OBJECTIVEDefining the margin of clinical target volume (CTV) is very important for three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiation therapy (IMRT). In this study, according to the comparison between gross tumor volume (GTV) silhouetted by radiology and pathology in non-small-cell lung cancer (NSCLC), we tried to define the correlation of GTV by radiology and pathology, and assess the degree of correlation to local microscopic extension (ME) among different pathologic types of NSCLC, so as to define the margin of CTV precisely.

METHODSFrom February 2001 to February 2002, forty-three NSCLC patients after surgical resection were studied. All patients had had CT scans of the chest before surgery and routine pathology examination after surgery. The tumor size at X (lateral direction), Y (ventrodorsal direction) and Z (craniocaudal direction) axes were measured on CT. Also by pathology examination, the tumor size at X, Y, Z axes and the degree of ME at X, Y, Z axes were measured, respectively.

RESULTSWithout taking into account the value of ME, there was almost total agreement on the GTV by radiology and pathology in three dimensions. The mean value of ME was 2.18 mm for adenocarcinoma (ADC) and 1.33 mm for squamous cell carcinoma (SCC) (P = 0.001). But, taking into account 95% of the ME, a margin of 7 mm and 5 mm must be allowed for ADC and SCC, respectively.

CONCLUSIONThere exists a correlation of GTV by radiology and pathology. In the target volume defining for 3DCRT and IMRT, we could use the GTV by radiology instead of the GTV by pathology, with the ME being different for ADC and SCC. To cover 95% of the ME, the margin from GTV to CTV must be extended to 7 mm and 5 mm for ADC and SCC, respectively.