The Collaborative International Dictionary of English v.0.48:

chemotherapeutic \chemotherapeutic\ chemotherapeutical
\chemotherapeutical\adj.
   of or pertaining to chemotherapy; using chemotherapy; having
   properties beneficial for chemotherapy.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

chemotherapeutic
    adj 1: of or relating to chemotherapy [syn: chemotherapeutic,
           chemotherapeutical]