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MO23 - Radiotherapy II: Lung Toxicity, Target Definition and Quality Assurance (ID 107)
- Event: WCLC 2013
- Type: Mini Oral Abstract Session
- Track: Radiation Oncology + Radiotherapy
- Presentations: 1
MO23.10 - Addition of EBUS-mapping of the mediastinum to PET/CT based selective nodal irradiation in NSCLC decreases geographical miss and nodal GTV volume (ID 2841)
10:30 - 12:00 | Author(s): S.T.H. Peeters
FDG-PET/CT based selective lymph node (LN) irradiation is the standard when using 3D-conformal techniques (3D-CRT) for locally advanced NSCLC. With 3D-CRT, adjacent LN not included in the target volume still receive a substantial radiation dose. With current new techniques (IMRT/VMAT), the radiation dose to non-involved LN decreases, which raises the question whether selective nodal irradiation based on PET/CT is still safe. We therefore evaluated the impact of adding EBUS-TBNA (endobronchial ultrasound guided transbronchial needle aspiration)-mapping of the mediastinal LN to PET/CT in avoiding geographical miss, and on the size of nodal GTV (gross tumor volume).
Consecutive NSCLC-patients referred for radiotherapy (RT) in 2012 who underwent EBUS-TBNA were included. False negative (FN) LN for different constellations of PET, CT and EBUS-TBNA based on literature data were calculated, to evaluate the safety of excluding LNs based on CT, PET and EBUS findings. A practical algorithm when to include LN in the GTV was made, and tested on our patients. Results are expressed as mean +/- SD and range.
Twenty-five consecutive patients with a full EBUS-TBNA mapping before RT were included: 11 women, 14 men; 17 adenocarcinoma, 8 squamous cell carcinoma; 14 right-sided and 11 left-sided tumors. Mean age: 62.5 +/- 9.7 years. All patients had stage III-disease based on PET-CT. LN stations 1,2R,2L,3,4R,4L,5,6,7,8,9,10-11L,10-11R were analyzed on CT- and PET-scan (=325 LN). Sixty-seven were enlarged (≥10mm), of which 63 were PET-positive. Twelve normal-sized LNs were PET-positive. Fifty LNs were investigated with EBUS-TBNA (mean: 2/patient +/-0.96;1-5): 28 were malignant, 22 normal. EBUS-TBNA detected 1 cancer-containing normal-sized LN without FDG-uptake, thus 1/25 geographical miss (4%). The cancer prevalence, taking into account the FN rate of EBUS of 20%, was calculated (Fig.1). With addition of EBUS, in PET-negative patients FN decreases with 10% for enlarged LN, and with 5% for normal-sized LN. An algorithm when to include a LN in the GTV is proposed (Fig.1). According to this algorithm, in our population 3/79 (4%) enlarged or PET-positive LN would be excluded from the GTV. At patient level, this was a GTV decrease in 3 (12%) patients.
When incidental nodal irradiation is low such as in IMRT or VMAT, EBUS-TBNA should be added to FDG-PET/CT for mediastinal staging. This avoids geographical miss in 4% of patients, and decreases the radiation volume in 12% of patients. A practical algorithm is proposed.
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