Magnetic resonance imaging of swallowing-related structures in nasopharyngeal carcinoma patients receiving IMRT: Longitudinal dose-response characterization of quantitative signal kinetics

Pharyngeal Constrictor Dose-Volume Histogram Metrics and Patient-Reported Dysphagia in Head and Neck Radiotherapy

AIMS

Head and neck radiotherapy long-term survival continues to improve and the management of long-term side-effects is moving to the forefront of patient care. Dysphagia is associated with dose to the pharyngeal constrictors and can be measured using patient-reported outcomes to evaluate its effect on quality of life. The aim of the present study was to relate pharyngeal constrictor dose-volume parameters with patient-reported outcomes to identify prognostic dose constraints.

MATERIALS AND METHODS

A 64-patient training cohort and a 24-patient testing cohort of oropharynx and nasopharynx cancer patients treated with curative-intent chemoradiotherapy were retrospectively examined. These patients completed the MD Anderson Dysphagia Inventory outcome survey at 12 months post-radiotherapy to evaluate late dysphagia: a composite score lower than 60 indicated dysphagia. The pharyngeal constrictor muscles were subdivided into four substructures: superior, middle, inferior and cricopharyngeal. Dose-volume histogram (DVH) metrics for each of the structure combinations were extracted. A decision tree classifier was run for each DVH metric to identify dose constraints optimising the accuracy and sensitivity of the cohort. A 60% accuracy threshold and feature selection method were used to ensure statistically significant DVH metrics were identified. These dose constraints were then validated on the 24-patient testing cohort.

RESULTS

Existing literature dose constraints only had two dose constraints performing above 60% accuracy and sensitivity when evaluated on our training cohort. We identified two well-performing dose constraints: the pharyngeal constrictor muscle D63% < 55 Gy and the superior-middle pharyngeal constrictor combination structure V31Gy < 100%. Both dose constraints resulted in ≥73% mean accuracy and ≥80% mean sensitivity on the training and testing patient cohorts. In addition, a pharyngeal constrictor muscle mean dose <57 Gy resulted in a mean accuracy ≥74% and mean sensitivity ≥60%.

CONCLUSION

Mid-dose pharyngeal constrictor muscle and substructure combination dose constraints should be used in the treatment planning process to reduce late patient-reported dysphagia.

The Use of MR-Guided Radiation Therapy for Head and Neck Cancer and Recommended Reporting Guidance

Although magnetic resonance imaging (MRI) has become standard diagnostic workup for head and neck malignancies and is currently recommended by most radiological societies for pharyngeal and oral carcinomas, its utilization in radiotherapy has been heterogeneous during the last decades. However, few would argue that implementing MRI for annotation of target volumes and organs at risk provides several advantages, so that implementation of the modality for this purpose is widely accepted. Today, the term MR-guidance has received a much broader meaning, including MRI for adaptive treatments, MR-gating and tracking during radiotherapy application, MR-features as biomarkers and finally MR-only workflows. First studies on treatment of head and neck cancer on commercially available dedicated hybrid-platforms (MR-linacs), with distinct common features but also differences amongst them, have also been recently reported, as well as "biological adaptation" based on evaluation of early treatment response via functional MRI-sequences such as diffusion weighted ones. Yet, all of these approaches towards head and neck treatment remain at their infancy, especially when compared to other radiotherapy indications. Moreover, the lack of standardization for reporting MR-guided radiotherapy is a major obstacle both to further progress in the field and to conduct and compare clinical trials. Goals of this article is to present and explain all different aspects of MR-guidance for radiotherapy of head and neck cancer, summarize evidence, as well as possible advantages and challenges of the method and finally provide a comprehensive reporting guidance for use in clinical routine and trials.

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).

Application of Artificial Intelligence in Radiotherapy of Nasopharyngeal Carcinoma with Magnetic Resonance Imaging

The value of automatic organ-at-risk outlining software for radiotherapy is based on artificial intelligence technology in clinical applications. The accuracy of automatic segmentation of organs at risk (OARs) in radiotherapy for nasopharyngeal carcinoma was investigated. In the automatic segmentation model which is proposed in this paper, after CT scans and manual segmentation by physicians, CT images of 147 nasopharyngeal cancer patients and their corresponding outlined OARs structures were selected and grouped into a training set (115 cases), a validation set (12 cases), and a test set (20 cases) by complete randomization. Adaptive histogram equalization is used to preprocess the CT images. End-to-end training is utilized to improve modeling efficiency and an improved network based on 3D Unet (AUnet) is implemented to introduce organ size as prior knowledge into the convolutional kernel size design to enable the network to adaptively extract features from organs of different sizes, thus improving the performance of the model. The DSC (Dice Similarity Coefficient) coefficients and Hausdorff (HD) distances of automatic and manual segmentation are compared to verify the effectiveness of the AUnet network. The mean DSC and HD of the test set were 0.86 ± 0.02 and 4.0 ± 2.0 mm, respectively. Except for optic nerve and optic cross, there was no statistical difference between AUnet and manual segmentation results (P > 0.05). With the introduction of the adaptive mechanism, AUnet can achieve automatic segmentation of the endangered organs of nasopharyngeal carcinoma based on CT images more accurately, which can substantially improve the efficiency and consistency of segmentation of doctors in clinical applications.

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.

Manual Therapy for Fibrosis-Related Late Effect Dysphagia in head and neck cancer survivors: the pilot MANTLE trial

INTRODUCTION

Late dysphagia that develops or persists years after head and neck cancer (HNC) is a disabling survivorship issue. Fibrosis is thought to stiffen connective tissues and compress peripheral nerve tracts, thereby contributing to diminished strength, flexibility, and in some cases denervation of swallowing muscles. Manual therapy (MT) is used in cancer survivors for pain and other indications, but it is unknown if increasing blood flow, flexibility and cervical range of motion (CROM) in the head and neck may improve late dysphagia.

METHODS AND ANALYSIS

Manual Therapy for Fibrosis-Related Late Effect Dysphagia (MANTLE) is a National Cancer Institute-funded prospective single-arm pilot trial evaluating the feasibility, safety and therapeutic potential of MT in patients with late dysphagia after radiotherapy (RT) for HNC. Disease-free survivors ≥2 years after curative-intent RT for HNC with at least moderate dysphagia and grade ≥2 Common Terminology Criteria for Adverse Events version 4.0 fibrosis are eligible. The target sample size is 24 participants who begin the MANTLE programme. MANTLE is delivered in 10 MT sessions over 6 weeks with an accompanying home exercise programme (HEP). Patients then transition to a 6-week post-washout period during which they complete the HEP and then return for a final post-washout evaluation. Feasibility (primary endpoint) and safety will be examined. Serial assessments include CROM, modified barium swallow studies, quantitative MRI, electromyography (optional) and patient-reported outcomes as secondary, tertiary and exploratory endpoints.

ETHICS AND DISSEMINATION

The research protocol and informed consent document was approved by the Institutional Review Board at the University of Texas MD Anderson Cancer Center. Findings will be disseminated through peer-reviewed publication that will be made publicly available on PubMed Central on acceptance for publication, in compliance with NIH public access policy.

TRIAL REGISTRATION NUMBER

NCT03612531.

Dysphagia after chemo-radiation for nasopharyngeal cancer: A scoping review

Objective

Nasopharyngeal cancer (NPC) has distinct characteristics regarding its global prevalence, initial presentation, management and patient outcomes compared to other subtypes of head and neck cancer (HNC). The mainstay of NPC treatment is chemo-radiation (C/RT) and while dysphagia is a known early and late toxicity of C/RT treatment, the nature of dysphagia post NPC treatment has had limited investigation. The objective of this review is to summarise the existing evidence regarding dysphagia following NPC to inform the future research agenda for this population. Dysphagia incidence, characteristic deficits observed across the phases of swallowing, efficacy of current dysphagia interventions, and effect on quality of life will be explored.

Data sources

Databases including MEDLINE, CINAHL, Embase, Scopus and Web of Science were included.

Methods

A scoping review was conducted according to PRISMA-ScR guidelines. Two independent reviewers screened selected full text articles.

Results

Of the initial 2495 articles found, 28 articles were included. Reports of penetration and aspiration varied widely (0%–91.6%), with high rates of silent aspiration identified in 2 studies (42%, 66%). Oral, pharyngeal and upper esophageal phase impairments were reported. Of these, upper esophageal stasis and multiple pharyngeal stage deficits were most prevalent. The pharyngeal constrictors were found to have a significant dose–effect relationship and shielding to the anterior neck field was effective to preserve swallowing function. Six treatment studies were identified with limited evidence supporting the use of neuromuscular electrical stimulation, dilatation and swallowing exercises. Quality of life was adversely affected.

Conclusions

Dysphagia is a prevalent early and late problem post NPC treatment, with impairments across all phases of the swallow. Studies on preventing dysphagia and treatment efficacy remain limited. More systematic study of the nature of dysphagia and the efficacy of treatment in this population is warranted.

Automatic registration of 2D MR cine images for swallowing motion estimation

PURPOSE

To automate the estimation of swallowing motion from 2D MR cine images using deformable registration for future applications of personalized margin reduction in head and neck radiotherapy and outcome assessment of radiation-associated dysphagia.

METHODS

Twenty-one patients with serial 2D FSPGR-MR cine scans of the head and neck conducted through the course of definitive radiotherapy for oropharyngeal cancer. Included patients had at least one cine scan before, during, or after radiotherapy, with a total of 52 cine scans. Contours of 7 swallowing related regions-of-interest (ROIs), including pharyngeal constrictor, epiglottis, base of tongue, geniohyoid, hyoid, soft palate, and larynx, were manually delineated from consecutive frames of the cine scan covering at least one swallowing cycle. We applied a modified thin-plate-spline robust-point-matching algorithm to register the point sets of each ROI automatically over frames. The deformation vector fields from the registration were then used to estimate the motion during swallowing for each ROI. Registration errors were estimated by comparing the deformed contours with the manual contours.

RESULTS

On average 22 frames of each cine scan were contoured. The registration for one cine scan (7 ROIs over 22 frames) on average took roughly 22 minutes. A number of 8018 registrations were successfully batch processed without human interaction after the contours were drawn. The average registration error for all ROIs and all patients was 0.36 mm (range: 0.06 mm- 2.06 mm). Larynx had the average largest motion in superior direction of all structures under consideration (range: 0.0 mm- 58.7 mm). Geniohyoid had the smallest overall motion of all ROIs under consideration and the superior-inferior motion was larger than the anterior-posterior motion for all ROIs.

CONCLUSION

We developed and validated a deformable registration framework to automate the estimation of swallowing motion from 2D MR cine scans.

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.

Modeling Dose Response for Late Dysphagia in Patients With Head and Neck Cancer in the Modern Era of Definitive Chemoradiation

PURPOSE

To develop personalized multivariate dose-response models for late dysphagia in patients with head and neck cancer treated in the modern era of combined chemotherapy with intensity-modulated radiation therapy.

PATIENTS AND METHODS

The analysis included 424 patients (oropharyngeal cancer [n = 295] and nasopharyngeal, hypopharyngeal, or laryngeal cancer [n = 129]) who received definitive chemoradiation between January 2004 and April 2009. The superior, middle, and inferior pharyngeal constrictor muscles were contoured. We calculated generalized equivalent uniform dose (gEUD) for each and the total constrictor muscle volume, with the volume effect parameter a varying from log10 a = -1 to +1 in steps of 0.1. We used the National Cancer Institute Common Toxicity Criteria for Adverse Events (version 3.0) to grade late dysphagia and logistic regression to evaluate the correlation of gEUD( a) with grade 2 or higher (≥ G2) and grade 3 or higher (≥ G3) late dysphagia at each value of a.

RESULTS

Median follow-up was 33.3 months (range, 6 to 69 months). There were 41 cases (10%) of ≥ G2 dysphagia and 22 cases (5%) of ≥ G3 dysphagia. Mean doses to the total constrictor ranged from 30.1 to 85.7 Gy (median, 61.2 Gy). The predicted rate of ≥ G2 dysphagia increased by approximately 3.4% per Gy at the mean dose, for which the probability of ≥ G2 dysphagia is 50%. The threshold mean total constrictor doses that limited rates of ≥ G2 and ≥ G3 dysphagia to < 5% were < 58 Gy and < 61 Gy, respectively. Other significant factors in the multivariate predictive model included disease site, mean dose to total constrictor muscle, and patient age.

CONCLUSION

Incidences of both ≥ G2 and ≥ G3 dysphagia were dependent on the mean radiation dose to the total constrictor muscle volume, disease site, and patient age. Limiting the total volume of constrictor muscle to < 58 Gy could keep the predicted rate of ≥ G2 dysphagia to < 5%.

MRI response of obturator internus muscle to carbon-ion dose in prostate cancer treatment

It is important to confirm the dose distribution and its biophysiological response in patients subjected to carbon-ion radiotherapy (CIRT) by using medical imaging methods. In this study, the correlation between the signal intensity changes of muscles observed in magnetic resonance imaging (MRI) after CIRT and planned dose distribution was evaluated. Seven patients were arbitrarily selected from among localized prostate cancer patients on whom CIRT was performed in our facilities in 2010. All subjects received the same dose of CIRT, namely, 57.6 Gy relative biological effectiveness (RBE) in 16 fractions. The following two types of images were acquired for each subject: planning computed tomography (CT) images overlaying the dose distribution of CIRT and MRI T2-weighted images (T2WI) taken 1 year after CIRT. The fusion image of the planning CT and MRI images was registered by using a treatment-planning system, and the CIRT dose distribution was compared with changes observed in the MRI of the obturator internus muscles located near the prostate. The signal changes in the axial image passing through the isocenter of the planning target volume were digitized, and a scatter diagram was created showing the relationship between the radiation dose and digitized signal changes. A strong correlation between the radiation dose and the MRI signal intensity changes was observed, and a quadratic function was found to have the best fit. However, estimating the dose distribution from the normalized MRI signal intensity is difficult at this point, owing to the wide variation. Therefore, further investigation is required.

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.

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

PURPOSE

To assess quantitative signal intensity (SI) kinetics obtained from serial MRI of swallowing muscles as a potential imaging biomarker of radiation-induced dysphagia in oropharyngeal cancer (OPC) patients receiving radiotherapy (RT).

METHODS

Patients were enrolled under an IRB approved Phase II/III randomized trial. Patients underwent serial MRIs at pre-, mid-, and post-RT. Normalized T1, T1+ contrast (T1 + C), and T2 SI for swallowing muscle volumes-of-interest (VOIs) were collected and delta SI changes (Δ) were calculated. Mid- and post-RT SI relative to baseline were assessed and correlations between radiation dose and percent change in SI were calculated. Independent samples' t-tests were used to compare the percent change of SI between patients divided into two groups based on dysphagia status post-RT.

RESULTS

Forty-six patients with stage III/IV HPV+ OPC were included in this study. Relative to baseline, mean T2 and T1 + C SIs for middle pharyngeal constrictor were both significantly higher at mid- and post-RT (p < 0.004 for all). Superior pharyngeal constrictor also showed a significant increase in T1 + C SI at mid-RT (p = 0.0004). Additional muscle VOIs showed significant changes post-RT, but not earlier at mid-RT. Both mid- and post-RT doses were significantly correlated with the percent change of normalized T2 and T1 + C SI for examined muscle VOIs (p < 0.002). Mean percent changes of normalized T2 SI at mid-RT relative to baseline for all muscle VOIs were significantly higher in patients who developed grade ≥2 dysphagia relative to patients with no/mild dysphasia (mean Δ%: 8.2% vs 1.9%; respectively, p = 0.002). However, at post-RT, these changes were only significant in T1 SI (11.2% vs -1.3%; p < 0.0001).

CONCLUSION

Signal intensity kinetics of radiation injury can be broadly correlated with the functional muscular defect. Serial MRI during the course of RT may provide an opportunity to quantitatively track muscular pathology for subclinical detection of patients at high risk to develop dysphagia.

Dose-volume correlates of mandibular osteoradionecrosis in Oropharynx cancer patients receiving intensity-modulated radiotherapy: Results from a case-matched comparison

PURPOSE

To determine dosimetric parameters associated with osteoradionecrosis (ORN) in oropharyngeal cancer (OPC) patients in the IMRT era.

MATERIAL AND METHODS

Subsequent to institutional review board approval, we identified ORN in OPC patients treated with IMRT from 2002 to 2013. 1:2 case-control matching was implemented. Mandibular dose-volume histograms (DVH) were extracted. Dosimetric parameters were compared using non-parametric stats. Recursive partitioning analysis (RPA) was done to identify DVH correlates of ORN.

RESULTS

68 ORN cases and 131 controls were matched. Median follow-up was 41months and median time to development of ORN was 16months. Mandibular mean dose was significantly higher in the ORN cohort (48.1 vs 43.6Gy, p<0.0001). However, the maximum dose was not statistically different. DVH bins from V35 to V73 were all significantly higher in the ORN cohort compared with controls (p<0.0006). Two DVH parameters were identified in RPA analysis, V43 and V58. The majority (81%) of ORN cases were observed with both V44≥42% and V58≥25%.

CONCLUSIONS

Our data demonstrate that a wide range of DVH parameters in the intermediate and high beam path were all significantly higher in ORN patients. Mandibular V44<42% and V58<25% represent reasonable DVH constraints for IMRT plan acceptability, when tumor coverage is not compromised.

A Magnetic Resonance Imaging-based approach to quantify radiation-induced normal tissue injuries applied to trismus in head and neck cancer

BACKGROUND AND PURPOSE

In this study we investigated the ability of textures from T1-weighted MRI scans post-contrast (T1w_post) to identify the critical muscle(s) for radiation-induced trismus.

MATERIALS AND METHODS

The study included ten cases (Trismus: ≥Grade 1), and ten age-sex-tumor-location-and-stage-matched controls treated with intensity-modulated radiotherapy to 70Gy@2.12Gy in 2005-2009. Trismus status and T1w_Post were conducted within one year post-radiotherapy. For the masseter, lateral and medial pterygoids, and temporalis (M/LP/MP/T), 24 textures were extracted (Grey Level Co-Occurrence (GLCM), Histogram, and Shape). Univariate logistic regression with Bootstrapping (1000 populations) was applied to compare the muscle mean dose (Dmean) and textures between cases and controls (ipsilateral muscles); candidate predictors were suggested by an average p≤0.20 across all Bootstrap populations.

RESULTS

Dmean to M/LP/MP (p=0.03/0.14/0.09), one MP/T (p=0.12/0.17), and three M (p=0.14-0.19) textures were candidate predictors. Three of these textures were GLCM- and two Histogram textures with the former being generally higher and the latter lower for cases compared to controls. The Dmean to M and MP, and Haralick Correlation (GLCM) of MP presented with the best discriminative ability (area under the receiver-operating characteristic curve: 0.85, 0.77, and 0.78), and the correlation between Dmean and this texture was weak (Spearman's rank correlation coefficient: 0.26-0.27).

CONCLUSIONS

Our exploratory study points towards an interplay between the dose to the masseter, and the medial pterygoid together with the local relationship between the mean MRI intensity relative to its variance of the medial pterygoid for radiation-induced trismus. This opens up for exploration of this interplay within the radiation-induced trismus etiology in the larger multi-institutional setting.

[Head and neck intensity-modulated radiation therapy: Normal tissues dose constraints. Pharyngeal constrictor muscles and larynx]

Radio-induced pharyngolaryngeal chronic disorders may challenge the quality of life of head and neck cancer long survivors. Many anatomic structures have been identified as potentially impaired by irradiation and responsible for laryngeal edema, dysphonia and dysphagia. Some dose constraints might be plausible such as keeping the mean dose to the pharyngeal constrictor muscles under 50 to 55Gy, the mean dose to the supra-glottic larynx under 40 to 45Gy and, if feasible, the mean dose to the glottic larynx under 20Gy. A reduction of the dose delivered to the muscles of the floor of the mouth and the cervical esophagus would be beneficial as well. Nevertheless, the publications available do not provide an extensive enough level of proof. One should consider limiting as low as possible the dose delivered to these structures without compromising the quality of irradiation of the target tumor volumes.

Big Data Analytics for Prostate Radiotherapy

Radiation therapy is a first-line treatment option for localized prostate cancer and radiation-induced normal tissue damage are often the main limiting factor for modern radiotherapy regimens. Conversely, under-dosing of target volumes in an attempt to spare adjacent healthy tissues limits the likelihood of achieving local, long-term control. Thus, the ability to generate personalized data-driven risk profiles for radiotherapy outcomes would provide valuable prognostic information to help guide both clinicians and patients alike. Big data applied to radiation oncology promises to deliver better understanding of outcomes by harvesting and integrating heterogeneous data types, including patient-specific clinical parameters, treatment-related dose-volume metrics, and biological risk factors. When taken together, such variables make up the basis for a multi-dimensional space (the "RadoncSpace") in which the presented modeling techniques search in order to identify significant predictors. Herein, we review outcome modeling and big data-mining techniques for both tumor control and radiotherapy-induced normal tissue effects. We apply many of the presented modeling approaches onto a cohort of hypofractionated prostate cancer patients taking into account different data types and a large heterogeneous mix of physical and biological parameters. Cross-validation techniques are also reviewed for the refinement of the proposed framework architecture and checking individual model performance. We conclude by considering advanced modeling techniques that borrow concepts from big data analytics, such as machine learning and artificial intelligence, before discussing the potential future impact of systems radiobiology approaches.