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Radiation Dose Comparison in Helical 4DCT and Cine 4DCT

T Lin

T Lin*, J Liu , J Fan , L Chen , R Price , C Ma , Fox Chase Cancer Center, Philadelphia, PA


WE-RAM2-GePD-I-2 (Wednesday, August 2, 2017) 10:00 AM - 10:30 AM Room: Imaging ePoster Lounge

Purpose: Using 4D CT (four-dimensional computed tomography) for radiotherapy treatment planning is prevalent for 4D estimation of respiratory motion in recent radiation treatment for certain treatment sites. Two types of scanner are commonly used: helical and Cine 4DCTs.This study is to compare the delivered dose from these two scanners with different treatment sites.

Methods: Cine 4DCT: GE Lightspeed 4DCT; Helical 4DCT: Siemens Somatom Definition AS 20, are the two scanners used in this study. Standard adult Body phantom with 10 cm CT chamber was used to measure CTDIs and DLPs (dose length product). Different Cine times with different cine time between images were changed to observe the different DLPs. 3 different respiratory rate protocols (>12, >9, >6 rpms) on helical 4DCT were tested. Image qualities (contrast and uniformity) were also compared between two types of 4DCT to observe the differences.

Results: 1. Cine 4DCT: longer Cine time/cine time between images will result in higher DLPs.2. Helical 4DCT: >6 rpm and >12 rpm protocols give similar DLPs, while >9 rpm protocol can deliver less dose.3. Both Cine and helical 4DCT provide similar image qualities.4. Helical 4DCT with >6 rpm and >12 rpm protocols delivered more doses than >9 rpm protocol which delivered comparable dose to the phantom with Cine mode with 7.1s cine time. Cine 4DCT with 6.1s cine time can deliver lower doses to this phantom measurement.

Conclusion: With the same image qualities, helical 4DCT can contribute ~15% higher doses compared to cine 4DCT; however, with shorter cine time (can be used for patients with shorter respiratory periods), cine mode can deliver much lower doses.

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