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Biomedical subjects

A M Koehler

Publications and source records attributed to A M Koehler.

14 recordsLinked to original sources
PubMed1979

Proton radiation as boost therapy for localized prostatic carcinoma.

A 160-MeV proton beam has been modified to irradiate patients with localized tumors by using convention treatment schedules. This proton beam has the physical advantage of megavoltage x-rays of reducing the radiation dose to normal tissues adjacent to the tumor volume. A perineal proton technique used as boost therapy (2,000 to 2,500 rads) was evaluated in the definitive irradiation of 17 patients with localized prostatic carcinoma. This technique allows repeated daily treatment of the carefully defined target volume with a precision of +/- 2 mm. Total dose to the prostatic tumor, but not to the posterior rectum, has been increased by 500 to 700 rads. After 12 to 27 months of observation, no noteworthy rectal reaction has developed in a patient, easily managed urethral strictures have developed in two patients, and all but one are locally controlled.

Adenocarcinoma↗
PubMed1978

A heavy particle comparative study. Part I: depth-dose distributions.

The results of a comparative study of heavy particles of interest in radiotherapy, with peaks spread over a depth of 10 cm, are reported in four parts. The introduction to this study and the depth-dose distributions of the particles, (n, pi-, p, He, C, Ne, and Ar ions) are reported herein. The results indicate that protons give the best localization of dose. The degree of localization of dose with heavy ions is reduced with increasing charge on the ion. For ranges less than 15cm, heavier ions such as neon and argon still have favourable dose localization; however, for ranges in excess of 15 cm, heavy ions such as argon are unfavourable but superior to fast neutrons because penetration can be controlled by modulation of energy or range.

Argon↗
PubMed1977

Proton irradiation of small choroidal malignant melanomas.

Five patients with choroidal malignant melanomas were treated with proton irradiation with a cyclotron. We developed an accurate method of aiming the proton beam within the eye. Four to five tantalum rings, 2 mm in diameter, were sutured to the sclera at the edges of the tumor, which is localized by indirect ophthalmoscopy and transillumination. The rings were used as markers for stereotactic radiography to align precisely the tumors with the proton beam. The patients were given a total tumor dose of 4,730 to 6,670 rads, delivered in five equal fractions, over a period of eight to nine days. All patients tolerated the treatments well without any adverse effects. The tumor response to therapy could not be evaluated at the completion of treatment since there was no immediate observable reaction of the tumor or of the surrounding retina. Although there has been no definite regression in any patient, we observed a change in the "color" of the tumor in the first two patients and resolution of two serous retinal detachments.

Choroid Neoplasms↗
PubMed1977

Partial body calcium determination in bone by proton activation analysis.

The feasibility of a new method for in vivo regional bone calcium measurement has been studied in phantoms using the 160 MeV Harvard cyclotron, Advantages include the capability of measuring bone calcium directly directly in a well defined anatomical region (such as one or several vertebrae) and restriction of the dose to the immediate region of interest. Proton activation of 40Ca (97% natural abundance) produces radionuclide 38K. Its 2-17 MeV gamma ray (T 1/2 = 7-71 min) is detected by a NaI counter. Separation of this activity from room background and interfering nuclides, 14O and 34Clm, proceeds by decay curve analysis. Phantom studies showed the dependence of 38K activity to be highly linear with calcium content (r= 0-998). Non-linearities with dose did not appear below the 20 rad level. The precision of measurements on a phantom with two calf vertebrae exposed to 2-4 rad was 3% and was mostly limited by counting statistics. System reproducibility on phantoms given a high dose proved better than 0-5%.

Activation Analysis↗
PubMed1976

Quantitative proton tomography: preliminary experiments.

An attempt has been made to see whether energetic protons (158 MeV) could be used instead of X-rays in computerized axial tomography to detect density differences of the order of those at which commercial X-ray tomographs cease to be useful. A circularly symmetrical phantom consisting of Lucite and sugar solutions was used, and density differences of 0-5% were reconstructed with reasonable accuracy from data obtained with very simple equipment. Discontinuities in either density or chemical composition, or both, seem to cause artifacts in the reconstruction. These may be related to the West-Sherwood effect.

Computers↗
PubMed1975

Explorotory study of proton radiation therapy using large field techniques and fractionated dose schedules.

Three patients have been treated with 160-MeV protons combined with high-energy photons to examine the advantages and difficulties associated with the clinical implementation of a program of large-field, fractionated-dose, protonradiation therapy. We havefound it necessary to 1) obtain an accurate three-dimensional determination of the treatment volume including the density of all tissues in the beam path; 2) construct an adequate bolus to compensate for tissue heterogeneities; 3) use much more precise and accurate immobilization and patient positioning devices than used in photon irradiation; 4) treat with both protons and photons so as to keep the skin dose within an acceptable level. IN TISSUES WITHOUT SIGNIFICANT INHOMOGENETIES DUE TO BONE AND AIR SPACES WE HAVE DELIVEREDA WELL-DEFINED DOSE TO INVOLVED TISSUES WHILE SPARING DISTAL SENSITIVE STRUCTURES. However, in those regions where there is much "fine structure" of tissue density, it has been difficult to compensate satisfactorily for the inhomogeneties.

Adult↗
PubMed1975

Proton irradiation of simulated ocular tumors.

Silicone sponges were sutured to the sclera of owl monkeys to create an indentation which would simulate a tumor of the posterior segment of the eye. A tantalum clip inserted in the silicone sponge served as a marker for radiographic localization of the simulated tumors. The acute lesions obtained on the retina and choroid after moderately high doses of proton irradiation suggest that this method of aiming the proton beam will be adquate for human clinical trials.

Animals↗
PubMedDate not supplied

Flattening of proton dose distributions for large-field radiotherapy.

Methods for obtaining flattened charged-particle dose distributions over large areas are described. The system being used at Harvard for proton radiotherapy is discussed in detail. It is an extension of usual multiple-scattering techniques to include blocking out some of the central peak, followed by rescattering to fill in the profile, resulting in flat distributions up to 30 cm in diameter. The unusually long source-to-skin distance (4.6-m SSD) plus the small lateral spread (2 mm rms) from multiple scattering in the patient results in little divergence of the beam throughout the treatment volume.

Protons↗
PubMedDate not supplied

Proton penetration and control in nonhomogeneous phantoms.

Accurate bolus is needed for extension of Bragg-peak therapy. Proton beam-stopping profiles in a lucite-styrofoam-tissue phantom and in a Rando phantom were recorded photographically. Air volumes caused the largest distortions. Lucite bolus was cut to achieve desired beam-stopping profiles. Verification of bolus effect in situ will be important to control beam penetration within 5 mm.

Models, Structural↗
PubMedDate not supplied

Proton beam irradiation for treatment of experimental human retinoblastoma.

Proton beam irradiation was used to treat human retinoblastoma (Y-79 cell line) grown subcutaneously in the athymic "nude" mouse. Thirty-four tumors were included in the experimental groups, of which twenty-three were irradiated and eleven served as controls. Tumors were irradiated with protons produced at the 160 megavolts Harvard cyclotron. The dose delivered to the tumor ranged from 7.5 to 27.5 proton gray in a single treatment, and 25.0 proton gray delivered in two fractions separated by 24 hours. Reduction of tumor growth was significantly greater than controls (p less than 0.001) with treatment doses greater than or equal to 17.5 proton gray. Histologic examination revealed a marked decrease of mitotic activity in all specimens examined 48 hours after treatment at these higher doses. Total regression without evidence of remaining malignant cells was noted in three tumors treated at 17.5 proton gray or above. Our results indicate that human retinoblastoma in a murine host, with a tumor mass similar to that seen in a clinical setting, is sensitive to radiation by high energy protons.

Animals↗