Table 2.

Much larger inter‐fractional CTV displacement measured by CBCT than the intra‐fractional one in PMRM‐IMRT for left‐sided breast cancer during peaceful breathing.

Paramaters	Direction	Number	Mean ± SD(mm)	≤2 mm	≤3 mm	≤4 mm
Intra‐fraction	X	900	0.3 ± 0.3	99.7%	100.0%	100.0%
	Y	900	0.5 ± 1.0	88.1%	96.5%	100.0%
	Z	900	0.5 ± 0.5	96.5%	99.5%	100.0%
	Sum	2700	0.4 ± 0.7	94.8%	98.7%	100.0%
Inter‐fraction	X	30	1.7 ± 1.2	40.0%	93.3%	96.6%
	Y	30	2.8 ± 2.3	46.6%	60.0%	63.3%
	Z	30	2.6 ± 2.2	50.0%	66.6%	70.0%
	Sum	90	2.4 ± 2.1	45.5%	73.3%	76.6%

X, Y, and Z values indicated the inter‐ or intra‐fractional CTV displacement in x (laterally), in y (longitudinally) and in z coordinate axis (vertically), respectively. Data presented as mean ± standard deviation (Mean ± SD) (mm). The values in the last three columns were the CTV coverage rates under the corresponding status when using CTV expanding values with 2, 3, and 4 mm, respectively. Abbreviations: PMRM‐IMRT = post modified radical mastectomy intensity‐modulated radiotherapy. CBCT = cone beam computed tomography.