HYBRID PLANNING A SIMPLE TECHNIQUE FOR CRANIOSPINAL IRRADIATION (CSI)

Purpose: A simple planning technique for craniospinal irradiation using Eclipse treatment planning system. Material and methods: In RT treatment planning, base plan optimization feature is used in sequential RT planning by anticipating the dose delivered to organ at risk (OAR) & planning target volume (PTV) in the base plan. In hybrid planning technique, the whole PTV is divided into two parts, Brain PTV & Spine PTV. Spine PTV is overlapped minimum 2-3 cm over the Brain PTV at their junction while creating structures for RT planning. Brain PTV is planned with conventional RT technique & the Spine PTV planned with rapid arc technique (VMAT). In the plan optimization process of spine PTV, first base plan is selected then the optimization parameter is set accordingly as per total prescribed dose of 36 Gy for both the PTVs. The base plan is the dose calculated plan which is incorporated in the rapid arc plan optimization hence the pre-existed doses of Brain PTV & OAR help to understand the plannerfor achieving desired planning objectives during Spine PTV, RT plan optimization. Finally for the dose calculation of Spine PTV RT plan, planner has to copy fields of Brain PTV & paste it in Spine PTV plan and need to calculate dose for these copied fields. The final plan contains a dose calculated of Brain PTV fields and Spine PTV fields termed as hybrid plan. Result: Reduction in the total number of monitor units is observed for the hybrid plan compared to single VMAT plan, which is statistically significant (p<0.05). Conclusion: Present study introduced the hybrid planning technique which can exploit benefits of conventional and modern techniques.