In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In this study , neurocognitive outcomes and neuroradiologic evidence of leukoencephalopathy were compared in children treated with intense central nervous system ( CNS ) - directed therapy ( P9605 ) versus those receiving fewer CNS - directed treatment days during intensive consolidation ( P9201 ) .
### Output Text:
In this study , neurocognitive outcomes and neuroradiologic evidence of leukoencephalopathy were compared in children treated with intense central nervous system ( CNS ) - directed therapy ( P9605 ) versus those receiving fewer CNS - directed treatment days during intensive consolidation ( P9201 ) . 