Application Note: ArcCHECK
Differences Between Original and New ArcCHECK® and Clinical Impact Application Note #01-15, Author: Jie Shi, PhD.
Purpose Sun Nuclear has recently transitioned production from the original ArcCHECK to a new version. The new ArcCHECK can be identified by the serial number on the product label (starts with ‘1222’), and the text on the electronics panel that states the instrument must be used with a PDI 3.0 and blue power/data cable. This document explains the differences between the original and new ArcCHECK instruments.
Differences Between Original and New ArcCHECK 1 2
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Sun Nuclear made design modifications in detectors and circuits to meet EU RoHS (Restriction of Hazardous Substances directive) requirements. RoHS design changes resulted in a reduction in detector overresponse to low energy photon scatter radiation, from ~20% in the original AC to ~5% in the new ArcCHECK (local difference). This may result in a relative dose overresponse of ~0.5% from the original ArcCHECK for a ≥10x10 cm2 field and less overresponse for smaller fields. In highly modulated beams, the higher overresponse effect of the original ArcCHECK may accumulate and result in lower gamma passing rates compared to the new ArcCHECK, if stringent criteria are used, such as 2%/2mm local difference.
Product Specification and Commonly Accepted Clinical Practice 1 2
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Both the original and new ArcCHECK instruments perform within the product specifications. Although there are no protocol recommendations on criteria or tolerance, including from AAPM, ESTRO, and ASTRO, there is published data. The AAPM TG-119 report presented an average gamma passing rate of 93% using 2D arrays for field by field, and 87% using film for composite IMRT QA, both with 3%/3mm global.1 A survey was conducted on the MedPhys list server in October, 2015 regarding VMAT QA using the original ArcCHECK. Using 3%/3mm criteria for gamma passing rate: 60% of the respondents use 95%; 38% use 90%; 2% use 85% as the tolerance for H&N plans (n=90). Considering the original ArcCHECK was introduced in 2009, and the new ArcCHECK in mid-2015, most of the survey respondents would likely have been original ArcCHECK users. Studies demonstrate that the TPS may also overestimate the scatter radiation regions. One way to compensate for overresponse from the TPS and ArcCHECK is to ensure the optimal DLG (dosimetric leaf gap) value and MLC transmission factor are used.2 The ultimate goal of IMRT/VMAT QA is to ensure the quality and safety of the patient treatment. When the QA in phantom fails, it is best to evaluate the impact in each anatomical structure using 3D DVH based software, such as 3DVH® which is compatible with the original and new ArcCHECK instruments.
Conclusions 1
The new ArcCHECK over-responds less than the original ArcCHECK; however: a. Both the original and new ArcCHECK instruments meet their product specifications. b.
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The difference between the original and new ArcCHECK instruments should have no noticeable effect on QA results when the commonly acceptable criteria and tolerance are used, which is 3%/ 3mm global gamma. When QA fails, the clinical impact should be evaluated in patient anatomy using 3DVH software.
G. A. Ezzell, et al, "IMRT commissioning: multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119," Med Phys 36, 53595373 (2009). D. Jacqmin, "Determining MLC Parameters for Eclipse Using Electronic Arrays," The 8th QA & Dosimetry Symposium, Orlando, Florida, February 27-28, 2015.
© 2015, Sun Nuclear Corporation, Document 1220044 Rev A, 04 November 2015 Corporate Headquarters 3275 Suntree Boulevard Melbourne, Florida 32940 +1 321-259-6862 www.sunnuclear.com
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