Improving the accuracy and consistency of clinical target volume delineation for rectal cancer by an education program

Table 1 Definitions and formulas of the indices used for comparison

	Indices	Definition	Formula
Indices for geometric comparison analysis	Dice similarity coefficient index	Intersection of Vstu and Vref divided by their average	2 (Vstu ∩ Vref)/(Vstu + Vref)
	Inclusiveness index	Intersection of Vstu and Vref divided by Vstu	(Vref ∩ Vstu)/Vstu
	Concordance index	Intersection of Vstu and Vref divided by their union	(Vref ∩ Vstu)/(Vref ∪ Vstu)
	Relative volume difference	Difference between Vstu and Vref divided by Vref and multiplied by 100	(Vstu-Vref)/Vref × 100
Indices for interobserver variation	Maximum volume ratio	Ratio of the maximum volume to minimum volume contoured by the participants	Vmax/Vmin
	Coefficient of variation	Standard deviation of the volumes contoured by the participants multiplied by 100 and divided by the mean value	SD × 100/mean

V_stu: Target volume delineated by the participants; V_ref: Standard target volume delineated by the expert; V_max: Maximum volume contoured by the participants; V_min: Minimum volume contoured by the participants; SD: Standard deviation.

Table 2 Quantitative analysis of target volume parameters

Indices	Before the education program	After the education program	t/Z value	P value
Volume (cm3)	809.82 ± 141.17 (624.69-1112.79)	705.21 ± 100.53 (603.97-949.53)	-3.180	0.001
Length (cm)	18.19 ± 1.01 (16.50-20.00)	17.77 ± 0.60 (17.00-19.00)	1.442	0.175
DSC	0.78 ± 0.06 (0.68-0.87)	0.84 ± 0.04 (0.71-0.88)	-2.621	0.009
IncI	0.69 ± 0.10 (0.57-0.83)	0.79 ± 0.08 (0.58-0.87)	-3.926	0.002
CI	0.65 ± 0.08 (0.52-0.77)	0.73 ± 0.06 (0.56-0.78)	-2.551	0.011
ΔV (%)	30.79 ± 10.65 (17.33-47.65)	21.43 ± 7.80 (12.93-41.70)	3.926	0.002

Data are presented as mean ± SD (range). DSC: Dice similarity coefficient index; IncI: Inclusiveness index; CI: Concordance index; ΔV (%): Relative volume difference.

Table 3 Quantitative analysis of interobserver variation

	Vmax (cm3)	Vmin (cm3)	Mean (cm3)	SD (cm3)	MVR	CV
Before the education program	1112.79	624.69	809.82	141.17	1.78	17.43
After the education program	949.53	603.97	705.21	100.53	1.57	14.26
Decrease ratio	14.67%	3.32%	12.92%	28.79%	11.80%	18.19%

V_max: Maximum volume contoured by the participants; V_min: Minimum volume contoured by the participants; SD: Standard deviation; MVR: Maximum volume ratio; CV: Coefficient of variation.

Table 4 Qualitative analysis of target volume variations

Parameters	Before the education program		After the education program		P value
	Yes	No	Yes	No
CTV start from the bifurcation of the common iliac artery	8 (61.54%)	5 (38.46%)	12 (92.31%)	1 (7.69%)	0.16
Delineate external iliac area	8 (61.54%)	5 (38.46%)	1 (7.69%)	12 (92.31%)	0.01
Delineate inguinal area	0 (0%)	13 (100%)	0 (0.00%)	13 (100%)	NA
Delineate ischiorectal fossa	7 (53.85%)	6 (46.15%)	1 (7.69%)	12 (92.31%)	0.03

CTV: Clinical target volume; NA: Not applicable.