Table 1. Dynamic changes of parotid volume and apparent diffusion coefficient (ADC) histogram parameters during radiotherapy in patients with nasopharyngeal carcinoma.

Parameters	Time point 1	Time point 2	Time point 3	P value
Volume	27.15 ± 6.53	19.47 ± 4.38*	16.60 ± 4.56*,§	< 0.001
ADCmean	726.5 ± 79.2	1084.6 ± 140.5*	1136.5 ± 187.0*	< 0.001
SD	177.3 ± 31.0	195.2 ± 34.2*	209.9 ± 36.8*,§	< 0.001
ADCmin	132.4 ± 127.5	426.1 ± 274.8*	476.8 ± 292.0*	< 0.001
ADCmax	1521.5 ± 194.2	1811.8 ± 223.3*	1882.8 ± 202.6*	< 0.001
5th percentile	449.3 ± 119.7	780.7 ± 164.2*	799.5 ± 230.3*	< 0.001
10th percentile	514.4 ± 104.2	847.3 ± 154.1*	875.4 ± 210.8*	< 0.001
25th percentile	613.8 ± 86.2	955.1 ± 142.1*	996.5 ± 193.4*	< 0.001
50th percentile	719.9 ± 75.9	1078.9 ± 140.9*	1130.6 ± 187.0*	< 0.001
75th percentile	831.7 ± 72.4	1205.8 ± 138.5*	1273.9 ± 183.2*,§	< 0.001
90th percentile	943.2 ± 76.1	1331.9 ± 140.1*	1404.1 ± 173.6*,§	< 0.001
Skewness	0.781 ± 0.806	0.308 ± 0.689*	0.418 ± 0.748*	0.003
Kurtosis	9.718 ± 2.609	6.815 ± 2.687*	7.120 ± 2.575*	< 0.001

Note: ADC_mean, ADC_min, and ADC_max are the mean, minimum, and maximum ADC values of all voxels within the volume of interest, respectively. SD is the standard deviation of ADC values. The 5^th, 10^th, 25^th, 50^th, 75^th, and 90^th percentiles are the ADC values at which 5%, 10%, 25%, 50%, 75%, and 90% of the voxel values that formed the histogram are found to the left, respectively. Skewness is the degree of histogram asymmetry around the mean. Kurtosis is a measurement of the histogram sharpness. Time point 1 was within 2 weeks before radiotherapy. Time point 2 was one month after radiotherapy. Time point 3 was four months after radiotherapy. P values were calculated by one-way analysis of variance.

The volume unit is cm³, and all the ADC histogram parameters are in the units of × 10^-6 mm²/s except for skewness and kurtosis.

* P < 0.05 compared to time point 1.

^§ P < 0.05 compared to time point 2.