A prospective longitudinal assessment of MRI signal intensity kinetics of non-target muscles in patients with advanced stage oropharyngeal cancer in relationship to radiotherapy dose and post-treatment radiation-associated dysphagia: Preliminary findings from a randomized trial

Advances in and applications of imaging and radiomics in head and neck cancer survivorship

PURPOSE OF REVIEW

Radiological imaging is an essential component of head/neck cancer (HNC) care. Advances in imaging modalities (including CT, PET, MRI and ultrasound) and analysis have enhanced our understanding of tumour characteristics and prognosis. However, the application of these methods to evaluate treatment-related toxicities and functional burden is still emerging. This review showcases recent literature applying advanced imaging and radiomics to the assessment and management of sequelae following chemoradiotherapy for HNC.

RECENT FINDINGS

Whilst primarily early-stage/exploratory studies, recent investigations have showcased the feasibility of using radiological imaging, particularly advanced/functional MRI (including diffusion-weighted and dynamic contrast-enhanced MRI), to quantify treatment-induced tissue change in the head/neck musculature, and the clinical manifestation of lymphoedema/fibrosis and dysphagia. Advanced feature analysis and radiomic studies have also begun to give specific focus to the prediction of functional endpoints, including dysphagia, trismus and fibrosis.

SUMMARY

There is demonstrated potential in the use of novel imaging techniques, to help better understand pathophysiology, and improve assessment and treatment of functional deficits following HNC treatment. As larger studies emerge, technologies continue to progress, and pathways to clinical translation are honed, the application of these methods offers an exciting opportunity to transform clinical practices and improve outcomes for HNC survivors.

Volumetric Assessment of the Anterior Digastric Muscles: A Deeper Understanding of the Volumetric Changes With Aging

BACKGROUND

Targeting the deeper, subplatysmal structures in the neck has recently grown in popularity. In particular, interventions targeting the "bulky" anterior digastric (AD) muscle have been described with excellent results. However, much remains to be understood about the deep anatomy of the neck and the age-associated changes of the AD.

OBJECTIVES

The aim of this study was to examine the relationship between AD volume and age.

METHODS

This retrospective study calculated the AD volume from MRI segmentation in subjects between the ages of 20 to 92 years, scans of whom had previously been recorded. Those with compromised imaging due to pathology or artifact were excluded. Subjects were divided into 4 age-defined cohorts for clinical applicability.

RESULTS

This study included 129 patients (male n = 64) with a mean age of 52.3. The AD volume of the reference group was 3.2 cm3. A linear decrease in muscle volume was observed with age compared with the reference group: 2.95 cm3 in the 45- to 54-year-old cohort (P = 0.3), 2.7 cm3 in the 55- to 64-year-old cohort (P = 0.05), and 2.45 cm3 in the >65-year-old cohort (P < 0.001). Male sex (P = 0.0001) and laterality (P = 0.003) were associated with significantly larger volumes. Overweight and obese BMI classification was not associated with a significantly different volume than normal or underweight subjects (P = 0.067).

CONCLUSIONS

The study findings suggest an age-associated reduction in AD volume. Gender and laterality significantly affected volume, whereas BMI did not. Although the results do not support the theory of muscular hypertrophy with aging, they reveal that the perceived bulkiness may be due to changes in the surrounding anatomy affecting the morphology of the AD and subsequent blunting of the cervicomental angle.

MR-Guided Adaptive Radiotherapy for OAR Sparing in Head and Neck Cancers

Simple Summary

Normal tissue toxicities in head and neck cancer persist as a cause of decreased quality of life and are associated with poorer treatment outcomes. The aim of this article is to review organ at risk (OAR) sparing approaches available in MR-guided adaptive radiotherapy and present future developments which hope to improve treatment outcomes. Increasing the spatial conformity of dose distributions in radiotherapy is an important first step in reducing normal tissue toxicities, and MR-guided treatment devices presents a new opportunity to use biological information to drive treatment decisions on a personalized basis.

Abstract

MR-linac devices offer the potential for advancements in radiotherapy (RT) treatment of head and neck cancer (HNC) by using daily MR imaging performed at the time and setup of treatment delivery. This article aims to present a review of current adaptive RT (ART) methods on MR-Linac devices directed towards the sparing of organs at risk (OAR) and a view of future adaptive techniques seeking to improve the therapeutic ratio. This ratio expresses the relationship between the probability of tumor control and the probability of normal tissue damage and is thus an important conceptual metric of success in the sparing of OARs. Increasing spatial conformity of dose distributions to target volume and OARs is an initial step in achieving therapeutic improvements, followed by the use of imaging and clinical biomarkers to inform the clinical decision-making process in an ART paradigm. Pre-clinical and clinical findings support the incorporation of biomarkers into ART protocols and investment into further research to explore imaging biomarkers by taking advantage of the daily MR imaging workflow. A coherent understanding of this road map for RT in HNC is critical for directing future research efforts related to sparing OARs using image-guided radiotherapy (IGRT).

An Investigation of the Mechanisms of Radiation-Induced Muscle Injury in a Tree Shrew (Tupaia belangeri) Model

Background

Animal models suitable for investigating mechanisms behind radiation-induced muscle injury are lacking. We developed a tree shrew model of such injury and investigated pathological changes and mechanisms.

Methods

Animals were divided into control (n = 5), radiation-induced acute injury (n = 5), and radiation-induced chronic injury (n = 5) groups. Tensor veli palatini (TVP) muscles of acute injury and chronic injury groups were dissected under a microscope at 1 and 24 weeks after radiation therapy, respectively. TVP muscles were stained with HE and Masson to visualize pathological changes. ELISA was performed to measure oxidative injury. RT-qPCR and immunohistochemical staining was performed to measure expression levels of miR-206 and histone deacetylase 4 (HDAC4).

Results

Compared to the control group, acute injury group showed a significant decrease in miR-206 expression (.061 ± .38, P < .05) and a significant increase in HDAC4 expression (37.05 ± 20.68, P < .05). Chronic injury group showed a significant decrease in miR-206 expression (.23 ± .19, P < .05) and a significant increase in HDAC4 expression (9.66 ± 6.12, P < .05).

Discussion

A tree shrew model of radiation-induced muscle injury was established by exposing TVP muscle region to radiation of 20-Gy. Experimental results indicated that injury caused by radiation persisted despite gradual healing of the TVP muscle and miR-206 regulatory pathway plays a key role in regulating radiation-induced muscle injury.

Intensity standardization methods in magnetic resonance imaging of head and neck cancer

Background and Purpose

Conventional magnetic resonance imaging (MRI) poses challenges in quantitative analysis because voxel intensity values lack physical meaning. While intensity standardization methods exist, their effects on head and neck MRI have not been investigated. We developed a workflow based on healthy tissue region of interest (ROI) analysis to determine intensity consistency within a patient cohort. Through this workflow, we systematically evaluated intensity standardization methods for MRI of head and neck cancer (HNC) patients.

Materials and Methods

Two HNC cohorts (30 patients total) were retrospectively analyzed. One cohort was imaged with heterogenous acquisition parameters (HET cohort), whereas the other was imaged with homogenous acquisition parameters (HOM cohort). The standard deviation of cohort-level normalized mean intensity (SD NMI_c), a metric of intensity consistency, was calculated across ROIs to determine the effect of five intensity standardization methods on T2-weighted images. For each cohort, a Friedman test followed by a post-hoc Bonferroni-corrected Wilcoxon signed-rank test was conducted to compare SD NMI_c among methods.

Results

Consistency (SD NMI_c across ROIs) between unstandardized images was substantially more impaired in the HET cohort (0.29 ± 0.08) than in the HOM cohort (0.15 ± 0.03). Consequently, corrected p-values for intensity standardization methods with lower SD NMI_c compared to unstandardized images were significant in the HET cohort (p < 0.05) but not significant in the HOM cohort (p > 0.05). In both cohorts, differences between methods were often minimal and nonsignificant.

Conclusions

Our findings stress the importance of intensity standardization, either through the utilization of uniform acquisition parameters or specific intensity standardization methods, and the need for testing intensity consistency before performing quantitative analysis of HNC MRI.

Advances in Imaging for HPV-Related Oropharyngeal Cancer: Applications to Radiation Oncology

While there has been an overall decline of tobacco and alcohol-related head and neck cancer in recent decades, there has been an increased incidence of HPV-associated oropharyngeal cancer (OPC). Recent research studies and clinical trials have revealed that the cancer biology and clinical progression of HPV-positive OPC is unique relative to its HPV-negative counterparts. HPV-positive OPC is associated with higher rates of disease control following definitive treatment when compared to HPV-negative OPC. Thus, these conditions should be considered unique diseases with regards to treatment strategies and survival. In order to sufficiently characterize HPV-positive OPC and guide treatment strategies, there has been a considerable effort to diagnose, prognose, and track the treatment response of HPV-associated OPC through advanced imaging research. Furthermore, HPV-positive OPC patients are prime candidates for radiation de-escalation protocols, which will ideally reduce toxicities associated with radiation therapy and has prompted additional imaging research to detect radiation-induced changes in organs at risk. This manuscript reviews the various imaging modalities and current strategies for tackling these challenges as well as provides commentary on the potential successes and suggested improvements for the optimal treatment of these tumors.

18FDG positron emission tomography mining for metabolic imaging biomarkers of radiation-induced xerostomia in patients with oropharyngeal cancer

Purpose

Head and neck cancers radiotherapy (RT) is associated with inevitable injury to parotid glands and subsequent xerostomia. We investigated the utility of SUV derived from ¹⁸FDG-PET to develop metabolic imaging biomarkers (MIBs) of RT-related parotid injury.

Methods

Data for oropharyngeal cancer (OPC) patients treated with RT at our institution between 2005 and 2015 with available planning computed tomography (CT), dose grid, pre- & first post-RT ¹⁸FDG-PET-CT scans, and physician-reported xerostomia assessment at 3-6 months post-RT (Xero 3-6 ms) per CTCAE, was retrieved, following an IRB approval. A CT-CT deformable image co-registration followed by voxel-by-voxel resampling of pre & post-RT ¹⁸FDG activity and dose grid were performed. Ipsilateral (Ipsi) and contralateral (contra) parotid glands were sub-segmented based on the received dose in 5 Gy increments, i.e. 0-5 Gy, 5-10 Gy sub-volumes, etc. Median and dose-weighted SUV were extracted from whole parotid volumes and sub-volumes on pre- & post-RT PET scans, using in-house code that runs on MATLAB. Wilcoxon signed-rank and Kruskal-Wallis tests were used to test differences pre- and post-RT.

Results

432 parotid glands, belonging to 108 OPC patients treated with RT, were sub-segmented & analyzed. Xero 3-6 ms was reported as: non-severe (78.7%) and severe (21.3%). SUV- median values were significantly reduced post-RT, irrespective of laterality (p = 0.02). A similar pattern was observed in parotid sub-volumes, especially ipsi parotid gland sub-volumes receiving doses 10-50 Gy (p < 0.05). Kruskal-Wallis test showed a significantly higher mean RT dose in the contra parotid in the patients with more severe Xero 3-6mo (p = 0.03). Multiple logistic regression showed a combined clinical-dosimetric-metabolic imaging model could predict the severity of Xero 3-6mo; AUC = 0.78 (95%CI: 0.66-0.85; p < 0.0001).

Conclusion

We sought to quantify pre- and post-RT ¹⁸FDG-PET metrics of parotid glands in patients with OPC. Temporal dynamics of PET-derived metrics can potentially serve as MIBs of RT-related xerostomia in concert with clinical and dosimetric variables.

Progressive muscle loss is an independent predictor for survival in locally advanced oral cavity cancer: A longitudinal study

BACKGROUND AND PURPOSE

To investigate the association between progressive muscle loss and survival outcomes of patients with advanced-stage oral squamous cell carcinoma (OSCC) undergoing surgery and adjuvant (chemo)radiotherapy.

METHODS

We analyzed the computed tomography (CT) scans of 155 patients with stage III-IVB OSCC at baseline, at simulation CT for radiotherapy, and at 3- and 9-months post-treatment. Skeletal muscle index (SMI) was measured using CT at the C3 vertebral level. The predictors of overall survival (OS) and recurrence-free survival (RFS) were evaluated using Cox regression models.

RESULTS

The median follow-up period was 75.0 months. Fifty-one patients (32.9%) developed recurrence, with the median time from the fourth CT to recurrence being 9.1 months. The SMI progressively decreased from baseline to simulation CT by 1.1% (p = 0.006), to 3 months post-treatment by 5.1% (p < 0.001), and to 9 months post-treatment by 15.6% (p < 0.001) in patients developing recurrence. Patients without recurrence lost SMI at the simulation CT by 0.7% (p = 0.001) and at 3 months post-treatment by 2.1% (p < 0.001); their SMI returned to the baseline level at 9 months post-treatment. SMI changes were weakly correlated with changes in body mass index (BMI) (Spearman ρ, 0.13; p = 0.11). In multivariate analysis, SMI changes (per 5% decrease) were independently associated with significantly worse OS (hazard ratio: 1.88, 95% confidence interval: 1.58-2.23; p < 0.001) and RFS (hazard ratio: 1.89, 95% confidence interval: 1.61-2.20; p < 0.001).

CONCLUSION

Progressive muscle loss was independently associated with worse survival outcomes in patients with stage III-IVB OSCC. Muscle loss might not be detected by changes in BMI.

Early MRI Blood Volume Changes in Constrictor Muscles Correlate With Postradiation Dysphagia

PURPOSE

Predicting individual patient sensitivity to radiation therapy (RT) for tumor control or normal tissue toxicity is necessary to individualize treatment planning. In head and neck cancer, radiation doses are limited by many nearby critical structures, including structures involved in swallowing. Previous efforts showed that imaging parameters correlate with RT dose; here, we investigate the role of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) blood volume (BV) changes in predicting dysphagia.

METHODS AND MATERIALS

This study included 32 patients with locally advanced oropharyngeal squamous cell carcinoma treated with definitive chemoradiation on an institutional protocol incorporating baseline and early midtreatment DCE-MRI. BV maps of the pharyngeal constrictor muscles (PCM) were created, and BV increases midtreatment were correlated with the following parameters at 3 and 12 months post-RT: RT dose, Dynamic Imaging Grade of Swallowing Toxicity swallow score, aspiration frequency, European Organisation for Research and Treatment of Cancer HN35 patient-reported outcomes, physician-reported dysphagia, and feeding tube (FT) dependence.

RESULTS

The mean BV to the PCMs increased from baseline to fraction 10, which was significant for the superior PCM (P = .006) and middle PCM (P < .001), with a trend in the inferior PCM where lower mean doses were seen (P = .077). The factors associated with FT dependence at 3 months included BV increases in the total PCM (correlation, 0.48; P = .006) and middle PCM (correlation, 0.50; P = .004). A post-RT increase in aspiration was associated with a BV increase in the superior PCM (correlation, 0.44; P = .013),and the increase in the total PCMs was marginally significant (correlation, 0.34; P = .06). The best-performing models of FT dependence (area under the receiver operating curve [AUC] = 0.84) and aspiration increases (AUC = 0.78) included BV increases as well as a mean RT dose to middle PCM.

CONCLUSIONS

Our results suggest that midtreatment BV increases derived from DCE-MRI are an early predictor of dysphagia. Further investigation of these promising imaging markers to assess individual patient sensitivity to treatment and the patient's subsequent risk of toxicities is warranted to improve personalization of RT planning.

The Changes in Pharyngeal Constrictor Muscles Related to Head and Neck Radiotherapy: A Systematic Review

It is well known that radiation damage of the pharyngeal constrictor muscles, the glottic larynx, and the supraglottic larynx may lead to dysphagia, an unwanted effect of head and neck radiotherapy. The reduction of radiotherapy-induced dysphagia might be achieved by adaptive radiotherapy. Although the number of studies concerning adaptive radiotherapy of head and neck cancer is continuously increasing, there are only a few studies concerning changes in dysphagia-related structures during radiotherapy.The goal of this review is to summarize the current knowledge about volumetric, dosimetric, and other changes of the pharyngeal constrictor muscles associated with head and neck radiotherapy. A literature search was performed in the MEDLINE database according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The conclusions of 8 studies that passed the criteria indicate a significant increase in the volume and the thickness of the pharyngeal constrictor muscles during radiotherapy. Moreover, the changes in magnetic resonance imaging signal intensity of the pharyngeal constrictor muscles correlate with the absorbed dose (typically higher than 50 Gy) and also with the grade of dysphagia. This systematic review presents 2 variables, which are suitable for estimation of radiotherapy-related pharyngeal constrictor muscles changes-magnetic resonance imaging signal intensity and the thickness. In the case of the thickness, there is no consensus in the level of the measurement-C2 vertebra, C3 vertebra, and the middle of the craniocaudal axis are used. It seems that reference to a position associated with a vertebral body could be more reproducible and beneficial for future research. Although late pharyngeal toxicity remains a challenge in head and neck cancer treatment, better knowledge of radiotherapy-related changes in the pharyngeal constrictor muscles contributes to adaptive radiotherapy development and thus improves the treatment results.

Repetitive MRI of organs at risk in head and neck cancer patients undergoing radiotherapy

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First review on MRI changes in head and neck organs at risk during radiotherapy.

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Focus on dynamics in salivary gland, muscle and bone in the head and neck region.

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Pointing out the limitations in implementing MRI in guiding radiation therapy.

With emerging technical advances like real-time MR imaging during radiotherapy (RT) with an integrated MR linear accelerator, it will soon be possible to analyze changes in the organs at risk (OARs) during radiotherapy without additional effort for the patients. Until then, patients have to undergo additional MR imaging and often without the same immobilization devices as used for radiotherapy. Consequently, studies with repetitive MRI during the course of radiotherapy are rare, with low patient numbers and with the challenge of registration between the different MR sequences and the varying imaging time points.

This review focuses on studies with at least two MRIs, one before and another either during or post-RT, in order to report on RT-induced changes in normal tissues and their correlation with toxicity. We therefore included clinical studies published in English until March 2019, with repetitive MRI of OARs in head and neck cancer patients receiving external beam radiotherapy. OARs analyzed were salivary glands, musculoskeletal structures and bones. MR sequences used included T1, T2, dynamic contrast enhanced (DCE) imaging, diffusion-weighted imaging (DWI), DIXON and MR sialography.