title: Clinical oxygen enhancement ratio of tumors in carbon ion radiotherapy: the influence of local oxygenation changes.
abstract: The effect of carbon ion radiotherapy on hypoxic tumors has recently been questioned because of low linear energy transfer (LET) values in the spread-out Bragg peak (SOBP). The aim of this study was to investigate the role of hypoxia and local oxygenation changes (LOCs) in fractionated carbon ion radiotherapy. Three-dimensional tumors with hypoxic subvolumes were simulated assuming interfraction LOCs. Different fractionations were applied using a clinically relevant treatment plan with a known LET distribution. The surviving fraction was calculated, taking oxygen tension, dose and LET into account, using the repairable-conditionally repairable (RCR) damage model with parameters for human salivary gland tumor cells. The clinical oxygen enhancement ratio (OER) was defined as the ratio of doses required for a tumor control probability of 50% for hypoxic and well-oxygenated tumors. The resulting OER was well above unity for all fractionations. For the hypoxic tumor, the tumor control probability was considerably higher if LOCs were assumed, rather than static oxygenation. The beneficial effect of LOCs increased with the number of fractions. However, for very low fraction doses, the improvement related to LOCs did not compensate for the increase in total dose required for tumor control. In conclusion, our results suggest that hypoxia can influence the outcome of carbon ion radiotherapy because of the non-negligible oxygen effect at the low LETs in the SOBP. However, if LOCs occur, a relatively high level of tumor control probability is achievable with a large range of fractionation schedules for tumors with hypoxic subvolumes, but both hyperfractionation and hypofractionation should be pursued with caution.
authors.affiliation: Department of Physics, Stockholm University, Stockholm, Sweden Laura.Antonovic@gmail.com.
authors.forename: Laura
authors.initials: L
authors.lastname: Antonovic
authors.affiliation: Department of Physics, Stockholm University, Stockholm, Sweden.
authors.forename: Emely
authors.initials: E
authors.lastname: Lindblom
authors.affiliation: Department of Radiation Physics and Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Dasu
authors.affiliation: Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark and Department of Experimental Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Niels
authors.initials: N
authors.lastname: Bassler
authors.affiliation: Next Generation Medical Physics Research Program and International Open Laboratories, National Institute of Radiological Sciences, Chiba 263-8555, Japan.
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Furusawa
authors.affiliation: Department of Physics, Stockholm University, Stockholm, Sweden Department of Oncology and Pathology, Karolinska Institute, Stockholm, Sweden.
authors.forename: Iuliana
authors.initials: I
authors.lastname: Toma-Dasu
mesh_terms: D002244:Carbon; D015687:Cell Hypoxia / Q000528:radiation effects*; D002470:Cell Survival / Q000528:radiation effects; D003198:Computer Simulation; D019583:Dose Fractionation, Radiation; D063193:Heavy Ion Radiotherapy / Q000379:methods*; D020450:Heavy Ions; D018499:Linear Energy Transfer; D008954:Models, Biological; D015233:Models, Statistical; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy*; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000528:radiation effects*; D016896:Treatment Outcome
chemical_list: D002244:Carbon; D010100:Oxygen
keywords: LOC; OER; RCR; TCP; carbon ion; fractionation; hypoxia
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