Hypoxic tumors (tumors with low oxygen levels) are noted as one of the main reasons for failure to control malignant tumors with radiation therapy. Since hyperbaric oxygen improves oxygen supply to hypoxic tumors, thus increasing their levels, hyperbaric oxygen has sound clinical grounds for being used alongside radiation therapy. This study published in the International Journal of Clinical Oncology goes over the rationale for using this combination in more detail <view study>