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

Abstract

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...

Comparison of Involved Field Radiotherapy versus Elective Nodal Irradiation in Stage IIIB/C Non-Small-Cell Lung Carcinoma Patients Treated with Concurrent Chemoradiotherapy: A Propensity Score Matching Study

“…The quantity of the incidental dose, elective nodal coverage, and its adequacy for the microscopic disease control was not tended in our PSM cohorts; however, these issues were addressed by Polish and Japanese retrospective studies [ 22 , 23 ]. Kepka et al estimated the incidental doses and V 40 values of 3D-CRT for specific LN stations with varying ENI extents (extended, limited, and omitted) in 220NSCLC patients [ 22 ].…”

“…The quantity of the incidental dose, elective nodal coverage, and its adequacy for the microscopic disease control was not tended in our PSM cohorts; however, these issues were addressed by Polish and Japanese retrospective studies [ 22 , 23 ]. Kepka et al estimated the incidental doses and V 40 values of 3D-CRT for specific LN stations with varying ENI extents (extended, limited, and omitted) in 220NSCLC patients [ 22 ]. They have noticed that the incidental irradiation of unintended LNs was apparent in case of limited ENI, such as uninvolved stations of 5 and 6, and lower parts of 3A and 3P were already irradiated while electively irradiating stations of 4R, 4L, 7, and ipsilateral hilum, but these stations were not adequately covered in IFRT, and levels 1 and 2 were not covered in any scenario.…”

Involved field radiotherapy (IFRT) versus elective nodal irradiation (ENI) for locally advanced non-small cell lung cancer: a meta-analysis of incidence of elective nodal failure (ENF)

“…(3) Concurrent or sequential use of chemotherapy with radiotherapy may also help control local diseases. (4) Although the elective nodal regions are not included in IFRT, they are incidentally irradiated with prophylactic doses, and the prophylactic doses may contribute to the low incidence of ENF [ 23 – 26 ]. Before this meta-analysis, despite the widespread abandoning of ENI for NSCLC patients, we still take a conservative approach in our department because existing evidence for this is insufficient.…”

Dose distribution and tumor control probability in out-of-field lymph node stations in intensity modulated radiotherapy (IMRT) vs 3D-conformal radiotherapy (3D-CRT) of non-small-cell lung cancer: an in silico analysis

“…To our knowledge this is the first study examining the dose distribution in elective lymph node stations adjacent to the CTV in the context of IF-IMRT in NSCLC. Several planning studies examined the potential benefits of incidental nodal irradiation of uninvolved lymph node regions when using 3D-CRT [ 7 , 8 , 20 , 21 ]. Even with PET-based IF-RT of stage III NSCLC, rates of out-of-field nodal recurrences can be as high as 10 % and therefore cannot be considered as insignificant [ 22 ].…”