Abstract
As part of the approval process for the use of scattered or uniform scanning proton therapy in National Cancer Institute (NCI)‐sponsored clinical trials, the Radiological Physics Center (RPC) mandates irradiation of two RPC anthropomorphic proton phantoms (prostate and spine). The RPC evaluates these irradiations to ensure that they agree with the institutions' treatment plans within criteria of the NCI‐funded cooperative study groups. The purpose of this study was to evaluate the use of an anthropomorphic spine phantom for proton matched‐field irradiation, and to assess its use as a credentialing tool for proton therapy beams. We used an anthropomorphic spine phantom made of human vertebral bodies embedded in a tissue substitute material called Muscle Substitute/Solid Rigid Number 4 (MS/SR4) comprising three sections: a posterior section containing the posterior surface and the spinous processes, and left and right (L/R) sections containing the vertebral bodies and the transverse processes. After feasibility studies at three institutions, the phantom, containing two thermoluminescent dosimeters (TLDs) for absolute dose measurements and two sheets of radiochromic film for relative dosimetry, was shipped consecutively to eight proton therapy centers participating in the approval study. At each center, the phantom was placed in a supine or prone position (according to the institution's spine treatment protocol) and imaged with computed tomography (CT). The images then were used with the institution's treatment planning system (TPS) to generate two matched fields, and the phantom was irradiated accordingly. The irradiated phantom was shipped to the RPC for analysis, and the measured values were compared with the institution's TPS dose and profiles using criteria of ± 7% for dose agreement and 5 mm for profile distance to agreement. All proton centers passed the dose criterion with a mean agreement of 3% (maximum observed agreement, 7%). One center failed the profile distance‐to‐agreement criterion on its initial irradiation, but its second irradiation passed the criterion. Another center failed the profile distance‐to‐agreement criterion, but no repeat irradiation was performed. Thus, seven of the eight institutions passed the film profile distance‐to‐agreement criterion with a mean agreement of 1.2 mm (maximum observed agreement 5 mm). We conclude that an anthropomorphic spine phantom using TLD and radiochromic film adequately verified dose delivery and field placement for matched‐field treatments.PACS number: 87.55.‐x, 87.55.N‐
Highlights
Proton therapy is increasingly popular and accessible as one of the most effective forms of cancer treatment
The Radiation Therapy Oncology Group and the Children’s Oncology Group, both funded by the National Cancer Institute (NCI), have created proton radiation therapy protocols for clinical trials
Owing to the need to enroll and manage patients with proton therapy in a consistent manner in these NCI-funded cooperative group clinical trials, the NCI requested that the Radiological Physics Center (RPC) develop a comprehensive approval process
Summary
Proton therapy is increasingly popular and accessible as one of the most effective forms of cancer treatment. 11 proton therapy centers operate in the United States, and 13 new centers are in development. As more proton therapy centers become operational, it is desirable to ensure that each center delivers clinically comparable treatment, such as consistent dose. Owing to the need to enroll and manage patients with proton therapy in a consistent manner in these NCI-funded cooperative group clinical trials, the NCI requested that the Radiological Physics Center (RPC) develop a comprehensive approval process. Proton therapy centers wishing to participate in NCI-sponsored clinical trials can apply for approval by completing the proton facility questionnaire, participating in the RPC’s annual remote audit program, submitting electronic treatment planning data, independently irradiating the RPC’s baseline proton phantoms with consistent results according to the RPC criteria, and passing an RPC dosimetry review visit. Details of the procedures can be found in the May 2013 issue of the RPC newsletter.[1]
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