Table 3.

Maximum dose in Gy (RBE) to organs at risk

	PSRS		5XSRS		2.5XSRS		PSRS vs 5XSRS	PSRS vs 2.5XSRS	5XSRS vs 2.5XSRS
Organ at risk	Mean	SD	Mean	SD	Mean	SD	P value	P value	P value
Right ocular globe	0.00	0.0	0.15	0.1	0.14	0.1	< 0.001*	< 0.001*	< 0.001*
Left ocular globe	0.14	0.3	0.22	0.1	0.18	0.1	0.47	0.71	0.24
Right optic nerve	4.18	2.2	5.32	1.6	5.41	1.6	0.008*	0.02*	0.69
Left optic nerve	5.26	2.3	6.14	1.5	5.94	1.6	0.042*	0.11	0.10
Optic chiasm	5.42	2.3	6.29	1.1	6.05	1.5	0.13	0.22	0.26
Temporal lobes	15.58	1.8	14.82	2.4	15.02	2.3	0.17	0.30	0.45
Hypothalamus	1.71	1.4	3.94	1.7	3.77	1.5	0.001*	<0.001*	0.64
Brainstem	7.87	2.8	8.42	2.4	8.20	2.9	0.35	0.47	0.63
Whole brain	19.09	1.7	19.18	1.7	19.17	1.8	0.67	0.68	0.92
Right cochlea	0.00	0.0	1.68	1.0	1.66	1.2	0.001*	0.003*	0.88
Left cochlea	0.02	0.1	1.38	1.1	1.32	1.3	0.004*	0.014*	0.55

Abbreviations: 2.5XSRS, 5XSRS = volumetric-modulated arc therapy using 2.5 mm and 5 mm multileaf collimators, respectively; PSRS = proton stereotactic radiosurgery; SD = standard deviation.

^⁎P ≤ 0.05 considered significant.

Maximum dose to organs at risk = highest dose delivered to a 0.01 cm³ volume within the structure.