  A dynamical system model for tumor -- immune system interaction together with
a method to mimic radiation therapy are proposed. A large population of virtual
patients is simulated following an ideal radiation treatment. A characteristic
parameter, the Immune System -- Tumor Efficiency Rate (ISTER), is introduced.
ISTER dependence of treatment success and other features is studied.
Statistical results allow us to give a patient classification scheme.
Radiotherapy treatment biological effective dose (BED) is thus optimized based
on the patient physical condition, following the ALARA (As Low As Reasonably
Achievable) criterion.
