[Evaluation of transit in vivo dosimetry using portal imaging and comparison with measurements using diodes]

In vivo dosimetry transit using portal imaging is a promising approach for quality assurance in radiotherapy. A comparative evaluation was conducted between a commercial solution, EPIgray(®) and an in vivo dosimetry control reference using semiconductors diodes.

The performance of the two in vivo dosimetry methods was assessed. The primary endpoint was the dose deviation between the reconstructed dose at the prescription point and the measured dose using the ionization chamber in phantoms or the calculated predictive dose by the treatment planning system with patients. The deviation threshold was set to ±5%. In total, 107 patients were prospectively included and treated with 3D-conformal radiotherapy (3D-CRT) or intensity-modulated radiotherapy (IMRT) techniques for tumours of the brain, chest and head and neck.

The dosimetric accuracy of EPIgray(®) in phantom were comparable to diodes in terms of repeatability (0.11%), reproducibility (0.29-0.51%) with a mean dose deviation of 0.17% (SD: 1.11). The rates of radiotherapy sessions out of the tolerance for the brain (3D-CRT and IMRT), thorax (3D-CRT) and the head and neck (IMRT) were respectively 0%, 9.6% and 5.3% with a mean dose deviation ranging between 0.49% and 1.53%. The mean of dose deviation between three consecutive sessions with EPIgray(®) validates 99.1% of treatments.

The performance of EPIgray(®) in in vivo dosimetry is consistent with the recommendations of the European Society for Radiotherapy and Oncology (ESTRO) and equivalent to semiconductor diodes for 3D-CRT. It also allows adequate control for IMRT, which is technically difficult to perform with the diodes.