Imaging for Target Delineation in Head and Neck Cancer Radiotherapy
Section snippets
Background
Radiotherapy is used for a large number of head and neck cancer cases, either as a radical treatment or postoperatively. As radiotherapy is a localized treatment the extent of the primary tumor and any regional metastasis, needs to be well known, for it to be efficient. The area chosen to be irradiated is called the target. The target is subdivided, by International Commission on Radiation Units and Measurements, into gross tumor volume (GTV), the gross extent and location of the tumor
Basic requirements for imaging in head and neck radiotherapy planning
A CT scan in treatment position ie, with the patient immobilized serves as the reference model of the patient for target definition and dose planning. The CT image serves as a direct source of data for dose calculation with X-rays, but can only serve as an indirect source of information for proton radiotherapy as the stopping power of protons and hence, dose calculation, can only be estimated from the CT number. Anatomic imaging needs to be geometrically accurate since not only the presence of
MRI for target delineation in head and neck cancer
Various studies on head-and-neck cancers report large variation in target contouring, even with the use of multiple imaging modalities21,27:
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Differentiation between the tumor and the surrounding healthy tissues on imaging studies ie, soft tissue contrast (expansion/shrinkage of volume).
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Disagreement between observers on tumor extensions such as perineural spread, (more or less “independent” localization).
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Lack of delineation protocols and guidelines.
The superior soft-tissue contrast of MRI in
PET/CT for target delineation in head and neck cancer
The developments of functional and structural imaging, including hybrid positron emission tomography and computed tomography scanner (PET/CT), has led to a paradigm shift in staging, treatment, target volume definition and response evaluation of patients with head and neck cancers.36,37 The most widely used and studied radiotracer for PET/CT in patients with head and neck squamous cell carcinoma (HNSCC) is the glucose analog 18F-Fluorodeoxyglucose (2-[18F]FDG) which depicts tumor metabolism. It
Multimodality approach in GTV delineation
Until recently, CT has been the most common imaging modality to delineate the tumor in radiation oncology. However, in this era of high precision RT there is increased interest in the role of MR and/or PET/CT (or PET/MRI) in GTV delineation. The use of these newer modalities may lead to better local control and improved quality of life due to dose intensification to the GTV and lesser dose to the surrounding normal tissues. The advantages of MRI over CT include superior soft-tissue contrast and
Future developments
The need for standardization of the tumor delineation has been widely confirmed.55 Furthermore, in radiation oncology, GTV delineation is one of the most important and time-consuming processes. Implementation of an automatic GTV delineation tool, which should be fast, accurate, robust, and flexible, would be a great improvement.66 Progress may also be expected from artificial intelligence. Yang et al. developed an automated multimodality segmentation framework for automatic target delineation
Conclusion
Radiation therapy planning in head and neck cancer is a complex process that requires a close multidisciplinary collaboration in which imaging, together with the clinical information, plays a crucial part in target selection and delineation of tumor volumes.
There is no solid evidence for which modality provides the most accurate illustration of the GTV tumor extension in all head and neck cancers and no modality seems to encompass all tumor involved tissues.60 However, a combination and
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Cited by (19)
The Use of MR-Guided Radiation Therapy for Head and Neck Cancer and Recommended Reporting Guidance
2024, Seminars in Radiation OncologyEvaluation of decentralised model-based selection of head and neck cancer patients for a proton treatment study. DAHANCA 35
2024, Radiotherapy and OncologyResponse Evaluation Following Radiation Therapy With <sup>18</sup>F-FDG PET/CT: Common Variants of Radiation-Induced Changes and Potential Pitfalls
2022, Seminars in Nuclear MedicineCitation Excerpt :Defining target volumes in RT planning is a crucial step and depends on high-quality imaging for specific characterization of tumor location and extent in order to achieve highest level of accuracy. Multimodal imaging is often adopted in RT planning and tumor delineation is ideally a multi-disciplinary task with radiation oncologist, radiologist and nuclear medicine physician working in close collaboration.24 The three volumes to consider in defining the RT target volumes are gross tumor volume (GTV) including involved lymph nodes, clinical target volume (CTV), and planning target volume (PTV).25
Co-registration of radiotherapy planning and recurrence scans with different imaging modalities in head and neck cancer
2022, Physics and Imaging in Radiation OncologyCitation Excerpt :If a patient is suspected of having a loco-regional recurrence after primary RT, a scan of the suspected area is usually performed. Traditionally, this involves a CT-scan, however, in some instances, MRI is preferred due to the higher contrasts of soft tissues and thus recommended by national guidelines for certain anatomical regions in the head and neck [6]. Co-registration method of planning-CT to recurrence-CT scans have been validated with mean surface distances ranging from 1 to 3 mm for DIR and between 1 and 1.5 mm for re-delineation uncertainty [7].
Telehealth in Multidisciplinary Target Delineation for Radiotherapy During the COVID-19 Pandemic. A Review and a Case
2022, Seminars in Nuclear MedicineCitation Excerpt :Unfortunately, the process of target delineation is associated with far greater uncertainties and inter-observer variation than the other steps of radiotherapy.22 Radiation oncology requires dedicated imaging protocols for therapy planning as well as a multidisciplinary collaboration between experts in oncology and medical imaging.23, 24 In our country, radiation oncology is performed in hospital radiotherapy centers by specialists in clinical oncology, that is, oncologists without specialist level training in imaging.