Validation of a high resolution solid state detector array for SBRT/SRS patient specific QA
PD-0812
Abstract
Validation of a high resolution solid state detector array for SBRT/SRS patient specific QA
Authors: Jelle Smeulders1, Thierry Gevaert1, Stijn Robbe1, Tim Everaert1, Adrian Gutierrez1, Anne-Sophie Bom1, Marlies Boussaer1, Mark De Ridder1
1UZ Brussel, Radiotherapy, Brussel, Belgium
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Purpose or Objective
The
myQA® SRS device (IBA, Brussels, Belgium), a recently
released high resolution detector array, was validated as a patient specific quality
assurance (PSQA) tool for stereotactic radiosurgery (SRS) and stereotactic body
radiation therapy (SBRT) by comparing PSQA field measurements with TPS calculations
and radiochromic film.
Material and Methods
Data from 35 SBRT and 15 SRS fields were collected using the myQA® SRS detector and dedicated phantom. The corresponding PSQA plans were delivered by a Truebeam STx (Varian, , USA) with 6 MV flattening filter free photon beams. The plans were selected to reflect a clinically relevant range of lesion sizes with GTV volumes ranging from 0.25 to 2.74 cc and 0.11 to 0.2 cc for SBRT and SRS cases, respectively. All SBRT plans were delivered using VMAT, while SRS plans were conformal arc therapy fields. Radiochromic film measurements were performed for ten SBRT and SRS fields each. TPS dose calculations were performed using Eclipse v15.6 (AAA) and Elements v2.0 (Pencil Beam) for SBRT and SRS plans respectively. The measurements were evaluated in the myQA software (Figure 1) using absolute gamma analysis with a criterion of 3% dose difference and 1 mm distance-to-agreement.
Figure 1: From left to right respectively, the dose distribution of
film, myQA measurement and gamma map of film to detector measurement comparison
for an ARC of a SRS plan of a PTV with a volume of 0.76cc.
Results
The mean gamma passing rate of the myQA®
SRS measurements in comparison to film was 96.5% and 97.8% for SBRT and SRS
fields, respectively. Only two fields out of 20 did not exceed a 95% passing
rate, both being VMAT fields. Comparisons of myQA® SRS measurements
against TPS dose calculations yielded a mean gamma passing rate of 97.6% for
SRBT cases and 93.5% for SRS cases. The mean gamma passing rate of SRS plans compared
to TPS becomes 98.2% after the removal of two fields characterized by low dose
spread (< 25 cGy) related to the MBM fields that is not correctly estimated
by the pencil beam algorithm.
Conclusion
The
myQA® SRS device was is a suitable tool for PSQA for SBRT and SRS treatments even in the
presence of small field conditions. Furthermore the device yields measurements
that are nearly equivalent to the golden standard being film measurements.