Oxygen enhancement ratios of cancer cells after exposure to intensity modulated X-ray fields; DNA damage and cell survival

Matsuya, Yusuke  ; McMahon, S. J.*; Butterworth, K. T.*; Naijo, Shingo*; Nara, Isshi*; Yachi, Yoshie*; Saga, Ryo*; Ishikawa, Masayori*; Sato, Tatsuhiko   ; Date, Hiroyuki*; Prise, K. M.*

Hypoxic cancer cells within solid tumours show radio-resistance, leading to malignant progression in fractionated radiotherapy. When prescribing dose to tumours under heterogeneous oxygen pressure with intensity-modulated radiation fields, intercellular signalling could have an impact on radiosensitivity between in-field and out-of-field cells. However, the impact of hypoxia on radio-sensitivity under modulated radiation intensity remains uncertain. In this study, we investigate the impact of hypoxia on in-field and out-of-field radio-sensitivities using two types of cancer cells. These in vitro measurements indicate that hypoxia apparently impacts out-of-field cells, although the OER values in out-of-field cells were smaller compared to those for in-field and uniformly irradiated cells. These decreased radio-sensitivities of out-of-field cells were shown as a consistent tendency for both DSB and cell death endpoints, suggesting that radiation-induced intercellular communication is of importance in treatment planning with intensity-modulated radiotherapy.