Evaluation of clinically involved lymph nodes with deformable registration in breast cancer radiotherapy

Abstract

Objectives: Modern radiotherapy (RT) techniques require careful delineation of the target. There is no particular RT contouring guideline for patients receiving NACT (neoadjuvant chemotherapy). In this study, we examined the distribution of pre-chemotherapy clinically positive nodal metastases. Methods: We explored the coverage rate of the RTOG breast contouring guideline by deformable fusion of 18-fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) scan. We retrospectively evaluated neoadjuvant chemotherapy patients. All PET-CT images were imported into the planning software. We combined the planning CT and the CT images of PET-CT with rigid and then a deformable registration. We manually contoured positive lymph nodes on the CT component of the PET-CT data set and transferred them to planning CT after fusion. We evaluated whether previously contoured lymphatic CTVs, according to the RTOG breast atlas, include GTV-LNs. Results: All breast cancer patients between October 2018- February 2021 were evaluated from the electronic database. There were 142 radiologically defined positive lymph nodes in 31 patients who were irradiated after NACT. Most LNs (70%) were in the level I axilla. Only 71.1% (n:101) of the whole lymph nodes in 10 patients were totally covered, 22.5% (n:32) partially covered and 6.4% %(n:9) totally under covered. Conclusions: The extent of regional nodal areas in the RTOG atlas may be insufficient to cover positive lymph nodes adequately. For patients with nodal involvement undergoing neoadjuvant chemotherapy, PET-CT image fusions can be helpful to be sure that positive lymph nodes are in the treatment volume. Advances in knowledge: RTOG contouring atlas may be insufficient to cover all involved lymph nodes after NACT. For patients with nodal involvement undergoing neoadjuvant chemotherapy, PET-CT image fusions may help to be sure that positive lymph nodes are in the treatment volume.

Molecular imaging as biomarker for treatment response and outcome in breast cancer

“…In this study, 32 out of 142 lymph nodes (23%) were only partially within the radiation field and 9 (6%) were totally uncovered with standard contouring according to the radiation therapy oncology group atlas with CT compared to [ 18 F]FDG-PET. 74 One study evaluating the clinical impact of [ 18 F]FDG-PET and multiparametric MRI in 18 centres in the Netherlands found that the highest impact and observer agreement for disease management was found using these imaging techniques for breast cancer compared to other cancer types, influencing disease management in 96% of all cases. 75 However, it is uncertain how (long-term) outcome such as recurrence- and complication rate is exactly affected by the addition of [ 18 F]FDG-PET, as no prospective comparative studies are available.…”

Changing Role of PET/CT in Cancer Care With a Focus on Radiotherapy

“…Integrating features and benefits from both modalities, PET/CT dual-modality imaging is consistently growing in part due to its variety of utilities, particularly in RT [9]. Specifically, PET/CT has revolutionized the identification and localization of cancerous lesions (not being able to be identified before the use of PET/CT) and has provided endless medical advances in the realms of not only cancer detection, but also improving the treatment and diagnostic accuracy, prognosis indication, and disease progression and/or response [10,11]. Delineation of tumor margins is an essential first step in the diagnosis and staging of cancerous lesions, and PET/CT has been demonstrated across various studies to improve the accuracy of margin delineation when compared to other image modalities alone [12][13][14][15].…”

“…Compared to either PET or CT alone, PET/CT has also been shown to have a high sensitivity in identifying distant metastases (Table 1) [15][16][17]. The ability to identify distant metastasis more effectively and gauge the size of a tumor using PET/CT has allowed clinicians to more effectively stage cancerous lesions and thus be able to better evaluate a patient's prognosis and devise more effective treatment plans [10,18,19]. More effective cancer staging with PET/CT can also be achieved by evaluating the extent of FDG uptake within the lesion, which varies between tumor subtypes [20][21][22].…”

“…Through previous studies, FDG-PET/CT involvement has led to substantial clinical impacts in high-risk primary breast cancer with a diagnosis from accurate detection of distant metastases and relevant incidental findings including diagnosis of synchronous diseases [ 33 ] as well as OMD. Furthermore, the RTOG atlas was found to be insufficient in adequately covering regional nodal areas such as positive lymph nodes after neoadjuvant systemic chemotherapy [ 10 ]. Given the lack of RT contouring guidelines for patients undergoing neoadjuvant systemic therapy, pre-systemic therapy- PET/CT fusion images are beneficial in contouring sites of positive lymph nodes based on the lymph node levels (axillary, internal mammary, supraclavicular) and ensuring they are in the CTV.…”