the number of times that patient 52604 had received a routine chest x-ray since 3 years ago.
select count(*) from procedures_icd where procedures_icd.icd9_code = ( select d_icd_procedures.icd9_code from d_icd_procedures where d_icd_procedures.short_title = 'routine chest x-ray' ) and procedures_icd.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 52604 ) and datetime(procedures_icd.charttime) >= datetime(current_time,'-3 year')