RIKEN Accel. Prog. Rep. 00 (0)Heavy-ion irradiation test of radiochromic films
T. Kambara,∗1 A. Yoshida,∗1 Y. Hayashi∗1 K. Ishii∗1 and T. Abe∗1
The heavy-ion irradiation of biological or industrial
samples requires the dose-distribution measurement ofa beam spot 5-10 cm in diameter. A radiochromic ﬁlmchanges its color according to the absorbed dose ofionizing radiation and enables two-dimensional highresolution dose-distribution measurements. It is easy
to handle and portable, and a personal computer cancapture its image with an inexpensive and common
image scanner and convert the numerical data of theimage to optical density (OD) as a function of the absorbed dose.1) Radiochromic ﬁlms are widely used inradiotherapy for dosimetry of high-energy photons.
In order to assess the usefulness of radiochromicﬁlms in our high-energy heavy-ion irradiation, wetested two types of ﬁlms, GAFCHROMICTM HD-V2
for a higher dose and EBT-3 for a lower dose,2) using
heavy ions with a wide range of linear energy transfer(LET). The irradiation targets were 4 cm × 5 cm rectangular segments of vendor-supplied 25 cm × 20 cm
sheets of the ﬁlms. The HV-D2 targets were irradiatedby C ions with LETs of 22.5 and 179 keV/µm, Ar ionswith LETs of 184 and 673 keV/µm, and Fe ions withLETs of 637 and 1061 keV/µm with dose ranging from
1 to 400 Gy, and the EBT-3 targets were irradiated byC ions with LET of 22.5keV/µm, Ar ions with LETof 184 keV/µm, and Fe ions with LET of 637 keV/µm
with dose ranging from 0.2 to 10 Gy.
The targets were irradiated at the E5B beamline of
the RIKEN Ring Cyclotron where the LET was adjusted by Al-plate degraders.3) The beam was collimated by a 20-mm-diameter aperture on a 10-mmthick brass plate about 153 mm upstream of the target.
Before and after the irradiation, the target wasscanned by an image scanner and converted to a 24-bit
75-dpi bitmap ﬁle. The numerical values of the three
primary colors (RGB) of each pixel were converted toOD values following the procedure described in Ref.
1). Although each of the RBG colors can yield ODdistributions, we show in the following the results forgreen, which is the most sensitive.
Figure 1 shows examples of images of the irradiatedtargets, the corresponding two-dimensional OD distributions, and its one-dimensional distribution along a
vertical line through the center: (a) an HD-V2 ﬁlm
irradiated by 200 Gy of 179-keV/µm C ions and (b)an EBT-3 ﬁlm irradiated by 10 Gy of 184-keV/µm Arions. The image in (a) is blurred since the C ionspassed through an 18.6-mm-thick degrader before thetarget. The image in (b) is clear; its OD distribution isﬂat in the beam spot and drops sharply within about 1
mm at the edge since the Ar ions did not pass through∗1RIKEN Nishina Centera degrader.

Fig. 1. Images, the corresponding OD distributions andone-dimensional vertical distributions through the center of films irradiated by (a) C ions after an 18.6-mmthick degrader and (b) Ar ions without a degrader.

We obtained the net OD distribution of a target as
the diﬀerence between the distributions before and after the irradiation, and we took the OD value at thecenter of the beam spot. Figure 2 compares the dose
dependence of the net OD value for diﬀerent irradiation conditions and ﬁlms.

Fig. 2. OD of the films irradiated by heavy ions with different LETs as functions of the absorbed dose.

The dose dependence of OD has a common feature:
it ﬁrst increases linearly and ﬁnally saturates above
200 Gy for HD-V2, but it does not saturate up to 10
Gy for EBT-3. It is higher for lighter ions and lower
LETs but does not strongly depend on the ion andLET, remaining within ±30 % overall, although theatomic number of the ions is diﬀerent by more than 4
and the LET is diﬀerent by nearly 50.
As a whole, the radiochromic ﬁlms can be usefulfor various heavy ions with a wide range of LETs toevaluate doses between 0.2 and 200 Gy and to measure
the two-dimensional dose distribution with a spatial
resolution of about 1 mm. The ﬁlms may also be usefulfor the comparison of irradiation dose between distantirradiation facilities since they are easily transportedand treated.
References1) T. Agematsu, H. Hanaya, T. Kojima, Radioisotopes 57,87 (2008) (Japanese).
2) http://www.gafchromic.com/
3) H. Ryuto, T. Abe, N. Fukunishi, M. Kase, Y. Yano, J.
Biomed. Nanotechnol. 2, 1 (2006).

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