Head and Neck Cancer Adaptive Radiation Therapy (ART): Conceptual Considerations for the Informed Clinician

Abstract

For nearly two decades, adaptive radiation therapy (ART) has been proposed as a method to account for changes in head and neck tumor and normal tissue to enhance therapeutic ratios. While technical advances in imaging, planning and delivery have allowed greater capacity for ART delivery, and a series of dosimetric explorations have consistently shown capacity for improvement, there remains a paucity of clinical trials demonstrating the utility of ART. Furthermore, while ad hoc implementation of head and neck ART is reported, systematic full-scale head and neck ART remains an as yet unreached reality. To some degree, this lack of scalability may be related to not only the complexity of ART, but also variability in the nomenclature and descriptions of what is encompassed by ART. Consequently, we present an overview of the history, current status, and recommendations for the future of ART, with an eye towards improving the clarity and description of head and neck ART for interested clinicians, noting practical considerations for implementation of an ART program or clinical trial. Process level considerations for ART are noted, reminding the reader that, paraphrasing Elbert Hubbard, "Art is not a thing, it is a way." "When an artist uses a conceptual form of art, it means that all of the planning and decisions are made beforehand and the execution is a perfunctory affair. The idea becomes a machine that makes the art."-Sol LeWitt (1) The concept of "adaptive radiation therapy" (ART) has been widely praised, serially modeled in silico, and heavily discussed, but to date, at a practical level, remains rarely implemented in vivo outside the research setting. We aim to discuss the "state of the ART" in head and neck therapy, with an emphasis on specification of the intent with which ART is performed; the terms of ART used, or a disambiguation of the nomenclature; technical

Analysis of skin dose distribution for the prediction of severe radiation dermatitis in head and neck squamous cell carcinoma patients treated with concurrent chemo‐radiotherapy

“…Notwithstanding the refinement of IMRT techniques in planning optimization, on the whole no specific constraints for the skin are available in the clinic, nor are indications on how to contour it in the irradiated area, nor are suggestions on how much should the PTV be cropped off the patient's external surface. In addition, no high‐level evidence mandates the need of adaptive replanning on a routine basis in case of weight loss or tumor shrinkage, events that frequently occur in patients undergoing chemo‐radiation for HNSCC. However, in these cases the risk of relative skin overdosage should be closely monitored: A pilot prospective study on 20 patients demonstrated that by adapting the dose distribution with a new plan from the fourth week of radiation the skin surface receiving >50 Gy could be significantly reduced.…”

A review of Image Guided Radiation Therapy in head and neck cancer from 2009–2019 – Best Practice Recommendations for RTTs in the Clinic

“…Adaptive Radiation Therapy is becoming more prevalent in RT practice, and is inherently reliant upon departmental IGRT protocols. A comprehensive discussion of ART is beyond the scope of this paper but has been well-covered by recent reviews [107,108]. The growing body of ART literature does however provide an insight into when volumetric changes are likely to be detected that merit replanning during the treatment course.…”

“…In contrast to traditional 'offline' ART strategies that involve replanning between fractions, 'online' ART enables plan adaption in response to daily volumetric changes while the patient remains on the treatment couch prior to treatment delivery [112]. Though still an emerging technology with limited clinical data available, online ART is commercially available with both MR-and CBCTbased treatment platforms [107]. Such systems represent a paradigm shift from linear workflow of conventional RT for RTTs at the treatment console, merging treatment planning with established practices in online IGRT [107,108].…”

“…Though still an emerging technology with limited clinical data available, online ART is commercially available with both MR-and CBCTbased treatment platforms [107]. Such systems represent a paradigm shift from linear workflow of conventional RT for RTTs at the treatment console, merging treatment planning with established practices in online IGRT [107,108]. As such, the technological and clinical requirements for online ART are likely to supersede traditional considerations of IGRT protocol development calling for increased education and training and clear protocols in adaptive and on-line approaches and thresholds [113].…”

“Après Mois, Le Déluge”: Preparing for the Coming Data Flood in the MRI-Guided Radiotherapy Era

“…Use of magnetic resonance imaging (MRI) rather than computed tomography (CT) for radiotherapy (RT) planning can be highly desirable because MRI visualizes soft tissues with superior contrast and resolution (1), introduces unique sequences and contrast agents for delineating specific tumors and anatomic subsites (1, 2), and permits daily adaptive radiotherapy (ART) without added CT radiation dose (3–5). MRI-guided ART (MRIgART) machines have advanced from low-field (0.35 Tesla) magnets with Cobalt-60 radiation sources (6) to diagnostic-strength magnetic fields (1.5 Tesla) fully integrated with linear accelerators (7, 8) in <5 years.…”