SU-E-T-125: High-Resolution Linear Diode Array for Use in Stereotactic Beam Commissioning

Task Group 106 discusses detector arrays and their usefulness in "soft-wedge" profile measurements. This study verifies an extension of their use; where a high-resolution linear diode array is used to measure profile scans for use in commissioning stereotactic beam. Small-field data is acquired with the LDA-99sc (IBA Dosimetry America, Memphis, TN), an array of 99 two-mm-diameter Hi-pSi diodes. These data are compared to data collected during serial scanning with an IBA SFD stereotactic diode.

Field measurements were taken at varying depths using an LDA-99sc in 1×1 cm² , 2×2cm² , and 3×3cm² fields of a Trilogy accelerator (Varian Medical Systems, Palo Alto, CA). These scans were duplicated in resolution and sample rate with an SFD scanning diode. Both techniques acquired point data in 1.0mm increments.

In identical conditions, the LDA-99sc provided readings with significantly less signal fluctuation than with traditional diode scanning; which is attributed to the reduction of water motion associated with detector travel during traditional scanning. This smoother data precluded the use of smoothing and filtration algorithms; allowing the beam to be modeled using raw data. The LDA-99sc measured an average penumbra of 0.1 mm wider than that which was measured with the diode. The LDA-99sc also measured an average field size of 0.3mm wider than that which was measured with the diode. With respect to time, a single profile scan (30cm-depth, 3×3cm² field) using the LDA-99sc took 31 seconds, while a diode scan took 229 seconds.

The LDA99 provided accurate commissioning-grade small-field beam profile data, as verified by comparison with diode scans, with a reduction of uncertainty in readings and a substantial reduction in time. Variation in penumbra and beam widths were deemed acceptable and can be attributed to the LDA-99sc data being raw, while the diode data was processed. Research supported in-part by IBA Dosimetry America.