Advanced imaging applied to radiotherapy planning in head and neck cancer: a clinical review

A plan comparison study between rapid arc and conventional intensity-modulated radiation treatment plans in nasopharyngeal carcinoma patients

Introduction

Head and neck cancers are one of the common malignancies in Indian population. It's entity, nasopharyngeal carcinoma is among the aggressive malignancies with its location and spread near very critical structures. Thus requires a highly conformal radiotherapy delivery techniques.

Purpose

The aim of the study is to dosimetrically evaluate and to compare Intensity modulated radiation therapy (IMRT) plans and RAPID ARC plans for irradiation of nasopharyngeal carcinoma.

Material and Method

A retrospective study is done on 10 nasopharyngeal carcinoma patients, who were treated with Radiotherapy at ATRCTRI Bikaner. Radiotherapy was delivered by IMRT technique (Total of 70 Gy in 33 fractions). Same patients are now planned on Rapid arc technique. Dosimetric comparison is done in terms of PTV coverage, OAR dose, conformity index, homogeneity index.

Result

PTV coverage is similar with both the plans. Homogeneity index is higher for IMRT plans 0.119+/- 0.020 compared to 0.104 +/- 0.018 for Rapid arc plans (statistically significant).The Rapid arc plans achieved slightly better conformity 1.018+/-0.09, whereas 1.105+/-0.12 for IMRT plans. Rapid arc achieved better results for OAR, statistically significant for Brainstem (54.4 +/-10.4 Gy for IMRT and 49.7+/-4.2 Gy for Rapid Arc, Lens (Left lens and Right lens received 10.55+/-5.8 Gy and 9.44+/-9.08 by IMRT and 6.12+/-6.1 Gy and 5.45+/-6.05 Gy for Rapid Arc), optic nerves (Right and Left optic nerve received 34.36 and 35.01 Gy for IMRT plans and 30.06 and 30.05 Gy for Rapid Arc plans. However the gains are statistically insignificant for spinal cord and vestibulocochlear nerve. No major difference found for Right and left parotid between both the arms.

Conclusions

Rapid Arc is better technique compared to IMRT for Nasopharyngeal carcinoma treatment, that provides better dose conformity, more homogeneous coverage and OAR sparing. However study is retrospective and has lesser patients, thus requires prospective study with more number of patients along with comparison of clinical outcome.

Clinical indications and acquisition protocol for the use of dynamic contrast-enhanced MRI in head and neck cancer squamous cell carcinoma: recommendations from an expert panel

BACKGROUND

The clinical role of perfusion-weighted MRI (PWI) in head and neck squamous cell carcinoma (HNSCC) remains to be defined. The aim of this study was to provide evidence-based recommendations for the use of PWI sequence in HNSCC with regard to clinical indications and acquisition parameters.

METHODS

Public databases were searched, and selected papers evaluated applying the Oxford criteria 2011. A questionnaire was prepared including statements on clinical indications of PWI as well as its acquisition technique and submitted to selected panelists who worked in anonymity using a modified Delphi approach. Each panelist was asked to rate each statement using a 7-point Likert scale (1 = strongly disagree, 7 = strongly agree). Statements with scores equal or inferior to 5 assigned by at least two panelists were revised and re-submitted for the subsequent Delphi round to reach a final consensus.

RESULTS

Two Delphi rounds were conducted. The final questionnaire consisted of 6 statements on clinical indications of PWI and 9 statements on the acquisition technique of PWI. Four of 19 (21%) statements obtained scores equal or inferior to 5 by two panelists, all dealing with clinical indications. The Delphi process was considered concluded as reasons entered by panelists for lower scores were mainly related to the lack of robust evidence, so that no further modifications were suggested.

CONCLUSIONS

Evidence-based recommendations on the use of PWI have been provided by an independent panel of experts worldwide, encouraging a standardized use of PWI across university and research centers to produce more robust evidence.

IR-Surviving NSCLC Cells Exhibit Different Patterns of Molecular and Cellular Reactions Relating to the Multifraction Irradiation Regimen and p53-Family Proteins Expression

Simple Summary

For the first time, we demonstrated that the significant decrease in p63/p73 expression together with the absence of functional p53 could underlie an increase in the fraction of polyploid cells, transformation rates, and the glycolytic NAD(P)H production in multifraction X-ray radiation exposure (MFR)-surviving cancer cells, providing conditions for radioresistance associated with epithelial–mesenchymal transition (EMT)-like process activation. During radiation therapy (RT), the treatment dose, fractionation, and dose limits for organs at risk (OARs) do not change between patients and are still prescribed mainly based on the Tumor, Node, Metastasis (TNM) stage, performance status, and comorbidities, taking no account of the tumor biology. Our data once again emphasize that non-small cell lung cancer (NSCLC) therapy approaches should become more personalized according to RT regimen, tumor histology, and molecular status of critical proteins.

Abstract

Radiotherapy is a primary treatment modality for patients with unresectable non-small cell lung cancer (NSCLC). Tumor heterogeneity still poses the central question of cancer radioresistance, whether the presence of a particular cell population inside a tumor undergoing a selective outgrowth during radio- and chemotherapy give rise to metastasis and tumor recurrence. In this study, we examined the impact of two different multifraction X-ray radiation exposure (MFR) regimens, fraction dose escalation (FDE) in the split course and the conventional hypofractionation (HF), on the phenotypic and molecular signatures of four MFR-surviving NSCLC cell sublines derived from parental A549 (p53 wild-type) and H1299 (p53-null) cells, namely A549FR/A549HR, H1299FR/H1299HR cells. We demonstrate that sublines surviving different MFR regimens in a total dose of 60 Gy significantly diverge in their molecular traits related to irradiation regimen and p53 status. The observed changes regarding radiosensitivity, transformation, proliferation, metabolic activity, partial epithelial-to-mesenchymal transition (EMT) program activation and 1D confined migratory behavior (wound healing). For the first time, we demonstrated that MFR exposure led to the significant decrease in the expression of p63 and p73, the p53-family members, in p53null cells, which correlated with the increase in cell polyploidy. We could not find significant differences in FRA1 expression between parental cells and their sublines that survived after any MFR regimen regardless of p53 status. In our study, the FDE regimen probably causes partial EMT program activation in MFR-survived NSCLC cells through either Vimentin upregulation in p53null or an aberrant N-cadherin upregulation in p53wt cells. The HF regimen likely less influences the EMT activation irrespectively of the p53 status of MFR-survived NSCLC cells. Our data highlight that both MFR regimens caused overall higher cell transformation of p53null H1299FR and H1299HR cells than their parental H1299 cells. Moreover, our results indicate that the FDE regimen raised the radioresistance and transformation of MFR-surviving NSCLC cells irrespectively of their p53 status, though the HF regimen demonstrated a similar effect on p53null NSCLC cells only. Our data once again emphasize that NSCLC therapy approaches should become more personalized according to radiation therapy (RT) regimen, tumor histology, and molecular status of critical proteins.

Patient-Centric Head and Neck Cancer Radiation Therapy: Role of Advanced Imaging

The traditional 'one-size-fits-all' approach to H&N cancer therapy is archaic. Advanced imaging can identify radioresistant areas by using biomarkers that detect tumor hypoxia, hypercellularity etc. Highly conformal radiotherapy can target resistant areas with precision. The critical information that can be gleaned about tumor biology from these advanced imaging modalities facilitates individualized radiotherapy. The tumor imaging world is pushing its boundaries. Molecular imaging can now detect protein expression and genotypic variations across tumors that can be exploited for tailoring treatment. The exploding field of radiomics and radiogenomics extracts quantitative, biologic and genetic information and further expands the scope of personalized therapy.

Comparison of Dosimetric Gains Provided by Intensity-Modulated Radiotherapy, Volume-Modulated Arc Therapy, and Helical Tomotherapy for High-Grade Glioma

PURPOSE

Because of the poor prognosis for high-grade glioma (HGG) patients, it is important to increase the dose of the tumor to improve the efficacy while minimizing the dose of organs at risk (OARs). Thus, we evaluated the potential dosimetric gains of helical tomotherapy (HT) versus intensity-modulated radiotherapy (IMRT) or volume-modulated arc therapy (VMAT) for high-grade glioma (HGG).

METHODS

A total of 42 HGG patients were retrospectively selected who had undergone helical tomotherapy; then, IMRT and VMAT plans were generated and optimized for comparison after contouring crucial neuronal structures for neurogenesis and neurocognitive function. IMRT and VMAT were optimized with the Eclipse treatment planning system (TPS) (Version 11.0.31) and HT using TomoTherapy Hi-Art Software (Version 2.0.7) (Accuray, Madison, WI, USA). All three techniques were optimized for simultaneously delivering 60 Gy to planning target volume (PTV) 1 and 50-54 Gy to PTV2. We also analyzed the homogeneity index (HI) and conformity index (CI) of PTVs and organ at risk (OAR) sparing.

RESULTS

There was no significant difference in the PTV coverage among IMRT, VMAT, or HT. As for the HI, HT plans (PTV1 HI: 0.09 ± 0.03, PTV2 HI: 0.17 ± 0.05) had the best homogeneity when compared to IMRT plans (PTV1 HI: 0.10 ± 0.04, PTV2 HI: 0.18 ± 0.04) and VMAT plans (PTV1 HI: 0.11 ± 0.03, PTV2 HI: 0.20 ± 0.03). The CI value of HT (PTV1 CI: 0.98 ± 0.03, PTV2: 0.98 ± 0.05) was closest to the optimal value. Except for the IMRT and VMAT groups, there were statistically significant differences between the other two groups of the CI values in both PTV1 and PTV2. The other comparison values were statistically significant except for the optic nerve, and VMAT had the best sparing of the optic chiasm. The mean and max doses of OARs declined significantly in HT.

CONCLUSIONS

For high-grade glioma patients, HT had superior outcomes in terms of PTV coverage and OAR sparing as compared with IMRT/VMAT.

Dosimetric comparisons of craniospinal axis irradiation using helical tomotherapy, volume-modulated arc therapy and intensity-modulated radiotherapy for medulloblastoma

Background

To evaluate the potential dosimetric gains of helical tomotherapy (HT) versus intensity-modulated radiotherapy (IMRT) and volume-modulated arc therapy (VMAT) for craniospinal axis irradiation (CSI) of medulloblastoma.

Methods

A total of 36 treatment plans were calculated retrospectively for 12 patients with medulloblastoma receiving CSI using HT with TomoTherapy Hi-Art Software (Version 2.0.7) (Accuray, Madison, WI, USA). For each case, the other two different delivery techniques were re-planned with IMRT/VMAT optimized with Eclipse treatment planning system (TPS) (Version 11.0.31). Homogeneity index (HI) and conformity index (CI) of the planning target volume (PTV) and organs at risk (OARs) sparing were analyzed. Differences in plans were evaluated using paired-samples t-test for various dosimetric parameters.

Results

HT yielded the highest CI in all PTV coverage including PTV of gross tumor volume (PGTV) (HT: 0.7163; VMAT: 0.6688; IMRT: 0.6096), PTVbrain (HT: 0.8490; VMAT: 0.8384; IMRT: 0.7815) and PTVspine (HT: 0.5904; VMAT: 0.5862; IMRT: 0.5797). Meanwhile, HT yielded better HI in PGTV (HT: 0.0543; VMAT: 0.0759; IMRT: 0.0736), PTVbrain (HT: 0.5525; VMAT: 0.5619; IMRT: 0.5554) and PTVspine (HT: 0.0700; VMAT: 0.0782; IMRT: 0.0877). As for OARs, HT demonstrated marked superiority in critical organs including maximal/mean doses of brainstem PRV, optical chiasm and optic nerves.

Conclusions

For CSI of medulloblastoma, HT offers superior outcomes in terms of PTV conformity, PTV homogeneity and critical OAR sparing as compared with IMRT/VMAT.

Palliation of Vertebral Metastases with Radiotherapy: Exploration of Volumetric-Modulated Arc Therapy From Development to Implementation in Routine Clinical Practice

The development of volumetric-modulated arc therapy (VMAT) in radiation therapy has allowed for improved dose escalation and a decrease in radiation-induced toxicities for patients. This article will describe a single centre's experience in development and implementation of VMAT for palliation of vertebral metastases. A retrospective planning analysis of 10 cases identified that utilization of VMAT decreases overall planning time with a statistically significant improvement in target coverage when compared with the current conventional technique. PTV Dmax (P = .02), PTV V95_{19Gy (95%)} (P = .01), dose conformation (P = 1.8e-004), and the homogeneity index (P = .019) were all superior for VMAT plans with an average PTV length of 22.46 cm. Another benefit of VMAT utilization is a significant decrease in treatment delivery time, which reduced treatment times from 9.95 minutes to 2.98 minutes. Immobilization was also carefully considered, and rotational errors were measured and fell within institutional tolerances when VMAT was delivered using simple immobilization devices. Clinical implementation of this technique, utilizing a highly conformal target volume to decrease radiation-induced toxicities and minimizing the length of time patients are required to maintain their treatment positions, aims to improve the palliative radiotherapy experience for patients with painful spinal metastases.

Functional magnetic resonance imaging of head and neck cancer: Performance and potential

Functional magnetic resonance imaging (MRI) of tumors of the head and neck usually encompasses diffusion-weighted imaging (DWI) and intravenous (IV) contrast T1 dynamic perfusion imaging (DCE-MRI or PWI). Both techniques can characterize different tissues by probing into their microstructure, providing a novel approach in oncological imaging. In this pictorial review, we will cover the important technical aspects of DWI and PWI, the pathophysiological background and the current applications and potential of these functional MRI techniques in the imaging of head and neck cancer.

Impact of Neuroradiology-Based Peer Review on Head and Neck Radiotherapy Target Delineation

BACKGROUND AND PURPOSE

While standard guidelines assist in target delineation for head and neck radiation therapy planning, the complex anatomy, varying patterns of spread, unusual or advanced presentations, and high risk of treatment-related toxicities produce continuous interpretive challenges. In 2007, we instituted weekly treatment planning quality assurance rounds as a joint enterprise of head and neck radiation oncology and neuroradiology. Here we describe its impact on head and neck radiation therapy target delineation.

MATERIALS AND METHODS

For 7 months, treatment planning quality assurance included 80 cases of definitive (48%) or postoperative (52%) head and neck radiation therapy. The planning CT and associated target volumes were reviewed in comparison with diagnostic imaging studies. Alterations were catalogued.

RESULTS

Of the 80 cases, 44 (55%) were altered, and of these, 61% had clinically significant changes resulting in exclusion or inclusion of a distinct area or structure. Reasons for alteration included the following: gross or extant tumor, 26/44 (59%); elective or postoperative coverage, 25/44 (57%); lymph nodes, 13/44 (30%); bone, 7/44 (16%); skull base, 7/44 (16%); normal organs, 5/44 (11%); perineural, 3/44 (7%); distant metastasis, 2/44 (5%); and eye, 1/44 (2%). Gross tumor changes ranged from 0.5% to 133.64%, with a median change in volume of 5.95 mm³ (7.86%). Volumes were more likely to be increased (73%) than decreased (27%).

CONCLUSIONS

A collaborative approach to head and neck treatment planning quality assurance has an impact. Cases likely to have challenging patterns of infiltrative, intracranial, nodal, orbital, or perineural spread warrant intensive imaging-based review in collaboration with a diagnostic neuroradiologist.

Perspectives on making big data analytics work for oncology

Oncology, with its unique combination of clinical, physical, technological, and biological data provides an ideal case study for applying big data analytics to improve cancer treatment safety and outcomes. An oncology treatment course such as chemoradiotherapy can generate a large pool of information carrying the 5Vs hallmarks of big data. This data is comprised of a heterogeneous mixture of patient demographics, radiation/chemo dosimetry, multimodality imaging features, and biological markers generated over a treatment period that can span few days to several weeks. Efforts using commercial and in-house tools are underway to facilitate data aggregation, ontology creation, sharing, visualization and varying analytics in a secure environment. However, open questions related to proper data structure representation and effective analytics tools to support oncology decision-making need to be addressed. It is recognized that oncology data constitutes a mix of structured (tabulated) and unstructured (electronic documents) that need to be processed to facilitate searching and subsequent knowledge discovery from relational or NoSQL databases. In this context, methods based on advanced analytics and image feature extraction for oncology applications will be discussed. On the other hand, the classical p (variables)≫n (samples) inference problem of statistical learning is challenged in the Big data realm and this is particularly true for oncology applications where p-omics is witnessing exponential growth while the number of cancer incidences has generally plateaued over the past 5-years leading to a quasi-linear growth in samples per patient. Within the Big data paradigm, this kind of phenomenon may yield undesirable effects such as echo chamber anomalies, Yule-Simpson reversal paradox, or misleading ghost analytics. In this work, we will present these effects as they pertain to oncology and engage small thinking methodologies to counter these effects ranging from incorporating prior knowledge, using information-theoretic techniques to modern ensemble machine learning approaches or combination of these. We will particularly discuss the pros and cons of different approaches to improve mining of big data in oncology.

Radiotherapy planning using MRI

The use of magnetic resonance imaging (MRI) in radiotherapy (RT) planning is rapidly expanding. We review the wide range of image contrast mechanisms available to MRI and the way they are exploited for RT planning. However a number of challenges are also considered: the requirements that MR images are acquired in the RT treatment position, that they are geometrically accurate, that effects of patient motion during the scan are minimized, that tissue markers are clearly demonstrated, that an estimate of electron density can be obtained. These issues are discussed in detail, prior to the consideration of a number of specific clinical applications. This is followed by a brief discussion on the development of real-time MRI-guided RT.

Characterizing Heterogeneity within Head and Neck Lesions Using Cluster Analysis of Multi-Parametric MRI Data

PURPOSE

To describe a methodology, based on cluster analysis, to partition multi-parametric functional imaging data into groups (or clusters) of similar functional characteristics, with the aim of characterizing functional heterogeneity within head and neck tumour volumes. To evaluate the performance of the proposed approach on a set of longitudinal MRI data, analysing the evolution of the obtained sub-sets with treatment.

MATERIAL AND METHODS

The cluster analysis workflow was applied to a combination of dynamic contrast-enhanced and diffusion-weighted imaging MRI data from a cohort of squamous cell carcinoma of the head and neck patients. Cumulative distributions of voxels, containing pre and post-treatment data and including both primary tumours and lymph nodes, were partitioned into k clusters (k = 2, 3 or 4). Principal component analysis and cluster validation were employed to investigate data composition and to independently determine the optimal number of clusters. The evolution of the resulting sub-regions with induction chemotherapy treatment was assessed relative to the number of clusters.

RESULTS

The clustering algorithm was able to separate clusters which significantly reduced in voxel number following induction chemotherapy from clusters with a non-significant reduction. Partitioning with the optimal number of clusters (k = 4), determined with cluster validation, produced the best separation between reducing and non-reducing clusters.

CONCLUSION

The proposed methodology was able to identify tumour sub-regions with distinct functional properties, independently separating clusters which were affected differently by treatment. This work demonstrates that unsupervised cluster analysis, with no prior knowledge of the data, can be employed to provide a multi-parametric characterization of functional heterogeneity within tumour volumes.

Pre-Chemoradiotherapy FDG PET/CT cannot Identify Residual Metabolically-Active Volumes within Individual Esophageal Tumors

Objective

To study whether subvolumes with a high pre-chemoradiotherapy (CRT) FDG uptake could identify residual metabolically-active volumes (MAVs) post-CRT within individual esophageal tumors. Accurate identification will allow simultaneous integrated boost to these subvolumes at higher risk to improve clinical outcomes.

Methods

Twenty patients with esophageal cancer were treated with CRT plus surgery and underwent FDG PET/CT scans before and after CRT. The two scans were rigidly registered. Seven MAVs pre-CRT and four MAVs post-CRT within a tumor were defined with various SUV thresholds. The similarity and proximity between the MAVs pre-CRT and post-CRT were quantified with three metrics: fraction of post-CRT MAV included in pre-CRT MAV, volume overlap and centroid distance.

Results

Eight patients had no residual MAV. Six patients had local residual MAV (SUV ≥2.5 post-CRT) within or adjoining the original MAV (SUV ≥2.5 pre-CRT). On average, less than 65% of any post-CRT MAVs was included in any pre-CRT MAVs, with a low volume overlap <45%, and large centroid distance >8.6 mm. In general, subvolumes with higher FDG-uptake pre-CRT or post-CRT had lower volume overlap and larger centroid distance. Six patients had new distant MAVs that were determined to be inflammation from radiation therapy.

Conclusions

Pre-CRT PET/CT cannot reliably identify the residual MAVs within individual esophageal tumors. Simultaneous integrated boost to subvolumes with high FDG uptake pre-CRT may not be feasible.

Functional imaging for radiotherapy treatment planning: current status and future directions-a review

In recent years, radiotherapy (RT) has been subject to a number of technological innovations. Today, RT is extremely flexible, allowing irradiation of tumours with high doses, whilst also sparing normal tissues from doses. To make use of these additional degrees of freedom, integration of functional image information may play a key role (i) for better staging and tumour detection, (ii) for more accurate RT target volume delineation, (iii) to assess functional information about biological characteristics and individual radiation resistance and (iv) to apply personalized dose prescriptions. In this article, we discuss the current status and future directions of different clinically available functional imaging modalities; CT, MRI, positron emission tomography (PET) as well as the hybrid imaging techniques PET/CT and PET/MRI and their potential for individualized RT.

The influence of MRI scan position on patients with oropharyngeal cancer undergoing radical radiotherapy

Background

The purpose of this study was to demonstrate how magnetic resonance imaging (MRI) patient position protocols influence registration quality in patients with oropharyngeal cancer undergoing radical radiotherapy and the consequences for gross tumour volume (GTV) definition and radiotherapy planning.

Methods and materials

Twenty-two oropharyngeal patients underwent a computed tomography (CT), a diagnostic MRI (MRI_D) and an MRI in the radiotherapy position within an immobilization mask (MRI_RT). Clinicians delineated the GTV on the CT viewing the MRI_D separately (GTV_C); on the CT registered to MRI_D (GTV_D) and on the CT registered to MRI_RT (GTV_RT). Planning target volumes (PTVs) were denoted similarly. Registration quality was assessed by measuring disparity between structures in the three set-ups. Volumetric modulated arc therapy (VMAT) radiotherapy planning was performed for PTV_C, PTV_D and PTV_RT. To determine the dose received by the reference PTV_RT, we optimized for PTV_C and PTV_D while calculating the dose to PTV_RT. Statistical significance was determined using the two-tailed Mann–Whitney or two-tailed paired student t-tests.

Results

A significant improvement in registration accuracy was found between CT and MRI_RT versus the MRI_D measuring distances from the centre of structures (geometric mean error of 2.2 mm versus 6.6 mm). The mean GTV_C (44.1 cm³) was significantly larger than GTV_D (33.7 cm³, p value = 0.027) or GTV_RT (30.5 cm³, p value = 0.014). When optimizing the VMAT plans for PTV_C and investigating the mean dose to PTV_RT neither the dose to 99% (58.8%) nor 95% of the PTV (84.7%) were found to meet the required clinical dose constraints of 90% and 95% respectively. Similarly, when optimizing for PTV_D the mean dose to PTV_RT did not meet clinical dose constraints for 99% (14.9%) nor 95% of the PTV (66.2%). Only by optimizing for PTV_RT were all clinical dose constraints achieved.

Conclusions

When oropharyngeal patients MRI scans are performed in the radiotherapy position there are significant improvements in CT-MR image registration, target definition and PTV dose coverage.

Quantitative Cherenkov emission spectroscopy for tissue oxygenation assessment

Measurements of Cherenkov emission in tissue during radiation therapy are shown to enable estimation of hemoglobin oxygen saturation non-invasively, through spectral fitting of the spontaneous emissions from the treated tissue. Tissue oxygenation plays a critical role in the efficacy of radiation therapy to kill tumor tissue. Yet in-vivo measurement of this has remained elusive in routine use because of the complexity of oxygen measurement techniques. There is a spectrally broad emission of Cherenkov light that is induced during the time of irradiation, and as this travels through tissue from the point of the radiation deposition, the tissue absorption and scatter impart spectral changes. These changes can be quantified by diffuse spectral fitting of the signal. Thus Cherenkov emission spectroscopy is demonstrated for the first time quantitatively in vitro and qualitatively in vivo, and has potential for real-time online tracking of tissue oxygen during radiation therapy when fully characterized and developed.

Volumetric modulated arc therapy: a review of current literature and clinical use in practice

Volumetric modulated arc therapy (VMAT) is a novel radiation technique, which can achieve highly conformal dose distributions with improved target volume coverage and sparing of normal tissues compared with conventional radiotherapy techniques. VMAT also has the potential to offer additional advantages, such as reduced treatment delivery time compared with conventional static field intensity modulated radiotherapy (IMRT). The clinical worldwide use of VMAT is increasing significantly. Currently the majority of published data on VMAT are limited to planning and feasibility studies, although there is emerging clinical outcome data in several tumour sites. This article aims to discuss the current use of VMAT techniques in practice and review the available data from planning and clinical outcome studies in various tumour sites including prostate, pelvis (lower gastrointestinal, gynaecological), head and neck, thoracic, central nervous system, breast and other tumour sites.

DCE-MRI: a review and applications in veterinary oncology

Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) is a functional imaging technique that assesses the physiology of tumour tissue by exploiting abnormal tumour microvasculature. Advances made through DCE-MRI include improvement in the diagnosis of cancer, optimization of treatment choices, assessment of treatment efficacy and non-invasive identification of prognostic information. DCE-MRI enables quantitative assessment of tissue vessel density, integrity, and permeability, and this information can be applied to study of angiogenesis, hypoxia and the evaluation of various biomarkers. Reproducibility of DCE-MRI results is important in determining the significance of observed changes in the parameters. As improvements are made towards the utility of DCE-MRI and interpreting biologic associations, the technique will be applied more frequently in the study of cancer in animals. Given the importance of tumour perfusion with respect to tumour oxygenation and drug delivery, the use of DCE-MRI is a convenient and powerful way to gain basic information about a tumour.

¹⁸F-FDG-PET imaging in radiotherapy tumor volume delineation in treatment of head and neck cancer

PURPOSE

To determine the impact of (18)F-fluorodeoxyglucose positron emission tomography (PET) in radiotherapy target delineation and patient management for head and neck squamous cell carcinoma (HNSCC) compared to computed tomography (CT) alone.

MATERIALS AND METHODS

Twenty-nine patients with HNSCC were included. CT and PET/CT obtained for treatment planning purposes were reviewed respectively by a neuroradiologist and a nuclear medicine specialist who were blinded to the findings from each other. The attending radiation oncologist together with the neuroradiologist initially defined all gross tumor volume of the primary (GTVp) and the suspicious lymph nodes (GTVn) on CT. Subsequently, the same radiation oncologist and the nuclear medicine specialist defined the GTVp and GTVn on (18)F-FDG-PET/CT. Upon disagreement between CT and (18)F-FDG-PET on the status of a particular lymph node, an ultrasound-guided fine needle aspiration was performed. Volumes based on CT and (18)F-FDG-PET were compared with a paired Student's t-test.

RESULTS

For the primary disease, four patients had previous diagnostic tonsillectomy and therefore, FDG uptake occurred in 25 patients. For these patients, GTVp contoured on (18)F-FDG-PET (GTVp-PET) were smaller than the GTVp contoured on CT (GTVp-CT) in 80% of the cases, leading to a statistically significant volume difference (p=0.001). Of the 60 lymph nodes suspicious on PET, 55 were also detected on CT. No volume change was observed (p=0.08). Ten biopsies were performed for lymph nodes that were discordant between modalities and all were of benign histology. Distant metastases were found in two patients and one had a newly diagnosed lung adenocarcinoma.

CONCLUSIONS

GTVp-CT was significantly larger when compared to GTVp-PET. No such change was observed for the lymph nodes. (18)F-FDG-PET modified treatment management in three patients, including two for which no curative radiotherapy was attempted. Larger multicenter studies are needed to ascertain whether combined (18)F-FDG-PET/CT in target delineation can influence the main clinical outcomes.

A review of the clinical evidence for intensity-modulated radiotherapy

AIMS

Intensity-modulated radiotherapy (IMRT) is a development of three-dimensional conformal radiotherapy that offers improvements in dosimetry in many clinical scenarios. Here we review the clinical evidence for IMRT and present ongoing or unpublished randomised controlled trials (RCTs).

METHODS

We identified randomised and non-randomised comparative studies of IMRT and conventional radiotherapy using MEDLINE, hand-searching Radiotherapy and Oncology and the International Journal of Radiation Oncology, Biology and Physics and the proceedings of the American Society for Therapeutic Radiology and Oncology and the European Society for Therapeutic Radiology and Oncology annual meetings. The metaRegister of Controlled Trials was searched to identify completed-unpublished, ongoing and planned RCTs.

RESULTS

Sixty-one studies comparing IMRT and conventional radiotherapy were identified. These included three RCTs in head and neck cancer (205 patients) and three in breast cancer (664 patients) that had reported clinical outcomes; these were all powered for toxicity-related end points, which were significantly better with IMRT in each trial. There were 27 additional non-randomised studies in head and neck (1119 patients), 26 in prostate cancer (>5000 patients), four in breast cancer (875 patients) and nine in other tumour sites. The results of these studies supported those of the RCTs with benefits reported in acute and late toxicity, health-related quality of life and tumour control end points. Twenty-eight completed-unpublished, ongoing or planned RCTs incorporating IMRT were identified, including at least 12,310 patients, of which 15 compared conventional radiotherapy within IMRT as a randomisation or pre-planned stratification.

DISCUSSION

Inverse-planned IMRT maintains parotid saliva production and reduces acute and late xerostomia during radiotherapy for locally advanced head and neck cancer, reduces late rectal toxicity in prostate cancer patients allowing safe dose escalation and seems to reduce toxicity in several other tumour sites. Forward-planned IMRT reduces acute toxicity and improves late clinician-assessed cosmesis compared with conventional tangential breast radiotherapy.

Molecular PET/CT imaging-guided radiation therapy treatment planning

The role of positron emission tomography (PET) during the past decade has evolved rapidly from that of a pure research tool to a methodology of enormous clinical potential. (18)F-fluorodeoxyglucose (FDG)-PET is currently the most widely used probe in the diagnosis, staging, assessment of tumor response to treatment, and radiation therapy planning because metabolic changes generally precede the more conventionally measured parameter of change in tumor size. Data accumulated rapidly during the last decade, thus validating the efficacy of FDG imaging and many other tracers in a wide variety of malignant tumors with sensitivities and specificities often in the high 90 percentile range. As a result, PET/computed tomography (CT) had a significant impact on the management of patients because it obviated the need for further evaluation, guided further diagnostic procedures, and assisted in planning therapy for a considerable number of patients. On the other hand, the progress in radiation therapy technology has been enormous during the last two decades, now offering the possibility to plan highly conformal radiation dose distributions through the use of sophisticated beam targeting techniques such as intensity-modulated radiation therapy (IMRT) using tomotherapy, volumetric modulated arc therapy, and many other promising technologies for sculpted three-dimensional (3D) dose distribution. The foundation of molecular imaging-guided radiation therapy lies in the use of advanced imaging technology for improved definition of tumor target volumes, thus relating the absorbed dose information to image-based patient representations. This review documents technological advancements in the field concentrating on the conceptual role of molecular PET/CT imaging in radiation therapy treatment planning and related image processing issues with special emphasis on segmentation of medical images for the purpose of defining target volumes. There is still much more work to be done and many of the techniques reviewed are themselves not yet widely implemented in clinical settings.

Coregistered FDG PET/CT-based textural characterization of head and neck cancer for radiation treatment planning

Coregistered fluoro-deoxy-glucose (FDG) positron emission tomography/computed tomography (PET/CT) has shown potential to improve the accuracy of radiation targeting of head and neck cancer (HNC) when compared to the use of CT simulation alone. The objective of this study was to identify textural features useful in distinguishing tumor from normal tissue in head and neck via quantitative texture analysis of coregistered 18F-FDG PET and CT images. Abnormal and typical normal tissues were manually segmented from PET/CT images of 20 patients with HNC and 20 patients with lung cancer. Texture features including some derived from spatial grey-level dependence matrices (SGLDM) and neighborhood gray-tone-difference matrices (NGTDM) were selected for characterization of these segmented regions of interest (ROIs). Both K nearest neighbors (KNNs) and decision tree (DT)-based KNN classifiers were employed to discriminate images of abnormal and normal tissues. The area under the curve (AZ) of receiver operating characteristics (ROC) was used to evaluate the discrimination performance of features in comparison to an expert observer. The leave-one-out and bootstrap techniques were used to validate the results. The AZ of DT-based KNN classifier was 0.95. Sensitivity and specificity for normal and abnormal tissue classification were 89% and 99%, respectively. In summary, NGTDM features such as PET Coarseness, PET Contrast, and CT Coarseness extracted from FDG PET/CT images provided good discrimination performance. The clinical use of such features may lead to improvement in the accuracy of radiation targeting of HNC.

MRI-based Treatment Planning with Electron Density Information Mapped from CT Images: A Preliminary Study

Nowadays magnetic resonance imaging (MRI) has been profoundly used in radiotherapy (RT) planning to aid the contouring of targets and critical organs in brain and intracranial cases, which is attributable to its excellent soft tissue contrast and multi-planar imaging capability. However, the lack of electron density information in MRI, together with the image distortion issues, precludes its use as the sole image set for RT planning and dose calculation. The purpose of this preliminary study is to probe the feasibility and evaluate an MRI-based radiation dose calculation process by providing MR images the necessary electron density (ED) information from a patient's readily available diagnostic/staging computed tomography (CT) images using an image registration model. To evaluate the dosimetric accuracy of the proposed approach, three brain and three intracranial cases were selected retrospectively for this study. For each patient, the MR images were registered to the CT images, and the ED information was then mapped onto the MR images by in-house developed software generating a modified set of MR images. Another set of MR images with voxel values assigned with the density of water was also generated. The original intensity modulated radiation treatment (IMRT) plan was then applied to the two sets of MR images and the doses were calculated. The dose distributions from the MRI-based calculations were compared to that of the original CT-based calculation. In all cases, the MRI-based calculations with mapped ED yielded dose values very close (within 2%) to that of the CT-based calculations. The MRI-based calculations with voxel values assigned with water density indicated a dosimetric error of 3–5%, depending on the treatment site. The present approach offers a means of utilizing MR images for accurate dose calculation and affords a potential to eliminate the redundant simulation CT by planning a patient's treatment with only simulation MRI and any available diagnostic/staging CT data.

Magnetic resonance imaging of oropharyngeal cancer

Magnetic resonance imaging (MRI) is a powerful tool for cross-sectional analysis of head and neck anatomy and pathology. This is especially true with regard to oropharyngeal neoplasms, where soft tissue spread, nodal disease, perineural extension, and osseous involvement may significantly alter therapy and prognosis. In this article, we will provide a background on oropharyngeal cancers and MRI techniques and strategies, describing potential advantages of MRI with regard to particular anatomic subsites of the oropharynx. Future imaging trends in perfusion and diffusion MRI of such cancers are also discussed.

Current concepts on imaging in radiotherapy

New high-precision radiotherapy (RT) techniques, such as intensity-modulated radiation therapy (IMRT) or hadrontherapy, allow better dose distribution within the target and spare a larger portion of normal tissue than conventional RT. These techniques require accurate tumour volume delineation and intrinsic characterization, as well as verification of target localisation and monitoring of organ motion and response assessment during treatment. These tasks are strongly dependent on imaging technologies. Among these, computed tomography (CT), magnetic resonance imaging (MRI), ultrasonography (US) and positron emission tomography (PET) have been applied in high-precision RT. For tumour volume delineation and characterization, PET has brought an additional dimension to the management of cancer patients by allowing the incorporation of crucial functional and molecular images in RT treatment planning, i.e. direct evaluation of tumour metabolism, cell proliferation, apoptosis, hypoxia and angiogenesis. The combination of PET and CT in a single imaging system (PET/CT) to obtain a fused anatomical and functional dataset is now emerging as a promising tool in radiotherapy departments for delineation of tumour volumes and optimization of treatment plans. Another exciting new area is image-guided radiotherapy (IGRT), which focuses on the potential benefit of advanced imaging and image registration to improve precision, daily target localization and monitoring during treatment, thus reducing morbidity and potentially allowing the safe delivery of higher doses. The variety of IGRT systems is rapidly expanding, including cone beam CT and US. This article examines the increasing role of imaging techniques in the entire process of high-precision radiotherapy.

Molecular Biology for the Radiation Oncologist: the 5Rs of Radiobiology meet the Hallmarks of Cancer

Recent advances in our understanding of the biology of cancer have provided enormous opportunities for the development of novel therapies against specific molecular targets. It is likely that most of these targeted therapies will have only modest single agent activities but may have the potential to accentuate the therapeutic effects of ionising radiation. In this introductory review, the 5Rs of classical radiobiology are interpreted in terms of their relationship to the hallmarks of cancer. Future articles will focus on the specific hallmarks of cancer and will highlight the opportunities that exist for designing new combination treatment regimens.

Hypoxic radiosensitization: adored and ignored

Since observations from the beginning of the last century, it has become well established that solid tumors may contain oxygen-deficient hypoxic areas and that cells in such areas may cause tumors to become radioresistant. Identifying hypoxic cells in human tumors has improved by the help of new imaging and physiologic techniques, and a substantial amount of data indicates the presence of hypoxia in many types of human tumors, although with a considerable heterogeneity among individual tumors. Controlled clinical trials during the last 40 years have indicated that this source of radiation resistance can be eliminated or modified by normobaric or hyperbaric oxygen or by the use of nitroimidazoles as hypoxic radiation sensitizers. More recently, attention has been given to hypoxic cytotoxins, a group of drugs that selectively or preferably destroys cells in a hypoxic environment. An updated systematic review identified 10,108 patients in 86 randomized trials designed to modify tumor hypoxia in patients treated with curative attempted primary radiation therapy alone. Overall modification of tumor hypoxia significantly improved the effect of radiotherapy, with an odds ratio of 0.77 (95% CI, 0.71 to 0.86) for the outcome of locoregional control and with an associated significant overall survival benefit (odds ratio = 0.87; 95% CI, 0.80 to 0.95). No significant influence was found on the incidence of distant metastases or on the risk of radiation-related complications. Ample data exist to support a high level of evidence for the benefit of hypoxic modification. However, hypoxic modification still has no impact on general clinical practice.