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: It is recommended that doxorubicin dosage be sharply restricted in children with Wilms tumor of the left kidney who receive postoperative irradiation .
### Output Text:
It is recommended that <span class="chemical">doxorubicin</span> dosage be sharply restricted in children with Wilms tumor of the left kidney who receive postoperative irradiation . 