An effective amount of {HEAD ~ a photosensitive agent} for PDT is administered to {TAIL ~ a patient} 
An effective amount of { HEAD ~ a photosensitive agent } for PDT is administered to { TAIL ~ a patient }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL