Presentation Estimation of normal tissue complication probability parameters for temporal lobes in carbon ion therapy for skull base tumors

Fukahori, Mai  ,  Matsufuji, Naruhiro  ,  Kanematsu, Nobuyuki  ,  Koto, Masashi  ,  Takagi, Ryo  ,  Ikawa, Hiroaki  ,  Naganawa, Kensuke  ,  Hasegawa, Azusa  ,  Tsuji, Hiroshi  ,  Kamada, Tadashi

Purpose: The aim of this study was to estimate normal tissue complication probability (NTCP) parameters after carbon ion radiation therapy (C-ion RT) for skull base tumor on late temporal lobes complications.Methods: A total of 39 patients were used to derive NTCP parameters. These patients included were treated with dose ranging from 48 Gy (RBE) up to 60.8 Gy (RBE) including dose escalation trial at the National Institute of Radiological Sciences (NIRS). The Lyman-Kutcher-Burman (LKB) model with DVH as a function of equivalent uniform dose (EUD) was used as a NTCP model. The end points for the analysis were Grade ≥1 and Grade ≥2 toxicity for the temporal lobes.Results: The resulting NTCP parameters were the volume effect parameter; n = 0.15 (95% CI: 0.13-0.17), the steepness of NTCP curve; m = 0.13 (0.081-0.22), the tolerance dose associated with 50% probability of complication; TD50 = 34.8 Gy (RBE) (32.9-36.8 Gy (RBE)) for Grade ≥1, n = 0.22 (0.19-0.26), m = 0.21 (0.13-0.34), TD50 = 33.2 Gy (RBE) (30.6-36.3 Gy (RBE)) for Grade ≥2.Conclusion: A new set of NTCP parameters for temporal lobes in C-ion RT was determined. The n and m values of C-ion RT are almost the same as that of photon therapy. TD50 parameters were almost unchanged with respect to each end point considered, the grade of late temporal lobes complication is not strongly dependent on dose. The new derived parameter values facilitate estimation of NTCP for temporal lobes in C-ion RT.
55th Particle Therapy Co-Operative Group

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