BELdART-2 was the continuation of the BELdART-1 project. It encompassed mailed audits for advanced and dynamic RT (e.g. IMRT, VMAT, Tomotherapy). This audit consisted of 2 parts:
- Control of basic dosimetry using alanine in a water tank
- Control of real plans on an EasyCube phantom (Sun Nuclear)
BELdART-2 used a combination of alanine-EMR-dosimetry and Gafchromic film dosimetry.
Within the framework of BELdART-2, all Belgian centers were offered the possibility to participate to a dosimetry audit without charge. The audit results were strictly confidential and were reported anonymously in frequency distribution formats.
Purpose of the audit
The purpose of the audit was to (1) verify the basic dosimetry of the linacs with a water tank using groups of 4 alanine pellets wrapped in plastic and (2) to verify the dose plans for a prostate case on the EasyCube phantom.
Materials & methods
The BELdART material was prepared before sending it to the clinic. We did also send the procedure to perform the audit. After the audit had been done, the material was sent back to us and analyzed.
For the basic dosimetry the groups of alanine were placed in a watertank and then irradiated with geometries of 10x10 cm² and 2x10 cm². The pellets were positioned at fixed depth using a holder. Besides, the hospitals had the choice to test wedged fields.
For the verification of the dose plan 4 alanine pellets were inserted in the central slice of the EasyCube phantom together with a film. Besides, we did send the images of the phantom which included transferred contours of a real prostate patient. We asked the physicist of the centers to build a plan according to the local rules, adding the same margins and using the same constraints as they would use for a patient.
We did also send a pmma plate with a piece of film and 4 pellets which we asked the clinics to irradiate them in the same session as the Easy Cube phantom. This was used to validate the film dosimetry with the One-Scan procedure (D. Lewis, A. Micke, X. Yu, M. F. Chan, Efficient protocol for radiochromic film dosimetry, Med. Phys. 39 (10), October 2012)
- All results were treated with confidence by BELdART. All measurements were internally “validated” before communicating with the participants.
- The relative deviation |δ| ≡ |(Dmeasured – Dcenter) x100 / Dcenter| was classified into four levels with respect to actions to be taken:
Within optimal level |δ| ≤ 3% Out of optimal level but “within tolerance level 3% < |δ| ≤ 5% Out of tolerance level 5% < |δ| ≤ 10% Alarm level |δ| > 10%
- The film dosimetry was evaluated with the Gamma evaluation algorithm which combines both dose difference and distance-to-agreement criteria.
Basic tests EPR