SU‐E‐T‐549: Hypofractionated Spine Radiotherapy: How Do You QA?

Purpose: To evaluate the ability of commercially available devices to perform IMRT QA measurements for plans involving small volume targets as in the case of single spine vertebra radiotherapy Methods: Seven (n=7) patient with metastatic spine lesions were treated using RapidArc plans. The plans were optimized so that a single arc was to deliver the dose of 4.0Gy per fraction for 5 fractions to the vertebral body while limiting the dose to the spinal cord. For each approved plan four (n=4) verification plans were developed corresponding to four different IMRT QA detectors (EBT2 film, IBA MatrixX, PTW Seven29, and Scandidos Delta4) employed for the evaluation of the patient IMRT QA. Each QA was evaluated for its agreement against the verification plan using the gamma index, profiles and planar isodose distribution agreement. Results: The Scandidos Delta4 device had the best agreement. The PTW Seven29 detector array had similar response to film measurements. The response of the PTW Seven29 array improved when the multiple, off centered measurements were averaged. The IBA MatriXX device had inferior response compared to the other detector arrays and had the lowest gamma passing ratesConclusion: The choice of the IMRT QA device has an important role in the results of the patient specific quality assurance of the delivered dose to the patient in the case of small targets as in the treatment of spinal targets.