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Abstract
The machine log files recorded by a scanning control unit in proton beam therapy system have been studied to be used as a quality assurance method of scanning beam deliveries. The accuracy of the data in the log files have been evaluated with a standard calibration beam scan pattern. The proton beam scan pattern has been delivered on a gafchromic film located at the isocenter plane of the proton beam treatment nozzle and found to agree within ±1.0 mm. The machine data accumulated for the scanning beam proton therapy of five different cases have been analyzed using a statistical method to estimate any systematic error in the data. The high-precision scanning beam log files in line scanning proton therapy system have been validated to be used for off-line scanning beam monitoring and thus as a patient-specific quality assurance method. The use of the machine log files for patient-specific quality assurance would simplify the quality assurance procedure with accurate scanning beam data.
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Fig. 1.
A scanned EBT3 film irradiated with the standard scan pattern composed of 5x5 points (230 MeV).
Fig. 2.
An example of scanning beam information recorded in the scanning control unit (Top left: x-position in time, top right: y-position in time, bottom left: monitor count in time, bottom right: x-position vs. y-position. Raw data without pedestal/noise reduction).
Fig. 3.
A scanning beam information recorded in the scanning control unit (one sample layer of a patient beam delivery plan).
Table 1.
The summary of pre-treatment QA log file analysis. The “ds” stands for the displacement of the recorded position from the planned position. For a given field (case), the entire energy layers (number of layers) have been analyzed.
| Cases | Number of layers | Average of ds | Standard deviation |
|---|---|---|---|
| [mm] | of ds [mm] | ||
| Case 1 | 15 | 0.09 | 0.09 |
| Case 2 | 17 | 0.11 | 0.10 |
| Case 3 | 23 | 0.15 | 0.07 |
| Case 4 | 18 | 0.10 | 0.11 |
| Case 5 | 11 | 0.06 | 0.14 |
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