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Optimal Dosimetric Planning in Stereotactic Radiosurgery for Perioptic Tumors: A Comparative Study Between CK Versus GK
k yoon*, B Cho , J Kwak , D Lee , D Kwon , S Ahn , S Lee , C Kim , S Roh , Y Cho , Asan Medical Center, Seoul, Songpa-gu
Presentations
SU-I-GPD-J-42 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: SRS for skull base perioptic tumors is challenging with concerns about the risk of radiation-induced optic neuropathy. For these cases, hypofractionation of SRS with an optimal dosimetric planning in terms of dose-volume constraints to the optic apparatus (OA) as well as higher dose to tumor may potentially reduce the risk of radiation toxicity with acceptable tumor control. Here we investigated dosimetric outcomes of the Cyberknife (CK) and the Gamma Knife (GK) for perioptic tumors.
Methods: We selected 18 perioptic tumors previously treated using CK between 2011 and 2015. All tumors harbored no margin from OA with 10 of them compressing or 8 abutting onto it on MRI. For dosimetric planning, thin-sliced CT and MR images were obtained and fused for delineation and contouring of both tumor and OA. Identical contour set was used to produce both CK and GK plans for each case. For 5 fraction treatment, the goal of dosimetric planning was to limit dose to OA with dose-volume constraints of Dmax <25 Gy and V20Gy <0.2 cc, while maintaining tumor coverage as high as possible with median prescription dose of 27.8 Gy. A paired data set of dosimetric parameters based on each modality was obtained and analyzed.
Results: Although all plans of both CK and GK complied with the dose-volume constraints to OA, tumor coverage (mean 94.4% in CK vs 88.5% in GK; P<0.001) and minimum dose to tumor (22.9 Gy vs 19.1 Gy; P<0.001) were significantly higher in CK than in GK. There were no differences in the conformity index (1.24 vs 1.27; P=0.825). The gradient index (3.39 vs 2.89; P=0.004) was significantly lower in GK than in CK.
Conclusion: These results suggest that CK inverse planning system appears to be more suitable for an optimal dosimetric planning for perioptic tumors than GK planning system.
Funding Support, Disclosures, and Conflict of Interest: Funding Support : This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (grant number) 2015M2A2A6A02045253. Disclosures and Conflict of interest : All authors declare that they have no competing interests.
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