Presenter(s)
E. E. Obi1, K. Scharf2, J. M. Kobeissi1, N. M. Woody1, R. W. Davis1, S. Parikh3, Q. Liu4, M. C. Ward5, D. M. Routman4, D. S. Buchberger1, and N. P. Joshi2; 1Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH, 2Rush University Medical Center, Chicago, IL, 3Wake Forest University School of Medicine, Charlotte, NC, 4Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 5Atrium Health Levine Cancer, Wake Forest School of Medicine, and Southeast Radiation Oncology Group, Charlotte, NC
Purpose/Objective(s): Surgical resection and radioactive iodine (RAI) are the primary drivers of Locoregional control (LRC) of Advanced Differentiated Thyroid Cancer (ADTC). In cases of high-risk disease post resection or for gross or unresectable disease, External beam radiotherapy (EBRT) can be considered to improve LRC. Traditionally, thyroid EBRT involved comprehensive elective nodal radiation (ENI), but this paradigm may not optimally balance toxicity and efficacy. This study investigates LRC with and without (ENI) for ADTC.
Materials/Methods: Patients with ADTC treated with definitive or post-operative RT were included from an IRB approved multi-institutional dataset. Patient radiation plans were reviewed and those where RT extended beyond the involved nodal compartment were classified as ENI. LRC and overall survival (OS) were estimated using the Kaplan-Meier method and impact of patient, tumor, and treatment factors were evaluated using Cox proportional hazards model.
Results: One-hundred eight patients (Male: n=52, 48%; Female: n=56, 52%) were included in this study. Median age was 66 years (range 27-95 years) with median follow up of 45 months. Median KPS was 80 (range 60-100). Of staged patients at diagnosis (n=92), 51 patients (55%) had stage I/II disease (dx) while 41 (45%) had stage III /IV dx. Ninety-eight patients had upfront surgery (Lobectomy n=11, 11%; Total thyroidectomy n=87, 89%). Forty-one patients (42%) had adjuvant EBRT as part of their initial course and 51 patients had EBRT at recurrence. Fifty-seven patients (53%) received RAI prior to EBRT. Indications for EBRT included gross residual disease (GRD) n=31, positive margin n=40, extranodal extension n=28, aggressive histology n=48. Median EBRT dose was 62.90 Gy [35-72 Gy] in 32 fractions (fx) [5-44 fx]. Seventy-seven patients (71%) received ENI while 31 patients (29%) did not have elective coverage. Median elective dose was 55.25 Gy [25-64 Gy]. At 3 years, overall LRC was 88% (ENI: 92.1%; No ENI: 75.6%) with no statistically significant difference between ENI and no ENI (HR 0.87, p=0.67). Among patients with no ENI, only two of the four locoregional failures were outside of the RT portal whereas among those with ENI, only one of the seven locoregional recurrences were outside of the RT portal. The 3-year OS was 77.5% with no statistically significant difference by ENI. Two patients (2%) required feeding tube placement post-EBRT and no patients required tracheostomy.
Conclusion: Modern EBRT with and without ENI was well tolerated with excellent LRC. Although ENI was associated with numerically higher 3-year LRC, the difference was not statistically significant. In the setting of multidisciplinary evaluation, focal EBRT to areas of known disease can be considered.