ESTRO 37 Abstract book

S1053

ESTRO 37

0.23±0.24% (PRIMO calculation), 0.28±0.16% (Acuros calculation). This data showed the compatibility between Monte Carlo (Penelope) and Acuros dose estimation in different tissues. Conclusion Monte Carlo accuracy and dose to medium estimation allow to better understand the dose deposited in the different part of a target, depending on their specific tissue composition. The difference is found to be significant. However, due to the small absolute dose difference, it is impossible to transfer this improved information into possible clinical outcome. EP-1935 Comparison of dosimetric characteristics in SBRT for lung with cyberknife, TOMOtherapy and VMAT M.J. Kim 1 , J.H. KIM 1 , K.S. PARK 1 , J.G. BAEK 1 , S.Y. KIM 1 , T.S. JEONG 1 , R.H. PARK 1 , D.M. JEONG 1 , J.H. CHO 1 1 Yonsei Cancer Center- Yonsei University, radiation oncology, Seoul, Korea Republic of Purpose or Objective The aim of this study is to evaluate the dosimetric characteristics of cyberknife with multi leaf collimator(CK_M) and fixed collimator(CK_F), volumetric modulated arc therapy with 10MV flattening filter-free beams(VM-F), Helical Tomotherapy with dynamic- jaw(HT), and to provide optimal modality in stereotactic radiotherapy(SBRT) for lung tumor. Material and Methods Eight patients with lung tumor were selected for this study, and grouped into classes by synchrony respiratory tracking system were used for cyberknife.(2-view lung tracking : 4cases, 0-view lung tracking : 4cases) New Treatment plans were created per patient, and the prescription dose was set as 60Gy in 4 fractions. Each plan was adjusted to be equivalent to each other; planning target volume (PTV) received ≥90% and the maximum PTV dose was limited to 120% of the prescription dose. For comparative purpose, conformity index(CI), homogeneity index(HI) and organs at risk(OAR) doses, monitor unites(MUs), treatment delivery times were assessed. Additionally, the regression analysis using target volumes receiving at 50%(V30), 30%(V18) of prescription dose were conducted in order to investigate the effects of tumor size on dose gradient and distance. Results 2-view lung tracking plans of CK_M and CK_F produced lower ipsilateral mean lung dose and lung volume received 30Gy(V30) , 15Gy(V15) than HT, VM-F. (CK_M V30: 28.12±12.99, CK_F V30: 38.13±39.29 vs. HT V30: 90.69±42.22, VM-F : 101.79±43.9 and V15 : 71.37±39.24, 90.46±51.15 vs. 226.22±89.43, 236.82±95.89) There were produced similar results of V30, V15 in 0-view lung tracking plans. The regression models showed that CK_M plans were significantly dose gradients for a short distance. There was no statistically significant difference between PTV doses in all plans, HT plans achieved a slightly superior homogeneity. (HI:1, p: 0.06) CK_M and CK_F plans had longer beam delivery times than others. (1267.5±326.18 vs1395±328.24)

Conclusion The plans of cyberknife with incise MLC is known to require long beam-on times and not show the best conformity, but achieves the shortest dose gradient range than other delivery techniques. EP-1936 A study on craniospinal irradiation in VMAT treatment use of different photon energy beams P. Mohandass 1 , D. Khanna 2 , N.K. Bhalla 1 , D. Manigandan 3 , C. Saravanan 1 , A. Puri 1 1 Fortis Hospital, Radiation Oncology, Mohali, India 2 Karunya University, Department of Physics - School of Science and Humanities, Coimbatore, India 3 Medanta The Medicity Hospital, Radiation Oncology, Gurgoan, India Purpose or Objective To study plan quality and deliverability on craniospinal irradiation (CSI) use of different photon energy in volumetric modulated arc therapy (VMAT). Material and Methods Three CSI patients treated with 23.4Gy/13fractions followed by boost dose were chosen for this study. All the plans were generated using VMAT technique for Elekta Synergy™ linear accelerator with 1cm leaf width at isocenter. In each case, 6MV (6X-6X) photon beam along with dual partial arcs were used for cranium (50°– 180°&180°–310°), upper spine (125°–180°& 180°–235°) and lower spine (110°–180°&180°–250°). Keeping all other parameters constant, by changing only photon energy, plans were re-planned for 4MV (4X-4X) and 4MV&6MV (4X-6X). For consistency, plans were generated by the same planner using Monaco™V5.1 treatment planning system (TPS). For plan evaluation, PTV covered by 95% of prescribed dose, conformity index (CI) and homogeneity index (HI) were analyzed. For organ at risk (OAR), mean dose and dose volume received by left lung, right lung, left eye, right eye, left parotid, right parotid, left kidney, right kidney, heart and liver were analyzed. Moreover, max dose to left lens, right lens and small bowel were analyzed. In addition, normal tissue (i.e., patient volume minus PTV) volume receiving dose >5Gy&>10Gy, normal tissue integral dose (NTID) (liter-Gray), total monitor unit (MU) and delivery time were compared. Results The CI for PTV was 1.0977±0.0165, 1.1063±0.0319 and 1.1083±0.1159 for 4X-4X, 6X-6X and 6X-4X respectively (p>0.05). Similarly, for HI was 0.0948±0.0078, 0.0895±0.0115 and 0.0941±0.0397 (p>0.05). The PTV coverage by 95% of prescribed dose slightly decreased in 4X-6X as compared to 4X-4X & 6X-6X (p>0.05). Moreover, the max dose was higher in 4X-6X as compared to 4X-4X & 6X-6X (p>0.05). The mean dose and dose volume received by left eye, right eye, left parotid, right parotid, left kidney, right kidney, heart and liver were showed less dose for 4X-4X as compared to 6X-6X, 4X-6X (p>0.05). Similarly, the slight increase of max dose was observed in 4X-4X as compared 6X-6X, 4X-6X for left lens, right lens