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M A Paciotti

Publications and source records attributed to M A Paciotti.

8 recordsLinked to original sources
PubMed1988

Radiation tolerance of the rat rectum to fractionated X-rays and pi-mesons.

A 2.5 cm segment of the rectum of female F344 rats was irradiated with up to 10 fractions of X-rays or pions. Transient signs of acute proctitis were followed by chronic rectal injury starting at about 2 months. Recto-vaginal fistulas were frequently observed in animals with severe chronic injury. Two patterns of chronic injury were observed, an early type consisting of deep ulcers and fistulas, and a late type characterized by vascular injury, fibrosis and mucosal cysts. In a 4-fraction X-ray experiment, the influence of a low-residue diet was compared with a regular diet, showing no significant differences in pathology or survival. Isoeffective doses were determined for the occurrence of severe rectal injury at 250 days. Fitting the data to an LQ-model yielded an alpha/beta ratio of 13 Gy for pions, and 6.5 Gy for X-rays. Increasing the overall treatment time from 9 days to one month gave a significant rise in isoeffective doses for chronic injury. This suggests that the more delayed types of injury did not develop independently from the acute mucosal changes. The RBE of pions for rectal injury at 250 days was 1.2 for single doses, increasing to about 1.4-1.5 at a dose per fraction of 4 Gy. These values are similar to those obtained in other acute and late responding tissues.

Animals↗
PubMed1985

Dosimetry comparison and characterisation of an Al K ultrasoft x-ray beam from an MRC cold-cathode source.

Ultrasoft x-rays of 0.3-5 keV have provided a unique tool for the investigation of intracellular mechanisms of radiation action in biological organisms, including mammalian cells. However, their use presents unique practical problems in dosimetry and experimental design. Detailed interpretation of the biological results requires reliable dosimetry and well characterised monoenergetic beams. This paper presents a comparison between two fundamentally different dosimetric techniques, namely the ionisation current in an extrapolation chamber and photon counts in a proportional counter. Agreement within 7% was obtained when these two methods were applied to an Al K x-ray beam (1.5 keV) from an MRC cold-cathode transmission target discharge tube as previously used in many biological experiments. Photographic film was calibrated as a relative dosimetric technique and used for investigation of the intensity uniformity of the radiation field. These techniques provide a comprehensive characterisation of the beam in the position of the biological cells, including photon flux (or absorbed dose rate), spectral purity (showing much less than 1% bremsstrahlung relative to characteristic Al x-rays) and uniformity over the irradiation area (within about 5% for mammalian cell irradiations).

Cell Survival↗
PubMed1978

Dose outside the treatment volume for irradiation with negative pions.

Irradiation of humans with negative pions requires a knowledge of the absorbed dose and radiation quality outside the primary pion beam. In conjunction with early clinical trials at LAMPF, experimental data have been obtained with microdosimetric techniques and multiwire proportional counters. Theoretical calculations have been made for the neutron contribution to the dose and are consistent with these data. Measurements were made with in 40 cm x 51 cm x 76 cm water phantom for a negative pion beam of initial momentum of 170 MeV/c, deltap = +/- 3MeV/c. The absorbed dose outside the treatment volume is the result of: (1) neutrons and photons from the pion interactions,(2) treatment room background and (3) peripheral muons, electrons and pions in the primary beam. The first two components are nearly isotropic and are congruent to 0.02% of the peak dose at a distance of 24 cm from the treatment volume; the third component is anisotropic and varies from 0.01 to 0.1% of the peak dose. Collimation of the bean increases the dose outside the treatment volume typically by 50%.

Elementary Particles↗
PubMedDate not supplied

Calculation of pion dose distributions in water.

Techniques for calculating negative pion beam depth and off-axis dose distributions in a water phantom have been developed at the Clinton P. Anderson Meson Physics Facility in Los Alamos. The superposition of the unmodulated depth-dose curve produced modulated depth-dose curves. The addition of the collimator neutron dose, which has been shown to depend on field size, to the modulated depth-dose curve yields the collimated depth-dose distributions. Off-axis dose distributions under a collimator are produced by calculating the distortion of the uncollimated beam caused by multiple Coulomb scattering and beam phase space. Several comparisons of calculated and measured distributions are shown with agreement of normally +/- 3% of peak dose of +/- 3 mm for a particular dose contour. These distribution are them modified by computerized tomographic data to give patient isodose distributions.

Elementary Particles↗
PubMedDate not supplied

Preclinical studies of dynamic treatment modes in pion therapy.

Preliminary results on a system for delivering dynamic pion radiotherapy treatments are reported. The desired treatment volume is scanned across a small, focused pion beam using a computer-controlled treatment couch. A computer-controlled rangeshifting device modulates the stopping pion depth distribution in coordination with the couch motion to conform the dose to the shape of the treatment volume. For certain shaped tumors, the system can result in substantial normal tissue dose sparing and better field flatness as compared to irradiation by static treatments with broad terms. The characteristics of this new system, plus preliminary results for typical dose distributions as measured with thermoluminescent dosimeters (TLDs), are presented.

Elementary Particles↗