Image quality of 4D in-treatment CBCT acquired during lung SBRT using FFF beam: a phantom study

Radiation Oncology

Table 1 Summary of four cone-beam CT imaging protocols used in this study

	3D		4D
	Pretreatment	In-treatment	Pretreatment	In-treatment
Image acquisition parameters
MV treatment beam	No	Yes	No	Yes
Tube voltage (kV)	120	120	120	120
Tube current (mA)	40	40	20	20
Exposure time (ms)	40	40	16	16
Collimator	M20	M20	S20	S20
Rotation angle (°)	360	360	200	200
Gantry speed (°/min)	360	–	67	–
Acquisition interval (°)	–	0.1	–	0.1
Estimated time (s)^a	60	99	180	55
Analysis results
#projections acquired	333	512	1010	266
Contrast (%)	9.6	10.1	8.0	5.5
Contrast-to-noise ratio	10.0	9.5	10.7	2.6
Overall uniformity (%)	98.5	98.0	97.1	89.1
Minimum uniformity (%)	98.8	98.4	98.4	95.7

The CBCT acquired without MV treatment beam delivery is denoted by pretreatment CBCT as it is acquired prior to treatment. The results of an initial image quality test for the listed protocols are summarized
^aThe time for the in-treatment CBCT images was estimated as the beam-on time expected to deliver the VMAT plan for patient 1. In general, the time to acquire an in-treatment CBCT image varies depending on the VMAT plan, which is concurrently delivered

ISSN: 1748-717X