Look at these sources:
Influential Factors and Synergies for Radiation-Gene Therapy on Cancer
There are a lot of disease types, so there are different databases:
RCDB: Renal Cancer Gene Database
Try to ask a question with key-words: cancer AND radiation sensitivity AND gene-database in google.com or NCBI
I've found these articles:
A genetic basis for the variation in the vulnerability of cancer to DNA damage
Integrating global gene expression and radiation survival parameters across the 60 cell lines of the National Cancer Institute Anticancer Drug Screen.
Investigation of Radiosensitivity Gene Signatures in Cancer Cell Lines
REG4, NEIL2, and BIRC5 Gene Expression Correlates with Gamma-radiation Sensitivity in Patients with Rectal Cancer Receiving Radiotherapy
Detecting differences in radiation sensitivity of people
Cancer genetics map for the only very importamt gene:
"The protein encoded by this gene belongs to the PI3/PI4-kinase family. This protein is an important cell cycle checkpoint kinase that phosphorylates; thus, it functions as a regulator of a wide variety of downstream proteins, including tumor suppressor proteins p53 and BRCA1, checkpoint kinase CHK2, checkpoint proteins RAD17 and RAD9, and DNA repair protein NBS1. This protein and the closely related kinase ATR are thought to be master controllers of cell cycle checkpoint signaling pathways that are required for cell response to DNA damage and for genome stability. Mutations in this gene are associated with ataxia telangiectasia, an autosomal recessive disorder. [provided by RefSeq, Aug 2010]"