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Modulated Electron Arc Therapy Using Photon MLC Monte Carlo Based Feasibility Study

C Ma*, D Parsons , X Gu , M Chen , W Lu , UT Southwestern Medical Center, Dallas, TX


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: Conventional electron treatment delivery utilizes an applicator with cutouts or specially designed electron MLC with reduced source-to-surface distance (SSD). Such configurations are infeasible for electron arc therapy due to potential collision between the patient and gantry. We propose to use photon MLC (pMLC) with 100 cm source-to-axis distance (SAD) for modulated electron arc therapy (MEAT). To investigate the feasibility of using pMLC for MEAT, we studied dosimetric characteristics using Monte Carlo (MC) simulations.

Methods: The EGSnrc MC-simulator was commissioned by matching calculated beam profiles and percentage depth dose curves (PDDs) with measured profiles and PDDs of static electron fields and then used to simulate dose under systematically-designed various electron arc delivery configurations. The dosimetric characteristics of field widths (3-5 cm transversely), lengths (10-30 cm longitudinally), and electron energies (6, 9, 12 MeV) were studied through analysis of PDDs, inline dose profiles at depth of 90% of the maximum dose (d₉₀) and profiles along the arcs of cylindrical water phantoms. The impacts of phantom curvatures and arc angles (60-180°) were also studied.

Results: Compared with 3 cm field width, PDDs with 5 cm show comparable d₉₀ and falloff. However, the bremsstrahlung dose component at isocenter is decreased by 50%. Field lengths did not significantly impact PDD, arc profiles (<1% deviations) with marginal increase of ~2% on the falloff of inline profiles. The dose falloff of arc profiles is sharper for higher energy and larger radius cylinders. The bremsstrahlung dose increases linearly with arc angle.

Conclusion: This study provided basic dosimetric characteristics for isocentric electron arc treatment using pMLC. Treatment planning studies using pMLC-modulated electron arc therapy are under way.


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