Methodology for analysis and reporting patterns of failure in the Era of IMRT: head and neck cancer applications
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RESEARCH
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Methodology for analysis and reporting patterns of failure in the Era of IMRT: head and neck cancer applications Abdallah S. R. Mohamed1,2*, David I. Rosenthal1, Musaddiq J. Awan3, Adam S. Garden1, Esengul Kocak-Uzel1,4, Abdelaziz M. Belal2, Ahmed G. El-Gowily2, Jack Phan1, Beth M. Beadle1, G. Brandon Gunn1 and Clifton D. Fuller1,5*
Abstract Background: The aim of this study is to develop a methodology to standardize the analysis and reporting of the patterns of loco-regional failure after IMRT of head and neck cancer. Material and Methods: Twenty-one patients with evidence of local and/or regional failure following IMRT for head-and-neck cancer were retrospectively reviewed under approved IRB protocol. Manually delineated recurrent gross disease (rGTV) on the diagnostic CT documenting recurrence (rCT) was co-registered with the original planning CT (pCT) using both deformable (DIR) and rigid (RIR) image registration software. Subsequently, mapped rGTVs were compared relative to original planning target volumes (TVs) and dose using a centroid-based approaches. Failures were then classified into five types based on combined spatial and dosimetric criteria; A (central high dose), B (peripheral high dose), C (central elective dose), D (peripheral elective dose), and E (extraneous dose). Results: A total of 26 recurrences were identified. Using DIR, recurrences were assigned to more central TVs compared to RIR as detected using the spatial centroid-based method (p = 0.0002). rGTVs mapped using DIR had statistically significant higher mean doses when compared to rGTVs mapped rigidly (mean dose 70 vs. 69 Gy, p = 0. 03). According to the proposed classification 22 out of 26 failures were of type A (central high dose) as assessed by DIR method compared to 18 out of 26 for the RIR because of the tendencey of RIR to assign failures more peripherally. Conclusions: RIR tends to assigns failures more peripherally. DIR-based methods showed that the vast majority of failures originated in the high dose target volumes and received full prescribed doses suggesting biological rather than technology-related causes of failure. Validated DIR-based registration is recommended for accurate failure characterization and a novel typology-indicative taxonomy is recommended for failure reporting in the IMRT era. Keywords: Patterns of failure, IMRT, Head-and-neck cancer, Deformable image registration
Introduction Intensity-modulated radiation therapy (IMRT) is one of the most important innovations in modern radiation therapy and represents a paradigm shift in the treatment of head and neck cancers (HNCs). However, there are certain hazards that may increase the risk of loco-regional failure * Correspondence: [email protected]; [email protected] 1 Head and Neck Section, Division of Radiation Oncology, Department of Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, Box 00971515 Holcombe Blvd, Houston, TX 77030, USA Full list of author information is available at the end of the article
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