LAUSR

Introduction The aim of this study is to quantitatively evaluate the dosimetric difference between 3D conformal radiation therapy (RT) and Helical Tomotherapy (HT) for mediastinal Hodgkin lymphoma by comparing the doses received by the different organs at risk close to the lesion. Methods Between 2015 and 2016, 15 patients with cervico-medistinal tumors were treated at the Centre Leon Berard. Four of them were treated by 3D conformal radiation therapy based on antero-posterior fields calculated with the TPS XiO® (superposition) and delivered with an Synergy® accelerator (MLC Agility®: 5 mm leafs). The others were treated by IMRT with Helical Tomotherapy using Accuray® dedicated console. To evaluate the impact of the treatment method, we realize the dosimetric study of the two techniques for each patient. The plans quality of the 3D and Helical Tomotherapy were compared in terms of target coverage, target mean dose, dose sparing of organ at risk. These parameters were defined with physician according to published data (recommendations of the ICRU 83, SFRO, Quantec…). We have especially collected pulmonary and cardiac dose of different volumes. Coverage of the targets volumes was also collected. Results A better target volumes coverage was ensured by the Tomotherapy for the whole patient cohort (98.9% of average cover with HT vs 91% en 3D). Cardiac volume covered by 5 Gy and 15 Gy are lower with 3D conformal RT, we observe a mean difference of 12% for the V5Gy and 8% for the V15Gy. The V20Gy and V30Gy of the lungs are higher with 3D technique (15% vs 26% and 3.6% vs 13.8% respectively). However in the most cases the mean dose of the lungs and the heart are lower in 3D (10.2 Gy vs 10.9 Gy and 13.6 Gy vs 15.9 Gy respectively). Conclusions Tomotherapy has generally better dosimetric results except for low doses. As Hodgkin lymphoma often occur in young population, problem of low doses and thus of second cancer radio-induced can be discuss. Further investigations are possible to determine the most appropriate treatment depending on patient and lymphoma localization.