Sci‐Thur PM Therapy‐05: Evaluation of male pelvic phantom for megavoltage cone‐beam computed tomography

Computed tomography (CT)‐based image guidance has the feature of including the tumour as well as normal tissue in the image localization process during radiation treatment. We propose to use a new anthropomorphic male pelvic phantom (CIRS Inc.) to test the feasibility of using a linear‐accelerator‐based megavoltage (MV) cone‐beam CT system for imaging the prostate. The objective of this work is to verify the tissue‐equivalency of the phantom to determine whether it is representative of prostate cancer patients. We evaluated the phantom in two ways. (1) The linear attenuation coefficient was determined by measuring the photon transmission through uniform samples of the phantom materials (e.g., prostate, muscle, bladder, etc.) using 60 Co (2) The phantom material CT numbers (kVCT) were compared to CT number data acquired from randomly selected planning CT scans of prostate cancer patients at our institution. The measured linear attenuation coefficients agreed to ∼ 1% of the manufacturer's specifications, while the reproducibility of the measurement was ∼ 1%. The kVCT numbers in the phantom were also in good agreement with the manufacturer's specifications and the patient data. However, the bony structures are comprised of solid average bone equivalent material (cortical and trabecular bone), which caused artifacts within some regions of the kVCT images. However, MVCT imaging is expected to suppress these artifacts. These findings indicate that the phantom is representative of prostate cancer patients and will be a valuable tool in investigating the feasibility of MV cone‐beam CT. This work was partially supported by Siemens Medical Solution USA, Inc.