Purpose: To introduce a practical method of using an Electron Density Phantom (EDP) to evaluate different dose calculation algorithms for photon beams in a treatment planning system (TPS) and to commission the Anisotropic Analytical Algorithm (AAA) with inhomogeneity correction in Varian Eclipse TPS. Methods and Materials: The same EDP with various tissue-equivalent plugs (water, lung exhale, lung inhale, liver, breast, muscle, adipose, dense bone, trabecular bone) used to calibrate the computed tomography (CT) simulator was adopted to evaluate different dose calculation algorithms in a TPS by measuring the actual dose delivered to the EDP. The treatment plans with a 6-Megavolt (MV) single field of 20 × 20, 10 × 10, and 4 × 4 cm 2 field sizes were created based on the CT images of the EDP. A dose of 200 cGy was prescribed to the exhale-lung insert. Dose calculations were performed with AAA with inhomogeneity correction, Pencil Beam Convolution (PBC), and AAA without inhomogeneity correction. The plans were delivered and the actual doses were measured using radiation dosimetry devices MapCheck, EDR2-film, and ionization chamber respectively. Measured doses were compared with the calculated doses from the treatment plans. Results: The calculated dose using the AAA with inhomogeneity correction was most consistent with the measured dose. The dose discrepancy for all types of tissues covered by beam fields is at the level of 2%. The effect of AAA inhomogeneity correction for lung tissues is over 14%. Conclusions: The use of EDP and Map Check to evaluate and commission the dose calculation algorithms in a TPS is practical. In Varian Eclipse TPS, the AAA with inhomogeneity correction should be used for treatment planning especially when lung tissues are involved in a small radiation field.

Purpose: The aim of this study was to develop an optimal protocol for imaging different body sites in patients during MV Cone Beam CT (MVCBCT) based IGRT for small field of view (FOV) imaging for Stereotactic Radiosurgery and other applications. Methods and Materials: Clinically delivered MVCBCT imaging systems have built‐in protocols that are optimized for large FOV imaging. For our protocol optimization study, we chose a field size of 12cm × 10cm to acquire CBCT images. Our study was conducted using our Siemens Oncor Impression Linac, an image quality phantom, an offline reconstruction tool prototype software, a prototype visualization tool, a dicom image extractor tool, and the ImageJ open source software from NIH. Five regions of the image quality phantom were imaged and the raw data was processed using the offline reconstruction tool by changing various reconstruction parameters. Our study was focused on two specific regions of the phantom, corresponding to electron densities of 9% and 17%. A useful projection image size of 448 × 373 pixels on the flat panel detector was used for the filtered backprojection. The dicom images were extracted with the dicom extractor from the reconstructed images for post processing and quantitative image analysis using the ImageJ software. Results: Our efforts in optimizing the image reconstruction and processing chain resulted in the development of protocols that result in superior images. We have developed quantitative methods to analyze the results and determine the optimal protocol. We are currently repeating the imaging process with the Image Quality phantom to check for reproducibility of our methods and protocols. Conclusions: Our preliminary result provides a valuable reference to setup an optimal protocol for using small field MVCBCT for IGRT. Once we confirm the reproducibility of our protocol, we plan on imaging a series of patients to clinically test the protocol.

Purpose: Electron Density Phantom (EDP) was used to evaluate dose calculation algorithms in Varian Eclipse Treatment Planning System (TPS) and to commission the Anisotropic Analytical Algorithm (Version 8.1.17, AAA_8117) with inhomogeneity correction for treatment planning. Methods and Materials: The EDP with various tissue equivalent plugs used to calibrate the CT simulator for dose calculation in Varian Eclipse TPS (Version 8.1.1.17) was adopted to evaluate different dose calculation algorithms in the TPS by measuring the actual dose delivered to the EDP prescribed by treatment plans. The treatment plans with field sizes of 20×20, 10×10, and 4×4 were created in the TPS using CT images of the EDP. The 200 cGy per fraction was prescribed to a point that is 4 cm behind the 8.2 cm long exhale‐lung tissue equivalent plug. Dose calculation for each plan was performed with calculation models of Pencil Beam Convolution (PBC_8117), the AAA_8117 without inhomogeneity correction, and the AAA_8117 with inhomogeneity correction, respectively. Then the individual plans were delivered to “treat” the EDP for measuring the actual dose. The 2‐D dose distributions were measured and analyzed with two independent methods (1) MapCheck, and (2) EDR‐2 film with RIT VXR‐16 Dosimetry Vidar System. The prescribed point dose was measured using an ion chamber. All the measured doses were compared with the calculated doses from the associated treatment plans. Results: The AAA_8117 with inhomogeneity correction is superior to the other algorithms in our study. The dose discrepancy is within 1% at the prescribed area. Conclusion: A practical method to evaluate different dose calculation algorithms in a TPS was proposed and performed in our study. Results suggest that the AAA_8117 with inhomogeneity correction should be used for treatment planning, especially when lung tissue is involved in the radiation field.