- 期刊
放射治療錐狀射束電腦斷層之輻射劑量-影像品質權衡評估
Trade-off Evaluation between Radiation Dose and Image Quality of Cone-beam Computed Tomography in Radiotherapy
摘要
錐狀射束電腦斷層（cone beam computed tomography, CBCT）已被廣泛的應用於臨床醫療之上，以提供病患高精確的放射治療，然而，每次治療前的定位CBCT 掃描將為病患帶來不可忽視的輻射風險，因此，本研究進行CBCT 輻射劑量-影像品質權衡評估以幫助減少病人之輻射劑量並維持影像品質。本研究使用擬人假體搭配底片，量測CBCT 在不同參數設定掃描下於肺中及體表之輻射劑量，並於掃描產生之影像評估其品質，最後結合劑量與影像品質之結果計算品質參考因子（quality reference factor）。結果顯示，減半管電流條件最能有效減少輻射劑量，相較於標準掃描條件，左、右肺分別可減少55.9%及58.4%的劑量，而使用外加濾器則可同時減少輻射劑量並改善影像中的條狀假影（streak artifacts），此外，適當使用縮限視野（field of view）可避免重要器官直接受到照射，進而降低其輻射劑量；而在影像品質上，減半管電流條件、使用外加濾器條件在肺臟區域中的SNR 相較於標準條件分別減少5.7%與0.9%。我們認為，適當的調整掃描參數將可有效的降低病患於CBCT 掃描中所接受的輻射風險並保持影像之品質。
並列摘要
Cone beam computed tomography (CBCT) has been widely applied in clinical radiation therapy to improve the accuracy of dose irradiation. However, the pre-treatment CBCT scan yields significant radiation risk to patients. In this study, the trade-off evaluation between radiation dose and quality of CBCT image was performed to reduce dose to patient as well as maintain the image quality. An anthropomorphic phantom coupled with Gafchromic films was used to measure the lung and skin dose from CBCT scans with different parameter sets. The simultaneously acquired CT images were employed to evaluate the image quality. At last, a quality reference factor was calculated by combining the results of dose measurement and image quality evaluation. The results showed that halving tube current can significantly reduce radiation dose. Comparing to the standard scanning parameter set, the doses to left and right lung can be reduced by 55.9% and 58.4%, respectively. By using an additional filter to remove low energy photons, the radiation dose can be lowered and the streak artifacts can be reduced. In addition, limited field of view (FOV) can avoid the exposure to critical organs, thereby minimized the absorbed dose. Comparing to the standard scanning parameters, CT scans using the halve tube current and additional filter slightly reduced the SNR in lung regions by 5.7% and 0.9%, respectively. In conclusion, we thought that properly adjusting the scanning parameter could usefully reduce the radiation risk to patients during CBCT scans.