In Vivo 3-D Dose Verification Using PET/CT Images After Carbon-Ion Radiation Therapy.

OBJECTIVE: To investigate the usefulness of positron emission tomography (PET) images obtained after carbon-ion irradiation for dose verification in carbon-ion radiotherapy. METHODS AND MATERIALS: An anthropomorphic head phantom was used in this study. Three cubes with volumes of 1, 4, and 10 ml were contoured as targets in the phantom CT through a treatment planning system. Treatment plans with six prescriptions from 2.5 to 10 Gy (2.5, 3, 5, 6, 8, and 10 Gy effective dose) were designed and delivered by 90° fixed carbon-ion beams, respectively. After irradiation of the phantom, a PET/CT scan was performed to fuse the treatment-planning CT image with the PET/CT image. The relationship between target volume and the standard uptake value (SUV) in PET/CT was evaluated for corresponding plan prescription. The MIM Maestro software was used for the image fusion and data analysis. RESULTS: SUV in the target had an approximate linear relationship with the effective dose. The same effective dose could generate a roughly equal SUV for different target volumes (p < 0.05). CONCLUSIONS: It is feasible to verify the actual 3-D dose distribution of carbon-ion radiotherapy by the approach in this study.

Evaluation of Proton Therapy Accuracy Using a PMMA Phantom and PET Prediction Module.

Purpose: Positron emission tomography (PET) scanning is a widely used method of proton therapy verification. In this study, a proton radiotherapy accuracy verification process was developed by comparing predicted and measured PET data to verify the correctness of PET prediction and was tested at the Shanghai Proton and Heavy Ion Center. Method: Irradiation was performed on a polymethyl methacrylate (PMMA) phantom. There were two dose groups, to which 2 and 4 Gy doses were delivered, and each dose group had different designed dose depths ranging from 5 to 20 cm. The predicted PET results were obtained using a PET prediction calculation module. The measured data were collected with a PET/computed tomography device. The predicted and measured PET data were normalized to similar PET amplitude values before comparison and were compared using depth and lateral profiles for the position error. The error was evaluated at the position corresponding to 50% of the maximum on the PET curves. The mean and standard deviation were calculated based on the data sampled in the scoring area. Gamma index analysis is also applied in the comparison. Results: In the depth comparison, the 2 and 4 Gy dose cases yielded similar mean depth errors between 1 and -1 mm, and the deviation was <2 mm. In the lateral comparison, the 2 Gy cases had a mean lateral error around 1 mm, and the 4 Gy cases had a mean lateral error <1 mm, with a standard deviation <1 mm for both the 2 and 4 Gy cases. All the cases have a gamma passing rate over 95%. Conclusion: The comparison of these PMMA phantom cases revealed good agreement between the predicted and measured PET data, with depth and lateral position errors <2 mm in total, considering the uncertainty. The comparison results demonstrate that the PET predictions obtained in PMMA phantom tests for single proton beam therapy verification are reliable and that the research can be extended to verification in human body treatment with further investigation.