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To estimate the doses of incidental irradiation in particular lymph node stations (LNS) in different extents of elective nodal irradiation (ENI) in 3D-conformal radiotherapy (3D-CRT) for non-small cell lung cancer (NSCLC). Methods. Doses of radiotherapy were estimated for particular LNS delineated according to the recommendations of the University of Michigan in 220 patients treated using 3D-CRT with different (extended, limited and omitted) extents of ENI. Minimum doses and volumes of LNS receiving 40 Gy or more (V 40 ) were compared for omitted vs. limited' extended ENI and limited vs. extended ENI. Results. For omission of the ENI the minimum doses and V 40 for particular LNS were significantly lower than for patients treated with ENI. For the limited ENI group, the minimum doses for LNS 5, 6 lower parts of 3A and 3P (not included in the elective area) did not differ significantly from doses given to respective LNS for extended ENI group. When the V 40 values for extended and limited ENI were compared, no significant differences were seen for any LNS, except for group 1/2R, 1/2L. Conclusions. Incidental irradiation of untreated LNS seems play a part in case of limited ENI, but not in cases without ENI. For subclinical disease the delineation of uninvolved LNS 5, 6, and lower parts of 3A, 3P may be not necessary, because these stations receive the substantial part of irradiation incidentally, if LNS 4R, 4L, 7, and ipsilateral hilum are included in the elective area while this is not case for stations 1 and 2.There is increasing evidence, derived especially from dose escalation studies that the omission of elective nodal irradiation (ENI) in radiotherapy of non-small cell lung cancer (NSCLC) results in a low incidence of isolated nodal failures (INF) [1Á 10]. The prerequisite for reporting on the incidence of INF after radiotherapy with the omission of ENI is an evaluation of incidental irradiation received by omitted nodal stations. In some cases the incidental irradiation may be enough to eradicate subclinical nodal disease [11]. Thus, although regional nodes are not purposefully included into the clinical target volume, they might actually receive elective irradiation. In the previous analysis of our data [12], the two-year cumulative incidence of INF for 185 patients treated with 3-dimensional conformal radiotherapy (3D-CRT) and different (limited or extended) extents of ENI was 12%.INF was defined as a regional failure occurring outside gross tumor volume (GTV) without previous or synchronous local progression regardless of the distant metastases status. There was no difference in the cumulative incidence of INF for patients treated with extended and limited mediastinal ENI. One of the possible explanations of this finding is that the incidental irradiation may play a role in the limited ENI.The low incidence of INF reported in the dose escalation studies may be related to the unintended dose received by lymph node stations (LNS) at risk. Published data on incidental irradiation in radiotherapy for lung c...

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