Search

Background: In the last two decades, there has been tremendous financial support, political will, and commitment to global malaria elimination focusing on endemic areas. This commitment and support have enabled a few countries to eliminate malaria, while others are making remarkable progress towards elimination. Nevertheless, in the Democratic Republic of the Congo (DRC), the status of Roll Back Malaria (RBM) impact indicators is unclear even though the country is one of the high burden malaria countries in the world. The study aimed to determine malaria morbidity and mortality at Kinshasa Referral General Hospital (KRGH) or the status of RBM impact indicators and factors associated with it.Methods: The study recruited 870 patients admitted at the KRGH in 2017 and 2018. Patient distribution by cause of admission was analysed. Malaria morbidity, mortality, and case-fatality-rates were estimated. A logistic regression model using malaria morbidity/mortality as the dependent variable was developed.Results: The morbidity rate was higher in 2018 than in 2017. Mortality and case-fatality-rates were comparable for the two years. Inpatients with low socioeconomic status (SES) were more than twice at risk of malaria morbidity/mortality than inpatients with high SES. The same results were found among city outskirts dwellers vis-a-vis city residents, with city residents faring better. Conclusion: Malaria morbidity and mortality in DRC were still high at the time of the study, affecting mostly people with low SES. Funding policies in the health sector need to be adjusted for DRC to address the current situation. Access to malaria health care services including drugs for low SES communities should be given priority.

To determine whether intratracheal (IT) lung protective manganese superoxide-plasmid/liposomes (MnSOD-PL) complex provided 'bystander' protection of thoracic tumors, mice with orthotopic Lewis lung carcinoma-bacterial beta-galactosidase gene (3LL-LacZ) were studied. There was no significant difference in irradiation survival of 3LL-LacZ cells irradiated, then cocultured with MnSOD-PL-treated compared with control lung cells (D0 2.022 and 2.153, respectively), or when irradiation was delivered 24 h after coculture (D0 0.934 and 0.907, respectively). Tumor-bearing control mice showed 50% survival at 18 days and 10% survival at 21 days. Mice receiving liposomes with no insert or LacZ-PL complex plus 18 Gy had 50% survival at 22 days, and a 20% and 30% survival at day 50, respectively. Mice receiving MnSOD-PL complex followed by 18 Gy showed prolonged survival of 45% at 50 days after irradiation (P < 0.001). Nested RT-PCR assay for the human MnSOD transgene demonstrated expression at 24 h in normal lung, but not in orthotopic tumors. Decreased irradiation induction of TGF-beta1, TGF-beta2, TGF-beta3, MIF, TNF-alpha, and IL-1 at 24 h was detected in lungs, but not orthotopic tumors from MnSOD-PL-injected mice (P < 0.001). Thus, pulmonary radioprotective MnSOD-PL therapy does not provide detectable 'bystander' protection to thoracic tumors.

A five-field conformal technique with three-dimensional radiation therapy treatment planning (3-DRTP) has been shown to permit better definition of the target volume for lung cancer, while minimizing the normal tissue volume receiving greater than 50% of the target dose. In an initial study to confirm the safety of conventional doses, we used the five-field conformal 3-DRTP technique. We then used the technique in a second study, enhancing the therapeutic index in a series of 42 patients, as well as to evaluate feasibility, survival outcome, and treatment toxicity. Forty-two consecutive patients with nonsmall-cell lung carcinoma (NSCLC) were evaluated during the years 1993–1997. The median age was 60 years (range 34–80). The median radiation therapy (RT) dose to the gross tumor volume was 6,300 cGy (range 5,000–6,840 cGy) delivered over 6 to 6.5 weeks in 180–275 cGy daily fractions, 5 days per week. There were three patients who received a split course treatment of 5,500 cGy in 20 fractions, delivering 275 cGy daily with a 2-week break built into the treatment course after 10 fractions. The stages of disease were II in 2%, IIIA in 40%, IIIB in 42.9%, and recurrent disease in 14.3% of the patients. The mean tumor volume was 324.14 cc (range 88.3–773.7 cc); 57.1% of the patients received combined chemoradiotherapy, while the others were treated with radiation therapy alone. Of the 42 patients, 7 were excluded from the final analysis because of diagnosis of distant metastasis during treatment. Two of the patients had their histology reinterpreted as being other than NSCLC, 2 patients did not complete RT at the time of analysis, and 1 patient voluntarily discontinued treatment because of progressive deterioration. Median follow-up was 11.2 months (range 3–32.5 months). Survival for patients with Stage III disease was 70.2% at 1 year and 51.5% at 2 years, with median survival not yet reached. Local control for the entire series was 23.3 ± 11.4% at 2 years. However, for Stage III patients, local control was 50% at 1 year and 30% at 2 years. Patients who received concurrent chemotherapy had significantly improved survival (P = 0.002) and local control (P = 0.004), compared with RT alone. Late esophageal toxicity of ≥Grade 3 occurred in 14.1 ± 9.3% of patients (3 of 20) receiving combined chemoradiotherapy, but in none of the 15 patients treated with RT alone. Pulmonary toxicity limited to Grades 1–2 occurred in 6.8% of the patients, and none developed ≥Grade 3 pulmonary toxicity. Patients with locally advanced NSCLC, who commonly have tumor volumes in excess of 200 cc, present a challenge for adequate dose delivery without significant toxicity. Our five-field conformal 3-DRTP technique, which incorporates treatment planning by dose/volume histogram (DVH) was associated with minimal toxicity and may facilitate dose escalation to the gross tumor. Radiat. Oncol. Invest. 7:297–308, 1999. © 1999 Wiley-Liss, Inc.

Irradiation therapy for lung cancer is mostly restricted to conventional methods. To improve therapeutic ratio, we have combined a treatment planning and a gene therapy approach. Three-dimensional conformal radiotherapy is described as carried out by methods of gene therapy for radiation protection using the manganese-superoxide-dismutase transgene delivered by inhalation gene transfer. These methods may improve therapeutic outcomes in lung cancer.

A measurable improvement in the efficacy of the three-dimensional radiotherapy (RT) of primary lung cancer patients with unresectable disease will require the development of a technique that increases the therapeutic ratio of dose delivered to the tumor volume relative to functional lung. A full course of definitive RT dose was delivered to six consecutive primary lung cancer patients using multiple fields with treatment portals tightly conformed to the tumor shape in beams-eye-view, using multileaf collimation. For each patient, a treatment planning dose/volume histogram (DVH) was constructed considering the most anatomically normal tissues in both the ipsilateral and contralateral lungs. When compared to a standard anteroposterior-posteroanterior (AP-PA) treatment plan followed by parallel-opposed oblique fields with conventional blocks, the five-field conformal technique yielded a significantly lower integral lung dose as determined by cumulative DVH data. We compared the data for total lung capacity in cubic centimeters from the treatment planning DVH with that obtained by pulmonary function tests and found good concordance. The present RT technique and patient evaluation program should provide a valuable approach toward improving the quality of life in irradiated lung cancer patients, and may also guide efforts by which to escalate the dose to a tumor volume in the chest. © 1995 Wiley-Liss, Inc.

The aim of the study was to analyze whether the fixation of the stereotactic frame is stable and whether the location of the treated target coincides with its anatomical location during Gamma Knife® surgery (GKS). Stereotactic MR examinations using the same high-resolution MRI protocol were performed before and after GKS in 18 consecutive patients. The stereotactic (x,y,z) coordinates for three different anatomical landmarks were independently defined three times in each study for each landmark of the images taken before and after GKS by two of the authors, resulting in a total of 648 coordinate definitions. The uncertainty in the readings of the coordinates for the anatomical landmarks was of the same magnitude as the difference in the coordinates before and after GKS in all but one patient. The differences in this one case were due to MR distortion and not to repositioning of the frame. The difference in the coordinates before and after treatment was not affected by the removal of one of the frontal fixation screws in one of the patients. The stereotactic frame position is stable and does not move.

Aim: The aim of this study was to evaluate AAPM TG-21-specifi c parameters for a miniature ion chamber, Exradin Model A16 (Standard Imaging, Inc., Middleton, Wisc., USA) for the out

It is known experimentally that a wedge transmission factor depends upon the field size and depth of measurement in particular. Dependence of the transmission upon depth has been attributed to a hardening of the incident beam through the filter, which preferentially absorbs the low‐energy photon of the bremsstrahlung component of that beam. We have attempted to separate this hardening effect from that of increased phantom scatter due to dose gradient induced by the wedge filter. Using an experimental wedge machined from cerrobend, the filter transmission at depth is measured and redefined relative to an ‘‘equally hardened’’ beam, obtained by filtering through a flat slab of equal thickness at the center of the wedge. Results of the Co‐60, 4‐, and 8‐MV wedged beams indicate that nearly half of the increase in the transmission at depth is due to the effect of dose‐gradient scatter in polystyrene phantom. Based on a simple relationship between primary and scattering radiation, an algebraic presentation is indeed in support of the dose gradient resulting in apparent increase in the wedge factors, at depth. Key words: wedge factor, beam hardening, Co‐60, x ray, dose gradient

The Presbyterian-University Hospital of Pittsburgh installed the first clinically designated Leksell gamma knife in the U.S. in August 1987. Gamma knife radiosurgery involves stereotactic target localization with the Leksell frame and subsequent closed-skull single-treatment session irradiation of a lesion with multiple highly focused gamma ray beams produced from 60Co sources. The hemispherical array of sources, the large number of small-diameter beams, and the steep dose gradients surrounding a targeted lesion make physical characterization of the radiation field complex. This paper describes the physical features and the operation of the gamma knife as well as the calibration procedures of the very small, well-collimated beams. The results of studies using in-phantom ion chamber, diode, film, and lithium fluoride thermoluminescent dosimetry were all in close agreement. Both single-beam and multiple-beam dose profiles were measured and reported for the interchangeable helmets, which have 4-, 8-, 14-, and 18-mm-diameter collimators. We also describe the dose calculation and treatment planning algorithm in the treatment planning system. Measurements of the accuracy of mechanical and radiation alignment are also performed and discussed.

Increasingly electron treatment fields are varying widely from small ocular ports to large breast square or long neck's rectangular ports. Their dose distributions are commonly calculated by pencil beam algorithms computing broad dose distributions from summing several elemental electron Pencils. Accurate electron pencil modeling (Pinnacle) requires determining the pencil's critical parameters including its spatial spread (/spl tau///spl rho/) typically one value for each electron beam energy. Spreads (/spl sigma//sub RMS-air/) are deduced from penumbral decrements (i.e., ICRU-35) of the broadest electron beam profiles in air, which algorithms scale to tissue through water-to-air ratios of electron mass-scattering powers (/spl tau///spl rho/). It is possible however, to assess pencil spreads (/spl sigma//sub RMS-water/) directly by ionization scans at depths in water for narrow blocked as well as broad electron fields at different source-to-skin distances (SSD). This paper presents extensive electron pencil spreads in rising field sizes and SSD between air and water, and assesses the media pencil spreads (/spl sigma/(RMS-air) /spl sigma//sub RMS-water/) ratios changing with typical treatment cutouts versus standard open fields. Gaussian pencil spreads (/spl sigma//sub RMS-air/) in air were found in direct constant proportionality (1/[2/spl pi/]/sup 1/2/) to penumbra widths for limited broad fields, but poorly correlated for narrow beams. Water widths and spreads showed limited constant scaling yet their ratios deviated significantly from proportionality for shrinking field ports. Hence for accurate clinical dose commission, an electron pencil that models small as well as large field treatments, may demand RMS values characterized both in air and water, and also scaled empirically with rising electron field diameters or treatment distances.

The concept of equivalent square has been looked at by many authors. The approaches range from simple approximations to summation methods and integration methods. These studies looked at output factors, collimator scatter, TMR, or percent depth dose. In this study, output factor, collimator factor, and TMR data were measured for rectangular and irregular fields for a Siemens MLC. The measurements were made for 6 and 18 MV photon beams. To provide comparison with previous studies, the field shapes described by Xiao et al., Phys. Med. Bio. 44, 1053-1065 (1999) and Yuen et al., Med. Phys., 26, 2385-2389 (1999) were used. It was found that the average field length approximation is accurate to within 3.4% for all parameters and fields studied. The average deviation for output factor was 0.1% for rectangular fields with 28 /30 fields within 1%. The average deviation was -1.1% for the irregular fields with 17/31 fields within 1%. The average deviation for TMR for rectangular fields was 0.3% with ah fields within 1%. For irregular fields the average was -0.6% with 24/31 within 1%. The average deviation was -1.1% for the irregular fields with 17/31 fields within 1%. The average deviation for collimator scatter factor for rectangular fields was 0.1% with 26/30 fields within 1%. For irregular fields the average was -0.8% with 21/31 within 1%. Thus a simple approximation can be used to determine dosimetric parameters for clinical fields with an accuracy better than 2%.

Metal Oxide-Silicon Field Effect Transistor or MOSFET radiation detectors have become excellent in-vivo dosimeters for radiation therapy, but the MOSFET dosimeter's responses to clinical electron beams have yet to be fully evaluated. The authors measured MOSFET dose responses to varying electron beam energies and angles on patients and anthropomorphic phantoms. MOSFET responses in mV per cGy are compared against electron skin doses determined using a thin parallel plate ionization chamber. Results indicate the MOSFET dosimeter is near energy independent to within 1%. The MOSFET responses are dependent on the electron source to patient skin distances (SSD) within +/-5%, indicative of some dependence on dose rate or accelerator pulse rate by the field effect transistor. These SSD responses compare favorably with the response typically observed with diode in vivo dosimeters, except at extremely short SSD (i.e., 95 cm) close to the mouth of the electron cones where both the chamber and the MOSFET or diode readings are difficult to interpret. MOSFET responses correlated within 2% of the doses in different electron field sizes including blocked or small cutout down to 4 cm. The authors concluded MOSFET is dosimeter suitable in electron beams and it necessitates only a nominal dose calibration factor for in-vivo dosimetry treatment field conditions, except when patient treatment distances are considerably greater (20 cm) than accelerator nominal isocenter.

When a shielding jaw or multiple leaf collimator (MLC) traverses across an X-ray field, it modulates the field photon intensity, thereby inducing dose distribution patterns in cross-beam profiles usually termed dynamic (DW) or virtual wedges (VW), or virtual filter for intensity modulated radiation treatment (IMRT). Measured virtual filtration or transmission factors have, unlike those of conventional metals, exhibited rapid drops with modulated field sizes and at times, shown a discontinuity in the transmission when the stepping segmental width is altered amid modulation. We formulated a generalized analytical virtual transmission factor VTF/sub /spl Delta// for a modulated photon beam irrespective of the accelerator (Varian, Siemens, Philips-Elekta) schemes of modulation. WTF/sub /spl Delta// equals a time integral of TR/sub p/(t) plus GR/sub s/(t), and respectively, are the filter modulation primary fraction and the scatter gradient. The modulation duration t or equivalently, is the accumulating counts of partial monitor units (MU). When tested against actual segmental treatment tables (SST Varian), the stated virtual transmission equation reproduced acceptably the measured (DW) factors and predicted their downward trends in the 6 MV photon beams with 60/spl deg/ and 45/spl deg/ DW filters. Further, it is shown that upon taking the primary fraction as the integrated MU-step function /spl delta/, and taking the number (n) of the modulating collimator steps to infinity n/spl rarr//spl infin/, one has the analytical virtual transmission approach the asymptotic value limit VTF/sub /spl Delta//(n/spl rarr//spl infin/)= 1/2 . This corollary theorem is shown supported by (Varian DW) virtual transmission factors as they taper to 0.48 and 0.51 experimental values.

Objective Clinical studies have demonstrated a significant association between the presence of extensive postlumbar discectomy peridural scar formation and the recurrence of low back and radicular pain. Low-dose perioperative radiation therapy has previously been demonstrated to inhibit peridural fibrosis after laminectomy in a rat model. The current study was designed to measure the effect of low-dose radiation on postlaminectomy peridural fibrosis development in a larger animal model. Methods Three dogs underwent a total of 12 lumbar hemilaminectomies. For each animal, two levels received 1) external beam radiation 24 hours before surgery, 2) surgery alone, or 3) radiation alone. Radiation was administered in a single fraction of 700 cGy using computed tomographic guidance for dosimetry planning. The isodose distribution was such that the dose conformed to the posterior epidural space with minimal exit dose to normal tissue. Port films were used to confirm the correct levels. Gadolinium-enhanced magnetic resonance imaging (MRI) of the lumbar spines was obtained before the animals were killed 12 weeks after surgery. The spines were harvested, and axial sections through the laminectomy defect were stained with hematoxylin and eosin and Masson's trichrome. All specimens were evaluated for extent of fibrosis along the dura, density of fibrosis, nerve root entrapment, and sublaminar fibrosis. Results There were no complications from the surgery, and no new neurological deficits were noted. There was a statistically significant difference between the irradiated and nonirradiated groups regarding the extent of fibrosis (P = 0.001) and the density of fibroblasts (P = 0.001). There was also a marked difference in nerve root entrapment (P = 0.182) and the presence of sublaminar fibrosis (P = 0.061) between the treatment and control groups. MRI revealed less gadolinium enhancement at the irradiated levels compared with the nonirradiated levels, confirming the usefulness of MRI in predicting the degree of epidural fibrosis. Conclusion Low-dose external beam radiation therapy administered 24 hours before laminectomy in a dog model significantly decreased the extent and density of peridural fibrosis as well as nerve root entrapment and sublaminar fibrosis. This treatment strategy may be efficacious in patients with recurrent radicular pain after lumbar discectomy that is thought to be secondary to peridural fibrosis on the basis of gadolinium-enhanced MRI studies, and who might benefit from reoperation for nerve root decompression.

A five-field conformal technique with three-dimensional radiation therapy treatment planning (3-DRTP) has been shown to permit better definition of the target volume for lung cancer, while minimizing the normal tissue volume receiving greater than 50% of the target dose. In an initial study to confirm the safety of conventional doses, we used the five-field conformal 3-DRTP technique. We then used the technique in a second study, enhancing the therapeutic index in a series of 42 patients, as well as to evaluate feasibility, survival outcome, and treatment toxicity. Forty-two consecutive patients with nonsmall-cell lung carcinoma (NSCLC) were evaluated during the years 1993-1997. The median age was 60 years (range 34-80). The median radiation therapy (RT) dose to the gross tumor volume was 6,300 cGy (range 5,000-6,840 cGy) delivered over 6 to 6.5 weeks in 180-275 cGy daily fractions, 5 days per week. There were three patients who received a split course treatment of 5,500 cGy in 20 fractions, delivering 275 cGy daily with a 2-week break built into the treatment course after 10 fractions. The stages of disease were II in 2%, IIIA in 40%, IIIB in 42.9%, and recurrent disease in 14.3% of the patients. The mean tumor volume was 324.14 cc (range 88.3-773.7 cc); 57.1% of the patients received combined chemoradiotherapy, while the others were treated with radiation therapy alone. Of the 42 patients, 7 were excluded from the final analysis because of diagnosis of distant metastasis during treatment. Two of the patients had their histology reinterpreted as being other than NSCLC, 2 patients did not complete RT at the time of analysis, and 1 patient voluntarily discontinued treatment because of progressive deterioration. Median follow-up was 11.2 months (range 3-32.5 months). Survival for patients with Stage III disease was 70.2% at 1 year and 51.5% at 2 years, with median survival not yet reached. Local control for the entire series was 23.3+/-11.4% at 2 years. However, for Stage III patients, local control was 50% at 1 year and 30% at 2 years. Patients who received concurrent chemotherapy had significantly improved survival (P = 0.002) and local control (P = 0.004), compared with RT alone. Late esophageal toxicity ofor =Grade 3 occurred in 14.1+/-9.3% of patients (3 of 20) receiving combined chemoradiotherapy, but in none of the 15 patients treated with RT alone. Pulmonary toxicity limited to Grades 1-2 occurred in 6.8% of the patients, and none developedor =Grade 3 pulmonary toxicity. Patients with locally advanced NSCLC, who commonly have tumor volumes in excess of 200 cc, presenta challenge for adequate dose delivery without significant toxicity. Our five-field conformal 3-DRTP technique, which incorporates treatment planning by dose/volume histogram (DVH) was associated with minimal toxicity and may facilitate dose escalation to the gross tumor.

Clinical studies have revealed a significant association between the presence of extensive postlumbar discectomy peridural scar formation and the reoccurrence of low back and radicular pain. Low-dose perioperative radiation therapy has been shown to inhibit scar formation. Its effect on peridural fibrosis, however, has not been studied.Thirty male Sprague-Dawley rats underwent L5 laminectomies. Ten rats each received a single fraction of 700-cGy external beam radiation to the lumbar spine 24 hours before surgery; 10 rats each received 700 cGy 24 hours after surgery. The remaining 10 rats served as a control group. All of the rats were killed 30 days after surgery. The spines were harvested, and axial histological sections through the laminectomy defect were evaluated. Each specimen was scored for extent, density, and arachnoidal involvement by fibrosis.There was a statistically significant difference between the treatment and control groups regarding the extent of fibrosis along the dura (P0.001), the density of fibroblasts (P0.005), and the arachnoid involvement (P0.01). There was no difference in fibrosis reduction between the groups receiving pre- and postlaminectomy radiation.Low-dose external beam radiation therapy administered before or after laminectomy in a rat model significantly decreases the extent, density, and arachnoidal involvement of peridural fibrosis. This technique may improve the outcome of patients who undergo reoperations for recurrent radicular and/or low back pain after successful lumbar discectomy in whom there is a significant amount of peridural fibrosis.

Purpose : Microdosimetric expectations of Boron contents are extracted from a CRAY-Monte Carlo stimulation of the nuclear reaction 10B(n, α)7Li as it occurs on a boronated membrane of a model cell and as the reaction fragments (α and Li) traverse into the cellular nucleus. Methods and Materials : The present microdosimetry calculation is based upon the assumption that the therapeutic advantage of boron neutron capture therapy (BNCT), while depending upon the RBE and LET of the reaction particles, is equally dependent on the boron carrier preferential localization to tumor tissue, and the boron selectivity to cancerous cells and its specificity within the subcellular compartments. In particular, boron fixes to cell membrane as it ought to, using monoclonal antibodies. The present Monte Carlo simulation computes stochastic expectations of α/Li energy depositions to the nucleus in a uniformly boronated membrane shell of a spherical cell. Differential energy gain was deduced from the stochastic energy depositions in events of neutron reactions with membrane boron compared against those with natural elements (O, H, N) in the cell. Results : Microdosimetry data are presented in terms of specific energy ( z keV μ 3 ) and lineal energy (keV/μ) functions of the nucleus-to-cell volume rations (NCVR). When folded with the geometric boron content and accounting for background reaction energies, the distributions yield effective energy gain to the cell nucleus per neutron capture event. Boron amount required to yield these energy gains found to be of the order of picograms of boron per gram of cell mass. Conclusions : The boron content as inferred by the present Monte Carlo microdosimetry compares well with that deliverable by present pharmacokinetic means, but are orders of magnitude (μ-grams) less than those deduced previously from anthropomorphic macrodosimetry.

Radical radiotherapy of pelvic malignancies (e.g., vulva, anus) includes therapeutic dosage to the inguinal nodes. To minimize the dosage to the femoral head, the transmission block technique has been developed to fully irradiate the central pelvis midplane and inguinal nodes. Originally, this technique compensated for dose inhomogeniety in the transverse plane only. In some patients, however, we have observed a significant dose variation along the sagittal plane. The authors have developed a lead compensation technique to homogenize the sagittal dose variations due to the longitudinal sloping in the patient, along with further refinements in this technique. Dosimetric and technical details are also discussed.

Mathematical models were developed to predict tolerance of brain tissue to stereotactic radiosurgery. The use of these formulas for predicting symptomatic brain necrosis from stereotactic radiosurgery with the 60Co gamma unit is discussed. Predicted dose-response curves for different collimator sizes were calculated. Dose-volume isoeffect curves for a 3% risk of brain necrosis from a single fraction radiosurgery were then derived. Dose-volume isoeffect curves for combinations of fractionated whole brain irradiation with radiosurgery boosts were also calculated. The predicted dose-volume isoeffect curves provide useful tolerance guidelines for the practice of stereotactic radiosurgery.

It is known experimentally that a wedge transmission factor depends upon the field size and depth of measurement in particular. Dependence of the transmission upon depth has been attributed to a hardening of the incident beam through the filter, which preferentially absorbs the low-energy photon of the bremsstrahlung component of that beam. We have attempted to separate this hardening effect from that of increased phantom scatter due to dose gradient induced by the wedge filter. Using an experimental wedge machined from cerrobend, the filter transmission at depth is measured and redefined relative to an "equally hardened" beam, obtained by filtering through a flat slab of equal thickness at the center of the wedge. Results of the Co-60, 4-, and 8-MV wedged beams indicate that nearly half of the increase in the transmission at depth is due to the effect of dose-gradient scatter in polystyrene phantom. Based on a simple relationship between primary and scattering radiation, an algebraic presentation is indeed in support of the dose gradient resulting in apparent increase in the wedge factors, at depth.

There are currently a number of radiobiological models to account for the effects of dose fractionation and time. Normalized total dose (NTD) is not another new model but is a previously reported, clinically useful form in which to represent the biological effect, determined by any specific radiobiological dose-fractionation model, of a course of radiation using a single set of standardized, easily understood terminology. The generalized form of NTD reviewed in this paper describes the effect of a course of radiotherapy administered with nonstandard fractionation as the total dose of radiation in Gy that could be administered with a given reference fractionation such as 2 Gy per fraction, 5 fractions per week that would produce an equivalent biological effect (probability of complications or tumor control) as predicted by a given dose-fractionation formula. The use of normalized total dose with several different exponential and linear-quadratic dose-fraction formulas is presented.

Purpose/Objective: In IMRT of tumors abutting critical structures, the PTV substantially overlaps with normal tissue volumes (NTV). Standard IMRT optimization techniques impose constraints only on the PTV and NTV and thus fail to modulate predictably the dose gradient in these overlapping regions. The purpose of this paper is to present the Transitional Boolean Dose Constraints Conjugation, or the TBDCC, optimization technique. This IMRT optimization technique uses constraints conjugation to achieve predictable IMRT dose gradients across overlapping tissue volumes. We report on the TBDCC technique and its effectiveness in more than 150 IMRT patients’ plans otherwise difficult to optimize by standard techniques. Patients presented include post-prostatectomy with iliac nodes, cervix with para-aortic nodes, large meningioma abutting optic nerves and chiasm, and mesothelioma invading the heart and lung pleura. Their comparative IMRT plans, with and without constraints conjugation, are presented.

An exact formula used for determination of the magnification of the target using the conventional stereotactic biplane radiographic imaging has been derived for the stereotactic frame.

We propose a mathematical model with the potential capability of predicting the probability of cure and of normal tissue damage in a cancer patient treated with radiation. The basic assumption of the model is that complications occur when small volumes of tissue are totally depleted of the stem cells that are necessary for the repair of radiation damage. We apply this model to the specific problem of radiation injury to the spinal cord (radiation myelitis) and derive a relation between the probability of this complication and the survival probability of individual stem cells. We will perform computer calculations of the complication probability as a function of the dose, fraction size and other parameters of the model and show that good agreement with experimental animal data for this complication can be obtained. Our main objective is to develop mathematical models that would predict the dependence of the probability of cure and of complications on the parameters of the radiation therapy treatment. Such models, together with modern computerized treatment planning techniques could aid the radiotherapist in choosing the optimum treatment strategy. Our approach is a generalization of the model of Munro and Gilbert (Munro, 1961) relating the probability of tumor control to the survival probability of individual tumor cells. We assume that complications arise from the local depletion of clonogenic stem cells and are thus able to relate the complication probability directly to the cell survival probability.

Abutment of unmodified electron fields to irradiate large areas can lead to significant dose inhomogeneities in the region of junction of the fields. In this paper we describe the design and dosimetric characteristics of a device developed to broaden the electron beam penumbra and thereby to improve the dose uniformity in the overlap region. The device is a high‐density triangular‐toothed comb capable of reducing the beam intensity without seriously degrading the beam energy. The effect of the comb is such that a single device will generate a beam penumbra which is broad and very nearly linear at all depths for all clinically used beam energies. Results are shown for various field configurations and energies. With a gap of 5.0 cm between the treatment cone and phantom surface the dose ‘‘ripple’’ in the region beneath the teeth was found not to exceed ±5% at 0.5‐cm depth.

We measured neutron time-of-flight spectra from 90 MeV protons and 140 MeV alpha particles bombarding thin targets of Al, Ni, Zr, and Bi at laboratory angles between 20\ifmmode^\circ\else\textdegree\fi{} and 135\ifmmode^\circ\else\textdegree\fi{}. The lowenergy (5 to 45 MeV) portions of the spectra were measured with 5 cm diameter by 5 cm deep NE-213 counters at 1 m flight paths with n-$\ensuremath{\gamma}$ pulse-shape discrimination. The high-energy (35 to 150 MeV) portions of the spectra were measured with 12.7 cm diameter by 10.2 cm deep NE-102 counters at flight paths of 2.0 to 5.0 m. The proton-induced measured neutron spectra reveal three distinct energy regions: a low-energy evaporation region, a high-energy region dominated by the quasifree scattering process, and an intermediate-energy region dominated by multistep, preequilibrium processes. In the latter two regions, the spectra show strong angular dependence. The alpha-particle induced neutron spectra show these same distinct energy regions plus an exponential falloff above the beam energy per nucleon. The neutron spectra are compared with earlier proton spectra produced also by 90 MeV protons and 140 MeV alpha particles. It is observed that the high-energy portions of the forward-angle neutron and proton cross sections are in ratios consistent with the idea that single nucleon-nucleon scattering dominates. For the heavy-mass targets, the low-energy evaporation regions show neutron yields larger than proton yields. The proton-to-neutron ratios observed in the high-energy continua are interpreted with a quasifree calculation fitted simultaneously to the proton and the neutron spectra. Preequilibrium calculations with the exciton model and the hybrid model reproduce the shape of the experimental angle-integrated energy spectra down to lower energies than the quasifree calculations. The exciton model calculations underestimate the magnitudes of the cross sections, while the hybrid model provides better absolute agreement. One of the preequilibrium calculations uses the method of Mantzouranis and Weidenm\"uller to predict angular distributions; we find that the predicted angular distributions overestimate the neutron yields at forward angles. The intranuclear-cascade model predicts proton-to-neutron ratios much smaller than experimentally observed in the high-energy forward-angle continua.NUCLEAR REACTIONS $^{27}\mathrm{Al}$, $^{58}\mathrm{Ni}$, $^{90}\mathrm{Zr}$, $^{209}\mathrm{Bi}$(p,n), ($\ensuremath{\alpha}$, n), ${E}_{\mathrm{p}}=90$ MeV; ${E}_{\ensuremath{\alpha}}=140$ MeV; ${\ensuremath{\theta}}_{L}=20\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}135\ifmmode^\circ\else\textdegree\fi{}$; measured $\frac{{d}^{2}\ensuremath{\sigma}}{d\ensuremath{\Omega}\mathrm{dE}}$; compared with available experimental proton spectra and with theoretical calculations including PWIA quasifree scattering, preequilibrium exciton, geometry-dependent hybrid, and intranuclear-cascade models.

Polyacrylamide-based tissue-equivalent phantoms simulating cortical bone and muscle are described. The equivalency is based upon similar elemental composition and density, and partial similarity in the morphology of bone. Satisfactory results were obtained when the phantoms were tested at low (20 keV) and high (15 MeV) gamma radiation. Applicability of this phantom material to neutron transport is discussed. The material can be molded and shaped and its composition is easily modified by altering the proportions of the constituents. Trace elements or radionuclides are easily added. Details of the physical and radiation characteristics of the formulated systems are given together with the manufacturing procedures.

Recently, we proposed a model for radiation damage to normal tissue (Yaes & Kalend, 1988), based on the assumption that, because of the limited mobility and reproductive capacity of stem cells (Hellmann & Botnick, 1977) in adult mammalian organs, for each organ there is a maximum volume, which we have called the “critical volume”, that can be repopulated and repaired by a single surviving stem cell. When a critical volume is totally depleted of stem cells, irreparable damage results; however, a single surviving stem cell within the critical volume prevents the damage from occurring. These assumptions constitute the “local stem cell depletion hypothesis” (Yaes & Kalend, 1988). For the spinal cord, we represent the critical volume as a transverse “slice” of thickness t, assumed to be small compared with lengths of spinal cord usually irradiated clinically. If irreparable damage occurs to a single slice, the long motor and sensory tracts passing through it would be damaged, giving rise to radiation myelitis.

Polyacrylamide-based tissue-equivalent phantoms simulating cortical bone and muscle are described. The equivalency is based upon similar elemental composition and density, and partial similarity in the morphology of bone. Satisfactory results were obtained when the phantoms were tested at low (20 keV) and high (15 MeV) gamma radiation. Applicability of this phantom material to neutron transport is discussed. The material can be molded and shaped and its composition is easily modified by altering the proportions of the constituents. Trace elements or radionuclides are easily added. Details of the physical and radiation characteristics of the formulated systems are given together with the manufacturing procedures.

Abutment of unmodified electron fields to irradiate large areas can lead to significant dose inhomogeneities in the region of junction of the fields. In this paper we describe the design and dosimetric characteristics of a device developed to broaden the electron beam penumbra and thereby to improve the dose uniformity in the overlap region. The device is a high-density triangular-toothed comb capable of reducing the beam intensity without seriously degrading the beam energy. The effect of the comb is such that a single device will generate a beam penumbra which is broad and very nearly linear at all depths for all clinically used beam energies. Results are shown for various field configurations and energies. With a gap of 5.0 cm between the treatment cone and phantom surface the dose "ripple" in the region beneath the teeth was found not to exceed +/- 5% at 0.5-cm depth.

Comments are given on the new TG‐21 protocol for the calibration of absorbed dose from electron beams. The technique for determining the energy of electron beams is discussed in detail and suggestions are made regarding removal of inconsistencies and ambiguities in the determination of electron beam energy. (AIP)

The Leksell gamma unit at the University of Pittsburgh uses 201 highly focused 60Co beams arranged in a hemispherical array. Selective beam blocking can be used to modify the treatment volume into ellipsoid shapes oriented in different directions to match better the shape of the target volume. Dose distributions for different blocking patterns were calculated using specially developed computerized 3-D treatment planning software. The changes in dose distribution with different blocking patterns predicted by computer were verified by film densitometry. Techniques for using selective beam blocking to match more closely the treatment volume to the intended target volume have the potential of reducing the likelihood of complications for radiosurgery with the Leksell gamma unit and need to be further developed.