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Evaluation of the ArcCheck Device for Patient-Specific Quality Assurance in Step-And-Shoot IMRT for Single-Fraction Spinal SBRT

J Daartz

J Daartz*, B Winey, M Bussiere, D Gierga, B Crawford, D Sedlacek, C Cotter, Massachusetts General Hospital, Boston, MA

SU-E-T-433 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Current standard for patient specific spine SBRT IMRT QA in our institution is a combination of a point dose measurement in solid water under delivery of the beams at actual treatment angles, and 2D planar verification using an ion chamber (IC) array with all beams delivered at standard gantry angle of zero.
The very small active area of ArcChecks diodes (~0.6mm2) has the potential to improve measurement accuracy in high dose gradient regions present in spinal SBRT. Given high clinical workload we seek to improve ease of workflow and decrease time necessary for patient-specific QA, by obtaining 2D verification and point dose measurement at actual treatment angles in one single measurement.

The results of 10 patient specific QA measurements, as performed with single-point and 2D IC array were compared to results obtained with ArcCheck. ArcCheck and 2D IC array pass rates are evaluated for 3%/3mm gamma criteria, single-point measurement based on percent deviation from QA plan dose. The constancy of the device was assessed by re-measuring the same treatment plan over the course of three weeks, and evaluating pass rate variation

The gamma pass rates are generally higher for ArcCheck (average 99.3%) than for Matrixx (average 93.1%). Average absolute deviation for the single-point IC measurement was 3.4%. Maximum variation in pass rate between any two ArcCheck measurements within the three-week evaluation period was 0.5%. Since ArcCheck allows for the use of an insert with an ion chamber in place, simultaneous redundant point measurement is possible with no time added

Based on our results patient-specific QA for spine SBRT treatments will be performed using ArcCheck with pass/fail criteria 98%. High sensitivity towards geometrical shifts necessitates careful initial alignment of the device.

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