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At least 307 records · Page 17Linked to original sources
PubMed1990

Preclinical studies with the Faure high energy neutron facility: response of pig skin to fractionated doses of fast neutrons (66 MeVp----Be).

The early and late responses of pig skin to fractionated doses of both unfiltered and filtered (i.e. hardened) neutrons using the Faure neutron therapy facility (66 MeVp----Be) were determined and compared with those following fractionated doses with 60Co gamma-rays. Dose-effect curves for the quantal responses of moist desquamation (early epithelial response) and dermal necrosis (late response) were fitted by probit analysis and ED50 values obtained. For a neutron fractionation scheme comprised of 12 fractions in 26 days, and using an unfiltered beam, the ED50 values for moist desquamation and dermal necrosis were 18.67 +/- 2.22 and 22.25 +/- 0.48 Gy, respectively, whereas in the case of the filtered beam, the corresponding ED50 values were 24.78 +/- 1.44 and 23.30 +/- 0.47 Gy. In order to provide a comparison, the values for 24 fractions of 60Co gamma-rays given in 39 days (a clinical protocol used in the Groote Schuur Hospital) were 74.02 +/- 2.92 and 66.72 +/- 1.93 Gy for moist desquamation and dermal necrosis, respectively. For the unfiltered beam, values for the comparative biological effectiveness (CBE) were 3.96 and 3.00 for the early and late skin response, respectively. The corresponding CBE values were for the filtered beam 2.99 and 2.86. These results for the Faure neutron therapy facility can be extrapolated to the human situation with a high degree of confidence, so that the neutron dose which would yield acceptable skin damage in patients may be determined using the data presented here.

Animals↗
PubMedDate not supplied

[Distribution of the relative biological effectiveness of fast neutrons according to the depth of the irradiated tissue].

A study was made of the dependence of relative biological effectiveness (RBE) and isoeffective dose of fast neutrons (produced by U-120 cyclotron) upon the depth of the exposed tissue. It was shown that the isoeffective dose and RBE vary significantly with the depth of the tissue-equivalent medium. The investigations were carried out with the purpose of improving the radiobiological and dosimetric techniques for the treatment of malignant tumors using a neutron beam from U-120 cyclotron.

Absorption↗
PubMed1990

Results of fast neutron therapy of adenoidcystic carcinomas of the head and neck at the neutron facility Hamburg-Eppendorf.

Between July 1977 and March 1988, 31 patients with an adenoidcystic carcinoma were treated with fast neutrons of a 14 MeV-DT-generator at our department. Primary locations were: parotid gland eight cases, paranasal sinus five cases, submandibular gland five cases, trachea four cases and other locations nine cases. The median follow-up of our patients was 16 months. Most of the patients had advanced tumors. The calculated local control rate is 65% at two years.

Adult↗
PubMed1976

Fast neutron and x-ray induced single strand DNA breaks in cultured mammalian cells.

The relative biologic effectiveness (RBE) of fast neutrons in the production of single strand DNA breaks is 1.6 as compared to that of 250 kVp x rays. Monolayers of L-929 cells were treated with dinitrophenol during irradiation to prevent the DNA strands from rejoining; the extent of DNA damage was measured by the alkaline sucrose sedimentation method. The RBE for DNA damage is essentially the same as the RBE measured by cell survival methods.

Animals↗
PubMed1989

Fast neutron radiotherapy for the treatment of carcinoma of the urinary bladder. A review of clinical trials.

The major clinical investigation employing fast neutrons in the treatment of invasive bladder cancer are reviewed. Although data suggest that preoperative radiation schedules employing neutrons may result in a greater degree of pathologic downstaging than conventional precystectomy photon regimens, this has not led to an improved survival rate for neutron-treated patients over photon-treated patients. Randomized clinical trials comparing primary neutron irradiation and primary photon irradiation do not disclose an advantage for neutrons over photons as measured by survival rate or freedom from local tumor recurrence. The late complications in normal pelvic tissues following neutron irradiation with low-energy beams exceed those experienced after photon irradiation and have led to an unexpectedly high rate of treatment-related morbidity and mortality. A partial explanation for the toxicity may be attributed to the use of neutron beams with poor depth dose characteristics for the treatment of what is a deep-seated malignancy. An additional explanation is the documented lack of a differential in radioresponsiveness to neutrons between the bladder primary tumor and adjacent normal pelvic tissues.

Carcinoma, Transitional Cell↗
PubMed1989

Fast neutron boost for the treatment of grade IV astrocytomas.

A previous study, on grade IV astrocytomas, compared a combination of photons and fast neutron boost to photons only, both treatments being delivered following a concentrated irradiation schedule. A slight improvement in survival was observed after neutron boost for non operated patients, but not for operated patients. Since death was always related to local recurrence and since no complication occurred after neutron boost, the neutron dose was increased from 6 to 7 Gy in January 1985. No improvement in survival was observed for patients treated with neutron boost after complete resection. After subtotal resection, the group that was treated with the higher neutron boost (7 Gy) showed a significant benefit in survival at twelve months. When patients had only a biopsy before irradiation, there was a benefit in survival after neutron boost, but no additional benefit was gained when the size of the neutron boost was increased from 6 to 7 Gy.

Brain Neoplasms↗
PubMed1991

Preliminary results of clinical application of reactor fast neutrons in radiation and combined therapy of patients with laryngeal carcinoma.

Since 1985 treatment of cancer patients on BR-10 reactor has been carried out in the Institute of Medical Radiology. Till May, 1989, 78 patients have received mixed gamma-neutron therapy and combined treatment (preoperative radiation therapy and surgery). Marked late local reactions (perichondritis) were observed only in three (7%) out of 42 patients treated with radical radiation therapy alone. 43 patients had a follow-up period of two years. Among them T2 tumors were registered in six (14%) cases, T3 in 28 (65%) cases, T4 in nine (21%) cases. Regional metastases were observed in 13 (30%) patients. 19 out of 27 patients (70%) treated with radical gamma-neutron therapy and 13 out of 16 patients (81%) treated with combined therapy using reactor fast neutrons as preoperative radiation therapy are alive two years without evidence of the disease.

Adult↗
PubMed1980

[Medical radiography with fast neutrons (author's transl)].

For physical reasons, radiography by neutrons produces radiographs which are quite different from x-ray images. Biological objects can be transradiated only by fast neutrons. Selective simultaneous recording of neutron images is accomplished best by using cellulose nitrate (CN) foils, used with a track etching method in order to exclude thermal neutrons and gamma quanta. A neutron-radiography set-up in connection with a research reactor is described, as well as optimal conditions for developing the CN foils and the optical display of the resultant image. Image quality of the individual CN foil is characterised by minimal interior unsharpness (35 mu) and a small range of blackening when compared with radiographic film (about 1). Image contrast can be increased by the use of many foils. In addition, this results in a reduction of maximal radiation dose to below 10 rem. Study of isolated spines has shown that fat and necrotic tumours can be demonstrated by neutron radiography without being superimposed by calcium-containing bone, even if these changes cannot be seen on a x-ray radiograph because of the regular bone structure. It appears that neutron radiography can be superior to conventional radiography for the diagnosis of abnormalities with bones, or of areas surrounded by bone. The use of neutron radiography in patients can, at the moment, only be justified for individuals undergoing neutron therapy for the treatment of tumours.

Fast Neutrons↗
PubMed1977

[Assesment of RBE of fast neutrons in Ehrlich ascites tumor cells by analysis of mitotic depression (author's transl)].

The depression of mitosis 1 hr following various doses of fast neutrons (6.2 Mev) and gamma rays was studied in an Ehrlich ascites carcinoma of mouse. Doses of 50, 100, 200 and 300 rad of either radiation yielded in the semilogarithmic plot a linear dose dependence of mitosis inhibition. From the regression straight line obtained the Relative Biological Effectiveness was determined, which declined from 2.8 at 50 rad to 1.8 at 300 rad neutron dose. The RBE is given analytically for the dose range investigated in dependence on neutron dose.

Animals↗
PubMed1988

Results of fast neutron therapy in advanced head and neck cancer.

Eighty-nine patients with advanced head and neck cancer were treated with a fast neutron beam of mean energy 5.6 MeV. The standard tumour dose was 1320 cGyn, gamma in 20 fractions over 4 weeks, but 13 patients with laryngeal cancer received 1200 cGyn, gamma. Complete remission was achieved in 50 patients (56%). Fifteen patients (17%) survived 2 years, 14 of them being symptom-free. Survival correlated with the stage of disease. Encouraging results were obtained for cervical node metastases, oropharynx and salivary gland cancer. In laryngeal and hypopharyngeal cancer, neutron therapy seems to be disadvantageous. The main reason for treatment failure was local recurrence. Two patients died of complications.

Adult↗
PubMedDate not supplied

Computer generation of dose distributions for a fast-neutron therapy beam.

A system has been developed for the computer generation of dose distributions for the MANTA-NRL fast-neutron radiotherapy beam. This program is based on scatter-air ratio (SAR) techniques. A method has been developed to unfold the effect of the neutron-beam profile in the derivation of SARs so that the SARs obtained are those which would be derived if the beam profile were flat. Tables of zero-area tissue-air ratios and SARs are presented. Comparisons of calculated and measured dose distributions are shown. An empirical correction to the usual SAR methods was required to obtain agreement between calculated and measured dose distributions at source-to-skin distances (SSD) which are different from the SSD at which the SAR are derived.

Computers↗
PubMed1989

Radiobiological intercomparisons of fast neutron beams used in therapy.

A research program was performed at Louvain-la-Neuve to systematically determine the RBE of fast neutrons for the growth inhibition in Vicia faba bean roots and for the regeneration of the intestinal crypts in mice. The following neutron beams were compared p(75) + Be, p(65) + Be, p(45) + Be, p(34) + Be, d(20) + Be, and d(50) + Be. The RBE-variation as a function of neutron energy is larger for the Vicia faba system than for the regeneration of the intestinal crypt cells. This can be related to the inherent differency of the biological systems, but also to the different dose ranges involved (0.33 to 0.56 Gy and 7.66 to 8.56 Gy, respectively). In the high energy range explored, defined by the reactions p(75) + Be to p(34) + Be RBE varies only between 0.92 and 1.28 for Vicia faba and 0.96 and 1.12 for crypt cells normalized to the p(65) + Be beam. By contrast the RBE at lower energy beams (d(20) + Be and d(14.5) + Be) reaches values between 1.5 and 1.6 Finally fractionation has shown to be likely more important at the high energy beams.

Animals↗
PubMed1989

Protection of cultured Chinese hamster ovary cells by the aminothiol WR-255591 from the lethal and DNA-damaging effects of fast neutrons.

We examined the radioprotective effect of the aminothiol WR-255591 on cultured aerated Chinese hamster ovary cells irradiated with cyclotron-generated fast neutrons. The effects of a 30 min pretreatment with 6 mM WR-255591 on the induction of DNA single-strand breaks (SSBs) and double-strand breaks (DSBs) were measured using alkaline (pH 12.1) and neutral (pH 7.0) filter elution, respectively. Molecular protection factors (PFs) calculated from these data were compared with the PF measured using the biological endpoint of cell survival. WR-255591 afforded significant protection against cell killing by neutrons (PF = 1.36) although protection was less efficient than against cell killing by gamma-rays (PF = 2.30). Whereas for gamma-rays, the PFs were in the order survival greater than or equal to DSB induction much greater than SSB induction, the magnitude of the modification of the induction of both SSBs (PF = 1.38) and DSBs (PF = 1.38) after neutron irradiation was the same as that of cell killing.

Animals↗
PubMed1982

Partial optimization of electrochemical-etching parameters for highly sensitive CR-39 fast neutron dosimeters.

Voltage gradient and frequency were studied for their influence on the electrochemical etching of CR-39 plastic irradiated with fission spectrum, fast neutrons. A power supply having outputs of up to 1.5 kV (rms) and 5 kHz was used. Differential voltage measurements under non-etching conditions indicated that the optimal values in electrochemical etching with this power supply would be 20 kV/cm and 1.3 kHz. That these parameters produced a maximum sensitivity was verified in subsequent electrochemical etching experiments for a standard 4 hr in 9N KOH with foils that were both unirradiated and irradiated. The introduction of a proton irradiator cover and a conventional etching step prior to the electrochemical etching, increased the sensitivity to neutrons (approximately 30-fold) and decreased the background track density to 4.4 +/- 0.6 tracks/cm2. The corresponding sensitivity was then 1.3 tracks/cm2/mrem with a minimum level of detectability (3 sigma) of 1.4 mrem.

Electrochemistry↗
PubMed1982

Results of d + T fast neutron irradiation on advanced tumors of bladder and rectum.

From November, 1975 to November, 1981, around 400 patients were irradiated with 14 MeV d + T fast neutrons at the Antoni van Leeuwenhoek Hospital in Amsterdam. Special interest was focused on inoperable tumors of bladder and rectum. During the pilot phase of the study 47 patients were treated, mostly via two parallel opposed ports with dosages that ranged from 18 to more than 22 Gy. Although persistent local control was achieved in 23 patients (48%), 14 patients (29%) died of severe complications. By the introduction of a six field technique, the fatal complication rate could be reduced significantly. Since May 1978 patients were randomized in a three arm trial, using two dose levels on the neutron site. The preliminary results of a group of 91 patients show a similar survival in the three treatment arms with a somewhat better local control rate for high dose neutrons. An attempt was made to estimate RBE values for tumor control and normal tissue reactions by comparing the data for neutron irradiation with the data obtained with photons on a similar group of patients. From the values derived it must be concluded that the gain for neutron irradiation on these tumors in the pelvis will be negligible.

Clinical Trials as Topic↗
PubMed1989

[Restoration of DNA supercoiling in fibroblasts in the rat subjected to gamma ray or fast neutrons].

Nucleoid sedimentation analysis was applied to the study of DNA supercoiling repair in cultured FR 3T3 fibroblasts exposed to low doses of fast neutrons or gamma-rays. Supercoiling was fully restored in both instances upon post-irradiation at 37 degrees C, but the rate of repair of neutron-induced lesions was lower than that for gamma-rays. Non-repairable breaks were not evidenced at the neutral pH used. We suggest that the non-repairable alkali-labile sites evidenced by others in neutron-irradiated DNA do not prevent strand break rejoining and subsequent recovery of the tertiary DNA structure.

Animals↗
PubMedDate not supplied

Computer dosimetry for flattened and wedged fast-neutron beams.

Beam flattening by the use of polyethylene filters has been developed for the 50-MeV d in equilibrium Be fast-neutron therapy beam at the Texas A&M Variable-Energy Cyclotron (TAMVEC) as a result of the need for a more uniform dose distribution at depth within the patient. A computer algorithm has been developed that allows the use of a modified decrement line method to calculate dose distributions; standards decrement line methods do not apply because of off-axis peaking. The dose distributions for measured flattened beams are transformed into distributions that are physically equivalent to an unflattened distribution. In the transformed space, standard decrement line theory yields a distribution for any field size which, by applying the inverse transformation, generates the flattened dose distribution, including the off-axis peaking. A semiempirical model has been constructed that allows the calculation of dose distributions for wedged beams from open-beam data.

Computers↗
PubMedDate not supplied

Measurement of dose distributions of linear energy transfer in matter irradiated by fast neutrons.

A detector has been developed and used to measure dose distributions versus linear energy transfer to thin gas targets in spherical geometry from fast neutron irradiation of tissue-equivalent plastic and carbon. The detector is a hemispherical proportional counter with a Cs(T1) scintillator at the center of the hemisphere. The coincidence of the proportional counter signals constrain the measurements to charged particles traversing the radius of the hemisphere. The charged particle energy deposition distributions are directly measured for a known pathlength. The A-150 kerma factor was measured at a neutron energy of 14.8 MeV and is in agreement with tabulated values. The carbon kerma factor measurements are less than the tabulated value at 14.8 MeV. The alpha-particle production in carbon was measured for neutron energies from 14.1 to 14.8 MeV and is compared with existing data.

Energy Transfer↗