Evaluation of microscopic tumor extension in non-small-cell lung cancer for three-dimensional conformal radiotherapy planning

Purpose: One of the most difficult steps of the three-dimensional conformal radiotherapy (3DCRT) is to define the clinical target volume (CTV) accordi ng to the degree of local microscopic extension (ME). In this study, we tri ed to quantify this ME in non-small-cell lung cancer (NSCLC), Material and Methods: Seventy NSCLC surgical resection specimens for which the border between tumor and adjacent lung parenchyma were examined on rout ine sections. This border was identified with the naked eye, outlined with a marker pen, and the value of the local ME outside of this border was meas ured with an eyepiece micrometer, The pattern of histologic spread was also determined. Results: A total of 354 slides were examined, corresponding to 176 slides f or adenocarcinoma (ADC) and 178 slides for squamous cell carcinoma (SCC), T he mean value of ME was 2.69 mm for ADC and 1.48 mm for SCC (p = 0,01), The usual 5-mm margin covers 80% of the ME for ADC and 91% for SCC. To take in to account 95% of the R-IE, a margin of 8 mm and 6 mm must be chosen for AD C and SCC, respectively. Aerogenous dissemination was the most frequent pat tern observed for all groups, followed by lymphatic invasion for ADC and in terstitial extension for SCC. Conclusion: The ME was different between ADC and SCC, The usual CTV margin of 5 mm appears inadequate to cover the ME for either group, and it must be increased to 8 mm and 6 mm for I-IDC and SCC, respectively, to cover 95% o f the ME. This approach is obviously integrated into the overall 3DCRT proc edure and with other margins. (C) 2000 Elsevier Science Inc.