(a) The Secretary may provide any veteran a medical examination, and hospital care, medical services, and nursing home care, which the Secretary determines is needed for the treatment of any cancer of the head or neck which the Secretary finds may be associated with the veteran's receipt of nasopharyngeal radium irradiation treatments in active military, naval, or air service.

(b) The Secretary shall provide care and services to a veteran under subsection (a) only on the basis of evidence in the service records of the veteran which document nasopharyngeal radium irradiation treatment in service, except that, notwithstanding the absence of such documentation, the Secretary may provide such care to a veteran who—

(1) served as an aviator in the active military, naval, or air service before the end of the Korean conflict; or

(2) underwent submarine training in active naval service before January 1, 1965.