- Personal Radiation Monitoring Service
- Equipment Calibration and Testing
- Radioanalytical Services
- Hire of Radiation Meters
- Ultraviolet Radiation (UVR) Services
- UV Data
- Buyer's Guide for Sun Protection
- Radiation Safety Advice and Risk Evaluation
- Australian Clinical Dosimetry Service
- National Diagnostic Reference Level Service
- Australian National Radiation Dose Register
- Radiotherapy Calibrations
For more information please get in touch with ARPANSA
- Phone Number+61 3 9433 2220
- Fax Number
- email ACDS
ACDS - Level II Audits
LEVEL II AUDITS
The ACDS Level II audit determines absorbed dose to water, for selected mega-voltage photon beams, within a simple phantom geometry. This is an audit of the beam models within a treatment planning system, where the phantom CT is supplied to the facility for treatment planning and delivery.
The Level II audit includes a number of modalities:
- VMAT (in trial)
- IMRT FFF
- VMAT FFF (in trial)
Dosimetry measurements are made in a custom phantom of CIRS solid water, using a 2D ionisation chamber array as a primary detector and supporting measurements with CC13 ionisation chambers. The 2D array is calibrated against a Farmer type ionisation chamber, which is traceable to the primary standard at ARPANSA.
For the 3DRT modality there are 12 cases in the audit, with the option of repeating these cases with multiple beam models. The 3DCRT modality consists of non-reference and wedged beams, measured with and without lung inhomogeneities. Figure 2 shows a schematic of some of the audit cases included in the 3DCRT modality.
Figure 2: Selection of 3DCRD cases in the Level II audit
Cases 13-16 consist of complex target volumes and diagnostic tests for 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 13-16 are repeated for the IMRT FFF and VMAT FFF modalities.
Case 13 – 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.
Case 14 & 15 – 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: Transverse view of the C-Shape with and without inhomogeneities
Case 16 – The 4L
The ACDS prescribed 4L test is an adaptation of a typical Monaco Treatment Planning System (IMPAC Medical Systems Inc., Elekta AB, Sweden) commissioning test (3), which consists of 4 nested ‘L’ shaped MLC patterns. The abutting regions of the MLCs between each ‘L’ shape allow assessment of the dosimetric leaf gap and inter leaf leakage, whilst the continuously blocked region shows the leaf transmission. An example of a 2D measured coronal plane of the 4L plan is shown in Figure 5.
The outcome for an individual case is determined using the measured 2D dose map.
For 3DCRT, the audit results are determined for each case using the dose variation between the Facility Stated Dose (planned dose) and the ACDS Measured Dose. A measurement case/plane is considered passed at the Optimal Level if the maximum absolute variation of the facility stated plan dose from the ACDS measured dose is within 3.3% for all assessed points. It is considered passed at the Action Level if the maximum absolute variation is between 3.3% and 5%. It is considered Out of Tolerance if the maximum absolute variation is outside 5%.
For IMRT and IMRT FFF, gamma criteria of 3%/3mm relative to 2Gy, with dose <20% suppressed, are assessed across the entire measurement plane for each case.
An overall Audit Outcome for each modality is determined, which is equal to the worst case outcome for each modality.
General audit pass criteria
|Out of Tolerance||Reported not scored
|3DCRT||< 3.3%*||> 3.3% and < 5%||> 5%||Any deliveries which are restricted for clinical use, repeated measurements, alternative scoring options and supporting measurements|
|IMRT & IMRT FFF||γ < 1 at 3%/3mm+
for > 97.5% points
|γ < 1 at 3%/3mm
for > 90% and < 97.5% points
|γ < 1 at 3%/3mm
< 90% points
*% dose variation = (Planned dose - ACDS measured dose) / ACDS measured dose
+ Gamma criteria relative to 2Gy, across entire CT dataset, with dose < 20% suppressed
- PatID-ACDSLII zip (2.25 mb) - updated March 2017
ACDS Audit Level II Documentation
- 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.
- 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.
- IMPAC Medical Systems I. Monaco Technical Reference: Post Modeling Adjustment of MLC Parameters. 2013.