Most side-effects disappear shortly after cancer treatment has finished. If you still experience some side effects from cancer treatment, read Nutrition During Cancer Treatment. You can then gradually resume a normal diet. However, if you continue to have eating problems, be sure to let your dietitian or doctor know.
If all side effects subside and a healthy body weight is maintained, you may start looking into adopting a healthy eating habit (if you haven't done so). If you've lost weight during cancer treatments and need to gain weight, read Cancer and Unintentional Weight Loss
General Nutrition Guidelines after Cancer Treatment and Healthy Eating