Exhibit Hall | Forum 7
Purpose: Replacing cut-outs and applicators for collimation of electron beams with the already installed photon multileaf collimator (pMLC) facilitates intensity modulation of electron beams. The aim of this work is to develop a treatment technique for pMLC based electron modulated arc therapy (EMAT), which extends modulated electron radiotherapy (MERT) by dynamic gantry rotation and dynamic pMLC movement during beam on.
Methods: To create EMAT plans, direct aperture optimization (DAO) is performed with electron arcs for all available electron beam energies. Next, arcs of energies with a high dose contribution to the target are doubled, while arcs of energies with a low contribution are removed and a new DAO is performed. Isocentric EMAT plans for a head and neck (H&N) case and a breast case are created and compared to isocentric MERT plans with three beam directions in terms of dosimetric treatment plan quality and estimated delivery time. The two EMAT plans are delivered on a TrueBeam in developer mode. The delivered dose distribution is measured using radiochromic films and compared to the Monte Carlo calculated dose distribution using a gamma analysis (3% (global), 2 mm, 10% dose threshold).
Results: The resulting EMAT plans consist of one 22 MeV half arc for the H&N case and two 22 MeV, two 12 MeV and one 9 MeV half arcs for the breast case. The EMAT plans reduce the delivery time by 77% for the H&N case and 42% for the breast case while increasing the homogeneity in the target in comparison to the MERT plans. The gamma passing rates are above 95% for all evaluated situations.
Conclusion: A pMLC based treatment technique for EMAT was developed. Improvements in dosimetric plan quality and delivery time of EMAT over MERT are indicated and the dosimetric accuracy was validated for two plans.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by grant 200021_185366 of the Swiss National Science Foundation and by Varian Medical Systems.
MLC, Electron Therapy, Treatment Techniques
TH- External Beam- Electrons: Development (new technology and techniques)