ESTRO 2020 Abstract book

S984 ESTRO 2020

The therapeutic potential of protons has not yet been fully realized due to uncertainties in proton range calculations. Proton imaging systems can reduce these uncertainties by directly and accurately calculating tissue water equivalent thicknesses (WETs). These WET values can be used to precisely calculate proton ranges within the patient, decreasing the need for range uncertainty margins. The purpose of this study is to demonstrate the development of a novel and clinically compatible proton imaging system design using a proton beam-integrating approach. The design consists of a large-volume scintillator detector that is capable of capturing a wide distribution of residual proton ranges emerging from the tissue. Material and Methods The organic liquid scintillator detector (20 × 20 × 20 cm 3 ) produces a 3D distribution of scintillation light in response to a mono-energetic, passively scattered proton beam delivery (180 MeV). A projection of the 3D light distribution is recorded using a charge-coupled device (CCD) placed along the beam’s-eye-view direction. An object placed between the proton source and the detector attenuates the proton beam by pulling back its original Bragg peak location within the scintillator. The CCD captures this pull- back in the form of cumulative pixel intensity loss. This intensity loss is correlated with the object WET using an energy-specific calibration curve, which was constructed by placing plastic water slabs of known WETs in front of the detector. A line-pair phantom designed for megavoltage photon imaging was chosen for determining the imaging resolution of the system. Selected inserts from a CT Hounsfield Unit phantom were used for testing the WET accuracy of the system. Finally, the system’s ability to reconstruct proton CT images from multiple projections of a human head replica was demonstrated using a filtered backprojection algorithm.

Conclusion In this preliminary work, we demonstrated a novel, simple, clinically feasible design for proton beam-integrated radiography and CT systems. We found the system to be capable of accurately measuring WETs. A further improvement in the accuracy is expected after correcting for proton-induced scatter. PO-1693 Correlation between SUVmax and Primary Tumor Volume in Cervical Cancer Received Radiation Therapy H. Lee 1 , S.G. Kim 1 , Y.S. Shim 2 , Y.S. Kim 3 , J.W. Shin 4 , K.B. Lee 4 , K.C. Lee 5 , S.H. Lee 5 1 Gil Medical Center- Gachon University of Medicine and Science, Department of Nuclear Medicine, Inchon, Korea Republic of ; 2 Gil Medical Center- Gachon University of Medicine and Science, Department of Radiology, Inchon, Korea Republic of ; 3 Gil Medical Center- Gachon University of Medicine and Science, Department of Inernal Medicine, Inchon, Korea Republic of ; 4 Gil Medical Center- Gachon University of Medicine and Science, Department of Obstetrics and Gynecology, Inchon, Korea Republic of ; 5 Gil Medical Center- Gachon University of Medicine and Science, Department of Radiation Oncology, Inchon, Korea Republic of Purpose or Objective The aim of this study is to analyze the correlation between the maximum standardized uptake value (SUVmax) in positron emission tomography/computed tomography (PET/CT) of primary tumor and primary tumor volume (pTV) response in cervical cancer patients treated with We conducted a retrospective review of 41 cervical cancer patients (stage I-II: n=23; stage III-IV: n=18) treated with RT with or without chemotherapy from August of 2009 until February of 2016. All patients received external beam radiation therapy and intracavitary brachytherapy. All patients (median, 56 years; range, 37-81 years) had 18F- FDG PET/CT scans performed before and after RT (pre- and post-RT). Measurement of pTV for the treatment response evaluation was performed by the diagnostic radiologist using magnetic resonance imaging or abdominopelvic CT. The The measuremets of pTV were performed at pre-, mid- and post-RT. The correlation between SUVmax and pTV response was evaluated and analyzed. The changes of pTV and SUVmax between pre-RT and post-RT were analyzed. The correlation between the pre-RT SUVmax and the pTV reduction rate (pTVRR) were also evaluated. Results The median duration of follow-up was 57 months (range 5- 99 months). The 5-year overall survival and progression radiation therapy (RT). Material and Methods

Results We evaluated the imaging properties of the system, including its spatial resolution (0.2 line-pairs/mm), modulation transfer function, and signal-to-noise ratio (26 dB at 0.08 mGy). Several optical imaging artifacts, including an optical point spread function, were also accounted for, resulting in image sharpening. We determined the WET accuracy using CT Hounsfield Unit phantom inserts, including solid water, acrylic, and cortical bone with a relative accuracy of -0.8%, 0.9%, and -2.4%, respectively. A qualitative analysis of the reconstructed proton CT slices demonstrated an ability to identify image features on the order of few millimeters.