Purpose/Objective(s)The conventional tomotherapy patient specific delivery QA (DQA) is performed by delivering the patient plan in a phantom and measuring the dose distribution. The measured dose distribution is compared with the calculated one in the phantom to determine if certain criterion can be satisfied. This practice involves phantom setup and thus is time-consuming and error-prone. Given confidence in couch motion and dose calculation, we can simplify the DQA process by performing an in-air fluence verification with the exit detector array. Therefore phantom setup can be eliminated and automated data analysis can be achieved.Materials/MethodsThe detector calibration consists of signal response calibration and dose rate calibration. A set of delivery procedures are performed to characterize the detector signal response with respect to jaw width and leaf patterns. A dose rate calibration is performed to determine the absolute dose rate with respect to the detector signal. The calibration process needs to be performed when changes occur along the beam line, such as target, MLC, or detector array. The detector calibration enables us to predict radiation fluence at each projection given the delivery plan. Once the detector calibration is done, the DQA workflow can be simplified as follows. Generate a DQA plan without a phantom on a DQA Station. Right click the DQA-TRMT procedure on the Operator Station to generate a static couch procedure. Deliver the procedure in air without couch motion and archive the patient. Then an automated data analysis is performed. The detector data are processed to generate 2D fluence maps at different angles. The fluence maps are then applied to the planning CT to calculate dose. A gamma-index analysis is applied with respect to the planning dose and a QA report is generated. A leaf sinogram is reconstructed and leaf errors are analyzed.ResultsTwelve randomly selected patient plans have been tested for 2D fluence map comparison. For the three fixed jaw settings, misuse of jaw size can be easily detected as a systematic change of detector signals. Averaged over all plans, 90% of leaf open time errors are within +/- 10 ms. Tallied where fluence is greater than 10% of its maximum, the minimum gamma pass rate of 2D fluence maps of 51 angles ranges from 93.9% to 100% using 2%-2mm criterion and from 84.4% to 100% using 2%-1mm. For the worst-case plan, the gamma pass rate is 98.1% averaged over 51 angles using 2%-2mm criterion and 93.7% using 2%-1mm. Without phantom placement, the DQA time is estimated to be reduced by 10% to 75% depending on specific situation.ConclusionsWith confidence in couch motion and dose calculation, tomotherapy DQA can be performed in-air and analyzed automatically. Without the need for phantom placement, positioning error is eliminated and setup/processing time significantly reduced. Purpose/Objective(s)The conventional tomotherapy patient specific delivery QA (DQA) is performed by delivering the patient plan in a phantom and measuring the dose distribution. The measured dose distribution is compared with the calculated one in the phantom to determine if certain criterion can be satisfied. This practice involves phantom setup and thus is time-consuming and error-prone. Given confidence in couch motion and dose calculation, we can simplify the DQA process by performing an in-air fluence verification with the exit detector array. Therefore phantom setup can be eliminated and automated data analysis can be achieved. The conventional tomotherapy patient specific delivery QA (DQA) is performed by delivering the patient plan in a phantom and measuring the dose distribution. The measured dose distribution is compared with the calculated one in the phantom to determine if certain criterion can be satisfied. This practice involves phantom setup and thus is time-consuming and error-prone. Given confidence in couch motion and dose calculation, we can simplify the DQA process by performing an in-air fluence verification with the exit detector array. Therefore phantom setup can be eliminated and automated data analysis can be achieved. Materials/MethodsThe detector calibration consists of signal response calibration and dose rate calibration. A set of delivery procedures are performed to characterize the detector signal response with respect to jaw width and leaf patterns. A dose rate calibration is performed to determine the absolute dose rate with respect to the detector signal. The calibration process needs to be performed when changes occur along the beam line, such as target, MLC, or detector array. The detector calibration enables us to predict radiation fluence at each projection given the delivery plan. Once the detector calibration is done, the DQA workflow can be simplified as follows. Generate a DQA plan without a phantom on a DQA Station. Right click the DQA-TRMT procedure on the Operator Station to generate a static couch procedure. Deliver the procedure in air without couch motion and archive the patient. Then an automated data analysis is performed. The detector data are processed to generate 2D fluence maps at different angles. The fluence maps are then applied to the planning CT to calculate dose. A gamma-index analysis is applied with respect to the planning dose and a QA report is generated. A leaf sinogram is reconstructed and leaf errors are analyzed. The detector calibration consists of signal response calibration and dose rate calibration. A set of delivery procedures are performed to characterize the detector signal response with respect to jaw width and leaf patterns. A dose rate calibration is performed to determine the absolute dose rate with respect to the detector signal. The calibration process needs to be performed when changes occur along the beam line, such as target, MLC, or detector array. The detector calibration enables us to predict radiation fluence at each projection given the delivery plan. Once the detector calibration is done, the DQA workflow can be simplified as follows. Generate a DQA plan without a phantom on a DQA Station. Right click the DQA-TRMT procedure on the Operator Station to generate a static couch procedure. Deliver the procedure in air without couch motion and archive the patient. Then an automated data analysis is performed. The detector data are processed to generate 2D fluence maps at different angles. The fluence maps are then applied to the planning CT to calculate dose. A gamma-index analysis is applied with respect to the planning dose and a QA report is generated. A leaf sinogram is reconstructed and leaf errors are analyzed. ResultsTwelve randomly selected patient plans have been tested for 2D fluence map comparison. For the three fixed jaw settings, misuse of jaw size can be easily detected as a systematic change of detector signals. Averaged over all plans, 90% of leaf open time errors are within +/- 10 ms. Tallied where fluence is greater than 10% of its maximum, the minimum gamma pass rate of 2D fluence maps of 51 angles ranges from 93.9% to 100% using 2%-2mm criterion and from 84.4% to 100% using 2%-1mm. For the worst-case plan, the gamma pass rate is 98.1% averaged over 51 angles using 2%-2mm criterion and 93.7% using 2%-1mm. Without phantom placement, the DQA time is estimated to be reduced by 10% to 75% depending on specific situation. Twelve randomly selected patient plans have been tested for 2D fluence map comparison. For the three fixed jaw settings, misuse of jaw size can be easily detected as a systematic change of detector signals. Averaged over all plans, 90% of leaf open time errors are within +/- 10 ms. Tallied where fluence is greater than 10% of its maximum, the minimum gamma pass rate of 2D fluence maps of 51 angles ranges from 93.9% to 100% using 2%-2mm criterion and from 84.4% to 100% using 2%-1mm. For the worst-case plan, the gamma pass rate is 98.1% averaged over 51 angles using 2%-2mm criterion and 93.7% using 2%-1mm. Without phantom placement, the DQA time is estimated to be reduced by 10% to 75% depending on specific situation. ConclusionsWith confidence in couch motion and dose calculation, tomotherapy DQA can be performed in-air and analyzed automatically. Without the need for phantom placement, positioning error is eliminated and setup/processing time significantly reduced. With confidence in couch motion and dose calculation, tomotherapy DQA can be performed in-air and analyzed automatically. Without the need for phantom placement, positioning error is eliminated and setup/processing time significantly reduced.
更多
原文链接
分享
引用
