Tüm beyi̇n radyoterapi̇si̇ alan hastalarin vmat tekni̇ği̇ i̇le hi̇pokampus korumali ve korumasiz olarak yeni̇den planlanarak doz volüm dağilimlarinin karşilaştirilmasi

REPLANNING OF THE PATIENTS WHO RECEIVED WHOLE BRAIN RADIOTHERAPY WITH HIPPOCAMPAL SPARING USING VMAT TECHNIQUE OR WITHOUT HIPPOCAMPAL SPARING AND COMPARISON OF THE DOSE VOLUME DISTRIBUTIONS Purpose To evaluate the feasibility of hippocampal sparing whole brain radiotherapy using VMAT technique in terms of target volume and organ at risk doses. Materials and Method: 10 anonymous patients received whole brain radiotherapy at Ege University Faculty of Medicine Department of Radiation Oncology from January to March 2017 were replanned. Using the CT simulation scan images, two treatment plans with or without hippocampal sparing were generated. All patients had their CT simulation images fused with axial MRI scans. While whole brain was contoured as target organ, optic nerves, chiasm, lenses, orbits and hippocampus were contoured as organ at risk.The hippocampus was contoured on T1-weighted MRI axial sequences following the ''Hippocampal Contouring: A Contouring Atlas for RTOG 0933''. The ''Hippocampal Avoidance Zone'' was generated by expanding the hippocampal contour by 5mm. Differently from without hippocampal sparing plan, whole brain planning target volume defined as the whole brain volume excluding the hippocampal avoidance region volume. VMAT technique was used for HA-WBRT plans and two lateral parallel opposed fields with conformal technique for non HA-WBRT. For both modalities 30 Gy in 10 fractions RT dose was prescribed for whole brain PTV. For treatment plans qualifying we used RTOG 0933 HA WBRT acceptable compliance criteria for target organ and organs at risk excepting orbit and lens and RTOG 0615 and RTOG 0539 for orbit and lens. In addition, the homogeneity index (HI) was calculated in both plans. Statistical comparisons between the two modalities treatment plans were performed using in SPSS software, version 18.0 using paired sample t test signed rank and an upper bound of p< 0.05. Results When analyzing the data, for both two modalities plans, we detected that optic nerves, chiasm and orbits' doses didn't exceed dose constraints. In HA-WBRT plans, lens dose is slightly above the limit with 8 Gy. While non HA-WBRT plan was adventageous regarding chiasm and lens doses, HA-WBRT was more adventageous regarding orbit dose (p<0.01). In HA-WBRT plans, hippocampus Dmax and Dmin are 14.2 Gy and 8.7 Gy, respectively and these doses are within the protocol criteria of 17 Gy and 10 Gy. Hippocampus Dmean is 10.4 Gy in HA-WBRT plans. Among two modalities, Hipokampus BEDlate effects and EQD2 is reduced by %80 with VMAT technique. In non HA-WBRT plans, mean HI of 0.08 compared to 0.21 for HA-WBRT was found and the difference was statistically significant (p<0.001). In terms of PTV whole brain D2%, D98% and V30Gy among two modalities, non HA-WBRT was superior for all of the parameters and the difference was statistically significant. However with HA-WBRT modality, target volume parameters' results were still within the protocol's criteria except V30Gy. Average hippocampus volume was 3.1 cm3. Conclusion In our study, hippocampus doses seem to provide the dose compliance criteria for HA-WBRT. Besides, all of the organs at risk doses excepting lens, are within the dose constraints, with no significant compromise from the target volume dose and homogenity. As a result, the feasibility of HA-WBRT technique in daily routine has been confirmed.