Is it permissible for a man to prepare a graduation research paper in the field of breast cancer radiation therapy, with all that this entails in terms of study, and perhaps speaking with female patients, and spending time in treatment centers?

The basic principle is that it is not permissible for males to view images of women's 'awrat (private parts) or to engage with them in private conversations that involve impropriety. However, if there is a need for males to study something related to women, and there are no female students available to fulfill this need, then there is no harm in that, due to the necessity and in order to achieve a benefit for the people.