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: About 2 / 3 of the patients in both Gamma Knife and radiofrequency groups showed improvements in bradykinesia and rigidity , although when considered as a group neither the Gamma Knife nor the radiofrequency group showed statistically significant improvements in UPDRS scores .
### Output Text:
About 2 / 3 of the patients in both Gamma Knife and radiofrequency groups showed improvements in bradykinesia and rigidity , although when considered as a group neither the Gamma Knife nor the radiofrequency group showed statistically significant improvements in UPDRS scores . 