title: Predicting the sensitivity to ion therapy based on the response to photon irradiation--experimental evidence and mathematical modelling.
abstract: OBJECTIVE
  The use of ion radiation therapy is growing due to the continuously increasing positive clinical experience obtained. Therefore, there is a high interest in radio-biological experiments comparing the relative efficiency in cell killing of ions and photons as photons are currently the main radiation modality used for cancer treatment. This comparison is particularly important since the treatment planning systems (TPSs) used at the main ion therapy Centers make use of parameters describing the cellular response to photons, respectively ions, determined in vitro. It was, therefore, the aim of this article to compare the effects of high linear energy transfer (LET) ion radiation with low LET photons and determine whether the cellular response to low LET could predict the response to high LET irradiation.
  
  
  METHODS
  Clonogenic cell survival data of five tumor cell lines irradiated with different ion beams of similar, clinically-relevant, LET were studied in relation to response to low LET photons. Two mathematical models were used to fit the data, the repairable-conditionally repairable damage (RCR) model and the linear quadratic (LQ) model.
  
  
  RESULTS
  The results indicate that the relative biological efficiency of the high LET radiation assessed with the RCR model could be predicted based only on the response to the low LET irradiation.
  
  
  CONCLUSIONS
  The particular features of the RCR model indicate that tumor cells showing a large capacity for repairing the damage will have the larger benefit from radiation therapy with ion beams.
authors.affiliation: Department of Oncology-Pathology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Chitralekha
authors.initials: C
authors.lastname: Mohanty
authors.affiliation: Department of Oncology-Pathology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Zielinska-Chomej
authors.affiliation: Department of Oncology-Pathology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Margareta
authors.initials: M
authors.lastname: Edgren
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Inage-ku, Chiba-shi, Japan.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Hirayama
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Inage-ku, Chiba-shi, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Murakami
authors.affiliation: Department of Oncology-Pathology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Bengt
authors.initials: B
authors.lastname: Lind
authors.affiliation: Medical Radiation Physics, Stockholm University and Karolinska Institutet, Stockholm, Sweden Iuliana.Livia.Dasu@ki.se.
authors.forename: Iuliana
authors.initials: I
authors.lastname: Toma-Dasu
mesh_terms: D002470:Cell Survival / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D018499:Linear Energy Transfer; D008954:Models, Biological; D008962:Models, Theoretical; D009369:Neoplasms / Q000532:radiotherapy*; D017785:Photons; D014407:Tumor Cells, Cultured
keywords: Clonogenic cell survival; high LET; linear energy transfer; low LET; relative biological effectiveness