An evaluation of the recommendations of the TG-25 protocol for determination of depth dose curves for electron beams using ionization chambers.

AAPM Radiation Therapy Committee Task Group 25 has recently outlined a protocol for the determination of relative dose curves for electron beams [Med. Phys. 18, 73-109 (1991)]. We have performed an evaluation of this protocol by comparing the central axis depth dose curves determined from measurements using two different ionization chambers and three different phantom materials. Measurements were made with a Farmer-type PTW and Capintec ionization chamber in solid water, PMMA, and clear polystyrene phantoms irradiated by 6- and 15-MeV electron beams. Central axis depth dose curves were generated from the measured depth-ionization data using the new protocol. For both the chambers and energies investigated in this study, excellent agreement was observed among all the depth doses in water obtained from measurements in all of the three phantoms studied.

Calibration of high-energy photon and electron beams for radiotherapy using AAPM 1983 and IAEA 1987 dosimetry protocols.

To follow up on the theoretical comparison of the IAEA 1987 and AAPM 1983 protocols for dosimetry calibration of high-energy photons and electrons [Med Phys. 18, 26-35 (1991)], results of a set of dosimetric measurements made with a Farmer type PTW and Capintec ionization chambers in solid water, PMMA, and polystyrene phantoms and exposed to a 4 MV photon beam from a Varian Clinac 4S at Yale, a 10 MV photon beam and 6 and 15 MeV electron beams from a Varian Clinac 1800 at Phelps Radiation Center, University of Connecticut, and a 25 MV photon beam from a Sagittaire at Yale, are presented. Because different methods are used for the determination of electron beam energies, the values of mean electron energy determined by the two protocols are different by up to 8%. However, for dose inter-comparison, the overall agreement between the two protocols is within 1% in most cases, with a maximum discrepancy of 3.3% in one case. For photons, the IAEA results are smaller than the AAPM results by 0.7% on the average, while maximum discrepancies are in the range of -0.4%-(-1%). In the case of 15 MeV electrons, the discrepancies between the two protocols are found to be in the range of -0.1%-1% and have an average value of 0.5%. In contrast to the above, a large discrepancy is observed between the two protocols for 6 MeV electrons. Depending upon the choice of phantom and ion chamber, this discrepancy is found to be in the range of -0.1%-(-3.3%).(ABSTRACT TRUNCATED AT 250 WORDS)

Animal model of spontaneous neoplasia based on lymph and cells collected from thoracic duct of normal dogs and dogs with malignant lymphoma.

Peripheral blood and thoracic duct lymph from normal dogs and dogs with a leukemic malignant lymphoma were compared for total and differential leukocyte count and lymph flow rate. Except for higher numbers of circulating atypical lymphocytes, the blood leukocyte count as well as the lymph cell count and flow rate were similar in both groups. Lymph cell differential pattersn in lymphoma dogs had higher numbers of lymphoblasts and minor cell types, plasmacytes, monocytes, and reticulum cells, plus degenerating and mitotic cells. There was a five-fold increase in the lymph leukocyte count shortly after irradiation in two lymphomatous dosg. Stained preparations of this lymph showed signs of 100% cell mortality. It was concluded that the thoracic duct lymph is a practical source of normal and cancerous lymphoid cells, and that the lymph and cells collected from dogs with malignant lymphoma are excellent models for certain studies of spontaneous neoplasia.

Computer generation of high-energy x-ray dose distributions.

A computer program for the generation of high-energy x-ray dose distributions has been developed. The program takes account of the fact that the x-ray beam profile, as affected by penumbra, wedges, beam blocks, or flattening filters, is one of the prime determinants of the dose distribution. Doses from primary and scattered radiation are calculated separately by using published tissue-air ratio (TAR) and scatter-air ratio (SAR) data. The dose from scattered radiation is determined by dividing the x-ray field into a series of scattered strips and summing the contribution from each. Wedges or beam blocks are taken into account simply by earning their actual coordinates and linear attenuation coefficients. The program may be used to design wedges, beam blocks, or flattening filters prior to fabrication. Complete libraries of dose distribution for 60Co, 2-, 4-, and 6-MV x rays have been generated.