Incidental irradiation of mediastinal and hilar lymph node stations during 3D-conformal radiotherapy for non-small cell lung cancer

Abstract

Purpose. 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 (V₄₀) were compared for omitted vs. limited+extended ENI and limited vs. extended ENI. Results. For omission of the ENI the minimum doses and V₄₀ 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 V₄₀ 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.