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M Yudelev

Publications and source records attributed to M Yudelev.

36 records · Page 2Linked to original sources
PubMed1996

RBE variation between fast neutron beams as a function of energy. Intercomparison involving 7 neutrontherapy facilities.

In fast neutron therapy, the relative biological effectiveness (RBE) of a given beam varies to a large extent with the neutron energy spectrum. This spectrum depends primarily on the energy of the incident particles and on the nuclear reaction used for neutron production. However, it also depends on other factors which are specific to the local facility, eg, target, collimation system, etc. Therefore direct radiobiological intercomparisons are justified. The present paper reports the results of an intercomparison performed at seven neutrontherapy centres: Orléans, France (p(34)+Be), Riyadh, Saudi Arabia (p(26)+Be), Ghent, Belgium (d(14.5)+Be), Faure, South Africa (p(66)+Be), Detroit, USA (d(48)+Be), Nice, France (p(65)+Be) and Louvain-la-Neuve, Belgium (p(65)+Be). The selected radiobiological system was intestinal crypt regeneration in mice after single fraction irradiation. The observed RBE values (ref cobalt-60 gamma-rays) were 1.79 +/- 0.10, 1.84 +/- 0.07, 2.24 +/- 0.11, 1.55 +/- 0.04, 1.51 +/- 0.03, 1.50 +/- 0.04 and 1.52 +/- 0.04, respectively. When machine availability permitted, additional factors were studied: two vs one fraction (Ghent, Louvain-la-Neuve), dose rate (Detroit), influence of depth in phantom (Faure, Detroit, Nice, Louvain-la-Neuve). In addition, at Orléans and Ghent, RBEs were also determined for LD50 at 6 days after selective abdominal irradiation and were found to be equal to the RBEs for crypt regeneration. The radiobiological intercomparisons were always combined with direct dosimetric intercomparisons and, when possible in some centres, with microdosimetric investigations.

Abdomen↗
PubMed1996

The application of a multirod collimator in fast neutron therapy.

The application of a novel multirod collimator in fast neutron therapy to produce irregularly shaped fields with partial transmission and fully blocked areas is discussed. The transmission through the tungsten rods is measured in free space in broad beam geometry. A model based on scatter analysis is applied in calculating the thickness of the rods required to produce partially blocked areas. The effect of a full beam block is also measured. Measurements have been made in a water phantom to confirm the computational model. The good agreement between the measured and calculated values demonstrates that the scatter model can be safely applied to fast neutron beam dose computations.

Cyclotrons↗
PubMed1996

A measurement of the fast-neutron sensitivity of a Geiger-Müller detector in the pulsed neutron beam from a superconducting cyclotron.

The kU value of a commercially available miniature energy compensated Geiger-Müller (GM) detector has been determined using the modified lead attenuation method of Hough. The measurements were made in a d(48.5)-Be neutron beam produced by the superconducting cyclotron based neutron therapy facility at Harper Hospital. The unique problems associated with making measurements in a 2 ms duration pulsed beam with a 20% duty cycle are discussed. The beam monitoring system, which allows the beam pulse shape at low beam intensities to be measured, is described. By gating the GM output with a discriminator pulse derived from the beam pulse shape, the gamma-ray count rates and dead-time corrections within the 2 ms pulse and between pulses can be measured separately. The kU value of (0.0245 +/- 0.0015) determined for this GM detector is consistent with the values measured by other workers with identical and similar detectors in neutron beams with comparable, but not identical, neutron spectra.

Biophysical Phenomena↗
PubMed1995

Description of a 3D conformal neutron and photon radiotherapy technique for prostate cancer.

Several methods have been described to improve the therapeutic ratio of radiotherapy in patients with locally advanced carcinoma of the prostate (LACaP). Studies have shown improved survival and local control in patients treated with neutron irradiation as opposed to photons alone. However, an increased complication rate was observed when conformal field design was not utilized. A 3D conformal mixed neutron/photon technique for LACaP has been developed at this institution. Field shaping for the neutron component is achieved with a multirod collimator. Prior to treatment, all patients undergo a conventional simulation followed by a treatment planning computed tomography (CT) scan. Contours of target and normal structures are entered into the 3D treatment planning system. Beam apertures are designed utilizing beam's eye view display. The photon dose is given in 10 fractions at 1.8 Gy each to the prostate and seminal vesicles (PSVs) and pelvic lymph node (PLN) volumes. The neutron dose is given in 15 fractions at 1.0 Gy per fraction to the PSV volume and 0.6 Gy to the PLN volume. The neutron portion includes a partial transmission block to achieve this dose differential. The treatment planning process, including beam weighting and custom block design, is described. Using these techniques, the neutron dose distributions to the target volumes, bladder, and rectum were comparable to those seen with four-field conformal photon irradiation.

Humans↗
PubMed1995

Alternating conformal neutron and photon irradiation for locally advanced adenocarcinoma of the prostate.

The substantial local failure rate for patients with locally advanced carcinoma of the prostate (LACaP) following photon irradiation, the association of local failure with a poor prognosis, and the promising results of mixed neutron/photon (40%/60%) radiotherapy supplied the rationale for this study. The purpose of this study was to evaluate the combined advantages of mixed neutron/photon (75%/25%) irradiation, 3D treatment planning, as well as fully conformal beam shaping capabilities in reducing the morbidity associated with neutron irradiation. The first 35 patients treated with this technique are the basis for this analysis. After CT stimulation and treatment planning, the normal tissue and target structures were entered into the 3D planning system. The neutron dose was delivered in 15 fractions at 1.0 Gy/fraction (NGy) to the prostate and seminal vesicles (PSV) and 0.6 NGy/fraction to the pelvic lymph nodes (LN). The photon dose was given in 10 fractions of 1.8 Gy each to both the PSV and LN volumes. Neutron and photon dose-volume histograms (DVHs) were generated in each patient for the prostate, seminal vesicles, lymph nodes, bladder, and rectum. The adequacy of the neutron and photon components of the treatment were compared with respect to target volume and normal tissue irradiation. Based on the DVH analysis, the prostate and seminal vesicles received the prescribed dose with both neutrons (99% +/- 2%) and photons (99% +/- 2%). There was no significant difference in the dose to the bladder and rectum for both the neutrons and photons. The acute treatment related reactions have been mild, with only one grade III bladder reaction. The 3D conformal technology utilized in this study has been shown to allow for the delivery of neutron irradiation with no increase in dose to the adjacent normal tissues compared with that achieved with conformal photon treatment. Further follow-up will reveal whether the dosimetric advantage demonstrated by this technique translates into an improved therapeutic ratio.

Adenocarcinoma↗
PubMed1995

Shielding and radiation safety around a superconducting cyclotron neutron therapy facility.

Prior to routine operation of the neutron therapy unit a radiation survey was performed in order to confirm the shielding design and to assure the safety of the personnel involved in the operation of the unit. The shielding requirements were calculated in accordance with NCRP Report No. 51. The contributions of the neutron and gamma dose equivalents have been measured separately outside the treatment room. The exposure outside the shield is negligible. In general, the measured values were lower than those derived from the shielding calculations. The highest total dose equivalents were registered at locations corresponding to the highest calculated values.

Cyclotrons↗
PubMed1995

Physical characteristics of a clinical d(48.5)+Be neutron therapy beam produced by a superconducting cyclotron.

The Harper Hospital and Wayne State University fast neutron therapy facility is the only one in the world to use a compact superconducting cyclotron and multirod collimator. Neutrons are produced by the interaction of the 48.5-MeV deuteron beam with a thick internal beryllium target and the compact accelerator is gantry mounted to allow full 360 degrees rotation of the neutron beam about the therapy couch. The deuteron beam strikes the beryllium target at a glancing angle. A flattening filter is used to flatten the asymmetric neutron beam which results from this geometry. Details of the flattening filter design and construction are discussed. The physical characteristics of the resulting neutron therapy beam were measured. The central axis depth-dose values are approximately equivalent to those of a 4-MV photon beam. The dose buildup curve reaches its maximum value at a depth of 9 mm in a water phantom and the surface dose is approximately 42%. The beam penumbra produced by the multirod collimator has been measured in terms of the distance between the 20% and 80% isodose lines. The penumbra width for a 10 x 10-cm2 field at a depth of 10 cm in a water phantom is 1.65 +/- 0.1 cm, and is comparable to that achieved with other high-energy neutron beams. The long-term stability of the dose monitoring system has been measured and found to be satisfactory. The physical characteristics of the neutron beam are comparable with those of other modern fast neutron therapy facilities.

Beryllium↗
PubMed1994

New understanding from Cf brachytherapy trials and considerations for neutron therapy of bulky gyn carcinoma for future.

PURPOSE: This study reviews the radiobiology of neutrons and the results and methods that have evolved in the Cf-252 neutron brachytherapy trials to postulate methods to explore for their potential applicability to fast neutron beam therapy. METHODS AND MATERIALS: The results of radiobiological experimental studies are reviewed for RBE for different fraction number and dose per fraction. RBE was always higher for fractionated neutrons based on comparison with isoeffective doses of photons. This is inherent in the basic radiobiological properties of photons. RBE was highest for low dose rate (LDR) Cf brachytherapy. RESULTS: Brachytherapy methods deliver radiation dose which is localized and conformal to the tumor. These methods have been used for Cf therapy and led to good tissue tolerance and local tumor control. The use of large dose/session (or fraction), small fraction number, short treatment times, followed by photon beam therapy has been the practice in Cf brachytherapy. It has been found that bulky or localized advanced tumors responded better if neutron treatment preceded the photon beam therapy. Therapeutic efficacy is dependent on the fraction size of neutrons and not the time duration of application. CONCLUSIONS: Available radiobiological data on neutron RBE with fraction number and size of dose and the favorable experience from Cf brachytherapy with up-front neutron applications suggest new avenues to explore for the neutron beam trials. The high efficacy noted for small volume dose, 10 to 20 Gy-eqs of dose per session, localized dose, conformal methods, small number of sessions, short treatment times and an up-front or early schedule in combining neutron and photon therapy suggests that similar schedules and methodology may also be effective for neutron beam therapy. Further clinical trials are indicated and bulky GYN tumors represents suitable tumors for study.

Animals↗
PubMed1992

RBE and OER measurements on the p(66) + Be neutron beam at Faure, South Africa.

Results reported are for single dose exposures and refer to 60Co-gamma-irradiation. The RBE determined by V79 cell survival and based on the Do ratio was found to be 1.70 +/- 0.4 ranging from 1.5 to 1.8. In the case of the regeneration of mouse jejunal crypts the RBE was calculated at ten cell survival and was found to be 1.68. The maximum acute mouse skin reaction at a skin score of 2.0 was found to be 2.1 while the average skin reaction was 1.7. Growth retardation of Vicia faba bean roots measured at the level of 50% indicated an average RBE of 3.0 and a range of 2.7 to 3.7. The OER obtained for V79 cell survival was found to be 1.7 to 1.8. Comparison is made with the RBE and OER measurements for the neutron facilities at Clatterbridge, Fermilab and Louvain-la-Neuve which produce neutrons by the same nuclear reaction and whose physical specifications closely resemble those of the Faure neutrons. This comparison indicates that the Faure beam shows no unusual biological features and that its biological effectiveness is in line with that expected from its physical characteristics.

Animals↗
PubMed1990

Radiobiological intercomparison of two clinical neutron beams using the regeneration of mouse intestinal crypts.

Determination of dose modification factor greatly facilitates the introduction of clinically proven neutron therapy schedules at new installations. We have compared the biological performance of the p(66)+Be neutron facility at Faure, South Africa, with the established p(65)+Be installation at Louvain-la-Neuve, Belgium. Filtration, D gamma/DT, dose rate and HVT 5/15 for the Louvain and Faure beam are: 2 cm, 2.5 cm polyethylene; 3%, 5%; 0.2 Gy/min, 0.4 Gy/min; and 20 cm and 19 cm respectively. Dosimetry was done in A-150 plastic. Irradiation of BALB/C mice was carried on according to the dose accumulation method in a perspex phantom at 5 cm depth and at an SSD of 150 cm at a field size of 28 X 28 cm2. Sections of the jejunum were prepared at each centre and analyzed by both. The RBE of the Faure beam determined at a survival level of 50 crypts ranged from 1.64 to 1.69. The dose modification factor RBE of the Louvain beam given by Beauduin et al. was 1.61 +/- 0.14. The dose modification factor of the Faure beam relative to the Louvain beam is thus 1.03 +/- 0.13 which could be expected from the similarity of the physical characteristics. Independent RBE measurements in a variety of systems also suggest similar biological properties. The depth variation of the RBE was found to be 4% (mouse gut) using 3 cm polyethylene filter over the depth range of 2.5 to 13.5 cm. This is in agreement with microdosimetry measurements using polyethylene filters of various thicknesses and with V79 measurements reported by Slabbert et al.

Animals↗
PubMed1990

A comparison of the gamma component of two high energy neutron therapy beams.

Reciprocal neutron dosimetry intercomparisons have been undertaken between the National Accelerator Centre (NAC), South Africa, and the Université Catholique de Louvain (UCL), Belgium. A comparison of the gamma components measured in the respective therapy beams using the classic twin-detector method formed part of the study. This is important in clinical applications since the biological effects of neutrons and gamma rays are different. The gamma component under various irradiation conditions was derived from pairs of measurements with tissue equivalent ionization chambers and Geiger-Müller counters. The gamma component expressed as a fraction of the gamma dose relative to the total dose agreed within less than 0.01, with the measurements with the NAC Geiger-Müller counters being consistently higher than those with the UCL counter. A re-evaluation of the kU value of the UCL Geiger-Müller counter reduces the differences to less than 0.005 at NAC and less than 0.002 for the measurements at UCL. The results obtained are highly satisfactory in view of the complexity and difficulty of the measurements.

Fast Neutrons↗
PubMed1986

Correlations of dose and time-dose-fractionation factors (TDF) with treatment results and side effects in cancer of the uterine cervix.

Treatment results and side effects were analyzed for 57 patients with stage IB-IIIA cancer of the uterine cervix who received external beam radiotherapy combined with intracavitary insertion of cesium-137 sources. The total dosage and time-dose-fractionation (TDF) factors were calculated at point A and at points of maximum exposure in the rectum and bladder. The overall 5-year survival was 62%, and 78% of the complete responders were free of disease at 5 years. A total of 12 patients (21%) developed rectal complications. Two patients (4%) had rectal fibrosis and proctitis; seven cases of rectal bleeding occurred (12%), and 3 patients (5%) developed rectovaginal fistulas. There was no correlation between dose and TDF at point A and treatment failure or appearance of rectal complications. However, the occurrence of radiation damage in the rectum was consistently associated with high values of TDF when they were calculated in the region of maximal exposure in the rectum. The results suggest that TDF may be a useful parameter for predicting radiation damage in combined external beam and intracavitary treatment of cervical cancer.

Female↗
PubMed1985

The effectiveness of multidrug treatment by bleomycin, methotrexate, and cis-platinum in advanced vaginal carcinoma.

A case of a female with advanced squamous carcinoma of the vagina is presented. Complete disappearance of the primary tumor and involved inguinal lymph nodes was achieved with three courses of the cis-platinum-containing chemotherapy regimen BMP administered prior to radiotherapy. The encouraging result obtained warrants the use of this combined treatment modality in other patients.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1978

Time-dose effects in the matching of adjacent radiotherapy fields.

When adjacent radiotherapy fields are treated in different times, the dose fraction at the junction of the fields is different from that within the portals. When the width of the gab between the fields is adjusted to produce equality of dose at the junction, it will not give equality with respect to radiobiological effect. The authors have used Ellis's NSD equation to take into account time-dose relationships in the matching of adjacent fields. Distribution of physical dose and biologically effective dose in the region near the junction of opposed pairs of parallel 60Co fields are given.

Radiotherapy↗