RESPONSE CHARACTERIZATION OF OC-1 RADIOCHROMIC FILM TO ULTRA-HIGH DOSE RATES FOR LIGHT ION BEAMS
PO-1549
Abstract
RESPONSE CHARACTERIZATION OF OC-1 RADIOCHROMIC FILM TO ULTRA-HIGH DOSE RATES FOR LIGHT ION BEAMS
Authors: Sophie Chiavassa1, Daphnée Villoing1, Charbel Koumeir2, Arnaud Guertin3, Ferid Haddad2, Vincent Métivier3, Freddy Poirier2, Vincent Potiron4, Stéphane Supiot5, Noel Servagent3, Gregory Delpon1
1ICO, Medical Physic, Saint-Herblain, France; 2GIP ARRONAX, Physic, Saint-Herblain, France; 3SUBATECH, UMR 6457, CNRS IN2P3, IMT Atlantique, Nantes University, Nantes, France; 4ICO, LabCT, Saint-Herblain, France; 5ICO, Radiotherapy, Saint-Herblain, France
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Purpose or Objective
The ARRONAX facility can deliver proton (68MeV) and
alpha (67.4MeV) beams at ultra-high dose rates (UHDR). Our preclinical beamlines
are specifically set up to easily shift between conventional and UHDR irradiation
conditions. A major challenge of these irradiations is to control their
dosimetry in both modes. As the use of two common radiochromic films, the GAFchromic™
EBT3 and EBT-XD films (Ashland, Inc.), was found to lead to non-negligible
overestimations of the net optical density (netOD) and hence the absorbed dose,
we evaluated the usability and the dose rate dependency of novel films from OrthoChromic
Inc., the OC-1 films. Additionally, the dose conversion process was
investigated for these films.
Material and Methods
We compared the response in netOD of OC-1 films after
proton and alpha irradiations at various mean dose rates (0.25, 40, 1500, 7500
and 60000 Gy/s), for 10 different doses (2-130 Gy). Additionally, these
irradiations were compared with photon beam irradiations at conventional dose
rate. We also monitored the stability over time of OC-1 films after a 20 Gy
irradiation, using a 6
MV photon beam from Varian Clinac. To compensate for the scanner variability,
we simultaneously monitored non-irradiated OC-1 and EBT-XD films, as well as a
3 Gy EBT-XD film (similar in netOD to a 20 Gy OC-1). These four films were repeatedly
digitized, up to 16 days after irradiation, using a V700 Photo Epson Perfection
flatbed color scanner. The films were analyzed using ImageJ software v1.53e,
and mean pixel values and associated standard deviations were measured on both
red and green channels.
Results
OC-1 films did not show any significant
difference in the netOD between conventional dose rate and UHDR dose rates up
to 60000 Gy/s, except at very low doses associated to higher uncertainties, for
3 Gy and below. The netOD of OC1-films was found to increase substantially in
the first hours following the irradiation, then to stabilize about 100h after
irradiation.
Conclusion
OC-1 films, that present the advantage of a large dynamic
dose range (0.1 – 100 Gy), did not show any impact of the mean dose rate up to 60000
Gy/s above 3Gy. Despite their unlamination, making them fragile and difficult
to handle, OC-1 films seem appropriate for a good control dosimetry of our
future UHDR experiments at the ARRONAX cyclotron. Users should however observe
a four days delay before film reading and analysis.