Table 3.

Effect modification of cranial radiotherapy dose-response for risk of meningioma^a

	N Total	N Cases	ERR/Gy	95% CI	P Interaction
Model 1: All patients	1262	93	0.30	0.03–unknown
Model 2: Age at diagnosis					0.86
0–4 y	2641	46	0.31	0.10–1.36
5–9 y	1583	26	0.31	0.10–1.35
10–17 y	1619	25	0.27	0.08–1.19
Model 3: Volume					0.98
Partial	313	14	0.30	0.09–1.32
Full	979	79	0.30	0.09–1.29
Model 4: Age at diagnosis and volume					0.55
0–4 y / partial	86	6	0.52	0.13–2.49
5–17 y / partial	227	8	0.22	0.05–1.06
0–4 y / full	380	40	0.29	0.09–1.28
5–17 y / full	569	39	0.30	0.09–1.32
Model 5: Sex					0.96
Male	3269	47	0.30	0.10–1.29
Female	2574	50	0.30	0.09–1.28

Abbreviations: ERR = excess relative risk; Gy = Gray; N = number; UNK = unknown.

^aAll models adjusted for sex, age at diagnosis (<5, 5–9, 10+ y), cranial radiotherapy (no, partial, full). Coefficients for those variables were fixed at the values estimated in model 1 to improve stability of the model fitting. For likelihood ratio tests (P interaction), fixed parameters were counted as free, resulting in conservative P-values.

^bDue to a very flat likelihood to the right of the maximum likelihood estimate, even much larger values are consistent with the data.