BELdART-3 is the continuation of the BELdART-1 and BELdART-2 project. It encompasses mailed audits for basic and advanced RT techniques in Belgium for Stereotactic Body Radiation Therapy (SBRT). The audit consists of 2 parts.
- Control of basic dosimetry using alanine in a water tank (with higher doses than those used in BELdART-2)
- Control of a real plan on a:
- STEEV Stereotactic End-to-End Verification Phantom (CIRS) for intracranial SBRT
- Lung phantom for extracranial SBRT (lung tumours)
Within the framework of BELdART-3, all Belgian centers are offered the possibility to participate to a dosimetry audit without charge. The audit results are strictly confidential and are reported anonymously in frequency distribution formats.
Purpose of the audit
The purpose of the audit is to (1) verify the basic dosimetry of the linacs for higher doses with a water tank using groups of 4 alanine pellets wrapped in plastic and (2) to verify the dose plans for a intracranial SBRT and extracranial SBRT plan.
Materials & methods
The BELdART material will be prepared before sending it to the clinic. We will also send the procedure to perform the audit. After the audit has been done, the material will be send back to us and analyzed.
For the basic dosimetry the groups of alanine will be placed in a watertank and irradiated with geometries of 10x10 cm² and 2x10 cm². The pellets are positioned at fixed depth using a holder. Besides, the hospitals have the choice to test wedged fields. For small fields, an extra test will be performed with RW3-slabs and 1 alanine pellet.
The STEEV head phantom contains an inner cube which has many possible film positions. In the center slice of this inner cube 1 piece of film will be placed in combination with 1 alanine pellet. Besides, one other piece of film will be put in another slice of the cube without an alanine pellet. We will also send the images of the phantom which includes contours which have been drawn in the same slices as the films. We ask 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 will also send a pmma plate with a piece of film and 4 pellets which we ask the clinics to irradiate them in the same session as the STEEV head phantom. This will be 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 are treated with confidence by BELdART. All measurements are internally “validated” before communicating with the participants.
- The relative deviation |δ| ≡ |(Dmeasured – Dcenter) x100 / Dcenter| is 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 is evaluated with the Gamma evaluation algorithm which combines both dose difference and distance-to-agreement criteria.