PubMed · 7429855
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M Tschurlovits. 1980. A method for calculating the dose commitment from bioassay data.. https://pubmed.ncbi.nlm.nih.gov/7429855/
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Adjustment factors (AF) for inhalation exposure to chemical agents during unconventional work schedules were derived on toxicokinetic bases. AFs depend on the half-life of the agent and on the work schedule. Because they are grossly affected by cumulation, AFs were calculated for steady-state conditions. They were based on the following measures of chemical body burden: (1) end-of-shift biological level as used previously by other investigators; and (2) areas under the curves, AUCexp, AUCday, and AUCweek, which correlate with average biological levels during the shift, work day, and work week, respectively. The dependence of AFs on the half-life was studied on 50 possible work schedules using agents with a half-life of 1 hr to 2 years. Based on the data, simple equations suitable for field conditions were derived for determination of AFs. Since AFs based on individual measures of body burden are not the same, the pharmacodynamics of the toxic endpoint should be considered when selecting the measure of body burden and the half-life for AF determination.
AIM: Three-dimensional inverse treatment planning with modulated beams was applied for dosimetric optimization of a lengthy (22 cm) and complex (concave-convex) shaped planning target volume (PTV) in the cervical and upper mediastinal regions. MATERIAL AND METHOD: The planning was done for 9 coplanar beams spaced evenly at 40 intervals. Properties of 15 MV photons from a linear accelerator were simulated. The optimization of the fluence modulation profiles for each beam was based on a definition of the desired/permitted relative dose levels in the PTV and organs at risk, and a definition of the strengths of the constraints to achieve these objectives. RESULTS: An adequate dose delivery to the PTV and protection of the spinal cord are completely achievable. The dose delivered to the lungs is clinically acceptable with respect to the risk of radiation-induced pneumonitis. For reasons of physics, no further decrease in the radiation burden on the lungs can be attained with X-rays without compromising the PTV coverage. The radiation burden on some critical part of normal tissues was effectively reduced by application of a dummy organ at risk. CONCLUSION: The inverse planning is an effective method for conformal radiotherapy of large tumors as well. However, the power of the technique is insufficient when the tolerance dose of the neighbouring normal tissue is too low and its volume effect is high. Although requiring further operator interactions, introduction of dummy organs at risk may be of help in reducing the radiation burden on normal tissues.
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