ESTRO 36 Abstract Book

S431 ESTRO 36 2017 _______________________________________________________________________________________________

statistically significantly reduced for all other treatment technique combinations when compared with IMRT in FB, and when proton therapy in DIBH was compared to proton therapy in FB. Heart dose and the ERRs of myocardial infarction and heart failure were significantly reduced when proton therapy in DIBH was compared to IMRT in DIBH. However, when proton therapy in FB was compared to IMRT in DIBH no statistically significant differences were seen for any doses or ERRs. To further analyze the differences between proton therapy in FB and IMRT in DIBH, the paired differences in heart dose from the techniques were calculated (proton therapy in FB minus IMRT in DIBH). The resulting median difference was 0.0 Gy (range -4.3 to 3.5), revealing that the relative benefit of these two techniques with respect to heart dose is patient-specific. Furthermore, mean DVHs for the heart show that, on average, the volume of the heart receiving a dose above about 7 Gy is greater for proton therapy in FB than it is for IMRT in DIBH (Figure 1).

image guided radiation therapy (IGRT) procedures, was released recently by Varian with new scan protocols. This study aimed to investigate the influence of parameters of the new protocols on the effective dose (E) compared to the previous version (V1.6). Material and Methods Effective dose of three scan protocols (head, t horax, and pelvis) were estimated using Monte Carlo s imulations. BEAMnrc and DOSXYZnrc user codes were used to simulate the OBI system integrated into a TrueBeam linac, and to calculate organ doses resulting from the protocols employed. Organ doses were evaluated for the ICRP adult male and female reference computational phantoms. The main differences between the software versions (V1.6) and (V2.5) are: (1) the beam width was extended to 214 mm instead of 198 mm, (2) the mAs values were increased to (150, 270, 1080) compared to (147, 267, 1056) for head, thorax, and pelvis, respectively, and (3) the projections number was increased to 500 for head scan compared to 367, and to 900 for thorax and pelvic scans instead of 660. Results The use of the scan protocols implemented in V2.5 resulted in increasing E of head scan by 13% and 12%, where E of V1.6 was 0.27 mSv and 0.44 mSv for male and female phantoms compared to 0.31 mSv and 0.49 mSv for V2.5, respectively. Parameters of the new protocols, also, led to rise E of thorax and pelvic scans by 16% and 17% for male, respectively, and by 16% for female. E of thorax and pelvic scans increased from 3.32 mSv and 5.95 mSv to 3.86 mSv and 6.88 mSv for male, respectively, and from 3.97 mSv and 11.38 mSv to 4.65 mSv and 13.16 mSv for female, respectively. Conclusion CBCT scans play a major role in radiotherapy treatment. The scan protocols with the new parameters were implemented into the new software to improve the image quality acquired with the scans, and to extend the field of view. This helps to improve the patient positioning on the treatment couch and deliver the specified dose to the patient with a high accuracy, and hence optimising the treatment output. The new head, thorax, and pelvic scans only increased E values by 12 – 13%, 16 – 17%, and 16%, respectively, for male and female. These increases are acceptable when compared to improvement of the treatment output. PO-0815 External neutron spectra measurements for a single room compact proton system R. Howell 1 , E. Klein 2 , S. Price Hedrick 3 , M. Reilly 4 , L. Rankine 5 , E. Burgett 6 1 UT MD Anderson Cancer Center Radiation Physics, Radiation Physics, Houston- TX, USA 2 Northwell Health System, Medical Physics, Lake Success, USA 3 Provision Center for Proton Therapy, Radiation Oncology, Knoxville, USA 4 Washington University, Radiation Oncology, St. Louis, USA 5 The University of North Carolina, Radiation Oncology, Chapel Hill, USA 6 Idaho State University, Nuclear Engineering, Pocatello, USA Purpose or Objective Secondary external neutrons are produced within the physical components of the proton beam line e.g., the double scatterer, modulation wheel, compensator, and field aperture. In passive scattered proton therapy, external neutrons account for a majority of neutron dose equivalent for small fields and up to 50 % for large fields. Spectra measurements are needed to fully and accurately understand neutron dose equivalent from external neutrons. Such data should be reported for proton beamlines from each manufacturer. Here, we focused on the single room compact proton system manufactured by

Conclusion DIBH and proton therapy both reduced the dose to cardiac structures and the risk of cardiac toxicity, compared to IMRT in FB, but no significant difference was found between IMRT in DIBH and proton therapy in FB. Therefore, with respect to cardiac toxicity, these data suggest that given a choice in techniques, IMRT in DIBH and/or proton therapy should be selected. However, the difference between IMRT in DIBH and proton therapy in FB is variable and should be evaluated on a patient-specific basis. PO-0814 The Influence of scans parameters on effective dose of CBCT scans used for IGRT proce dures Abuhaimed 1 , C. J. Martin 2 , M. Sankaralingam 3 1 King Abdulaziz City for Science and Technology, Department of Applied Physics, Riyadh, Saudi Arabia 2 University of Glasgow, Department of Clinical Physics, Glasgow, United Kingdom 3 Beatson West of Scotland Cancer Centre, Department of Radiotherapy Physics, Glasgow, United Kingdom Purpose or Objective A new software with a version of (V2.5) of On-Board imager (OBI) system, which is utilized in the clinic for