taxonomy
TH- External Beam- Photons: Development (new technology and techniques)
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