Abstract
BackgroundThis study investigates the effect of gantry speed on 4DCBCT image quality and dose for the Varian On-Board Imager®.MethodsA thoracic 4DCBCT protocol was designed using a 125 kVp spectrum. Image quality parameters were evaluated for 4DCBCT acquisition using Catphan® phantom with real-time position management™ system for gantry speeds varying between 1.0 to 6.0°/s. Superior-inferior motion of the phantom was executed using a sinusoidal waveform with five second period. Scans were retrospectively sorted into 4 phases (CBCT-4 ph) and 10 phases (CBCT-10 ph); average 4DCBCT (CBCT-ave), using all image data from the 4DCBCT acquisitions was also evaluated. The 4DCBCT images were evaluated using the following image quality metrics: spatial resolution, contrast-to-noise ratio (CNR), and uniformity index (UI). Additionally, Hounsfield unit (HU) sensitivity compared to a baseline CBCT and percent differences and RMS errors (RMSE) of excursion were also determined. Imaging dose was evaluated using an IBA CC13 ion chamber placed within CIRS Thorax phantom using the same sinusoidal motion and image acquisition settings as mentioned above.ResultsSpatial resolution decreased linearly from 5.93 to 3.82 lp/cm as gantry speed increased from 1.0 to 6.0°/s. CNR decreased linearly from 4.80 to 1.82 with gantry speed increasing from 1.0 to 6.0°/s, respectively. No noteworthy variations in UI, HU sensitivity, or excursion metrics were observed with changes in gantry speed. Ion chamber dose rates measured ranged from 2.30 (lung) to 5.18 (bone) E-3 cGy/mAs.ConclusionsA quantitative analysis of the Varian OBI’s 4DCBCT capabilities was explored. Changing gantry speed changes the number of projections used for reconstruction, affecting both image quality and imaging dose if x-ray tube current is held constant. From the results of this study, a gantry speed between 2 and 3°/s was optimal when considering image quality, dose, and reconstruction time. The future of 4DCBCT clinical utility relies on further investigation of image acquisition and reconstruction optimization.
Highlights
This study investigates the effect of gantry speed on 4DCBCT image quality and dose for the Varian On-Board Imager®
Work conducted by Onishi et al showed that patients staged with T1 and T2 non-small cell lung cancer (NSCLC) treated with Stereotactic body radiotherapy (SBRT) had cumulative local control rates better than 70 % at 5 years; this is in contrast to local control rates of 50 % with a 5-year survival of approximately 15–30 % for patients treated with conventionally fractionated radiotherapy [1]
This study investigates the effect of gantry speed on 4DCBCT image quality and dose using the On-Board Imager® (OBI) on the EdgeTM radiosurgery system (Varian Medical System, Palo Alto, CA)
Summary
This study investigates the effect of gantry speed on 4DCBCT image quality and dose for the Varian On-Board Imager®. Stereotactic body radiotherapy (SBRT) has become a form of treating inoperable non-small cell lung cancer (NSCLC) in its early stages [1]. Work conducted by Onishi et al showed that patients staged with T1 and T2 NSCLC treated with SBRT had cumulative local control rates better than 70 % at 5 years; this is in contrast to local control rates of 50 % with a 5-year survival of approximately 15–30 % for patients treated with conventionally fractionated radiotherapy [1]. Five-year relative survival rates for lung cancers remains somewhat low at 18 %, attributed to more than one-half of diagnoses made at a distant stage [2]. Though initial clinical results of SBRT for lung cancer are promising, there remain technical complexities that must be addressed. Margin reduction is possible for SBRT, having subsequent implications for reducing mean lung dose [8]
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