Synchrotron radiation-based experimental determination of the optimal energy for cell radiotoxicity enhancement following photoelectric effect on stable iodinated compounds.
This study was designed to experimentally evaluate the optimal X-ray energy for increasing the radiation energy absorbed in tumours loaded with iodinated compounds, using the photoelectric effect. SQ20B human cells were irradiated with synchrotron monochromatic beam tuned at 32.8, 33.5, 50 and 70 keV. Two cell treatments were compared to the control: cells suspended in 10 mg ml(-1) of iodine radiological contrast agent or cells pre-exposed with 10 microM of iodo-desoxyuridine (IUdR) for 48 h. Our radiobiological end point was clonogenic cell survival. Cells irradiated with both iodine compounds exhibited a radiation sensitisation enhancement. Moreover, it was energy dependent, with a maximum at 50 keV. At this energy, the sensitisation calculated at 10% survival was equal to 2.03 for cells suspended in iodinated contrast agent and 2.60 for IUdR. Cells pretreated with IUdR had higher sensitisation factors over the energy range than for those suspended in iodine contrast agent. Also, their survival curves presented no shoulder, suggesting complex lethal damages from Auger electrons. Our results confirm the existence of the 50 keV energy optimum for a binary therapeutic irradiation based on the presence of stable iodine in tumours and an external irradiation. Monochromatic synchrotron radiotherapy concept is hence proposed for increasing the differential effect between healthy and cancerous tissue irradiation.
Corde
S
S
INSERM U647 Rayonnement Synchrotron et Recherche Médicale, Université Joseph Fourier & ID17 Biomedical Beamline of European Synchrotron Radiation Facility, CHU A Michallon, BP 217, 38043 Grenoble 09, France.
Joubert
A
A
Adam
J F
JF
Charvet
A M
AM
Le Bas
J F
JF
Estève
F
F
Elleaume
H
H
Balosso
J
J
D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D016923:Cell Death; D002470:Cell Survival; D003287:Contrast Media / Q000493:pharmacokinetics; D006258:Head and Neck Neoplasms / Q000473:pathology*; D006801:Humans; D007065:Idoxuridine / Q000493:pharmacokinetics / Q000494:pharmacology*; D007455:Iodine / Q000493:pharmacokinetics* / Q000494:pharmacology; D019384:Nucleic Acid Synthesis Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D011836:Radiation Tolerance; D011838:Radiation-Sensitizing Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014964:X-Ray Therapy / Q000379:methods*
D003287:Contrast Media; D019384:Nucleic Acid Synthesis Inhibitors; D011838:Radiation-Sensitizing Agents; D007455:Iodine; D007065:Idoxuridine