TABLE 4.

Number of Radiation Exposed Cases and Parameter Estimates for Modifiers of the Linear Component (β) of the Excess Relative Risk (ERR) Radiation Dose Model with Additive Adjustment for Treatment with Chemotherapy^a

Modifier	Cases	β	γ1	γ2	γ3	RR0.2 Gyb	RR10 Gyb	θ
None	927	5.45	0.016	−0.001	−0.281	2.7	30.4	2.55
Gender
Male	345	6.79	0.0145	−0.001	−0.280	3.1	37.3	2.60
Female	582	5.12				2.6	28.3
P valuec		0.35
Chemotherapy
No	797	5.47	0.009	−0.001	−0.277	2.7	29.1	2.67
Yes	130	6.66				3.1	35.3
P value		0.36
Alkylating agentd
No	831	5.42	0.016	−0.001	−0.282	2.7	30.2	3.81
Yes	96	5.31				2.7	29.5
P value		0.91
Age at exposure (years)
<1	146	9.17	0.019	−0.001	−0.290	3.9	51.9	2.69
1–4	380	7.80				3.5	44.3
5–9	214	4.18				2.3	24.2
10–14	128	3.88				2.2	22.6
15–19	59	1.51				1.5	9.4
P value		<0.001
Attained age (years)
<20	109	11.54	–0.021	−0.001	−0.162	4.0	61.4	5.89
20–29	248	12.23				4.2	65.0
30–39	284	11.41				4.0	60.7
40–49	141	3.59				1.9	19.8
50–59	101	2.06				1.5	11.8
60+	44	1.40				1.4	8.3
P value		<0.001
Time since exposure (years)
<10	42	2.76	0.005	−0.001	−0.204	1.8	17.1	3.35
10–14	65	3.39				1.9	20.8
15–19	128	8.28				3.3	49.3
20–24	119	7.64				3.1	45.5
25–29	183	14.01				4.9	82.6
30–34	118	9.06				3.5	53.8
35–39	77	4.91				2.4	29.6
40–44	70	3.65				2.0	22.3
45–49	64	3.16				1.9	19.4
50+	61	1.54				1.4	10.0
P value		<0.001
Study group
Non-CCSS	755	5.47	0.022	−0.001	−0.284	2.7	31.6	1.96
CCSS	172	4.21				2.3	24.6
P value		0.68
Number of treatments (all data)e
1	783	5.51	0.016	−0.001	−0.276	2.7	30.9	2.61
≥2	144	5.36				2.9	30.1
P valuec		0.84
Number of treatments (Non-CCSS data)e,f
1	636	5.55			–0.301	2.0	–g
≥2	119	5.83				2.1	–g
P valuec		0.73
Number of treatments (CCSS data)e,f
1	147	5.79	–0.062			–g	32.1	2.36
≥2	25	4.50				–g	25.2
P valuec		0.38

^aModel for the ERR with continuous radiation dose: ERR(d) = βd exp{γ₁d + γ₂d² + γ₃ln(d)} with linear parameter β and the γ parameters defining the curvature. Models fitted with an additive adjustment for treatment with chemotherapy, x_t, RR(d, x_t) = 1 + ERR(d) + θx_t. Models adjusted for study, sex, age and other study-specific factors (see text). For modifiers, βd was replaced by (∑_j β_j z_j d), where z_j was a zero/one indicator variable for the jth category and β_j represented the linear parameter within the jth category. Number of cases reflect radiation exposed only, with nonexposed cases numbering 143.

^bFitted RR at 0.2 and 10 Gy, the approximate trials-weighted mean doses in exposed participants in non-CCSS (0.22 Gy) and CCSS (9.3 Gy) studies.

^cP value for J − 1 degrees of freedom likelihood ratio test of homogeneity, β₁ = … = β_J.

^dTreatment with an alkylating agent replaces chemotherapy as an adjustment variable.

^eThere was no single definition for fractionation across studies. Length of time between fractions, dose per fraction and reason for fractionation differed in each study. In general, one treatment course included all fractions of radiation dose received within six months in most studies and at least a one year interval for tinea capitis.

^fEvaluation used AIC-preferred models: the linear-exponential (log) model, β_j, γ₃, for non-CCSS data and the linear-exponential (linear) model, β_j, γ₁, for the CCSS data.

^gNot in applicable dose range and estimate omitted.