Question

improve: By using PET, it may allow identification of patients who achieved pathologic complete response to radiation therapy before surgery.

Accepted Answer

1) the it makes the subject obscure2) dangling participle ("using") and "it"=> fix by swapping for active subject and verb Using PET, clinicians may be able to identify patients who have responded completely to radiation therapy and may not require surgery.

Front	improve: By using PET, it may allow identification of patients who achieved pathologic complete response to radiation therapy before surgery.
Back	1) the it makes the subject obscure 2) dangling participle ("using") and "it" => fix by swapping for active subject and verb Using PET, clinicians* may be able to identify patients who have responded completely to radiation therapy and may not require surgery.*

Pet Patients Radiation Therapy Surgery Subject Improve By