The effect on minimum tumor dose of restricting target-dose inhomogeneity in optimized three-dimensional treatment of lung cancer.
An examination was made of the effect upon the minimum tumor dose of a limit placed on the variation of dose across target. If the required level of target dose uniformity is slightly relaxed, a substantial improvement in the minimum tumor dose might appear. It was conjectured that this effect could be seen with treatments optimally planned and evaluated in three-dimensions. A model of advanced carcinoma of the lung treated with a computer controlled accelerator was used to test this hypothesis. A mathematical program for optimizing beam weights was used to determine the largest minimum tumor dose possible. In the six cases tested, a minimum tumor dose of greater than 80 Gy could be delivered if a 20% inhomogeneity limit was accepted. The minimum tumor dose fell to the range 44-64 Gy when the inhomogeneity limit was tightened to 13-17%. The results imply a need to examine the choice of a required level of dose uniformity from the range of values suggested in the 2-dimensional planning literature. If a strict bound-on-dose uniformity is preserved, mechanisms--such as formal optimization--which can reduce target dose inhomogeneity will be valuable.
Joint Center for Radiation Therapy, Boston, Massachusetts 02115.
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M
Langer
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P
Kijewski
R
R
Brown
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C
Ha
D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008433:Mathematics; D008962:Models, Theoretical; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D011881:Radiotherapy, Computer-Assisted; D013679:Technology, Radiologic