Abstract Book

S1080

ESTRO 37

3 Hiroshima University, Department of Radiation Oncology- Institute of Biomedical & Health Sciences, Hiroshima, Japan 4 Hiroshima University, Medical and Dental Sciences Course- Graduate School of Biomedical & Health Sciences, Hiroshima, Japan 5 University of Tokyo, Department of Nuclear Engineering and Management- School of Engineering, Tokyo, Japan 6 Hiroshima University Hospital, Radiation Therapy Section- Department of Clinical Support, Hiroshima, Japan Purpose or Objective Previously, we demonstrated Lipiodol-related dose enhancement using 10 MVX flattening filter free (FFF) beams for Liver stereotactic body radiotherapy (SBRT). The objective of this study was to reveal the relative biological effectiveness (RBE) and relative dose-rate effectiveness (RDRE) values by the Lipiodol using 6 and 10 MVX FFF beams with Monte Carlo calculation. Material and Methods 6 and 10 MVX FFF beams were delivered by TrueBeam linear accelerator (Varian Medical Systems, Palo, Alto, USA). The Lipiodol (3 × 3 × 3 cm 3 ) was located at the depth of 5 cm in water. The dose enhancement factor (DEF) and the dose-mean lineal energy D values were calculated from Monte Carlo calculation with Particle and Heavy Ion Transport code System (PHITS). According to the microdosimetric kinetic model (MK model), the cell killing of the human liver hepatocellular cells (HepG2) were calculated from the D values. The RBE MK was determined as the ratio of the dose at 10% survival fraction (D 10% ) of 6 and 10 MVX to 200 kVX. The RBE DEF was determined as the ratio of D 10% without to with Lipiodol. In addition, the RDRE was defined as the ratios of D 10% with 0.1-24 Gy/min to 2 Gy/min.

probabilities in the Markov chain, with the NTCP and SPCIP for each organ at risk (OAR) being time-variable. To demonstrate functionality, the model was applied to a paediatric patient presenting with base of skull chordoma. Results The model was successfully developed and verified to compare clinical outcomes for proton and X-ray treatment plans. This clinical outcome is quantified by Kaplan-Meier survival curves and the quality adjusted life expectancy (QALE) which accounts for the potential negative effects of a treatment, such as radiation- induced injuries or radiation-induced second cancers, on the quality of life of the patient. Conclusion The functionality of the model was demonstrated using the example patient. Other example patients will be considered in future applications of the model. In addition to base of skull chordoma, other treatment sites may be considered that are not typically associated with proton therapy, but where there is an elevated risk present with X-ray therapy. EP-1985 Analysis of HBV after CRT in patients with hepatocellular carcinoma using the Lyman NTCP model W. Huang 1 , Z. Li 2 , Y. Dong 3 1 Shandong Cancer Hospital, Radiation Oncology 6, Jinan, China 2 Shandong Cancer Hospital, Radiation Oncology, Jinan, China 3 University of Jinan-Shandong Academy of Medical Sciences, School of Medicine and Life Sciences, Jinan, China Purpose or Objective To analyze the correlation of hepatitis B virus (HBV) reactivation with patient-related and treatment-related dose-volume factors, and to describe the feasibility of HBV reactivation analyzed by a normal tissue complication probability (NTCP) model for patients with hepatocellular carcinoma (HCC) treated with conformal radiotherapy (CRT). Material and Methods 90 HBV-related HCC patients treated with CRT were enrolled in this retrospective study and were followed from June, 2009 to December, 2015. The parameters (TD 50 (1), n, and m) of the modified Lyman Kutcher Burman (LKB) NTCP model were derived using maximum likelihood estimation. Bootstrap and leave-one-out were employed to test the generalizability of the results for use in a general population. Results Radiation-induced liver diseases (RILD) were 17.8%, HBV reactivation was 22.2%, and HBV reactivation-induced hepatitis was 21.1%, respectively. In multivariate analysis, the V45, and V30 were associated with HBV reactivation. TD 50 (1), m and n were 32.3Gy, 0.55 and 0.71, respectively, for HBV reactivation. Bootstrap and leave-one-out results showed that the HBV parameter fits were extremely robust. Conclusion A modified Lyman NTCP model has been established to predict HBV reactivation for patients with HCC who received CRT. The finding derives parameters set to predict potential endpoints of HBV reactivation. EP-1986 Relative biological effectiveness and relative dose-rate effect on Lipiodol based on the MK model D. Kawahara 1 , N. Hisashi 2 , O. Shuichi 3 , S. Akito 3 , K. Tomoki 3 , S. Tatsuhiko 4 , T. Masato 4 , T. Sodai 5 , O. Yoshimi 6 , M. Yuji 3 , N. Yasushi 3 1 Hiroshima University, Graduate School of Biomedical & Health Sciences, Hiroshima, Japan 2 Hiroshima Heiwa Clinic- State of the Art Treatment Center, Radiation therapy, Hiroshima, Japan

Results The RBE MK

in the Lipiodol was larger than that in the water for 6 and 10 MVX FFF beams. The average RBE exp was 1.20 for 6 MVX FFF beams and 0.95 for 10 MVX FFF beams. The RDRE was 0.99-1.33 Gy for 6 MVX and 0.98- 1.32 Gy for 10 MVX beams. The RDRE was higher with low-dose rate for 6 and 10MVX. The deviation of RDRE in the water and the Lipiodol were small within 1%. Conclusion The RBE and RDRE were calculated using MK model. The RBE enhancement were confirmed in presence of the Lipiodol, but the dose-rate effect was not affected from energy and materials. EP-1987 TCP and Gaussian Radiosensitivities P. Stavrev 1 , N. Stavreva 1 , A. Nahum 2 , D. Pressyanov 1 1 Sofia University “St. Kliment Ohridski”, FACULTY OF PHYSICS, Sofia, Bulgaria 2 Liverpool University, Physics Department, Liverpool, United Kingdom