International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationDesigning Targets for Elective Nodal Irradiation in Lung Cancer Radiotherapy: A Planning Study
Introduction
A recent publication providing recommendations for delineation of lymph node stations (LNS) for the purpose of CT planning for lung cancer (1) was a first attempt to generate consensus in this field. Even if the elective nodal irradiation (ENI) is abandoned in many radiation oncology services, the design of elective fields for some clinical purposes (e.g., postoperative radiotherapy for N2 disease) is still a matter of debate. Senan et al.(2) showed large variation in the generation of postoperative radiotherapy volumes by experienced clinicians, which demonstrates the need for standardization of the target volume definition for ENI in lung cancer. Thus, despite a real clinical need for such guidelines, the published recommendations known as the Atlas of University of Michigan (UM) (1) based on radiological and anatomical data have not yet been validated in clinical practice. That is, there is no description of the coverage of those CT-defined three-dimensional (3D) volumes with “standard, traditional” two-dimensional (2D) elective fields for non–small cell lung cancer (NSCLC), as, for example, defined by Radiation Therapy Oncology Group's RTOG 94-10 criteria 3, 4. LNS coverage issues may be further compromised when applied to their associated planning target volumes (PTVs), which would by definition account for demonstrated lymph node mobility (5) and setup uncertainty as required by the International Commission on Radiation Units and Measurements criteria ICRU 62 (6). Of course, treatment planning performed with awareness of the revised volume definitions together with their PTV expansions, could be used to adjust field borders (2D) or beam arrangements (3D). However, having dealt with target volume coverage issues, additional concerns related to the organs at risk could arise. That is, it is unclear whether 3D plans generated to account for the revised LNS PTVs will lead to treatments that are at least equally safe with respect to critical structures as those fields based on traditional 2D portals.
This planning study was undertaken to evaluate the clinical implications of adhering to the recommendations of the recently published atlas for delineation of mediastinal and hilar LNS for use in conformal 3D radiotherapy treatment planning. The specific aims were (1) to evaluate doses received by particular LNS delineated according to recommendations when the “standard” (2D) elective fields are applied for tumors of different lobes and (2) to evaluate doses to the critical structures in 3D plans for ENI delineated according to the UM recommendations while incorporating the ICRU criteria for margins in conformal techniques.
Section snippets
Delineation of the LNS
The study was approved by institutional review board as part of a large retrospective study. The CT scans of five lung cancer patients without evident nodal metastases and primary tumor visualized on CT, treated previously by lobectomy, were selected from the radiation planning database. The axial CT thickness was 3 mm for three cases and 5 mm for 2 cases. The LNS were defined using a soft-tissue scan window width of 400 and CT scan level at +20. For visualization of segmental and lobar
Composite CTV and PTV coverage
For each of the five cases, the six 2D and six 3D plans for various ENI settings (right upper lobe, with and without inclusion of ipsilateral SC-LNS; left upper lobe, with and without inclusion of ipsilateral SC-LNS; right lower lobe; and left lower lobe) were generated, resulting in 30 2D and 30 3D plans. As defined by the treatment directive, PTVs in 3D-constructed plans were covered by 90% isodose. However, in 8 (27%) of the 30 3D plans, <0.05% of the composite PTV was not covered by 90%
Discussion
Traditionally constructed 2D fields did not entirely cover LNS delineated according to the recommendations of the Atlas of UM. Because of inappropriate coverage, such treatment plans would not be acceptable in clinical practice and would require enlarging the portals appropriately. Does it prove that traditionally used anatomic landmarks visible on 2D imaging are no longer valid for ENI portals creation or contrarily that the recommendations studied are of no value and should be modified? The
Acknowledgments
We thank the participants of the 2006 IAEA Consultants' meeting on Elective Nodal Irradiation in Lung Cancer (Vienna, Austria) for inciting the first author to perform this work, and especially Branislav Jeremic M.D. for his precious scientific advice. The participants of the consultant meeting included Jose Belderbos, M.D., Ph.D., Branislav Jeremic, M.D., Lucyna Kepka, M.D., Feng-Ming Kong, M.D., Ph.D., Mary Martel, Ph.D., and Gregory Videtic, M.D., in alphabetical order.
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Cited by (6)
Target volume for postoperative radiotherapy in non-small cell lung cancer: Results from a prospective trial
2013, Radiotherapy and OncologyCitation Excerpt :Comparison of our digitally reconstructed radiograph with CTV/PTV projection leads us to conclude that our 3D-planned target volume was very similar to the traditional less extensive 2D planned field including only mediastinum and ipsilateral hilum used in some studies [21,22]. A previous planning study showed that 3D planning is not necessarily related to the reduction in the target volume and doses to the critical structures [23]. However, the 3D planning gives assurance that the LNSs of interest are actually fully encompassed with the prescribed dose.
Computed tomographic atlas for the new international lymph node map for lung cancer: A radiation oncologist perspective
2013, Practical Radiation OncologyCitation Excerpt :Medially, station 1R and 1L are separated by the midline of the trachea while excluding the thyroid gland. The remaining borders for station 1 have been previously described by Kepka et al.7 The anterior border is defined as the deep surface of the sternomastoid muscle and the deep cervical fascia and posterior parts of the ribs and clavicle excluding sternohyoid and sternothyroid muscles in the lower parts. The posterolateral border is the anterior and lateral border of the anterior scalene muscle, in the lower parts the medial anterior border of thesubclavian artery.
Addressing the challenge of proper delineation of lymph node stations in modern radiotherapy for lung cancer
2018, Journal of Radiation ResearchModern radiotherapy in limited and extensive stage small-cell lung cancer
2016, Principles and Practice of Radiotherapy Techniques in Thoracic MalignanciesRadiochemotherapy and fractionation in locally advanced non-small-cell lung cancer
2016, Principles and Practice of Radiotherapy Techniques in Thoracic MalignanciesLung cancer: Elective nodal irradiation
2012, Turk Onkoloji Dergisi
This work was supported by a UICC International Cancer Technology Transfer (ICR/07/043/2007) fellowship.
Conflict of interest: none.