I usually advise that vaccinations may not "work" as well during / after treatment than with an intact immune system. Therefore I sometimes advise patients to carry out potential vaccinations before treatment commences. This is of course restricted to patients receiving rather extensive radiation therapy with larger fields. The immune suppression due to an RT of a vestibularis schwannoma or a limited prostate cancer is considerably smaller than what will happen if you perform adjuvant RT for breast cancer with complete ENI or an extensive pelvic RT.