Journals

arxiv.org e-Print Archive - Medical Physics
A list of recent preprint articles in this field, with a link to a searchable archive that dates back to 1992.
http://arxiv.org/list/physics.med-ph/recent

International Journal of Radiation Oncology Biology Physics
Commonly known as the Red Journal and is the official journal of the ASTRO, American Society for Therapeutic Radiology and Oncology. Papers in this journal are usually written by both medical physicists and medical oncologists/radiologists.
http://www.sciencedirect.com/science/journal/03603016

Medical Physics
Medical Physics is the scientific journal of the American Association of Physicists in Medicine. Calendar of Events in Medical Physics and Links to Abstracts of Articles available free.
http://www.medphys.org/

PubMed
PubMed is the National Library of Medicine's search service that provides access to over 11 million citations in MEDLINE, PreMEDLINE, and other related databases, with links to participating online journals.
http://www.ncbi.nih.gov/entrez/query.fcgi?db=PubMed

Radiotherapy and Oncology
The official journal of ESTRO (European Society for Therapeutic Radiology and Oncology). Similar to International Journal of Radiation Oncology Biology Physics except mostly authored by clinical researchers from Europe.
http://www.sciencedirect.com/science/journal/01678140