Program Information
Synthetic Photon Energy On LINAC for Radiation Therapy
Q Wu1*, J Addido2 , T Zhuang3 , S Zhou4 , (1) Duke University Medical Center, Durham, NC, (2) Duke Kunshan University, Kunshan, ,(3) Cleveland Clinic Foundation, Cleveland, OH, (4) University of Nebraska Medical Center, Omaha, NE
Presentations
TH-CD-708-11 (Thursday, August 3, 2017) 10:00 AM - 12:00 PM Room: 708
Purpose: Modern linear accelerator (LINAC) is often equipped with multiple photon energies. This versatility facilitates the choice of proper energy for each individual case. However, it also demands a premium in purchase and maintenance cost and increased efforts in quality assurance. The questions therefore arise whether it is necessary to have so many energies and whether there is any alternative. In this study, we propose a synthetic formula that can generate any equivalent photon energy from only two energies.
Methods: Photon beams are commonly characterized by the percent depth doses (PDDs) in water phantom at a fixed source to surface distance (SSD) for a range of field sizes and the profiles at a few depths, where the PDD is the most important quantity associated with the energy. In this study, PDDs from a Varian Truebeam LINAC of 6, 10 and 15 MV were used to demonstrate the principle. PDDs for a synthetic 10MV photon energy were constructed from 6 and 15MV PDDs, and least square fit was performed. The principle was further validated in a 5-field 10MV prostate plan.
Results: It is possible to construct a synthetic 10MV photon beam using only 6 and 15MV beams, and the coefficients vary with field size. The root mean square error (RMSE) is less than 0.5% - lower than most algorithm commissioning tolerances. In the prostate example, the dose difference between the actual 10MV plan and the composite of 6MV and 15 MV plan is within 1%.
Conclusion: A LINAC with two photon energies is capable of producing dosimetrically equivalent plans of any energy in-between through synthesis. Therefore, it is unnecessary to have more than two energies on a LINAC. This study also provides mechanism to treat a patient with an equivalent plan by using neighboring energies when actual photon energy is unavailable.
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