Napapat Amornwichet MD, Presenter: Nothing to Disclose

"Purpose/Objective(s):Craniospinal irradiation (CSI) is a complex technique due to its large and irregular target volume. It is difficult to achieve target coverage and homogeneity by using conventional 3D method. In this study, multi-isocenter IMRT and 3D conventional radiation were compared in terms of target coverage, homogeneity and normal organs avoidance.""Materials/Methods:Data of thirteen patients who were treated with CSI was re-planned using 3D conventional and multi-isocenter IMRT. Target volume (PTV brain, PTV spinal sac) and OARs (heart, lungs, liver and both kidneys) were contoured. IMRT plan consisted of two to three isocenters. The first isocenter was at PTV brain with four non-opposing fields. The second and third isocenters were at PTV spinal sac with three posterior fields by gantry angle of 150,180 and 210 degree. All fields for PTV brain and spinal sac were optimized together. Photon energy was 6 MV. 3D plan were composed of two lateral opposing whole brain fields and one or two posterior spinal field(s). The dose prescription was 36 Gy in 20 fractions. Target coverage and homogeneity were evaluated with Dmax , Dmean, Dmin, V95%, Quality of coverage (QOC) and homogeneity indices (HI) using Radiation Therapy Oncology Group (RTOG) criteria. Normal organs sparing was assessed with Dmax , Dmean, V1Gy, V5Gy, V10Gy, V20Gy and V30Gy. All parameters of both plans were compared using student’s T-test.""Results:Multi-isocenter IMRT significantly improved target coverage and homogeneity as compared to 3D conventional technique. Mean Dmax and Dmin were 3,887 cGy and 3,506 cGy for IMRT and 4,113 cGy and 3,255 cGy for 3D, respectively (with the p value Conclusions:Craniospinal irradiation using multi-isocenter IMRT technique was superior than 3D conventional radiation in target coverage and homogeneity while significantly decreased high dose volume to normal organs. This dosimetric advantage was attractive for further clinical evaluation.

Amornwichet, N, Multi-isocenter IMRT vs 3D Conventional Technique for Craniospinal Irradiation: A Dosimetric Analysis.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9020189.html