Abstract
In this report, we present the commissioning and validation results for a commercial proton pencil beam scanning RayStation treatment planning system. The commissioning data requirements are (1) integrated depth dose curves, (2) spot profiles, (3) absolute dose/monitor unit calibration, and (4) virtual source position. An 8-cm parallel plate chamber was used to measure the integrated depth dose curves by scanning a beam composed of a single spot in a water phantom. The spot profiles were measured at 5 different planes using a 2-dimensional scintillation detector. The absolute dose/monitor unit calibration was based on dose measurements in single-layer fields of size 10 × 10 cm2. The virtual-source position was calculated from the change in spot spacing with the distance from the isocenter. The beam model validation consisted of a comparison against commissioning data as well as a new set of verification measurements. For end-to-end testing, a series of phantom plans were created. These plans were measured at 1 to 3 depths using a 2-dimensional ion chamber array and evaluated for gamma index using the 3% and 3 mm criteria. The maximum deviation for spot sigma measured versus calculated was -0.2 mm. The point-dose measurements for single-layer beams were within ± 3%, except for the largest field size (29 × 29 cm2) and the highest energy (226 MeV). The point doses in the spread-out Bragg peak plans showed a trend in which differences > 3% were seen for ranges > 30 cm, field sizes > 15 × 15 cm2, and depths > 25 cm. For end-to-end testing, 34 planes corresponding to 13 beams were analyzed for gamma index with a minimum pass rate of 92.8%. The acceptable verification results and successful end-to-end testing ensured that all components of the treatment planning system were functional and the system was ready for clinical use.
Highlights
IntroductionPencil beam scanning (PBS) is a technology in proton therapy [1] that can reduce the need for field-specific hardware (apertures and compensators) and offers better dose conformity to the target
Pencil beam scanning (PBS) is a technology in proton therapy [1] that can reduce the need for field-specific hardware and offers better dose conformity to the target
We found that the RS planning system underestimated doses for beams that had field sizes . 15 3 15 cm2 and energy . 218 MeV
Summary
Pencil beam scanning (PBS) is a technology in proton therapy [1] that can reduce the need for field-specific hardware (apertures and compensators) and offers better dose conformity to the target. In our PBS beam delivery system, a 3-dimensional target is divided into layers that are positioned at a user-defined interval. Commissioning of a proton pencil beam TPS from the most distal layer to the most proximal layer sequentially. The dose is deposited through individual spots that can have unique intensities and positions. One advantage of PBS is that inverse planning provides the ability to have multiple dose levels in a target within a single field (dose painting). PBS beams can be optimized to provide both distal and proximal dose conformity to the target volume
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