TU-E-BRB-06: Results from Multiple Radiations of an Anthropomorphic Spine Phantom

Abstract

Purpose: To credential institutions to participate in an IMRT‐dose painting spine metastasis protocol. Method and Materials: A mailable anthropomorphic spine phantom was developed and shipped to 21 institutions interested in participating in protocols sponsored by the National Cancer Institute (NCI). The phantom was a modification of the Radiological Physics Center's lung‐thorax phantom. An insert was designed to simulate a solid water spinal cord surrounded by a high impact polystyrene bone structure. An acrylic planning target volume is adjacent to the bone structure. The insert houses radiochromic film and TLD. The phantom also contains an esophagus, a heart and two lungs. Institutions were asked to image the phantom, create an IMRT plan to deliver 6 Gy to at least 90% of the PTV, perform their normal IMRT QA, and deliver the treatment plan to the phantom. The spinal cord dose was limited to 3.75 Gy to a volume of less than 0.35 cc and 2.63 Gy to a volume of less than 1.2 cc. The following criteria were applied: PTV TLD ±7%, ≥85% of the pixels in regions of interest in the axial and sagittal planes must pass a gamma criteria of 5%, 3 mm, and the plan must comply with the protocol. Results: 21 institutions irradiated the phantom 24 times. 8 of the irradiations failed the criteria. 4 of the failing irradiations passed the TLD criterion, but did not pass the gamma criterion. 4 irradiations failed both the TLD and gamma criteria. One of these also failed the plan criteria. The 3 institutions that irradiated the phantom twice all passed on the second irradiation. Conclusion: The phantom is a useful tool in credentialing institutions to participate in protocols. The investigation was supported by PHS grants CA10953 and CA81647 awarded by the NCI, DHHS.