(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: To automate solid water phantom setup with light-dependent-resistors (LDR) utilizing light field as a guide, to build a device for self-aligning setup without user intervention, to replace any light field-related QA tests with an automated system, to eliminate inter-observers variation, and to quantify the device's setup accuracy and precision.
Methods: Linac rooms have no natural light present because they are fully shielded and have a maze. This controlled light environment provides an ideal occasion for LDR application. Our first prototype auto-setup device was constructed with 2 LDRs. It had one-dimensional movement capability achieved with a recycled Varian MLC driving motor (Figure 1a), which has a precision of 0.1 mm and a programmable microcontroller. The physical size of the LDRs is 4 mm in diameter. Its interior design exhibits an inter-digital pattern (Figure 1b). TrueBeam high resolution KV imaging was used to measure and evaluate the device's auto-alignment accuracy (Figure 1c). Also used optical surface monitoring system (OSMS) to record alignment accuracy in both Y (longitudinal) and X (lateral) directions (Figure 1d-e).
Results: Initial experiments indicated that building a self-aligning solid water phantom was feasible. With our device, accurate phantom setup was achieved in seconds. Self-aligned setup accuracy observed with KV imaging (N=10) was 0.33 mm±0.25mm [range, 0-0.7mm], when the device was positioned in the longitudinal direction. Setup accuracy observed with OSMS (N=18) was 0.38 mm±0.32mm [0-1.2mm]. The device was also positioned in the lateral direction for the OSMS measurement, accuracy (N=11) was 0.11mm±0.1mm [0-0.3mm].
Conclusion: This work demonstrates an automated setup device built with LDRs. Preliminary results show that this novel design may replace and even eliminate all user dependent light-radiation field coincidence checks performed by observers and can greatly shorten phantom setup time. This principle can be naturally extended to all dose measuring devices.
Keywords
Quality Assurance, Autocorrelation Function
Taxonomy
IM/TH- Formal quality management tools: General (most aspects)
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