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Commissioning the Eclipse Pencil Beam for Low Energy X-Rays

M Cherven

M Cherven*, J Burmeister, J Rakowski, M Snyder, Wayne State University, Detroit, MI

SU-E-T-617 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To use an existing treatment planning system to configure a low energy beam in order to evaluate the possibility of applying such a beam to intensity modulated radiation therapy (IMRT). It has been shown that low energy photons combined with heavy metal contrast can provide a higher relative biological effectiveness (RBE) through Auger electron production. Achieving a higher RBE may provide additional treatment options for patients with tumor types, such as glioblastoma, that are resistant to megavoltage therapy.

Methods: A set of low energy photon beam data was generated using Monte Carlo simulation, put into appropriate w2CAD formatting, and imported into Varian Eclipse TPS to provide a set of depth dose curves and profiles. Additional beam data was calculated and a low energy beam was configured using the Pencil Beam Convolution algorithm. Treatment plans investigating dose distribution of the beam utilizing IMRT techniques were created to evaluate the usefulness of this technique.

Results: The Eclipse TPS is able to model the dose distributions that would be produced by a low energy beam in a solid water phantom. In theory we could apply this model to IMRT treatment techniques to provide a more conformal dose distribution. Dose enhancement due to heavy metal contrast will initially be included as a simple scaling of the dose within the target region. The inclusion of heterogeneity corrections is difficult due to the enhanced photoelectric effect in bone at low energies, and is under investigation.

Conclusion: Eclipse is capable of modeling a low energy photon beam using the pencil beam algorithm for calculation on homogeneous phantoms. Further investigation is needed to determine the ability of the treatment planning system to assist in low energy photon treatment planning, with the eventual goal of providing a higher RBE therapy option for resistant tumor types.

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