PET/CT of breast cancer regional nodal recurrences: an evaluation of contouring atlases

Abstract

Background: To validate the Radiation Therapy Oncology Group (RTOG) and European Society for Radiotherapy and Oncology (ESTRO) breast cancer nodal clinical target volumes (CTVs) and to investigate the Radiotherapy Comparative Effectiveness Consortium (RADCOMP) Posterior Neck volume in relation to regional nodal recurrences (RNR). Methods: From a population-based database, 69 patients were identified who developed RNR after curative treatment for breast cancer. RNRs were detected with 18-fluorodeoxyglucose-positron emission tomographycomputed tomography (PET/CT). All patients were treatment-naïve for RNR when imaged. The RTOG and ESTRO nodal CTVs and RADCOMP Posterior Neck volumes were contoured onto a template patient's CT. RNRs were contoured on each PET/CT and deformed onto the template patient's CT. Each RNR was represented by a 5 mm diameter epicentre, and categorized as 'inside', 'marginal' or 'outside' the CTV boundaries. Results: Sixty-nine patients with 226 nodes (median 2, range 1-11) were eligible for inclusion. Thirty patients had received adjuvant tangent and regional nodal radiotherapy, 16 tangent-only radiotherapy and 23 no adjuvant radiotherapy. For the RTOG CTVs, the RNR epicentres were 70% (158/226) inside, 4% (8/226) marginal and 27% (60/ 226) outside. They included the full extent of the RNR epicentres in 38% (26/69) of patients. Addition of the RADCOMP Posterior Neck volume increased complete RNR coverage to 48% (33/69) of patients. For the ESTRO CTVs, the RNR epicentres were 73% (165/226) inside, 2% (4/226) marginal and 25% (57/226) outside. They included the full extent of the RNR epicentres in 57% (39/69) of patients. Addition of the RADCOMP Posterior Neck volume increased complete RNR coverage to 70% (48/69) of patients. Conclusions: The RTOG and ESTRO breast cancer nodal CTVs do not fully cover all potential areas of RNR, but the ESTRO nodal CTVs provided full coverage of all RNR epicentres in 19% more patients than the RTOG nodal CTVs. With addition of the RADCOMP Posterior Neck volume to the ESTRO CTVs, 70% of patients had full coverage of all RNR epicentres.

Evaluation of apical clips placed during axillary dissection demonstrates potential under‐coverage of axillary radiation therapy target volumes during breast cancer regional nodal irradiation

“…3 Mapping patterns of regional recurrences using PET and MRI against consensus contouring guidelines has been attempted. [26][27][28][29] Axillary level I to III recurrences accounted for 74.3% of all regional nodal recurrences in one analysis 27 and 60% of all regional nodal recurrences in another analysis in which half of the cohort received adjuvant nodal irradiation. 26 It is uncertain to date whether potential under-coverage of axillary nodal tissue as identified in our study has contributed towards established patterns of relapse.…”

Tricks and tips for target volume definition and delineation in breast cancer: Lessons learned from ESTRO breast courses

“…The differences in level 2 recurrences were more significant between the atlases, favouring the ESTRO CTVn_level 2 with 78% of the recurrences within its volumes compared to only 68% within the RTOG volumes [8]. Other studies have also compared recurrence patterns in relation to the ESTRO versus RTOG volumes [8,11,26,32] but these studies can be misleading: some studies compared the volumes of primary presentation of disease, some did not indicate the primary stage of disease or treatment (extent of surgery, systemic therapy, radiation volumes) and included relapse-only cases and others used deformable registration to reproduce the site of recurrence which may lead to a false evaluation [8,11,26,32].…”

“…It is unclear if these only occurred with locally advanced disease. However, the location of recurrences within RTOG and outside ESTRO CTVn_level 1 was not demonstrated [8].…”

“…Studies focusing on regional relapse patterns demonstrated that, in pT1-2 pN0-1 breast cancer patients, only 4% of regional recurrences were situated outside ESTRO and inside RTOG defined lymph nodes CTVs and up to 28% out of field recurrences occurred in patients with pT3-pT4 or pN2-N3 disease [11]. Additionally, even though ESTRO CTVn_level 1 is significantly smaller than RTOG level 1 volume, 87% of the recurrences were within ESTRO volumes compared to 91% of the recurrences within those defined by RTOG [8]. It is unclear if these only occurred with locally advanced disease.…”

“…Disease stage, tumour location, extent of lymph node involvement, pre-treatment imaging, pathology including molecular characteristics, muscle invasion, distance to skin or thoracic wall, extent of lymphovascular invasion, surgical margins, extent of surgery and response to therapy all have implications for defining the target volumes for regional nodal irradiation [7,8].…”