Table 1.

Stage of evaluation of NTCP models.

Level	Description
1a	External validation in separate dataset using new technology in another center
1b	External validation in separate dataset using new technology in same center or same technology in another center
2a	External validation in separate dataset using nonrandom split in test and validation set
2b	External validation in separate dataset using random split in test and validation set
3	Development and internal validation
4a	Multivariable NTCP model without internal or external validation
Level 4b	Univariable NTCP model without internal or external validation

Abbreviation: NTCP, Normal Tissue Complication Probability.