[Article] Evaluation d’une Dosimétrie In Vivo de Transit utilisant l’Imageur Portal et Comparaison avec Les Mesures par Diodes*

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

P. Royer^a,c,d,e, V. Marchesi^a, V. Rousseau^b, I. Buchheit^a, D. Wolf^c,d,e, D. Peiffert^a,c,d,e, A. Noël^a,c,d,e
a Radiotherapy department, institut de cancérologie de Lorraine Alexis-Vautrin, 6, avenue de Bourgogne, 54500 Nancy, France
b Dosisoft SA, 45, avenue Carnot, 94230 Cachan, Francec
c UMR 7039, centre de recherche en automatique de Nancy (Cran), BP 70239, 54506 Vandoeuvre-lès-Nancy cedex, France
d UMR 7039, université de Lorraine, BP 70239, 54506 Vandoeuvre-lès-Nancy cedex, Francee
e UMR 7039, CNRS, BP 70239, 54506 Vandoeuvre-lès-Nancy cedex, France

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

Methods: 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 andthe 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 patientswere 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.

Results: The dosimetric accuracy of EPIgray^® in phantom were comparable to diodes in terms of repea-tability (0.11%), reproducibility (0.29–0.51%) with a mean dose deviation of 0.17% (SD: 1.11). The ratesof radiotherapy sessions out of the tolerance for the brain (3D-CRT and IMRT), thorax (3D-CRT) and thehead and neck (IMRT) were respectively 0%, 9.6% and 5.3% with a mean dose deviation ranging between0.49% and 1.53%. The mean of dose deviation between three consecutive sessions with EPIgray^® validates 99.1% of treatments.

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