SU-E-T-103: An Evaluation of Multiple Irradiations of the IROC Houston QA Center Anthropomorphic Liver Phantom

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Abstract

Purpose:

Analyze the results from irradiations of an anthropomorphic liver phantom based on irradiation technique and number of isocenters used for the SBRT delivery.

Methods:

The phantom consists of a water-fillable plastic shell that has a polystyrene insert, representing the liver which includes two Solid WaterTM targets (PTV1 and PTV2) mimicking liver metastases. The two targets, PTV1 and PTV2 are non-coplanar and are an ovoid 2 cm in diameter and 2.5 cm long and a 3 cm diameter sphere, respectively. Each PTV houses one TLD and 2 planes of radiochromic film. The phantom and a motion table to simulate respiratory motion is sent to institutions sthat are instructed to design and deliver a stereotactic treatment plan that delivers 6 Gy to ≥ 95% of each PTV. The maximum motion of the phantom on the motion table was 1 cm in the superior-inferior direction.

Results:

Irradiations from 93 institutions have been analyzed. The acceptance criteria are ±7% for the TLD and 85% of the pixels in a region surrounding each PTV passing a ±7%/4 mm global gamma analysis. Sixty-seven (71%) irradiations meet this criteria. The majority, 74 (80%), of the irradiations were performed with IMRT. 73% of the IMRT deliveries were within criteria and 68% of the 3D CRT delivery were within criteria. 32 of the irradiations had a single isocenter plan, 50 were performed with two isocenters and 11 irradiations were performed with CyberKnife and TomoTherapy units where the concept of isocenter is not applicable. The pass rate for the single, dual and no isocenter irradiations were 69%, 74% and 73%, respectively and are not statistically different.

Conclusion:

The pass rate for the anthropomorphic liver phantom is approximately 70%. There does not seem to be any correlation with number of isocenters used or irradiation technique used for the delivery.

This work was supported by PHS CA180803 awarded by NCI, DHHS

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