Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Experimental study of the 165Ho(p,n) nuclear reaction for production of the therapeutic radioisotope 165Er
Introduction
Radiolanthanides are increasingly applied for therapeutic purposes [1]. Incorporation of Auger-electron emitters within a cell nucleus produces high radiotoxicity by deposition of a concentrated amount of energy, emitted in the form of Auger- and Coster-Kronig-electrons. 165Er (T1/2 = 10.3 h) decays by electron capture without any accompanying gamma radiation which makes it from this point an ideal radionuclide for Auger-electron therapy. All labeling techniques used for the three-valent radionuclides can be adapted to labeling of bio-conjugates [2]. It was proposed previously for use in diagnostic nuclear medicine through X-ray detection, especially in conjunction with multiwire proportional-counter cameras [3].
The radionuclide 165Er can be produced by various routes at reactors and accelerators [2]. The labeling of radiopharmaceuticals requires high specific activity, a requirement that can hardly fulfilled with (n,γ) reactions at fission reactors.
In the frame of the investigation of production routes of therapeutic radioisotopes we decided to make a systematic study of the charged particle production routes of 165Er. We have reported some preliminary data for the reactions 165Ho(p,n)165Er [4], 165Ho(d,2n)165Er [4], natEr(p,x)165Tm → 165Er [5], natEr(d,x)165Tm → 165Er [6] at different international conferences. Final data were published only for the natEr(d,x)165Tm → 165Er reaction [7], [8]. Here we present the final experimental results on 165Ho(p,n)165Er in detail.
In the literature, we found only one earlier experimental data set on cross-sections of the 165Ho(p,n) reaction reported by Beyer et al. [2] up to 18 MeV. By comparing these data with the results of our a priori model calculations remarkable disagreements in the energy scale can be noticed. We decided to re-measure the excitation function to clear the situation: either to support or to correct the data measured earlier.
Section snippets
Experimental methods
The experimental method used was similar to the technique described in our numerous earlier publications on charged particle induced nuclear reactions for production of medically relevant radioisotopes. Here, we report only on the most salient features related to reliability of the measured data. More details can be found in [9], [10].
The excitation function was measured by an activation method using the stacked foil technique. Commercial (Goodfellow) Ho target foils (25 μm) and Ti monitor foils
Evaluation of the earlier experimental data
Only one earlier experimental work was found in the literature reported by Beyer et al. [2]. The cross section data for the 165Ho(p,n)165Er reaction were measured by an activation method at an external cyclotron beam using Ho2O3 oxide pellet targets and gamma-spectrometry. Thick (6.5 mm) pellet targets were irradiated and cut into very thin slices (1–2 μm) with a microtome. The separate cuttings or group of cuttings were measured with a high resolution HPGe spectrometer. The actual beam energy
Results
The excitation function of the simultaneously re-measured monitor reaction is shown in Fig. 1 in comparison with the recommended data. The good agreement was obtained after small corrections on the beam intensity (5% comparing to the result of the Faraday-cup) and on the primary beam energy (0.5 MeV). As it can be seen the agreement is good over the whole energy range.
The longer lived radioactive endproducts of Ho and Er produced in proton induced reactions on Ho in the investigated energy range
Theoretical calculations
Theoretical cross-sections for the investigated reaction were calculated by means of the computer codes ALICE-IPPE [23], [24], EMPIRE-II [25] and GNASH [26] using the Recommended Input Parameter Library (RIPL-2) of the IAEA [27]. In Fig. 3 we also plotted the results of the MENDL-2P theoretical cross section database [28] produced earlier in IPPE (Obninsk) with systematic ALICE-IPPE calculations on broad scale of isotopes. At the first attempt an a priori calculation was performed without any
Integral yields
From SPLINE fit to our experimental points and to the data of Beyer et al. [2] thick target yields (physical yields) were calculated as a function of the incident energy. The results are presented in Fig. 5. The thick target yields at typical energies available at small cyclotrons (Ep = 11 MeV and Ep = 15 MeV) are 41 MBq/μAh = 11 GBq/C and 75 MBq/μAh = 21 GBq/C, respectively.
Conclusions
In this paper, we present cross-sections values for the reaction 165Ho(p,n)165Er up to 37 MeV incident proton energy. Our newly measured excitation function is adjusted to the well known excitation function of natTi(p,n)48V monitor reaction measured simultaneously and is hence very accurate concerning the energy scale and the number of bombarding particles. Our experimental curve shows significant (∼2 MeV) energy shift to lower energies when compared to the results of Beyer et al. [2], indicating
References (28)
- et al.
Study of activation cross-sections of deuteron induced reactions on erbium: production of radioisotopes for practical applications
Nucl. Instr. and Meth. B
(2007) - et al.
Study on production of 103Pd and characterisation of possible contaminants in the proton irradiation of 103Rh up to 28 MeV
Nucl. Instr. and Meth. B
(2000) - et al.
Activation cross-sections of long-lived products of proton-induced nuclear reactions on zinc
Appl. Radiat. Isotopes
(2005) FGM – a flexible gamma-spectrum analysis program for a small computer
Comput. Phys. Commun.
(1985)- et al.
Determination of the external beam energy of a variable energy multiparticle cyclotron
Appl. Radiat. Isotopes
(1996) - et al.
New cross-sections and intercomparison of proton monitor reactions on Ti, Ni and Cu
Nucl. Instr. and Meth. B
(2002) Radiolanthanides in endoradiotherapy: an overview
Radiochim. Acta
(2007)- et al.
The Auger-electron emitter 165Er: excitation function of the 165Ho(p,n)165Er process
Radiochim. Acta
(2004) - et al.
Radiations emitted in the decay of 165Er: a promising medical radionuclide
Med. Phys.
(1977) - F. Tárkányi, A. Hermanne, S. Takács, F. Ditrói, B. Király, S.F. Kovalev, A.V. Ignatyuk, Investigation of new routes for...
Study of activation cross sections of deuteron-induced reactions on erbium for applications
J. Label. Compd. Radiopharm.
Cited by (21)
Cross-section measurement of thulium radioisotopes with an 18 MeV medical PET cyclotron for an optimized <sup>165</sup>Er production
2023, Applied Radiation and IsotopesNon-conventional radionuclides: The pursuit for perfection
2022, Nuclear Medicine and Molecular Imaging: Volume 1-4Experimental study of α-particle induced reactions on natural erbium for the production of Auger-emitters <sup>167</sup>Tm, <sup>165</sup>Er and <sup>169</sup>Yb
2021, Applied Radiation and IsotopesCitation Excerpt :The results obtained in this work are generally consistent with (Király et al., 2008b) and (Saito et al., 2019) and with the simulation results (Fig. 9). 165Er can be obtained by irradiating holmium with protons (Beyer et al., 2004; Tárkányi et al., 2008a; Gracheva et al., 2020) and deuterons (Tárkányi et al., 2008b; Hermanne et al., 2013), according to reactions 165Ho(p,n)165Er and 165Ho(d, 2n)165Er. The maximum cross section for the first process is ~170 mb at 10 MeV (Tárkányi et al., 2008a), for the second one this value reaches ~600 mb at 14 MeV.
<sup>165</sup>Er: A new candidate for Auger electron therapy and its possible cyclotron production from natural holmium targets
2020, Applied Radiation and IsotopesCitation Excerpt :Based on the characteristics mentioned above, 165Er could be proposed as a promising candidate for Auger-electron therapy. 165Er can be produced via several production routes by charged particle induced reactions (Table 1) (Sadeghi, 2010; Tárkányi et al., 2008, 2009; Zandi, 2012). The highest cross-section values were reported for indirect production routes 166Er (d,3n)165Tm → 165Er (Route 1; theoretical cross-section 1523.9 mbarn) and 166Er (p,2n)165Tm → 165Er (Route 2; 1263.3 mb).
Excitation functions for production of <sup>46</sup>Sc by deuteron and proton beams in <sup>nat</sup>Ti: A basis for additional monitor reactions
2014, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and AtomsCitation Excerpt :Contributions of reactions on other stable Ti isotopes are very low (abundances in natTi are 10 times lower) but the (d,α) reaction with positive Q-value on 49Ti explains the low cross sections below 10 MeV found in [38,45]. The over-all uncertainties on cross section values for references [40–49] are 10–12% and are obtained by of the contributions of uncertainties on beam current, number of target atoms, decay characteristics, efficiency calibration and statistical as stated in the respective publications. For references [32–39] the uncertainties to be mentioned in the database were taken from the original publications or, if information was not available or incomplete, adapted using the contributing elements as stated in previous sentence.