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Dependence of Imaging Dose On Image Quality of Free-Breathing 3DCBCT of Moving Tumors

K Kauweloa

K Kauweloa1,2*, J Park1, W Song1, (1) Center for Advanced Radiotherapy Technologies and Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California, (2) Department of Physics, San Diego State University, San Diego, California

SU-E-J-8 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: To evaluate the impact on free-breathing CBCT (FBCBCT) image quality to properly visualize the motion range of moving tumors as a function of imaging dose.
Methods: A multi-purpose body phantom (QUASAR) with a cylindrical cedar wood (density = 0.330g/cc), and an embedded 3-cm diameter Polystyrene sphere (density = 0.855g/cc) were used to simulate lung tumor motion. Varian Trilogy with OBI system was used to acquire CBCT images (high-dose mode: 125kVp, 80mA, 25ms/frame & low-dose mode: 110kVp, 20mA, 20ms/frame). As the FBCBCT projections were acquired, the sphere moved in accordance to 30 simulated sinusoidal patient breathing patterns using a programmable motion platform, which were given the parameters: inhalation-to-exhalation (I/E) ratio ranging from 1-0.2131, amplitudes of 1 and 3 cm, and periods 2, 4, and 6 seconds. Following the acquisition of FBCBCT images, the ITV contrast, defined as = (target pixel values inside the sphere - avg. pixel values in background)/(avg. pixel values in background), were calculated per image slice.
Results: All parameters, I/E ratio, period, and amplitude did not seem to have much impact on the percentage change of the ITV contrast as a function of imaging dose. The percentage-change for all coronal images with a reduced ITV contrast when going from high-dose to low-dose was -4.61 ± 3.04%, while the percentage-change for all coronal images with an increased ITV contrast when going from high-dose to low-dose, was 8.19 ± 3.61%. The overall percentage-change of all 30 coronal images was 5.21 ± 6.49%.
Conclusions: We found that imaging dose did not have much impact on the visibility of the ITV volume, irrespective of the amplitude, I/E ratio, or period. Thus, it seems that low-dose FBCBCT may be just as suitable for clinical use while sparing a significant imaging dose to the patients.

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