Head and Neck Cancer

PV QA 2 - Poster Viewing Q&A 2

MO_40_2533 - Local regional patterns of failure following postoperative IMRT for anaplastic thyroid cancer

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Local regional patterns of failure following postoperative IMRT for anaplastic thyroid cancer
A. Jethanandani1,2, M. Kamal1,3, M. E. Cabanillas1, A. S. Mohamed1, R. Ferrarotto1, M. Zafereo1, A. S. Garden1, W. H. Morrison1, H. D. Skinner1, S. J. Frank1, J. Phan1, J. Reddy1, D. I. Rosenthal1, C. D. Fuller1,4, and G. B. Gunn1; 1The University of Texas MD Anderson Cancer Center, Houston, TX, 2The University of Tennessee Health Science Center College of Medicine, Memphis, TN, 3Clinical Oncology and Nuclear Medicine Department, Ain Shams University, Cairo, Egypt, 4University of Texas Graduate School of Biomedical Sciences, Houston, TX

Purpose/Objective(s): Given the potential for local regional recurrences (LRR) in patients (pts) with anaplastic thyroid cancer (ATC) both within and outside the postoperative (PO) radiation therapy (RT) target volume (TV), and lack of a current PO-RT standard in ATC, this study was conducted to inform treatment strategies. Defining an optimal PO-IMRT approach is particularly relevant since novel neoadjuvant systemic therapy strategies are emerging that may allow for more pts with ATC to undergo surgical resection.

Materials/Methods: Medical records were retrospectively reviewed from 01/00-08/17 for ATC pts evaluated at our institution. Pts were eligible for this analysis if they had undergone macroscopically complete resection (R0 or R1), received PO-IMRT to ≥ 45 Gy at our institution, and had follow-up CT imaging available to assess for any LRR. LRRs were then segmented on diagnostic CTs demonstrating recurrence (rCTs). Separately segmented gross tumor volumes (rGTVs) were reviewed by head and neck radiation oncologists, and rCTs were then co-registered with initial treatment planning CTs (pCTs) using a validated deformable image registration methodology (VelocityAI 3.0.1). Mapped rGTVs were compared relative to original planning TVs and dose using a centroid-based approach. Failures were classified into 5 types based on established spatial and dosimetric criteria; A (central high dose), B (central elective dose), C (peripheral high dose), D (peripheral elective dose), and E (extraneous dose).

Results: 129 pts received neck RT for ATC at our institution. 19 pts received PO-IMRT ≥ 45 Gy following R0/R1 resection. 4 IMRT plans were not retrievable, and 1 pt did not have follow up CTs available. Thus, 14 pts formed the analyzable cohort. All were Caucasian; median age was 66 years; 57% were male; 71% were stage IVB; and 64% had R1 resection. Median RT dose was 63 Gy (range: 60-69.3); median dose per fraction was 2 Gy (range: 1.5-2.2); and all pts received systemic therapy. Minimum follow up for pts without LRR was 5.7 months. 4 pts (31%) developed a LRR and 13 individual rGTVs were identified (6 in 1 pt, 3 in 1 pt, and 2 pts with 2 each). Median time to LRR was 7.4 months (range: 0-13.6). Of rGTVs, 1 was local (thyroid bed) and 12 were regional (5 central compartment/paratracheal, 4 lateral neck, 2 peri-parotid, and 1 retropharyngeal). Type A was the most common failure classification (38.5%), followed by Types C (23%), D (15.4%), E (15.4%), and B (7.7%).

Conclusion: The pattern of failure identified in a third of pts who developed LRR after macroscopically complete resection and PO-IMRT suggests that multiple strategies would be needed to overcome the LRR variety observed in this cohort. Since a “radioresistant” pattern predominated (e.g. Type A-C) and given that RT dose intensification strategies would be limited due to the usual location of TVs in the lower neck, investigational strategies seek to improve upon current outcomes incorporating targeted therapy and/or immunotherapy with RT.

Author Disclosure: A. Jethanandani: None. M. Kamal: None. A.S. Mohamed: None. R. Ferrarotto: None. M. Zafereo: None. A.S. Garden: None. W.H. Morrison: Advisory Board; Regeneron. Stock; Merck, Baxter, Johnson and Johnson. Member; NCCN Nonmelanoma Skin and Merkel Cell Committees. S.J. Frank: Research Grant; C4 Imaging, ELEKTA, U19. Founder and Director; C4 Imaging. Honoraria; ELEKTA, Varian Medican Systems, Inc. Advisory Board; Varian Medican Systems, Inc. Stock; C4 Imaging. Royalty; C4 Imaging. Patent/License Fees/Copyright; C4 Imaging. Chairman; American Brachytherapy Society. Director; C4 Imaging. Director-at-large; North America Skull Base Society. J. Phan: None. D.I. Rosenthal: Advisory Board; BMS. C.D. Fuller: Research Grant; National Institutes of Health, National Science Foundation, Elekta AB. Grant funding; Elekta AB. Honoraria; Nederlandse Organisatie voor Wetenschappelijk Onde. Consultant; Elekta AB, Nederlandse Organisatie voor Wetenschappelijk Onde. Travel Expenses; Elekta AB, Nederlandse Organisatie voor Wetenschappelijk Onde. Reviewer; Radiological Society of North America. Associate Editor; Radiographics. Data Management Task Force Committee Member; MR-LinAc Consortium. Member; National Cancer Institute. Task Group Member; American Association of Physicists in Medicine. G.B. Gunn: Associate Medical Director; MD Anderson Cancer Center - Proton Therapy.

Amit Jethanandani, MPH

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