Beldart: A Radiotherapy Dosimetry Audit Program Using Alanine/EPR and Film Dosimetry
Abstract
Purpose
To assess the dosimetric accuracy of radiotherapy treatments mainly in Belgium through a program of external dosimetry audits, evaluating the commissioning and clinical implementation of photon and electron beam models in treatment planning systems (TPS).
Methods
A combination of alanine/electron paramagnetic resonance (EPR) and radiochromic film dosimetry was used for absolute point dose and two-dimensional dose distribution measurements, respectively. For photon beams, audits included basic dosimetric checks in water and end-to-end (E2E) tests using anthropomorphic phantoms for volumetric modulated arc therapy (VMAT), intracranial stereotactic radiosurgery (SRS), and lung stereotactic body radiotherapy (SBRT). Films were analyzed using triple-channel dosimetry and gamma evaluation. All measurements for an audited beam are performed on the same day to allow identification of the source of potential problems during the E2E test. For electron beams, only the beam output is checked.
Results
Since September 2016, 106 audits were performed, comprising 261 photon beams and 71 electron beams. All beams were within ±5% for the photon basic tests. For electron beams, 95% were within ±5%. For VMAT E2E audits (104 beams), 99% of alanine measurements were within ±3% in the prostate and seminal vesicles and 97% of films achieved >90% passing rates using 3%/3 mm gamma criteria. For SRS audits (61 beams), 95% of alanine measurements were within ±5%. Film analysis using 5%/1 mm gamma criteria yielded >90% passing rates for 97% of beams in large and small regions. For SBRT audits (46 beams), all beams were within ±5% for the alanine measurements. The films were analysed with gamma criteria 5%/1mm (film in target) and 3%/2mm (film on top of lungs). 98% and 87% of the films had a passing rate >90% for the target and top-of-lungs, respectively.
Conclusion
The results show that the dosimetric accuracy in Belgian clinics is outstanding across the audited techniques.