Level III audits
The ACDS Level III audit determines absorbed dose to water delivered to selected points within an anthropomorphic phantom. This is an end-to-end audit where the phantom undergoes all steps within the radiotherapy treatment chain.
The Level III audit includes a number of optional modalities, which can be completed by the facility to reflect their clinical practice:
- 3DCRT
- IMRT
- VMAT
- IMRT FFF (in trial)
- VMAT FFF (in trial)
- SABR (in field trial)
Figure 1: Custom CIRS thorax phantom
Dosimetry measurements are made in a custom CIRS IMRT Thorax phantom, using a ‘TomoElectrometer’ multi-channel electrometer (Standard Imaging), with Farmer type and CC13 ionisation chambers as the primary detectors. Ion chambers are calibrated by the national primary standards laboratory at ARPANSA. As recommended by TRS-398, the ACDS uses ion chamber calibration factors determined in high-energy beams of similar quality (referred to as 'Directly measured').
3DCRT
For 3DCRT cases the scoring criteria have been applied to 100% of the scored points (i.e. the audit outcome is derived from the point that returns the maximum absolute local dose variation).
IMRT and VMAT
The scoring criteria are applied to 94% of the points (i.e. the audit outcome is derived from the local dose variation returned after the worst point at each beam energy is excluded). If the absolute local dose variation of a point is outside ±8%, the point will not be excluded and an Out of Tolerance outcome will be returned.
Audit cases
Cases 1-4
For the 3DCRT modality there are 4 cases in the audit, with the option of repeating these cases with multiple beam models. The 3DCRT modality consists of reference and wedged beams, measured with and without lung inhomogeneity. A schematic of the cases is shown in Figure 2.
Figure 2: 3DCRT
Cases 5-8
Cases 5-8 consist of complex target volumes for inclusion in the IMRT and VMAT modalities. The facility has the option to include as many IMRT and/or VMAT beam models in the audit as applicable to their clinical practice. Cases 5-8 are repeated for the IMRT FFF and VMAT FFF modalities.
Case 5 – The ‘Chair’ Test
The chair test is an adaptation of the test described by Van Esch et al. [1], where a chair-like fluence (Fig. 3) is delivered by dynamic MLC movement. The test aims to separate the effects of leaf transmission from dosimetric leaf separation in a single test.
Figure 3: The 'Chair' test
Case 6 & 7 – The C-Shape
The C-Shape target volume has been adapted from AAPM: TG119 [2], a horseshoe shaped target volume surrounding a central avoidance structure. Two treatment plans for the C-Shape are required; with and without inhomogeneities (Fig 4).
Figure 4: C-Shape with and without lung inhomogeneities
Case 8 – The Complex Case
The ACDS derived the ‘complex’ case from elements of IMRT/VMAT practice observed in the clinic. The complex case (Fig.5) consists of two adjacent target structures, with varying dose objectives, and an exclusion sphere fully encompassed by the higher dose target.
Figure 5: The Complex Case
Audit outcome
The audit results are determined ‘point-by-point’ for each case using a percentage deviation of the facility stated dose (planned) from the ACDS determined dose (measured). An overall audit outcome is determined for each modality, the facility chooses to include in the audit. The local dose variation from each scored measurement point is assessed according to the following criteria.
| Pass (optimal level) | Pass (action level) | Out of tolerance | Reported not scored (RNS) |
|---|---|---|---|
| ≤ 3.3%* | > 3.3% and ≤ 5% | > 5% |
|
Datasets for download (last updated 24 September 2019)
-
ACDS Level III CT dataset (Red Phantom)
* - If you are having difficulty downloading this file, please contact ACDS at acds
arpansa.gov.au for the latest dataset. - ACDS Level III CT dataset (Yellow Phantom) * - If you are having difficulty downloading this file, please contact ACDS at acdsarpansa.gov.au for the latest dataset.
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Winston Lutz
* Ensure downloading correct fusion dataset, corresponding with phantom that was scanned at your facility (Red or Yellow)
ACDS audit level III documentation
References
[1] Van Esch A, Bohsung J, Sorvari P, Tenhunen M, Paiusco M, Iori M, et al. Acceptance tests and quality control (QC) procedures for the clinical implementation of intensity modulated radiotherapy (IMRT) using inverse planning and the sliding window technique: experience from five radiotherapy departments. Radiotherapy and Oncology 2002;65(1):53-70.
[2] Ezzell GA, Galvin JM, Low D, Palta JR, Rosen I, Sharpe MB, et al. Guidance document on delivery, treatment planning, and clinical implementation of IMRT: report of the IMRT Subcommittee of the AAPM Radiation Therapy Committee. Medical physics 2003; 30(8):2089-115.
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