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ACDS - Level II Audits

Audit Index:

LEVEL II AUDITS

Definition

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 model 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; 3D Conformal Radiotherapy (3DCRT), Intensity Modulated Radiotherapy (IMRT) and Intensity Modulated Radiotherapy with Flattening Filter Free (IMRT FFF).

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.

Audit Outcome

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 criterial
  Pass
(Optimal Level)
Pass
(Action Level)
Out of Tolerance Reported not scored
(RNS)
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

CT Datasets

Note: The RT structures attached to the CT datasets are only applicable if completing the IMRT section of the audit. Please ignore if completing the 3D CRT section only.

ACDS Audit Level II Documentation

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