Abstract
We present here a novel method for using a single device in the daily quality assurance (QA) of pencil beam scanning (PBS) proton beams and an improved method for uniform scanning (US). The device can be used to measure the spot position, spot sigma, range, output, collinearity of the X‐ray system and proton beam, and to QA the first scatterers and a number of other imaging and mechanical checks. We have performed the daily QA according to this procedure for more than six months in both a PBS gantry and a US gantry. All of the tests were found to be sensitive and accurate enough to determine if the property being tested is within the tolerance. The output has remained within the ±2% tolerance, with the majority of measurements within ±1%, and the range was within ±0.5mm. The collinearity of the proton beam in both gantries is within the ±1mm tolerance in both X and Y directions for all measurements. A novel procedure to measure the functionality of the first scatterers in the US gantry is included in the QA procedure. It was found to be sensitive enough to pick up the thinnest scatterer of 0.6 mm in both possible failure methods — when it always remains in the beam or in the case when it never goes into the beam. The daily QA procedure presented here can be implemented at PBS or US proton therapy centers with a minimal outlay for equipment and setup time. The procedure can be performed in less than 30 min, and has been found to be accurate and reliable enough for the QA of a proton therapy gantry before patient treatment every day.PACS number: 87.55.Qr
Highlights
A thorough quality assurance (QA) program is essential in any radiotherapy modality to ensure the safe and accurate treatment of patients
Mechanical and imaging After six months of performing daily QA with this procedure, we found that the alignment of the markers on the QA3 were always within tolerance after the correction was made with the VeriSuite X-ray imaging system
These patient positioning system (PPS) positions remained within ± 2.1 mm, with the largest variation in the Z direction and the majority of points within ± 1 mm of the baseline value
Summary
A thorough quality assurance (QA) program is essential in any radiotherapy modality to ensure the safe and accurate treatment of patients. There are a number of devices available that are designed to measure a specific property of the proton beam, which together could be used to create a thorough QA program. Ding et al[3] published a method of using a commercially available Sun Nuclear QA3 device (Melbourne, FL) designed for photon/electron linacs for the QA of uniform scanning (US) proton beams. They were able to measure the output, range, and symmetry of the beam in a single measurement. Pencil beam scanning (PBS) proton beams have an added complexity that makes daily QA measurements more difficult. Potential treatment errors can occur if the individual spot positions are not accurate or if there is a large change in the spot size due to changes in the beam optics or scattering material in the beam line
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