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Results for “Elementary Particles”

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At least 1,063 records · Page 59Linked to original sources
PubMed1980

Pions for radiotherapy at TRIUMF.

Beams of negative pi-mesons (pions) have depth-dose characteristics which are favorable for radiation therapy. As well, the densely ionizing radiations resulting from pion capture give pion beams an increased RBE and reduced OER, largely confined to the treatment volume. Three facilities capable of testing pion beams for therapy now exist: TRIUMF in Vancouver, LAMPF in New Mexico and SIN in Villigen, Switzerland. Patient treatment is already underway at LAMPF and will commence at TRIUMF in November, 1979, and at SIN in 1980. Pre-clinical studies of the pion beam at TRIUMF have confirmed the predicted physical and radiobiologic properties of this new type of radiation. Fractionated irradiation of mouse skin suggests an RBE of 1.4 -- 1.6 for small treatment volumes receiving 10 dose fractions of peak pions. Single dose studies with cultured cells give an RBE for peak pions of 1.2 -- 1.5 and an oxygen gain factor of 1.2. The results are generally in good agreement with those obtained at LAMPF and SIN. Techniques have been developed which facilitate the delivery of well-defined dose distributions with uniform biologic effect throughout the treatment volume.

Animals↗
PubMed1980

Theoretical studies of image artifacts and counting losses for different photon fluence rates and pulse-height distributions in single-crystal NaI(T1) scintillation cameras.

Using computer simulations, we have developed a theoretical model to explain the correlation between counting losses and image artifacts in single-crystal NaI(T1) scintillation cameras. The theory, valid for scintillation cameras of the Anger type, is based on the physical properties of the NaI(T1) crystal. Based on a statistical model using random numbers, pulse trains of the light pulses from scintillations were simulated. Pulse-height distributions for different event rates were calculated, with various Compton distributions. Images of point sources and line sources were generated. Counting losses and image artifacts were dependent on the shape of the pulse-height distribution. The calculated counting losses decreased with larger Compton distributions, due to increasing numbers of pileup events in the energy window; this also caused severe image distortion. The improvement of the spatial resolution with pileup rejection was demonstrated. The theoretical results are in good agreement with experimental results obtained previously. It is concluded that, in modern cameras, the decay time of the scintillation determines the amount of pileup, and the resolving time of the electronics governs the count rates. The results indicate that in some modern cameras the limits of the count-rate capacity in Anger cameras may be reached.

Elementary Particles↗
PubMed1975

[Preoperative radiotherapy of bladder cancer].

Based on the observation of 58 patients with carcinoma of the bladder the effect of preoperative irradiation is reported. After application of 3500 Rad in about four weeks the examination of the surgery preparations revealed histological absence of tumor cells in one third of the cases approximately. The irradiation technique used is described and also the effects and side-effects of synchronization induced by 5-fluorouracil in a part of the group. Consequences for the therapeutic proceeding with regard to the carcinoma of the bladder are discussed.

Bone Marrow Diseases↗
PubMed1975

[Relative biological efficiency of electron and photons of a 42-MeV- betatron. LD 50/30 in mice].

The LD 50/30d in young NMRI mice was determined. Comparison was made for 200 kVp X-rays, Cobalt-60 gamma rays, 35 MeV electrons and 42 MV bremsstrahlung. The dose rate was in all experiments between 60 and 80 rd per minute. The beam geometry and the spatial dose distributions were held as equal as possible. With 200 kVp X-rays as unity the same RBE factor (0.80 plus or minus 0.05) resulted for Cobalt-60 gamma rays, 35 MeV electrons and 42 MV bremsstrahlung.

Animals↗
PubMed1975

Clinical trials with new radiation modalities.

I would suggest that the investigation of a new clinical modality involves a major commitment by the whole clinical group of the department involved and not just by the people chosen to be the primary investigators. As a base for comparison, it requires a detailed knowledge of the results and sites of failures and complications of the therapy used by that department. To make adequate relative biologic effect studies for the new modality, suitable comparative, quantitative tissue and tumor assays have to be done with photons and these could be done and established before the new modality came on line. For the Phase III trial, which is usually considered a randomized comparative trial, it can be argued (and a method is proposed) for the use of a non-randomized study to make the maximum use of patients coming to the centre.

Clinical Trials as Topic↗
PubMed1975

[The photon-stationary-field therapy with the 42 MeV betatron using wedge filters].

The dose distribution in photon beams from a 42 MeV betatron using wedge filters of lead with different angles of slope is described. The wedge coefficient to be considered at a field size of 10 X 10 cm is given. The scope for isodoses modified by wedge filters is discussed with regard to stationary-field photon therapy.

Elementary Particles↗