Biomedical Engineering, Vol. 48, No. 1, May, 2014, pp. 912. Translated from Meditsinskaya Tekhnika, Vol. 48, No. 1, Jan.Feb., 2014, pp. 710. Original article submitted June 18, 2013.
Portable Neutron Generators in Medicine A. A. Lychagin
Portable neutron generators developed at the AllRussian Scientific Research Institute of Automatics (Moscow) and their potential applications for radiobiological experiments and therapy are considered. Experience in the use of such generators at the Medical Radiological Scientific Center, Ministry of Health of Russian Federation, is reviewed.
Introduction
es of this type. PNGs are simple and friendly in use. Small size allows PNGs to be accommodated in small rooms. Therefore, PNGs can be used in the majority of cancer departments. PNGs increase the number of patients receiving neutron therapy in combination with gamma therapy. PNGs are commercially available from the All Russian Scientific Research Institute of Automatics (Moscow).
Radiobiological parameters of rigid ionizing radia tion (neutrons and light ions) allow the radioresistivity of some malignant tumors to be overcome, thereby increas ing the efficacy of radiation therapy. The feasibility of the use of neutron radiation in therapy of malignant tumors of some histological types and localization is due to pri mary mechanisms of energy exchange in radiobiological processes [1]. The effect of neutrons with energy 14 MeV is due to heavy nuclear recoil (HNR) and its increase with neutron energy. The HNR contribution at neutron energy 1 MeV is 510%, whereas at neutron energy 14 MeV it is 1520%. Given the value of relative biological efficiency (RBE) of HNR (10 and more), the mean OBE coefficient for the neutrons is 1.74.2 depending on the type of biological object. Neutron generators based on neutron reaction T(d,n)4He are used as sources of neutron radiation with energy 14 MeV. The parameters of the reaction provide large energy (Q = 17.6 MeV) and virtually isotropic neu tron yield, which is appropriate for radiobiological research and radiation therapy. For deuteron energy 150200 keV, the energy range is ±7% relative to En = 14.1 MeV. Deuterons are accelerated using cascade generators. Deuteron cascade generators are used for treatment of cancer patients at the Urals Center (Snezhinsk, Russia), and medical centers of Hamburg, Heidelberg, and Munster (Germany). Portable neutron generators (PNGs) based on sealed tubes are less expensive than other therapeutic apparatus
Use of Portable Neutron Generators in Medicine PNGs available from the AllRussian Scientific Research Institute of Automatics have been used at the Medical Radiological Scientific Center, Ministry of Health of the Russian Federation, for more than 10 years. The use of PNGs for therapy of cancer patients is the sub ject of studies carried out at the center. The first type of neutron generators used at the Medical Radiological Scientific Center was the pulse neutron generator ING03 (Fig. 1). The pulse duration for this generator is 1 μsec, while the pulsetopulse rep etition frequency is 1100 Hz. At accelerating voltage 130 kV and frequency 50 Hz, the mean neutron flux is 1010 neutrons per sec. The cytogenetic effect of ionizing radiation of differ ent types was tested using pulse neutron generators, gamma apparatuses Luch1, Gammacell, and Issledovatel, as well as biological objects of various types: cell cultures, tumors of rats and mice, and lymphocytes of human blood. The biological objects of different types (from yeast cells to mice and rats) were comparatively tested for radiation dose and combination of radiation sources. The effect of pulse repletion frequency (5, 10, 50, and 75 Hz) and combination of neutron and gamma
Medical Radiological Scientific Center, Ministry of Health of Russian Federation, Obninsk, Russia; Email:
[email protected]
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Fig. 1. Pulse neutron generator ING03.
of neutron and gamma radiation using various biological objects. Small size of PNG allowed an experimental setup for combined neutron and gamma radiation to be devel oped for such research (Fig. 2). The experimental setup was developed on the basis of the ING031 neutron gen erator and standard therapeutic gammaapparatus Luch 1 (60Co). Experiments using the apparatus were devoted to research into the effect of pulse repetition frequency and the relative contribution of neutron and gamma radiation. The results of the tests were reported in [912], as well as in the Proceedings of Conference on Portable Neutron Generators and Related Technology (Moscow, October 2012 [13]). Combined radiation has been used in therapy of tumors in pets (dogs and cats) [14] (Fig. 3). In accordance with the requirements of the radiation therapy, dose received by adjacent healthy tissues should not exceed 1015% of the therapeutic dose. The patient should be protected using a special system including a beam collimator. In this case, the radiation beam power can be increased. The pulse neutron generators ING031 fail to generate such increased radiation power. The time of continuous work (15 min) imposes a limit on the inte gral therapeutic dose. A new generation of continuous neutron generators with radiation power >2⋅1012 neutron/sec is available from the AllRussian Scientific Research Institute of Automatics. The NG24 prototype [15] is now being test ed at the Medical Radiological Scientific Center (Fig. 4). This generator was used in radiobiological experi ments and allowed the dose load to be measured using a human body phantom. A model for radiobiological pro tection was constructed. This model included a collima
Fig. 2. Coaxial localization of neutron generator (top) and thera peutic gammaapparatus Luch1 (bottom).
radiation on survival of melanoma cells B16 was tested together with clonogenic activity. The results of the tests were reported in [214]. In recent years, many radiobiologists and medical physicists have focused their research on the combination
Fig. 3. Exposure of a cat with mammary gland cancer.
Portable Neutron Generators in Medicine
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imental method of pulse radiation dosimetry within the range 10–4107 Gy/sec. Neutron radiation dose of the ING03 and NG14 generators was monitored using a RTW 3001 Farmer tuliptype ionizing chamber with UNIDOS electrometer (volume 0.6 cm3, plastic A150 and Mg walls) and a cylin drical chamber with graphite walls (volume 0.6 cm3). A DKS101 dosimeter was also used. Relative contribution of neutron and gamma radia tion was determined using a doubledetector method. The two detectors are tuliptype ionizing chambers (plastic and airequivalent, plastic A150 and Mg walls). The gamma radiation component was measured using proportional dosimeters DRG01M1 and RAD72 insensitive to neutron radiation. The error of the neutron dosimetry was 1215%; the error of the gamma dosime try was 57%. The dose of the neutron flux with energy 14 MeV was determined using an INPA automatic sensor available from the AllRussian Scientific Research Institute of Automatics. A stilbenebased scintillation detector was used as the monitor (size, 20 × 50). The detector was connected to an FEU87 photomultiplier. The detection threshold was maintained at the level providing differential detec tion of neutrons and gamma quanta. The total radiation dose of neutrons and gamma quanta was proportional to the flux emitted from the target. The normalization coefficient of the absolute scale was determined from analysis of 27Al activation and track detectors based on 238U, 235U, and 239Pu. The dose value was calculated from tabular data on the kerma factor [17].
Fig. 4. Continuous portable neutron generator.
tor based on the NG24 and experimental sample [16]. The beam profile shown in Fig. 5 demonstrates that this protection is rather effective.
Dosimetric Support and Methods of Experimental Estimation of Radiation Fields
cGy/min
A mixed dose of combined neutron and gamma radi ation is the main factor determining the choice of exper
Gamma Neutron + gamma
cm Fig. 5. Beam profile.
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The neutron and gamma component ratio depended on the targettoobject distance. Therefore, the experi mentally determined ratio was taken into account in dose calculation. The total error of the neutron dosimetry was 12 15%; the error of the gamma dosimetry was 57%.
Conclusion Our radiobiological study allowed some important factors of dosimetry and radiation protection to be deter mined. A prototype medical apparatus for neutron therapy was constructed at the Medical Radiological Scientific Center on the basis of the NG24 generator with output 2⋅1011. This apparatus is now undergoing dosimetric and clinical tests. Such portable apparatuses would allow increasing the number of patients receiving combined exposure to fast neutron and gamma radiation. REFERENCES 1.
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