Nucleair Technologisch Centrum


Universiteit Hasselt - Knowledge in action


The BELdART-project was a collaboration between the Nuclear Technologic Center (NuTeC) and the College of Physicians and the Belgian Hospital Physicists Association (BHPA).

The project, supported by the Federal Agency for Nuclear Control (FANC), encompassed a basic audit of each clinical radiation device in all Belgian radiotherapy departments. This basic audit consisted of a dosimetrical check of all the photon and electron beams and a check of the most important mechanical parameters. In total 31 centers (representing 208 beams) were audited by the end of the project. The project was worldwide the first large scale dosimetry audit using alanine-EMR-dosimetry.

Within the framework of BELdART, all Belgian centers were offered the possibility to participate to a dosimetry audit without charge. During a period of three years all radiotherapy centers were visited (about 80 linacs and 230 beams). The BELdART project was a scientific project because it is the first national audit program using alanine-EMR-dosimetry worldwide. The project was financed by the Belgian Federal Agency for Nuclear Control (FANC). 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 verify the output of external radiotherapy devices in reference and non-reference conditions in an independent way.

  • In clinical routine high energy photon beams with and without wedge/ MLC- collimator and electron beams are used. An experimental verification of the dose calculated by the treatment planning system (TPS) is essential to maintain a steady quality assurance in radiotherapy.
  • In this protocol, the audit team performed a minimal mechanical verification of the LINAC, together with measurements of the absorbed dose to water delivered at a reference depth for a series of experiments covering reference and non-reference conditions, conform to international audits. The center calculated the number of monitor units (MU) to irradiate the alanine dosimeters to a requested dose, following the local procedure as it is used in clinical practice for patients.
  • The audits encompassed only clinically used radiation beams: all photon beams and one low and one high energy (R50 > 7cm) electron beam.

Materials & methods

The audit encompassed an on site visitation of one BELdART employee who would perform the verifications with BELdART material, together with the local radiation physicist.

  • A mechanical verification encompassed the verification of the dimension of the reference radiation field (10 x 10 cm2) and a verification of the position of the isocenter and laser lines
  • The dosimetrical verification was performed by measuring the described absorbed dose in water at a predefined depth as stated in the “Procedure instructions”. The alanine dosimeters were delivered packed in a waterproof, air evacuated sealing. Each holder contained 4 alanine pellets whereby a mark indicated the center of the 4 pellets. 
  • Yearly 4 radiotherapy centers were given the opportunity to simultaneously participate with the BHPA audit using the BHPA ionization chamber.
  • Dose to water Dw at the reference point was measured using four alanine dosimeters which was measured at the NuTeC-EMR-Laboratory. The measuring procedure was inspired by and the dosimetry is traceable (water calorimetry) to the German laboratory of Standardization PTB in Braunschweig. Moreover, the alanine response was benchmarked regularly with ionization chamber measurements in the frame of the BHPA-auditing.

Reporting results

  • All results were treated with confidence by BELdART. All measurements were internally “validated” before communicating with the participants.
  • The relative deviation |δ| ≡ |(DmeasuredDcenter) 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%
  • Validated results were communicated to the local radiation physicist and the responsible radiation oncologist. Results “out of tolerance level” were discussed within the BELdART team, together with the local radiation physicist. All findings were treated in strict confidence by the BELdART team.
  • The results of the audit were meant to be an independent verification of the beam output and "treatment'" quality and could not replace a beam calibration as performed by a qualified radiation physicist. THE RESULTS SHOULD NEVER BE CONSIDERED AS A CERTIFICATE FOR THE QUALITY OF A RADIOTHERAPY TREATMENT.
  • Depending on the results the following actions were undertaken:
    • All observed deviations are “within tolerance level” : a detailed overview of the results will be send to the radiation physicist and the responsible radiation oncologist of the center.
    • At least one observed deviation is “out of tolerance”, but all deviations are smaller than the “alarm level”: the center is informed about the “out of tolerance level” with the request to organize a second test. All results “within tolerance” are communicated.
      • If all results of the second test are within tolerance level: all results will be mailed and the cause of the deviation should be communicated as well as the actions to avoid the problem in the future.
      • If the second test is not finished, the deviation “out of tolerance” is considered to be confirmed by the first measurement. The results will be communicated to the radiation physicist and the responsible radiation oncologist.
      • If the second test confirms the deviation out of tolerance: results are mailed to the radiation physicist and the responsible radiation oncologist with confirmation of the observed deviation. The BELdART team will contact the radiation physicist to discuss the case.
    • At least one observed deviation is at “alarm level” : same procedure as described above, but prior to mailing the results, the BELdART team contacts the local radiation physicist and announces a significant deviation and organizes a second test.
    • If the second test confirms the large deviation: both results will be send to inform the radiation physicist and the responsible radiation oncologist of the center so that they can take action.

Final project status

The following map shows the locations of the clinics that were audited: