If participant is found to be eligible to take part in this study, participant will be assigned to a radiation level of HYDRA radiation based on when participant joins this study. Up to 5 dose levels of HYDRA radiation will be tested. Up to 10 participants will be enrolled at each dose level. The first group of participants will receive the lowest dose level. Each new group will receive a higher dose than the group before it, if no intolerable side effects were seen. This will continue until the highest tolerable dose of HYDRA radiation is found.