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R L Maughan

Publications and source records attributed to R L Maughan.

At least 37 records · Page 2Linked to original sources
PubMed1998

Direct determination of kerma for a d(48.5) + Be therapy beam.

An experimental determination of the neutron kerma ratio between muscle tissue and A-150 plastic was performed at the newly commissioned d(48.5)+ Be therapy facility in Detroit. Low-pressure proportional counters with separate walls made from A-150 plastic, graphite, zirconium oxide and zirconium served to measure ionization yield spectra. The absorbed dose in the wall of each counter was determined and rendered the A-150 and carbon kerma directly, whilst that for oxygen was deduced from differences between the matched metal oxide and metal pair. This enabled the evaluation of an effective kerma ratio as a function of radiation field size and hydrogenous filtration. Although filtration was observed to harden the beam, the application of a single kerma ratio for the various irradiation conditions investigated was found to be appropriate. A neutron kerma ratio of 0.90+/-0.03 was assessed for the Detroit facility, which is lower at the 1sigma level than the 0.95 currently recommended in the dosimetry protocol for high-energy neutron beams.

Carbon↗
PubMed1998

Measurement of the neutron sensitivity of TLD-300 irradiated in a tissue equivalent phantom by d(48.5) + Be neutrons.

The neutron sensitivities of the total response (kT) as well as of separate peaks 3 (k3) and 5 (k5) on the glow curve were measured for CaF2:Tm (TLD-300) thermoluminescent dosimeters. The TLD-300 were encapsulated in A-150 TE plastic and located at different depths in the water phantom. The phantom was irradiated with neutrons produced by the d(48.5) + Be reaction at the superconducting cyclotron of the Gershenson Radiation Oncology Center at Harper Hospital. A set of measurements, based on the use of a TE ionization chamber and Geiger-Müller (GM) counter was used to measure the neutron (Dn) and gamma (D gamma) dose at these locations. The neutron sensitivities of the TLDs were thus derived by comparison with the results obtained with the twin detector method. The average neutron sensitivities relative to gamma of the total response and the responses of single peaks 3 or 5 are 0.215 +/- 0.016, 0.126 +/- 0.010, and 0.357 +/- 0.014, respectively. A linear relationship was found between the ratio of the areas under peak 3 to that under peak 5 and the ratio of the gamma dose to the total dose.

Calibration↗
PubMed1998

A light localizer for use at large distances from a radiation source.

In the superconducting cyclotron used for neutron therapy at Harper Hospital, space limitations prevented the use of a simple conventional light localizing system, employing a single mirror and a light source. The superconducting magnet coil is close to the neutron producing target and the vacuum window separating the acceleration chamber from atmospheric pressure is situated approximately 56 cm from this target. Therefore, the light localizing system must be designed to incorporate lenses, mirrors, an optical fiber light pipe and adjustment motors, in order to make the system compact enough to fit in the available space and to allow easy access for adjustment and alignment. The design of the light localizing system is explained in detail.

Biophysical Phenomena↗
PubMed1997

Dose equivalents to neutron therapy facility staff due to induced activation.

The sources of the induced activity from the d(48.5)+Be fast neutron therapy beam of the Harper Hospital superconducting cyclotron have been investigated. The distribution of activity in the treatment room was measured, and the levels of dose equivalent to the staff were established. Activation spectra were measured with a high purity RE-Ge detector. Peaks corresponding to 28Al, 56Mn, 24Na, 64Cu, 66Cu, and 187W were present in the spectra. The dose equivalents due to the induced activation were measured by means of an ionization chamber type survey meter at six locations in the room. Irradiations of 120 monitor units were given at 15-min intervals, thus simulating the clinical situation. The measurements were made between the irradiations. The highest levels were registered around the treatment head. Two patterns are clearly distinguishable in these measurements. A fast decaying component with approximately 2 min half-life can be ascribed predominantly to 28Al and a slow growing component reaching saturation after about 4-5 treatments is associated with the presence of 56Mn. For uniform treatment load the activation build-up in each location was similar every day of the week with minimal values measured after the week end shut down. Personnel monitoring is achieved with dosimeters capable of detecting an extended range of neutron energies as well as beta rays and photons. Correlation between the number of fields treated and the doses to the radiation therapy technologists was shown. The mean dose equivalent received by the therapists is 7.1 +/- 0.2 microSv per treatment field. Means of reducing personnel dose equivalent levels are proposed.

Cyclotrons↗
PubMed1997

The elemental composition of tumors: kerma data for neutrons.

The elemental composition of a variety of tumor samples, including squamous cell lung carcinoma, sarcoma, adenoid cystic carcinoma, melanoma, and rectal carcinoma have been measured by combustion analysis. Hydrogen, carbon, nitrogen, and oxygen content have been determined. Using the elemental neutron kerma data published in ICRU Report #46 the neutron kerma factors for the various tumor samples have been calculated in the energy range 11 eV to 29 MeV. The average neutron kerma values for all tumor samples are approximately 6%-7% lower than those for average soft tissue in the energy range of interest in fast neutron therapy (energies > 1 MeV).

Biophysical Phenomena↗
PubMed1996

Hip stiffness following mixed conformal neutron and photon radiotherapy: a dose-volume relationship.

PURPOSE: To determine the relationship between dose, volume, and the incidence of hip stiffness in patients who received conformal neutron irradiation for prostate cancer. METHODS AND MATERIALS: A series of dose-searching studies using neutron irradiation for prostate cancer were performed to determine the optimal dose, fraction size, field size, technique, and proportions of photon and neutron dose. Neutron doses ranged from 9 to 20 Gy and photon doses ranged from 0 to 38 Gy. Data were analyzed by using a hip stiffness grading scale. RESULTS: Hip stiffness was recorded on follow-up examination in 30% of patients (40 out of 132) treated with fast neutrons or mixtures of fast neutron and photon radiation for prostate cancer. Hip stiffness was categorized as none (Grade 0, 92 patients), mild (Grade 1, 24 patients), moderate (Grade 2, 10 patients), or severe (Grade 3, 6 patients). The incidence of hip stiffness differed significantly by dose and volume in the five dose levels studied (p < 0.001). CONCLUSIONS: By using a mixture of conformal neutron and photon irradiation and limiting the total neutron dose to less than 13 Gy, hip stiffness toxicity could be reduced to acceptable levels.

Aged↗
PubMed1996

A multirod collimator for neutron therapy.

PURPOSE: To design, construct, and commission a multirod collimator for producing irregularly shaped fields in neutron radiation therapy. To demonstrate the reliability and applicability of this device to routine use with a superconducting cyclotron for neutron therapy. METHODS AND MATERIALS: A multirod collimator has been designed, constructed, and thoroughly tested to investigate its radiological properties; neutron transmission characteristics, beam profiles, and penumbral widths as a function of field size and depth in a phantom, and the spatial resolution of the rod array, have been measured. A wide variety of irregularly shaped fields, used routinely in neutron radiation therapy, have been produced, including fields that incorporate partial transmission blocks. The performance of the collimator has been closely monitored over a period of 20 months to accurately assess reliability. RESULTS: The multirod collimator has been in routine use for 32 months, and during this time a total of 7025 neutron fields has been treated. For the latter 20 months of this period, detailed performance records show that collimator failure has caused 28.4 h of downtime during the patient treatment day. Only 5.25 h of this downtime was experienced in the last 12 months (0.22% of the available treatment time). The results of collimator attenuation and beam profile measurements show that the radiological properties of the collimator are comparable to those of other collimator systems used for neutron radiation therapy. Isodose measurements in a water phantom show that the spatial resolution of the rods is superior to that of the leaves used in neutron multileaf collimators. The ability of the multirod collimator to produce many irregularly shaped fields commonly encountered in neutron radiation therapy has been demonstrated. Shaped fields for prostate, head and neck, soft tissue sarcomas, lung, thyroid, rectum, bladder, colon, breast, pancreas, and gynecological tumors have been produced. For some prostate cases, the device has been used to produce partial transmission blocks. CONCLUSIONS: A novel multirod collimator has been designed, constructed, and successfully applied in the routine treatment of neutron radiation therapy patients.

Cyclotrons↗
PubMed1996

Comparison of hyperfractionated conformal photon with conformal mixed neutron/photon irradiation in locally advanced prostate cancer.

In an attempt to improve the probability of complication-free local control for patients with locally advanced prostate cancer, a series of dose-finding studies have been conducted at Wayne State University using conformal neutron and hyperfractionated photon irradiation. In total, 96 patients with locally advanced prostate cancer (T3/T4 N0/N1 M0, and/or Gleason score > or = 8) were treated in two prospective studies. Forty-seven patients received conformal neutron/photon (15 NGy + 18 PhGy) and 49 patients were treated in a dose-escalation study using conformal photons (25 patients/78 Gy and 24 patients/83 Gy minimum dose). The median follow-up for both studies was 20 months (range 6-36 months). There was no significant difference in the rate of chronic gastrointestinal (GI) or gastrourinary (GU) morbidity between the two groups. However, the neutron treated patients had a significantly higher rate of moderate (14%) and severe (12%) hip stiffness. The rates of prostate-specific antigen (PSA) decline and 12-month negative biopsy were comparable. In conclusion, the therapeutic gain of neo-adjuvant hormonal therapy in combination with photon hyperfractionation to 83 Gy appears identical to that seen with the mixed neutron-photon dose of 15 NGy + 18 PhGy. Further efforts at improving the therapeutic ratio of radiotherapy for patients with locally advanced prostate cancer should be undertaken.

Adenocarcinoma↗
PubMed1996

Cryogenic aspects of the operation of a superconducting cyclotron-based neutron therapy facility.

The Harper Hospital superconducting cyclotron, which is used for neutron radiation therapy, is a unique device. It is the first superconducting cyclotron to be installed in a hospital. The novel magnet cryostat can be rotated through 360 degrees without spilling liquid and whilst remaining vented to a low pressure return line for collection of the boil-off gas. The mode of operation of the cryogenic magnet is described in detail. Some of the problems associated with the cryogenic nature of the cyclotron including those problems encountered in operating a helium liquefaction system in a hospital are discussed. At the present time the magnet is kept cold by filling the cryostat with approximately 75 L of liquid helium each day before patient treatments begin. This is a time-consuming process. The possibility of modifying the helium gas recovery and liquefaction system so that a continuous liquid helium supply could be delivered to the magnet cryostat is discussed.

Cancer Care Facilities↗
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 dosimetry system for boron neutron capture therapy based on the dual counter microdosimetric technique.

A dosimetric technique based on proportional counter microdosimetry has been developed for the dosimetry of mixed radiation fields employed in boron neutron capture therapy (BNCT). The technique has been successfully used to measure the gamma, fast neutron and the boron dose rates in the mixed radiation field from a 252Cf source. The measured fast neutron and boron dose rates are in good agreement with the calculations and the measurements reported by other researchers. A systematic discrepancy is observed in the gamma dose rate measurements, with the present measurements being approximately 35% lower than those reported elsewhere.

Boron Neutron Capture Therapy↗
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↗
PubMed1996

Microdosimetric specification of the radiation quality of a d(48.5)+Be fast neutron therapy beam produced by a superconducting cyclotron.

The proportional counter microdosimetric technique has been employed to quantify variations in the quality of a d(48.5)+Be fast neutron beam passing through a homogeneous water phantom. Single event spectra have been measured as a function of spatial location in the water phantom and field size. The measured spectra have been separated into component spectra corresponding to the gamma, recoil proton and alpha plus heavy recoil ion contribution to the total absorbed dose. The total absorbed dose normalized to the "monitor units" used in daily clinical use has been calculated from the measured spectra and compared to the data measured with calibrated ion chambers. The present measurements agree with the ion chamber data to within 5%. The RBE of the neutron beam is assumed to be proportional to the microdosimetric parameter y* for the dose ranges pertinent to fractionated neutron therapy. The relative variations in y*, assumed to be representative of variations in the RBE are mapped as a function of field size and spatial location in the phantom. A variation in the RBE of about 4% for points within and 8% for points outside a 10 cm x 10 cm field is observed. The variations in the RBE within the beam are caused by an increase in the gamma component with depth. An increase in the RBE of about 4% is observed with increasing field size which is attributed to a change in the neutron spectrum. Compared to the uncertainties in the prescribed dose, associated with uncertainties in the clinically used RBE, variation in the RBE between various tissues, and other dosimetric uncertainties caused by factors such as patient inhomogeneities, patient setup errors, patient motion, etc., the measured spatial RBE variations are not considered significant enough to be incorporated into the treatment planning scheme.

Biophysical Phenomena↗
PubMed1996

The mechanism of local tumor irradiation combined with interleukin 2 therapy in murine renal carcinoma: histological evaluation of pulmonary metastases.

We have demonstrated that tumor irradiation enhanced the therapeutic effect of interleukin 2 (IL-2) on pulmonary metastases from a murine renal adenocarcinoma, Renca. To investigate the mechanism of interaction between tumor irradiation and IL-2 therapy, we have histologically evaluated the effects of each therapy alone or in combination on Renca pulmonary metastases. Following treatment of established lung metastases with irradiation and IL-2 therapy, lung sections were processed for H&E or immunohistochemical staining. We found that tumor irradiation or IL-2 therapy locally induced vascular damage, resulting in multifocal hemorrhages and mononuclear cell mobilization in the lung tissue. This effect was amplified in lungs treated with the combined therapy. Immunohistochemistry showed that irradiation produced a macrophage influx into irradiated tumor nodules, and systemic IL-2 therapy induced T-cell infiltration in tumor nodules. Lungs treated with the combined therapy exhibited massive macrophage, T-cell, and natural killer cell mobilization in disintegrating tumor nodules and in the lung tissue. This combined therapy caused a decrease in the number of proliferating tumor cells and an increase in the number of apoptotic cells, which were more marked than with either therapy alone. We suggest that the macrophages mobilized by radiation-induced tissue injury could play a role in phagocytosis of apoptotic tumor cells, processing and presenting of tumor antigens for a systemic immune response activated by IL-2. Tumor destruction may result from the concomitant action of activated T cells, natural killer cells, and macrophages infiltrating the tumor nodules.

Animals↗
PubMed1995

Local tumor irradiation augments the response to IL-2 therapy in a murine renal adenocarcinoma.

We have previously demonstrated that local tumor irradiation effectively enhanced the therapeutic effect of IL-2 therapy on pulmonary metastases from a murine renal adenocarcinoma, Renca. Irradiation with 300 rad to the left lung only, followed by systemic IL-2 therapy, results in increased tumor reduction in both lungs, suggesting that radiation enhances the systemic effect of immunotherapy. In this study, we show that irradiation of the tumor-bearing organ is essential for the combined effect of both modalities. This effect is radiation dose-dependent as increases in the radiation dosage result in greater tumor reduction in the irradiated field as well as systemically in nonirradiated fields when combined with immunotherapy. We find that irradiation has a direct inhibitory effect on Renca cell growth in vitro. Irradiation of Renca cells also causes an upregulation in H-2Kd class I MHC antigen detectable at 300 rad and more pronounced with 800 rad. By in vivo selective depletion of lymphocyte subsets, we demonstrate the involvement of Lyt-2+ and L3T4+ T cell subsets and AsGM1+ cells, including NK cells, in the antitumor effect mediated by tumor irradiation and IL-2 therapy. Immunohistochemistry studies, performed on lung sections, showed a significant infiltration of CD3+ T cells and macrophages in the tumor nodules following treatment with tumor irradiation and IL-2 therapy. Our studies indicate that the mechanism of interaction between tumor irradiation and immunotherapy may include radiation-induced alterations in the tumor growth and antigenicity which may enhance or trigger an anti-tumor response elicited by IL-2 and mediated by T cells, AsGM1+ cells, and macrophages.

Adenocarcinoma↗
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

Radiation-induced effects on murine kidney tumor cells: role in the interaction of local irradiation and immunotherapy.

Local tumor irradiation enhances the effect of interleukin-2 (IL-2) therapy in the Renca murine renal adenocarcinoma model. To investigate the mechanism(s) of this interaction, we studied the in vitro and in vivo effects of irradiation on the tumor cells. Tumor cells from in situ irradiated renal tumors had diminished proliferation in vitro. A similar growth inhibition was noted following injection of irradiated Renca cells into naive mice, but this effect could be overcome by injecting more cells. Histologic evaluation of tumors derived from irradiated cells revealed a decrease in mitosis and an increase in multinucleated giant cells, apoptosis and micronecrosis. The presence of irradiated tumor reduced the growth of nonirradiated tumor cells when both were injected into separate flanks of the same animal, suggesting that irradiated tumor cells may trigger a systemic antitumor response. Interleukin-2 therapy given after injection of irradiated tumor cells caused a significant increase in leukocytic infiltrates and micronecrosis. Our findings indicate that radiation directly affects tumor growth and induces a systemic mechanism which could be enhanced by IL-2.

Animals↗