ABSTRACT
The current induced in the outer circuit of a fast response ionization chamber exposed to pulsed radiation consists of two components, a fast one induced by free electrons and a slow one induced by ions. The fast electron component may be used for the representation of the shape of the ionizing pulse. In order to avoid interference with the slow ion current, the latter has to be removed from the signal. This is achieved by deriving a voltage course from the chamber signal which fits the shape of the ion component and subtracting this from the entire signal. The function of the electronic circuit used for this purpose is described. Some considerations about the time resolution of the chamber gas are to be found in the appendix.
Subject(s)
Radiation, Ionizing , Electronics , Electrons , Ions , Particle AcceleratorsABSTRACT
Three models of the charge collection process in small dosimetric ionization chambers exposed to pulsed radiation are discussed. All three models allow for the presence of a free-electron component in the charge transfer, incorporating this into the model in slightly different ways, and the resulting collection efficiency formulae are compared over the range of variables normally met within clinical dosimetry. Measurements of the free-electron fraction for plane-parallel ionization chambers and for a Baldwin-Farmer 0.6 cm3 chamber are presented. The proportion of free electrons at the normal operating voltage is often high in small chambers but it is obvious that this can only lead to an increase in collection efficiency if the f-value calculated for purely ionic conduction allows for some improvement. Thus, a 50% free-electron fraction in a chamber which collects ions with efficiency f = 0.9950 at low pulse doses will increase this efficiency to only 0.9982. The same chamber, at the same operating voltage, and therefore the same free-electron fraction, if exposed to larger pulse doses, yielding an efficiency of 0.9531 as calculated for ions alone, would have a true efficiency of 0.9830-a large change.
Subject(s)
Electrons , Radiometry/methods , Biophysical Phenomena , Biophysics , Models, Theoretical , Radiometry/instrumentation , Radiometry/statistics & numerical dataABSTRACT
Variations of regimens of total body irradiation (TBI) were investigated in the dog as a preclinical model for bone marrow transplantation. Inactivation of hemopoietic precursor cells (CFU-GM) was studied following irradiation of marrow in vitro, following TBI at sublethal doses in vivo and following autologous transplantation of marrow obtained after sublethal TBI. Inactivation and recovery of CFU-GM as well as restoration of hemopoiesis following autologous transplantation was independent of the dose rate, but nadirs of blood counts were lower following sublethal TBI with the higher dose rate. Acute non-hemopoietic toxicity of TBI depended on the dose, the dose rate and the total treatment time and not on the fractionation regimen. At a total dose of 25 Gy acute mortality was prevented by prophylactic administration of oral, non-absorbable antibiotics. Late mortality was due to degenerative and autoimmune-like disorders with or without infections and to malignant tumors. Evaluation of long-term survival is still preliminary, since surviving dogs of two groups (10 Gy as single dose, 25 Gy as hyperfractionated TBI) have not yet reached the median survival time of their group. So far, long-term survival depended on the total dose (p = 0.05) and, possibly, the fractionation regimen (p = 0.12). The latency period until development of malignant tumors was influenced by the total doses given in the same treatment time (p = 0.05) and by the total treatment time for equal doses (p = 0.04). It was concluded that TBI at a low dose rate may give the best therapeutic ratio of inactivation of hemopoietic precursor cells to acute toxicity.(ABSTRACT TRUNCATED AT 250 WORDS)
Subject(s)
Bone Marrow Transplantation , Hematopoietic Stem Cells/radiation effects , Radiotherapy Dosage , Whole-Body Irradiation/methods , Animals , Clinical Protocols , Dogs , Female , Male , Time FactorsABSTRACT
Eleven adults have been transplanted for various reasons between July 1979 and July 1982: 2 with aplastic anemia (AA), 1 with paroxysmal nocturnal hemoglobinuria (PNH), 8 with acute leukemia (AL). Four patients suffered from acute lymphocytic leukemia (ALL) and four from acute non-lymphocytic leukemia (ANLL). Two of them were transplanted in relapse, 1 in a partial remission, and 5 in complete remission. All patients were in their late stage of disease. The PNH-patient had an identical twin, 8 patients had an HLA- and MLC compatible sib, 1 an unrelated donor, and 1 was transplanted from his father. Four patients are alive, 2 more than 3 years: 1 with AA and 1 with ALL who was transplanted in relapse. Six patients died of infectious complications (4 of interstitial pneumonia, 1 of a candida sepsis, 1 of acute toxoplasmosis). Patients living more than 3 weeks had a take. Acute graft-versus-host (GvH) disease did not present a major problem. All patients received methotrexate for GvH-prophylaxis, in three instances the marrow was additionally pre-incubated with anti-T-cell globulin.
Subject(s)
Anemia, Aplastic/surgery , Bone Marrow Transplantation , Hemoglobinuria, Paroxysmal/surgery , Leukemia/surgery , Acute Disease , Adult , Female , Graft vs Host Reaction , Humans , Male , Methotrexate/therapeutic use , Middle Aged , Postoperative Complications/mortalityABSTRACT
In order to reduce the exposure of the lung and oesophagus during whole-body irradiation with cobalt-60 gamma rays the dose rate delivered to the lungs and the neck is diminished by means of a filter. Because of its special shape, sternum and columna vertebralis obtain the unreduced dose. The filter is constructed for irradiation in antero-posterior direction. A fixed position of the patient is not necessary.
Subject(s)
Lung/radiation effects , Radioisotope Teletherapy , Cobalt Radioisotopes/therapeutic use , Esophagus/radiation effects , Filtration/instrumentation , HumansABSTRACT
A boy with severe Aplastic Anemia (AA) and a girl with Acute Lymphoblastic Leukemia (ALL) in relapse have been grafted with marrow from HL-A identical, mixed leukocyte culture (MLC) negative siblings after appropriate immunosuppressive and antileukemic therapy. Both of them are well 7 and 2 months after transplantation respectively. Bone marrow transplantation should be considered in children with AA and ALL in relapse, if HL-A identical, MLC negative siblings are available.
