Morad Erraoudi - Department of physics, Faculty of sciences, University Mohammed V in Rabat, Morocco
Kaoutar El Bouchiti - Mohammed VI University of Health Sciences, Casablanca, Morocco
Yassine Herrassi - Iba Dosimetry Schwarzenbruck, Germany
mohamed El ghalmi - Faculty of Sciences, LPHE-M&S, Mohammed V University, Rabat
Yassir Raoui - Université Mohammed V de Rabat
Youssef Bouzekraoui - Hassan First University of Settat, High Institute of Health Sciences, Laboratory of Sciences and Health Technologies, Settat, Morocco
FARIDA BENTAYEB - Departement of Physics, Laboratory of High Energy Physics, Modelling and Simulation, Faculty of Science, Mohammed V Agdal University, Rabat, Kingdom of Morocco
Lalla Btissam Drissi - ۱Department of physics, Faculty of sciences, University Mohammed V in Rabat, Morocco

Introduction: Treatment of pelvic bone metastases using a Halcyon machine, mostly presents some difficulties to plan, especially for big volumes because of the machine field size. The purpose of this study is to use two lateral isocenters in the treatment of pelvic bone metastases with the Halcyon machine, in order to overcome its limitations in treating large volumes.Material and Methods: We report a retrospective study of ۸ patients who received radiotherapy for pelvic bone metastases, all treated by two different VMAT techniques. The first technique was performed by two longitudinal isocenters (LONI) and the second by two lateral isocenters (LATI) respecting the authorized distance longitudinally between two isocenters which must be less than ۸ cm. For each isocenter, two opposite arcs are used for all treated patients.Results: The plans conformity index (CI) assessment shows no difference between the two used techniques for all the treated patients. Remarkable coverage of PTVs was obtained in lateral isocenter (LATI) with ۹۶.۲% compared to ۹۴%.۶% for LONI, as well as the maximum dose which was ۱۰۹.۴% for LATI versus ۱۱۲.۳% for LONI. However, the Conformation number (CN) that takes into account both healthy tissue and organ at risk protection was improved by ۷.۳% by using LATI.Conclusion: A very satisfactory result has been obtained in the treatment of pelvic bone metastases with LATI. With this technique, we can exceed the limits of the Halcyon machine and process larger volumes.

VMAT, Pelvic, Radiotherapy, PTV, Halcyon Machine