Abstract

BackgroundThe 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 MethodsTwenty-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).ResultsA 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.ConclusionsRIR 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13014-016-0678-7) contains supplementary material, which is available to authorized users.

Highlights

  • 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)

  • Using deformable image registration (DIR), recurrences were assigned to more central target volumes (TVs) compared to registration techniques (RIR) as detected using the spatial centroid-based method (p = 0.0002). recurrence gross tumor volume (rGTV) mapped using DIR had statistically significant higher mean doses when compared to rGTVs mapped rigidly

  • 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

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Summary

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). Several previous efforts have addressed the importance of studying the patterns of failure after IMRT treatment of HNCs, [2, 4, 9,10,11,12,13] with most reporting failures as “infield”, “marginal” or “outfield” based on the percentage of overlap between the failure volume and the respective TV on the treatment planning CT (pCT) [4, 9, 10, 12, 13]. Emerging data demonstrate the superiority of deformable image registration (DIR) compared to RIR in registering pCT to on-treatment CT or conebeam CT in the setting of image guided radiotherapy (IGRT) for HNCs [15,16,17]. 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

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