Medische dosimetrie


Universiteit Hasselt - Knowledge in action


The BELdART-project is 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), encompasses a basic audit of each clinical radiation device in all Belgian radiotherapy departments. This basic audit consists 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) will be audited by the end of the project. The project is worldwide the first large scale dosimetry audit using alanine-EMR-dosimetry.

Within the framework of BELdART, all Belgian centers are offered the possibility to participate to a dosimetry audit without charge. During a period of three years all radiotherapy centers will be visited (about 80 linacs and 230 beams). The BELdART project is a scientific project because it is the first national audit program using alanine-EMR-dosimetry worldwide. The project is financed by the Belgian Federal Agency for Nuclear Control (FANC). 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 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 will perform 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 will calculate 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 encompasses only clinically used radiation beams: all photon beams and one low and one high energy (R50 > 7cm) electron beam.

Materials & methods

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

  • A mechanical verification encompasses 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 is performed by measuring the described absorbed dose in water at a predefined depth as stated in the “Procedure instructions”. The alanine dosimeters are provided in a dedicated watertight encapsulation for each experiment.
  • Yearly 4 radiotherapy centers are given the opportunity to simultaneously participate with the BHPA audit using the BHPA ionization chamber.
  • Dose to water Dw at the reference point is measured using four alanine dosimeters which will be read out at the NuTeC-EMR-Laboratory. The measuring procedure is inspired by and the dosimetry is traceable (water calorimetry) to the German laboratory of Standardization PTB in Braunschweig. Moreover, the alanine response is benchmarked regularly with ionization chamber measurements in the frame of the BHPA-auditing.

Reporting results

  • All results are treated with confidence by BELdART. All measurements are internally “validated” before communicating the the participants.
  • The relative deviation |δ| ≡ |(DmeasuredDcenter) 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%
  • Validated results will be communicated to the local radiation physicist and the responsible radiation oncologist. Results “out of tolerance level” will be discussed within the BELdART team, together with the local radiation physicist. All findings are treated in strict confidence by the BELdART team.
  • The results of the audit are meant to be an independent verification of the beam output and "treatment'" quality and can 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 are 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

hier de kaart met audits plaatsen. De kaart op de bestaande website is denk ik oud.

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