Validation of the performance of 3-D detector arrays for radiotherapy verifications

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Introduction Intensity modulated radiotherapy (IMRT/VMAT) is a complex procedure requiring proper dosimetric verification. IMRT dose distributions are characterized by high degree of modulation and by steep dose gradients. The fluence measurements for individual beams or at individual angle are not sufficient for evaluation of total dose distribution and for assuring patient safety. Purpose A number of electronic systems which allow for a pre-treatment plan verification based on reconstruction of the total dose distributions have been developed recently (Delta4, ArcCHECK, Octavius, etc.). A method of validation of such systems tested on the above listed devices is presented here. Materials and methods The method requires anthropomorphic phantoms and dosimetric films. In order to measure dose distributions in various cross-sections of the phantom the film dosimeters were used (Gafchromic EBT-3). The phantoms of the material and shape equivalent to the Delta4, ArcCkeck and Octavious detector arrays were developed. This film dosimetry methodology was used as a benchmark to test and validate the performance of commercially available 3-D verification systems. The gamma formalism was used for evaluation and comparison of the measured and calculated dose distributions. Results The results of comparisons of film measurements performed in test phantoms with dose distribution reconstructed with: Delta4, ArcCHECK and Octavious for a group of patient plans are presented as the percentage of passing points (PPP) for Γ ⩽ 1 criterion. Conclusion The 3-D verification systems and their reconstruction algorithms have to be validated with independent measurements or calculations before use in clinical practice.