~ ) perpnmn 7'mc*a Rad/m. Mere., Vol. 22, Nee !-4, pp. 867-1~, 1993

ltlmvm" =___*.c,~ Ltd Prild in Omst Ikimin.

0969-11078/94 $6.00+.00

ESTIMATE OF THE ABSORBED DOSE DUE TO 2°Ne BEAM AND ITS FRAGMENTS PRODUCED IN INTERACTIONS WITH

TISSUE-EQUIVALENT MATERIALS

A. GOLOVOmS~o,* S. TRm~A~OVA,* R. As~,t c. TosrAIN,t O. ToVS~T,t R. Bl~SOT,~ F. ~ t B. KUBWA~t and C. BoacsM

*JINR, Laboratory of Nuclear R~ons , 141980 Duima, Russia; ~ANIL, BP 5027, F-14021 C--n, Prance; ~..IPN, BP No. 1, F-91406 Orsay, France; §IFA, P.O. Box MG-6, R-76900 Magmmle-Buclm~t, Rommua

ABSTRACT

CR-39 and CN-85 plastic detectors were used for estimating the absorbed dose due to both 77.1 MeV-nuc1-1 2°Ne GANIL beam and its fragments, with charge of 3 < ZF < 9, formed in interactions of prhneries with water and plexiglas. Preliminary results on the depth dose distributions are presented in this report.

KEYWORDS

2o Ne accelerated ions, plastic track detectors, depth dose distribution.

~TRODUCTION

The absorbed dose Da is defined by the energy E deposited in a given mass of matter M: D, = j~ (where D,, E and M is in Gray, Joule and kg, respectively). In the first approach the interactions of radiation with matter may be characterized by a linear energy transfer, which for charged particles of energy E is equivalent to the energy loss dE/dx in the medium. The elementary dose dDa is then linked to dE/dx through the relation: dD, = 1.6.10 -7. @. ~ , where

is the fluence in particles per cm 2 and dE/dx is in MeV.cm 2.mg -1. If the analytical expression for calibration, i.e. the track diameter DT versus the energy loss dE/dx , and track diameter spectra at the surfaces of plastic sheets are known, one can obtain dE/dx-spectra and then the elementary absorbed dose can be found by summing the energy depositions per dE/dx-interval. The calibration curves, DT = f(dE/dx), the track diameter spectra, the achieved detector ch~ge resolution and the yields of different fragments obtained in this experiment are given in. another our paper (Golovchenko et al., 1992). It should be noted that the calibration curve in the region of high energy loss reaches practically a plateau (see, for instance, Tretyakova et al., 1984). To determine correct dose values in this dE/dx-region we used extrapolated DT-values (Golovchenko et al., 1992) which were compared with those calculated using the usual relation between the energy and the energy loss for the given particle.

EXPERIMENT AND RESULTS

Four stacks composed of plexiglas- and water-target and track detectors, CR-39 (TASTRAK, 750-~m- and 400-~m-thick) and CN-85 (KODAK, 100-/~m-thick), were exposed to a 77.1 MeV.nucl. -1 a°Ne beam at GANIL. The details of irradiation conditions are shown in Table 1.

In addition the calibration experiments with 9 MeV.nuc1-1 4He- and 12C-ions were performed at the U-20O cyclotron (JINR, Dubna). After exposures the CR-39 sheets were etched in 6N NaOH solution (6 h and 20 or 30 h respectively for stacks 1 and 2, at 70°C) and the CN-85 layers, also in 6N NaOH, 2 h at 50°C. The track diameter distributions at the surface of plastic sheets were measured by means of semiautomatic image analyzer MOP-Videoplan (Austria).

867

A. GOLOVCHENKO ~ aL.

Table 1. The details of irradiation conditions.

Stack Z°Ne beam fluence number Composition of the stack [particles.cm -~]

1 pkxiglas (8.8 mm)+CR-39 (8.Trnm) ~ 107 2 water (9.8 mm)+CR-39(6.6mm)+CN-85(lmm ) ~, 8.6- l0 s

+CR-39(8.1mm) CE-39(6.2mm)+CN-85(0.Tmm)+CR-39(4.2mm)

CR-39 and CN-85, total thickness of 8.6 mm 3 ~, 10 4 4 ~. 4.6" l 0 s

Figure l(a,b) shows the depth dose distributions in plexiglas and in water. The distributions have long tails beyond the stopping points of Ne-ions (i.e. beyond the Brngg peak). These tails are due to nuclear fragments (from Li to F) produced in interactions of the primary ZONe beam with the nuclei from plexig]as and water are formed. It should be noted that the maximal error in measured cu~_e due to the calibration and neglecting of the target fragmentation is estimated to be about 10% to the total dose. It is evident that solid state nuclear track detectors, namely CR-39, are a possible instrument to measure the absorbed dose for radiotherapy purposes.

o O

® o

O

~ T Q~

O

o 0

/! • °e |

. ~ . . . . ~ , . e ~ . ~ . . e . e, ~ 4 ° 4 :

l

i~,I° ,N eC

• . . , . . • , . . . i . . . , . • .

4 8 12 16

0

0 v - (

0

20 O Penetrat ion ~lepth [mm of plemslas]

• . . i . • . | • • • i i , J

8 16 24 Penetrat ion depth [~_~_ of water]

b)

32

2O Fig.l(a,b). The absorbed dose normalized to the Ne-ions fluence versus the penetration depth in plexiglas (a) and in water (b). The filled circles as well as solid line represent our measurements and the dashed line is the calculation based on simple transforming the dE/dx-values to the absorbed dose (rinse dispersion is not taken into account). The arrows indicate contamination of the dose by the ~ven charge.

REFERENCES

Golovchenko, A., S. Tretyakova, R. Anne, C. Tostsin, G. Tousset, R. Bimbot, F. CLzpier, B. Kubica and C. Borcea (1992). CR-39 charge resolution and relative yields of nuclear fragments

produced in interactions of 77.1 MeV/nucleon Ne beam with water. In press. T r e t y a ~ z , S.P., C. Borcea and R. Kalpa~chiew (1984). The use of CR-39 plastic detector for

the detection and identification of ions with 2 < Z < 5. NucL. Instr. MetA. 221,371-377.