Table 2.

Estimated sample size required to detect a given HR for all subsequent malignancies after proton therapy compared with photon therapy, with 80% power using 2-sided 5% significance tests according to cumulative incidence of second malignant neoplasm occurring 5+ years after diagnosis

Cumulative incidence (%) of subsequent malignancies by 15 y (photon therapy control group)	Number of pediatric cancer survivors per radiation therapy group	Expected number of subsequent malignancies based on cumulative incidence (photons)	HR with 80% power
1%	5000	50	0.5
	8000	80	0.6
	10,000	100	0.65
	15,000	150	0.7
1.5%	3000	45	0.5
	6000	90	0.6
	10,000	150	0.7
	15,000	225	0.75
2%	2500	50	0.5
	4000	80	0.6
	8000	160	0.7
	12,000	240	0.75
2.5%	2000	50	0.5
	3000	75	0.6
	6000	150	0.7
	10,000	250	0.77

Abbreviation: HR = hazard ratio.