Is Every Measurement Necessary? Reducing Commissioning Measurements through Electron Utilization Analysis
Abstract
Purpose
To quantify the usage of different electron beam treatments and use that data to develop recommendations for maximizing efficiency in electron output factor measurements.
Methods
For a large center with a main campus and 14 satellite facilities, the clinical treatment records of every patient treated with electrons were examined for a one-year period. For each treatment, when possible, the beam energy, applicator size, SSD, and cutout dimensions were recorded. The cutout width (smaller dimension) was rounded down to the next lowest integer value. Cutout widths were analyzed because that is the dimension for which the output factor is most sensitive to a small change. After excluding Total Skin Electron patients and other special procedures, as well as treatments for which there was inadequate data, 351 patient records were examined.
Results
The widths were categorized by beam energy, SSD, and applicator. The vast majority of treatments were made with 6, 9, or 12 MeV beams at 100 or 105 SSD. Utilization of 20 MeV beams (<2%) and 25 cm applicators (<3%) was minimal. Similarly, only 8.5% of treatments required an SSD of 110 cm.
Conclusion
Electron cutout factor tables are measured at machine commissioning to reduce the need for patient-specific measurements. This process is made more efficient if the table is limited to only those situations likely to arise in clinical practice. These data suggest that not including data for 20 MeV beams, the 25x25cm applicator, and SSDs greater than 105 provides a significant reduction in commissioning time while maintaining 87-95% clinical coverage. This would require a slight increase in patient-specific output factor measurements, but provide a large decrease (as much as 65%) in measurements needed to create the table during commissioning.