Delineation of Gross Tumor Volume (GTV) for Radiation Treatment Planning of Locally Advanced Rectal Cancer Using Information From MRI or FDG-PET/CT: A Prospective Study

The Role of MRI and PET/CT in Radiotherapy Target Volume Determination in Gastrointestinal Cancers-Review of the Literature

Positron emission tomography with computed tomography (PET/CT) and magnetic resonance imaging (MRI) could improve accuracy in target volume determination for gastrointestinal cancers. A systematic search of the PubMed database was performed, focusing on studies published within the last 20 years. Articles were considered eligible for the review if they included patients with anal canal, esophageal, rectal or pancreatic cancer, as well as PET/CT or MRI for radiotherapy treatment planning, and if they reported interobserver variability or changes in treatment planning volume due to different imaging modalities or correlation between the imaging modality and histopathologic specimen. The search of the literature retrieved 1396 articles. We retrieved six articles from an additional search of the reference lists of related articles. Forty-one studies were included in the final review. PET/CT seems indispensable for target volume determination of pathological lymph nodes in esophageal and anal canal cancer. MRI seems appropriate for the delineation of primary tumors in the pelvis as rectal and anal canal cancer. Delineation of the target volumes for radiotherapy of pancreatic cancer remains challenging, and additional studies are needed.

Clinical use of positron emission tomography for radiotherapy planning - Medical physics considerations

PET/CT imaging plays an increasing role in radiotherapy treatment planning. The aim of this article was to identify the major use cases and technical as well as medical physics challenges during integration of these data into treatment planning. Dedicated aspects, such as (i) PET/CT-based radiotherapy simulation, (ii) PET-based target volume delineation, (iii) functional avoidance to optimized organ-at-risk sparing and (iv) functionally adapted individualized radiotherapy are discussed in this article. Furthermore, medical physics aspects to be taken into account are summarized and presented in form of check-lists.

Positron emission tomography and magnetic resonance imaging combined with computed tomography in tumor volume delineation: A case report

BACKGROUND

Accurate delineation of the target area for patients with hypopharyngeal cancer is the key to achieving an ideal radiotherapy effect. Since computed tomography (CT) alone can no longer meet the treatment needs, fusing CT images with magnetic resonance imaging (MRI) or positron emission tomography (PET) images can overcome the disadvantages of CT. Herein, we present a clinical case of hypopharyngeal cancer to delineate the tumor volume using combined MRI-CT and PET-CT fusion images to examine if they could accurately cover the tumor volume.

CASE SUMMARY

A 67-year-old male patient with hypopharyngeal carcinoma could not tolerate chemotherapy and surgery due to complicated health issues such as diabetic nephropathy and other underlying diseases. After multidisciplinary consultations, clinicians eventually agreed to undergo radiotherapy to control the progression of his tumor. He was examined by CT, MRI, and 18-fluorodeoxyglucose-PET for treatment planning, and CT images were fused with PET and MRI images while delineating tumor volume.

CONCLUSION

The image fusion of MRI-CT and PET-CT has both advantages and disadvantages. Compared with CT images alone, the combination of MRI-CT and PET-CT fusion images can precisely cover the gross tumor volume in hypopharyngeal carcinoma and avoid overestimation or incomplete coverage of tumor volume.

Changes in treatment intent and target definition for preoperative radiotherapy after 18F-Fluorodeoxyglucose positron emission tomography in rectal cancer: A Meta-analysis

PURPOSE

To evaluate the impact of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) on changes in treatment plan and target definition for preoperative radiotherapy in patients with rectal cancer.

METHODS

Embase, PubMed, and Cochrane Library were searched up to November 2020 for all studies investigating the role of preoperative FDG PET in patients who underwent neoadjuvant radiotherapy before curative-intent surgery. The proportion of patients whose treatment plan (curative vs. palliative intent) or target definition was changed after FDG PET was analyzed. A random-effects model was used for pooled analysis. The change in target definition was compared between conventional radiological imaging-based target volume [gross tumor volume (GTV) or planning target volume (PTV)] and PET-based target volume (GTV or PTV) using the standardized mean difference (SMD) and 95% confidence interval (CI).

RESULTS

A total of 336 patients from twelve studies were included. In eight studies, PET changed either the treatment intent or target definition in 24.8% of patients (95% CI 15.1% to 37.9%, I² = 69%). In ten studies, the PET-based GTV was lower than the conventional imaging-based target volume (SMD -7.0, 95% CI -1.39 to -0.01). However, there was no significant difference between conventional imaging-based and PET-based PTV (SMD -0.07, 95% CI -0.75 to 0.62). In six studies evaluating the initial staging based on PET, the initial staging (nodal or metastasis status) was changed in 53 of 229 patients (23.1%). Newly detected or additional distant metastases were identified in 22 patients (9.6%) after FDG PET.

CONCLUSION

The use of FDG PET influences radiotherapy planning in a fourth of patients with rectal cancer. FDG PET can provide additive information for accurate tumor delineation, although PET-based PTV did not significantly change. These findings suggest that FDG PET may be beneficial to patients with rectal cancer before establishing a radiotherapy plan.

FDG-PET/CT and MR imaging for target volume delineation in rectal cancer radiotherapy treatment planning: a systematic review

Aim:

The aim of this systematic review was to synthesise and summarise evidence surrounding the clinical use of fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (FDG-PET/CT) and magnetic resonance imaging (MRI) for target volume delineation (TVD) in rectal cancer radiotherapy planning.

Methods:

PubMed, EMBASE, Cochrane library, CINAHL, Web of Science and Scopus databases and other sources were systematically queried using keywords and relevant synonyms. Eligible full-text studies were assessed for methodological quality using the QUADAS-2 tool.

Results:

Eight of the 1448 studies identified met the inclusion criteria. Findings showed that MRI significantly delineate larger tumour volumes (TVs) than FDG-PET/CT while diffusion-weighted magnetic resonance imaging (DW-MRI) defined smaller gross tumour volumes (GTVs) compared to T2 weighted-Magnetic Resonance Image. CT-based GTVs were found to be larger compared to FDG-PET/CT. FDG-PET/CT also identified new lesions in 15–17% patients and TVs extending outside the routinely used clinical standard CT TV in 29–83% patients. Between observers, delineated volumes were similar and consistent between MRI sequences, whereas interobserver agreement was significantly improved with FDG-PET/CT than CT.

Conclusion:

FDG-PET/CT and DW-MRI appear to delineate smaller rectal TVs and show improved interobserver variability. Overall, this study provides valuable insights into the amount of attention in the research literature that has been paid to imaging for TVD in rectal cancer.

Value of PET imaging for radiation therapy

This comprehensive review written by experts in their field gives an overview on the current status of incorporating positron emission tomography (PET) into radiation treatment planning. Moreover, it highlights ongoing studies for treatment individualisation and per-treatment tumour response monitoring for various primary tumours. Novel tracers and image analysis methods are discussed. The authors believe this contribution to be of crucial value for experts in the field as well as for policy makers deciding on the reimbursement of this powerful imaging modality.

Value of PET imaging for radiation therapy

This comprehensive review written by experts in their field gives an overview on the current status of incorporating positron emission tomography (PET) into radiation treatment planning. Moreover, it highlights ongoing studies for treatment individualisation and per-treatment tumour response monitoring for various primary tumours. Novel tracers and image analysis methods are discussed. The authors believe this contribution to be of crucial value for experts in the field as well as for policy makers deciding on the reimbursement of this powerful imaging modality.

Trimodality PET/CT/MRI and Radiotherapy: A Mini-Review

Computed tomography (CT) has revolutionized external radiotherapy by making it possible to visualize and segment the tumors and the organs at risk in a three-dimensional way. However, if CT is a now a standard, it presents some limitations, notably concerning tumor characterization and delineation. Its association with functional and anatomical images, that are positron emission tomography (PET) and magnetic resonance imaging (MRI), surpasses its limits. This association can be in the form of a trimodality PET/CT/MRI. The objective of this mini-review is to describe the process of performing this PET/CT/MRI trimodality for radiotherapy and its potential clinical applications. Trimodality can be performed in two ways, either a PET/MRI fused to a planning CT (possibly with a pseudo-CT generated from the MRI for the planning), or a PET/CT fused to an MRI and then registered to a planning CT (possibly the CT of PET/CT if calibrated for radiotherapy). These examinations should be performed in the treatment position, and in the second case, a patient transfer system can be used between the PET/CT and MRI to limit movement. If trimodality requires adapted equipment, notably compatible MRI equipment with high-performance dedicated coils, it allows the advantages of the three techniques to be combined with a synergistic effect while limiting their disadvantages when carried out separately. Trimodality is already possible in clinical routine and can have a high clinical impact and good inter-observer agreement, notably for head and neck cancers, brain tumor, prostate cancer, cervical cancer.

Recent advances of PET imaging in clinical radiation oncology

Radiotherapy and radiation oncology play a key role in the clinical management of patients suffering from oncological diseases. In clinical routine, anatomic imaging such as contrast-enhanced CT and MRI are widely available and are usually used to improve the target volume delineation for subsequent radiotherapy. Moreover, these modalities are also used for treatment monitoring after radiotherapy. However, some diagnostic questions cannot be sufficiently addressed by the mere use standard morphological imaging. Therefore, positron emission tomography (PET) imaging gains increasing clinical significance in the management of oncological patients undergoing radiotherapy, as PET allows the visualization and quantification of tumoral features on a molecular level beyond the mere morphological extent shown by conventional imaging, such as tumor metabolism or receptor expression. The tumor metabolism or receptor expression information derived from PET can be used as tool for visualization of tumor extent, for assessing response during and after therapy, for prediction of patterns of failure and for definition of the volume in need of dose-escalation. This review focuses on recent and current advances of PET imaging within the field of clinical radiotherapy / radiation oncology in several oncological entities (neuro-oncology, head & neck cancer, lung cancer, gastrointestinal tumors and prostate cancer) with particular emphasis on radiotherapy planning, response assessment after radiotherapy and prognostication.

Benefits of Using a Spatially-Variant Penalty Strength With Anatomical Priors in PET Reconstruction

In this study, we explore the use of a spatially-variant penalty strength in penalized image reconstruction using anatomical priors to reduce the dependence of lesion contrast on surrounding activity and lesion location. This work builds on a previous method to make the local perturbation response (LPR) approximately spatially invariant. While the dependence of lesion contrast on the local properties introduced by the anatomical penalty is intentional, the method aims to reduce the influence from surroundings lying along the lines of response (LORs) but not in the penalty neighborhood structure. The method is evaluated using simulated data, assuming that the anatomical information is absent or well-aligned with the corresponding activity images. Since the parallel level sets (PLS) penalty is convex and has shown promising results in the literature, it is chosen as the representative anatomical penalty and incorporated into the previously proposed preconditioned algorithm (L-BFGS-B-PC) for achieving good image quality and fast convergence rate. A 2D disc phantom with a feature at the center and a 3D XCAT thorax phantom with lesions inserted in different slices are used to study how surrounding activity and lesion location affect the visual appearance and quantitative consistency. A bias and noise analysis is also performed with the 2D disc phantom. The consistency of the algorithm convergence rate with respect to different data noise and background levels is also investigated using the XCAT phantom. Finally, an example of reconstruction for a patient dataset with inserted pseudo lesions is used as a demonstration in a clinical context. We show that applying the spatially-variant penalization with PLS can reduce the dependence of the lesion contrast on the surrounding activity and lesion location. It does not affect the bias and noise trade-off curves for matched local resolution. Moreover, when using the proposed penalization, significant improvement in algorithm convergence rate and convergence consistency is observed.

Positron emission tomography with computed tomography imaging (PET/CT) for the radiotherapy planning definition of the biological target volume: PART 2

AIM

Positron Emission Tomography with Computed Tomography (PET/CT) has been proven to be useful in the definition of Radiotherapy (RT) target volume. In this regard, the present expert review summarizes existing data for pancreas, prostate, gynecological and rectum/anal cancer.

METHODS

A comprehensive search of published original article was made, based on SCOPUS and PubMed database, selecting the paper that evaluated the role of PET/CT in the definition of RT volume.

RESULTS

FDG-PET has an important and promising role for pancreatic cancer. Choline PET/CT could be useful for identifying high-risk volumes for prostate cancer; while PSMA PET/CT is still under evaluation. FDG PET/CT in gynecological cancers has been shown to impact external-beam RT planning. The role of FDG-PET for Gross Tumor volume identification is crucial, representing a useful and powerful tool for anal and rectal cancer.

CONCLUSION

Taken together, molecular and functional imaging approaches offer a major step to individualize radiotherapeutic approach.

An assessment of set up position for MRI scanning for the purposes of rectal cancer radiotherapy treatment planning

INTRODUCTION

A magnetic resonance (MR) scanner for radiotherapy treatment simulation was commissioned in our department in June 2013. Practical set up and MR image quality trade-offs using a variety of patient positions and immobilisation devices routinely used in the treatment planning of rectal cancer patients were considered. The study also aimed to investigate the MR compatibility of the device materials with a focus on temperature changes during routine clinical examinations.

METHODS

Ten volunteers were scanned: (1) Prone on a Civco Contoura Bellyboard (BBB), (2) Prone on a Civco MR Series Bellyboard (WBB), (3) Prone with no bellyboard and (4) Supine. All scans were performed with a T₂ weighted (T₂ -w) turbo spin echo (TSE) sequence. Images were scored by five assessors for: (1) ease of identifying specific organs, (2) overall image quality and (3) signal to noise ratio (SNR). Temperature changes were measured for each volunteer in each position.

RESULTS

Both expert scores and SNR analysis demonstrated that images obtained in the supine position allowed for easier and clearer delineation of the organs. Image factors such as artefacts and noise, along with the overall image quality, also performed better in the supine position. The carbon fibre bellyboard did not demonstrate significant heating during scanning with the T₂ -w TSE transverse sequence.

CONCLUSIONS

A supine position was determined to be superior to the other positions in a majority of comparisons. The volunteers did not experience any increased temperature changes during scanning on the bellyboard in comparison to the other positions.

Neoadjuvant PET and MRI-based intensity modulated radiotherapy leads to less toxicity and improved pathologic response rates in locally advanced rectal cancer

Background

Neoadjuvant chemoradiation (NeoCRT) is standard of care for the treatment of locally advanced rectal cancer (LARC). Contemporary radiation techniques and pre-treatment imaging may impact toxicities and pathologic response (PR). Herein we compare intensity modulated radiotherapy (IMRT) and advanced pre-treatment imaging in the neoadjuvant treatment of LARC and resulting impact on toxicities and pathologic outcomes relative to 3 dimensional conformal radiotherapy (3DCRT).

Methods

LARC patients treated at 4 large academic centers in the US from 2007-2016 were reviewed. Patients received 5-FU-based NeoCRT concurrently with IMRT or 3DCRT. PR was recorded as none, partial, or complete. Common terminology for adverse events version 4 was used to grade toxicities. Toxicity rates were compared using Chi-square analysis. Multivariable models were fit adjusting for age, gender, pre-tx CT to identify independent predictors of PR and toxicity.

Results

A total of 128 patients were analyzed: 60.1% male and 39.8% female, median age 57.7 years (range, 31-85 years). Clinical characteristics were similar across RT groups. The outcome of partial and complete PR was similar for IMRT and 3DCRT (48.1%, 23.1% vs. 31.7%, 23.3%), respectively. After adjusting for gender, age, and pre-RT chemotherapy type, IMRT and pretreatment PET and/or MRI imaging was significantly associated with increased odds for complete and partial response (OR =2.95, 95% CI: 1.21-7.25, P=0.018; OR =14.70, 95% CI: 3.69-58.78, P<0.0001). Additionally, IMRT was associated with reduced rates of dehydration, dermatitis, rectal pain, rectal bleeding, and diverting ostomy (P<0.05). Overall rates of grade 2 and higher toxicities were significantly reduced in IMRT vs. 3DCRT after adjusting for confounders (OR =0.27, 95% CI: 0.08-0.87).

Conclusions

NeoCRT IMRT with pretreatment PET and/or MRI for LARC leads to reduced acute toxicities and improved PR compared to 3DCRT. Given the challenges associated with prospective validation of these data, IMRT with pretreatment PET and/or MRI should be considered standard treatment for LARC.

Current Methods to Define Metabolic Tumor Volume in Positron Emission Tomography: Which One is Better?

Numerous methods to segment tumors using ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG PET) have been introduced. Metabolic tumor volume (MTV) refers to the metabolically active volume of the tumor segmented using FDG PET, and has been shown to be useful in predicting patient outcome and in assessing treatment response. Also, tumor segmentation using FDG PET has useful applications in radiotherapy treatment planning. Despite extensive research on MTV showing promising results, MTV is not used in standard clinical practice yet, mainly because there is no consensus on the optimal method to segment tumors in FDG PET images. In this review, we discuss currently available methods to measure MTV using FDG PET, and assess the advantages and disadvantages of the methods.

Target volume delineation of anal cancer based on magnetic resonance imaging or positron emission tomography

Purpose

To compare target volume delineation of anal cancer using positron emission tomography (PET) and magnetic resonance imaging (MRI) with respect to inter-observer and inter-modality variability.

Methods

Nineteen patients with anal cancer undergoing chemoradiotherapy were prospectively included. Planning computed tomography (CT) images were co-registered with 18F–fluorodexocyglucose (FDG) PET/CT images and T2 and diffusion weighted (DW) MR images. Three oncologists delineated the Gross Tumor Volume (GTV) according to national guidelines and the visible tumor tissue (GTV_T). MRI and PET based delineations were evaluated by absolute volumes and Dice similarity coefficients.

Results

The median volume of the GTVs was 27 and 31 cm³ for PET and MRI, respectively, while it was 6 and 11 cm³ for GTV_T. Both GTV and GTV_T volumes were highly correlated between delineators (r = 0.90 and r = 0.96, respectively). The median Dice similarity coefficient was 0.75 when comparing the GTVs based on PET/CT (GTV_PET) with the GTVs based on MRI and CT (GTV_MRI). The median Dice coefficient was 0.56 when comparing the visible tumor volume evaluated by PET (GTV_{T_PET}) with the same volume evaluated by MRI (GTV_{T_MRI}). Margins of 1–2 mm in the axial plane and 7–8 mm in superoinferior direction were required for coverage of the individual observer’s GTVs.

Conclusions

The rather good agreement between PET- and MRI-based GTVs indicates that either modality may be used for standard target delineation of anal cancer. However, larger deviations were found for GTV_T, which may impact future tumor boost strategies.

On a prolonged interval between rectal cancer (chemo)radiotherapy and surgery

Preoperative radiotherapy (RT) or chemoradiotherapy (CRT) is often required before rectal cancer surgery to obtain low local recurrence rates or, in locally advanced tumours, to radically remove the tumour. RT/CRT in tumours responding completely can allow an organ-preserving strategy. The time from the end of the RT/CRT to surgery or to the decision not to operate has been prolonged during recent years. After a brief review of the literature, the relevance of the time interval to surgery is discussed depending upon the indication for RT/CRT. In intermediate rectal cancers, where the aim is to decrease local recurrence rates without any need for down-sizing/-staging, short-course RT with immediate surgery is appropriate. In elderly patients at risk for surgical complications, surgery could be delayed 5-8 weeks. If CRT is used, surgery should be performed when the acute radiation reaction has subsided or after 5-6 weeks. In locally advanced tumours, where CRT is indicated, the optimal delay is 6-8 weeks. In patients not tolerating CRT, short-course RT with a 6-8-week delay is an alternative. If organ preservation is a goal, a first evaluation should preferably be carried out after about 6 weeks, with planned surgery for week 8 if the response is inadequate. In case the response is good, a new evaluation should be carried out after about 12 weeks, with a decision to start a 'watch-and-wait' programme or operate. Chemotherapy in the waiting period is an interesting option, and has been the subject of recent trials with promising results.

18 F-FDG PET/CT for planning external beam radiotherapy alters therapy in 11% of 581 patients

BACKGROUND

¹⁸ F-FDG PET/CT (FDG PET/CT) used in radiotherapy planning for extra-cerebral malignancy may reveal metastases to distant sites that may affect the choice of therapy.

AIM

To investigate the role of FDG PET/CT on treatment strategy changes induced by the use of PET/CT as part of the radiotherapy planning. 'A major change of treatment strategy' was defined as either including more lesions in the gross tumour volume (GTV) distant from the primary tumour or a change in treatment modalities.

METHODS

The study includes 581 consecutive patients who underwent an FDG PET/CT scan for radiotherapy planning in our institution in the year 2008. All PET/CT scans were performed with the patient in treatment position with the use of immobilization devices according to the intended radiotherapy treatment. All scans were evaluated by a nuclear medicine physician together with a radiologist to delineate PET-positive GTV (GTV-PET).

RESULTS

For 63 of the patients (11%), the PET/CT simulation scans resulted in a major change in treatment strategy because of the additional diagnostic information. Changes were most frequently observed in patients with lung cancer (20%) or upper gastrointestinal cancer (12%). In 65% of the patients for whom the PET/CT simulation scan revealed unexpected dissemination, radiotherapy was given - changed (n = 38) or unchanged (n = 13) according to the findings on the FDG PET/CT.

CONCLUSION

Unexpected dissemination on the FDG PET/CT scanning performed for radiotherapy planning caused a change in treatment strategy in 11% of 581 patients.

Semiautomatic tumor segmentation with multimodal images in a conditional random field framework

Volumetric medical images of a single subject can be acquired using different imaging modalities, such as computed tomography, magnetic resonance imaging (MRI), and positron emission tomography. In this work, we present a semiautomatic segmentation algorithm that can leverage the synergies between different image modalities while integrating interactive human guidance. The algorithm provides a statistical segmentation framework partly automating the segmentation task while still maintaining critical human oversight. The statistical models presented are trained interactively using simple brush strokes to indicate tumor and nontumor tissues and using intermediate results within a patient's image study. To accomplish the segmentation, we construct the energy function in the conditional random field (CRF) framework. For each slice, the energy function is set using the estimated probabilities from both user brush stroke data and prior approved segmented slices within a patient study. The progressive segmentation is obtained using a graph-cut-based minimization. Although no similar semiautomated algorithm is currently available, we evaluated our method with an MRI data set from Medical Image Computing and Computer Assisted Intervention Society multimodal brain segmentation challenge (BRATS 2012 and 2013) against a similar fully automatic method based on CRF and a semiautomatic method based on grow-cut, and our method shows superior performance.

Rectal Radiotherapy--Intensity-modulated Radiotherapy Delivery, Delineation and Doses

The use of intensity-modulated radiotherapy in rectal cancer is attractive in that it may reduce acute and late toxicities and potentially facilitate dose escalation. Intensity-modulated radiotherapy probably has a role in selected patients, but further investigation is required to identify the parameters for selection. Delineation of specific nodal groups allows maximal sparing of bladder and small bowel. In locally advanced tumours a simultaneous integrated boost allows dose escalation incorporating hypofractionation and a shorter overall treatment time. However, due to a sparsity of data on late toxicity in doses ≥ 60 Gy, doses at this level should be used with caution, ideally within prospective trials. Future studies investigating dose escalation must ascertain late toxicity as well as local control, as both can significantly affect quality of life and without both, the risk-benefit ratio cannot be calculated.

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.

Phase II study of computed tomography-guided (125)I-seed implantation plus chemotherapy for locally recurrent rectal cancer

BACKGROUND AND PURPOSE

This trial evaluated the efficacy and safety of CT guided (125)I-seed implantation (CTII) plus chemotherapy with fluorouracil, leucovorin, and irinotecan (FOLFIRI) compared with FOLFIRI alone as second-line treatment for locally recurrent rectal cancer (LRRC).

MATERIAL AND METHODS

Patients with LRRC who received one prior chemotherapy regimen were enrolled and divided randomly assigned to FOLFORI alone (Arm A) and FOLFORI plus CTII (Arm B). The primary endpoint was local control time (LCT). Overall survival (OS) and treatment related adverse events (TRAEs) were also observed.

RESULTS

Fifty-seven patients were enrolled from October 2008 and December 2014. Twenty-seven were assigned into Arm A and 30 into Arm B. The overall response rate of locally recurrent tumor was improved to 100% in Arm B versus 29.6% in Arm A (P<0.001). A significant longer LCT was observed in Arm A (P<0.001); median LCT was 12 months in Arm B versus 4 months in Arm A. A borderline significant improvement in OS was also observed in Arm B (P=0.0464); median OS was 25 months in Arm B versus 19 months in Arm A. For patients without distant metastases, median OS was 37 months in Arm B versus 21 months in Arm A (P=0.0101). For patients with (neo)adjuvant radiotherapy (ART), a longer LCT and OS were also found in Arm B (P<0.001 and P=0.0217, respectively). TRAEs were not serious generally. There was no statistically significant difference in treatment related toxicity between Arm A and B both for all patients and patients receiving ART.

CONCLUSIONS

CTII plus FOLFIRI improves the LCT with tolerable toxicities as a second-line treatment in patients with local recurrent rectal cancer, and is helpful to prolong the OS, particularly in patients without distant metastases or with a history of radiotherapy.

Review of potential improvements using MRI in the radiotherapy workflow

The goal of modern radiotherapy is to deliver a lethal amount of dose to tissue volumes that contain a significant amount of tumour cells while sparing surrounding unaffected or healthy tissue. Online image guided radiotherapy with stereotactic ultrasound, fiducial-based planar X-ray imaging or helical/conebeam CT has dramatically improved the precision of radiotherapy, with moving targets still posing some methodical problems regarding positioning. Therefore, requirements for precise target delineation and identification of functional body structures to be spared by high doses become more evident. The identification of areas of relatively radioresistant cells or areas of high tumor cell density is currently under development. This review outlines the state of the art of MRI integration into treatment planning and its importance in follow up and the quantification of biological effects. Finally the current state of the art of online imaging for patient positioning will be outlined and indications will be given what the potential of integrated radiotherapy/online MRI systems is.

FDG PET/CT in the management of colorectal and anal cancers

OBJECTIVE

CT remains the imaging modality of choice in the diagnosis of colorectal cancer (CRC) and anal cancer. However, advances in imaging have expanded the role of MRI and PET/CT. This article focuses on the evolving role of FDG PET/CT in the diagnosis, radiation therapy planning, therapy assessment, and posttherapy monitoring of CRC and anal cancer.

CONCLUSION

FDG PET/CT is a valuable imaging modality that impacts the clinical management of patients with CRC and those with anal cancer.

The value of magnetic resonance imaging for radiotherapy planning

The success of highly conformal radiotherapy techniques in the sparing of normal tissues or in dose escalation, or both, relies heavily on excellent imaging. Because of its superior soft tissue contrast, magnetic resonance imaging is increasingly being used in radiotherapy treatment planning. This review discusses the current clinical evidence to support the pivotal role of magnetic resonance imaging in radiation oncology.

Diffusion-weighted imaging of the male pelvis

Diffusion-weighted (DW) imaging is playing an increasingly important role in disease detection, prognostication, and monitoring of treatment response. Particularly in the realm of oncology, the potential applications for DW imaging continue to expand. In this article, the authors detail the role of DW imaging for pathologic processes involving the male pelvis. The authors describe the current data, new insights, and ongoing controversies regarding DW imaging of the male pelvis with a particular emphasis on oncologic applications. The authors also discuss imaging techniques and common pitfalls for DW imaging in this anatomic region.

Diagnostic accuracy of 18F choline PET/CT using time-of-flight reconstruction algorithm in prostate cancer patients with biochemical recurrence

PURPOSE

Image quality (IQ) of PET in voluminous body regions can be limited, which impairs the assessment of small metastatic lesions. Time-of-flight (TOF) reconstruction algorithm may deliver an increase of spatial resolution. The purpose of this study was to evaluate the impact of TOF on IQ, lesion detection rate, lesion volume (V) and SUVmax in F choline PET/CT of prostate cancer patients with biochemical recurrence compared to standard PET/CT reconstruction (standard).

PATIENTS AND MATERIALS

During a period of 9 months, 32 patients with prostate cancer (mean [SD] age, 71 [7.8] years) and biochemical recurrence were included in this prospective institutional review board-approved study. Each patient underwent a state-of-the-art 3-dimensional F choline PET/CT. A total of 76 lesions were assessed by 2 board-certified nuclear medicine physicians and a third-year resident. Lesion volume and SUVmax of local recurrence, lymph nodes, and organ metastases were compared between TOF and standard. Image quality and lesion demarcation were rated according to a 5-point Likert-type scale. Interobserver agreement was assessed.

RESULTS

Eight additional lesions were detected using TOF (SUVmax, 3.64 [0.95]; V, 0.58 cm [0.50]). Image quality was reduced (IQ standard, 1.28; TOF, 1.77; P < 0.01) in calculated TOF images, although quality of lesion demarcation was improved (lesion demarcation: standard, 1.66; TOF, 1.26; P < 0.01). SUVmax was significantly increased in TOF images (SUVmax standard, 6.9 [4.1]; TOF, 8.1 [4.1]; P < 0.01), whereas V did not show significant differences (V standard, 5.3 [10.4] cm; TOF, 5.4 [10.3] cm; P = 0.41). Interobserver agreement was good for combined ratings (1 + 2 and 3 + 4).

CONCLUSIONS

Application of TOF seems to be of additional value to detect small metastatic lesions in patients with prostate cancer and biochemical recurrence, which may have further clinical implications for secondary treatment.

Rectal tumour volume (GTV) delineation using T2-weighted and diffusion-weighted MRI: Implications for radiotherapy planning

PURPOSE

To compare the rectal tumour gross target volume (GTV) delineated on T2 weighted (T2W MRI) and diffusion weighted MRI (DWI) images by two different observers and to assess if agreement is improved by DWI.

MATERIAL AND METHODS

27 consecutive patients (15 male, range 27.1-88.8 years, mean 66.9 years) underwent 1.5T MRI prior to chemoradiation (45Gy in 25 fractions; oral capecitabine 850mg/m(2)), including axial T2W MRI (TR=6600ms, TE=90ms) and DWI (TR=3000ms, TE=77ms, b=0, 100, 800s/mm(2)). 3D tumour volume (cm(3)) was measured by volume of interest (VOI) analysis by two independent readers for the T2W MRI and b800 DWI axial images, and the T2W MRI and DWI volumes compared using Mann-Whitney test. Observer agreement was assessed using Bland-Altman statistics. Significance was at 5%.

RESULTS

Artefacts precluded DWI analysis in 1 patient. In the remaining 26 patients evaluated, median (range) T2W MRI MRI and DWI (b=800s/mm(2)) 3D GTVin cm(3) were 33.97 (4.44-199.8) and 31.38 (2.43-228), respectively, for Reader One and 43.78 (7.57-267.7) and 42.45 (3.68-251) for Reader Two. T2W MRI GTVs were slightly larger but not statistically different from DWI volumes: p=0.52 Reader One; p=0.92 Reader Two. Interobserver mean difference (95% limits of agreement) for T2W MRI and DWI GTVs were -9.84 (-54.96 to +35.28) cm(3) and -14.79 (-54.01 to +24.43) cm(3) respectively.

CONCLUSION

Smaller DWI volumes may result from better tumour conspicuity but overall observer agreement is not improved by DWI.

Tumor volumes measured from static and dynamic 18F-fluoro-2-deoxy-D-glucose positron emission tomography-computed tomography scan: comparison of different methods using magnetic resonance imaging as the criterion standard

OBJECTIVE

The objective of this study was to compare the accuracy of calculating the primary tumor volumes using a gradient-based method and fixed threshold methods on the standardized uptake value (SUV) maps and the net influx of FDG (Ki) maps from positron emission tomography-computed tomography (PET-CT) images.

MATERIALS AND METHODS

Newly diagnosed patients with head and neck cancer were recruited, and dynamic PET-CT scan and T2-weighted magnetic resonance imaging were performed. The maps of Ki and SUV were calculated from PET-CT images. The tumor volumes were calculated using a gradient-based method and a fixed threshold method at 40% of maximal SUV or maximal Ki. Four kinds of volumes, VOLKi-Gra (from the Ki maps using the gradient-based method), VOLKi-40% (from the Ki maps using the threshold of 40% maximal Ki), VOLSUV-Gra (from the SUV maps using the gradient-based method), and VOLSUV-40% (from the SUV maps using the threshold of 40% maximal SUV), were acquired and compared with VOLMRI (the volumes acquired on T2-weighted images) using the Pearson correlation, paired t test, and similarity analysis.

RESULTS

Eighteen patients were studied, of which 4 had poorly defined tumors (PDT). The positron emission tomography-derived volumes were as follows: VOLSUV-40%, 2.1 to 41.2 cm (mean [SD], 12.3 [10.6]); VOLSUV-Gra, 2.2 to 28.1 cm (mean [SD], 13.2 [8.4]); VOLKi-Gra, 2.4 to 17.0 cm (mean [SD], 9.5 [4.6]); and VOLKi-40%, 2.7 to 20.3 cm (mean [SD], 12.0 [6.0]). The VOLMRI ranged from 2.9 to 18.1 cm (mean [SD], 9.1 [3.9]). The VOLKi-Gra significantly correlated with VOLMRI with the highest correlation coefficient (PDT included, R = 0.673, P = 0.002; PDT excluded, R = 0.841, P < 0.001) and presented no difference from VOLMRI (P = 0.672 or 0.561, respectively, PDT included and excluded). The difference between VOLKi-Gra and VOLMRI was also the smallest.

CONCLUSIONS

The tumor volumes delineated on the Ki maps using the gradient-based method are more accurate than those on the SUV maps and using the fixed threshold methods.

Clinical application of multimodality imaging in radiotherapy treatment planning for rectal cancer

Radiotherapy plays an important role in the treatment of rectal cancer. Three-dimensional conformal radiotherapy and intensity-modulated radiotherapy are mainstay techniques of radiotherapy for rectal cancer. However, the success of these techniques is heavily reliant on accurate target delineation and treatment planning. Computed tomography simulation is a cornerstone of rectal cancer radiotherapy, but there are limitations, such as poor soft-tissue contrast between pelvic structures and partial volume effects. Magnetic resonance imaging and positron emission tomography (PET) can overcome these limitations and provide additional information for rectal cancer treatment planning. PET can also reduce the interobserver variation in the definition of rectal tumor volume. However, there is a long way to go before these image modalities are routinely used in the clinical setting. This review summarizes the most promising studies on clinical applications of multimodality imaging in target delineation and treatment planning for rectal cancer radiotherapy.

Challenges in the neoadjuvant treatment of rectal cancer: balancing the risk of recurrence and quality of life

The management of patients with rectal cancer has improved substantially-assisted by refinements in surgical technique, the increasing accuracy of preoperative imaging, more precise delivery of radiotherapy¸and more informative feedback from the histopathologist. Multidisciplinary teams have been the key to this success. Future challenges facing multidisciplinary teams include individually tailoring therapy - in particular in deciding who does and does not need radiotherapy, utilising new radiotherapy techniques such as intensity-modulated radiotherapy and image-guided radiotherapy and new systemic therapies, and electing patients for whom chemoradiotherapy might be potentially curative without surgical resection after complete clinical response. Hence, there is an increasing focus on developing predictive and prognostic molecular biomarkers. This paper explores the background to common variations in practice, and the current and future challenges in the neoadjuvant treatment of rectal cancer.

Clinical utility of integrated positron emission tomography/computed tomography imaging in the clinical management and radiation treatment planning of locally advanced rectal cancer

PURPOSE

The role of 18F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) in the staging and radiation treatment planning of locally advanced rectal cancer is ill defined. We studied the role of integrated PET/CT in the staging, radiation treatment planning, and use as an imaging biomarker in rectal cancer patients undergoing multimodality treatment.

METHODS AND MATERIALS

Thirty-four consecutive patients with T3-4N0-2M0-1 rectal adenocarcinoma underwent FDG-PET/CT scanning for staging and radiation treatment planning. Planned clinical management was compared before and after the addition of PET/CT information. Three radiation oncologists independently delineated CT-based gross tumor volumes (GTVCT) using clinical information and CT imaging data, as well as gradient autosegmented PET/CT-based GTVs (GTVPETCT). The mean GTV, interobserver concordance index (CCI), and proximal and distal margins were compared. The maximal standardized uptake value (SUVmax), metabolic tumor volume (MTV), and dual-time point PET parameters were correlated with clinicopathologic endpoints.

RESULTS

Clinical management was altered by PET/CT in 18% (n = 6) of patients with clinical upstaging in 6 patients and radiation treatment planning altered in 5 patients. Of the 30 evaluable preoperative patients, the mean GTVPETCT was significantly smaller than the mean GTVCT volumes: 88.1 versus 102.8 cc (P = .03). PET/CT significantly increased interobserver CCI in contouring GTV compared with CT only-based contouring: 0.56 versus 0.38 (P < .001). The proximal and distal margins were altered by a mean of 0.4 ± 0.24 cm and -0.25 ± 0.18 cm, respectively. MTV was inversely associated with 2-year progression-free survival (PFS) and overall survival (OS): smaller MTVs (<33 cc) had superior 2-year PFS (86% vs 60%, P = .04) and OS (100% vs 45%, P < .01) compared with larger MTVs (>33 cc). SUVmax and dual-time point PET parameters did not correlate with any endpoints.

CONCLUSIONS

FDG-PET/CT imaging impacts overall clinical management and is useful in the radiation treatment planning of rectal cancer patients by decreasing interobserver variability in contouring target boost volumes. Pretreatment MTV may provide useful prognostic information and requires further study.

Potential Clinical Applications of PET/Magnetic Resonance Imaging

Hybrid PET/magnetic resonance (MR) imaging, which combines the excellent anatomic information and functional MR imaging parameters with the metabolic and molecular information obtained with PET, may be superior to PET/computed tomography or MR imaging alone for a wide range of disease conditions. This review highlights potential clinical applications in neurologic, cardiovascular, and musculoskeletal disease conditions, with special attention to applications in oncologic imaging.

Integrated peripheral boost in preoperative radiotherapy for the locally most advanced non-resectable rectal cancer patients

BACKGROUND AND PURPOSE

Few studies have explored the potential clinical advantages of dose escalation and integrated boosts for patients with non-resectable locally advanced rectal cancer. The possibility of escalating dose to non-resectable regions in these patients was the aim of this study.

PATIENTS AND METHODS

Seven patients with locally very advanced rectal tumours (sacrum overgrowth or growth into pelvic side walls) were evaluated. Intensity modulated photon and pencil beam scanning proton plans with simultaneously integrated boosts (45 Gy to elective lymph nodes, 50 Gy to tumour and 62.5 Gy to boost area in 25 fractions) were compared.

RESULTS

Target coverage was achieved with both photon and proton plans. Estimated risks of acute side effects put the two patients with the largest tumours at unacceptable risk for intestinal toxicity, regardless of modality. The remaining five patients had beneficial sparing of dose to the small intestine with protons.

CONCLUSIONS

Adding boost to areas where rectal tumours infiltrate adjacent non-resectable organs is an attractive option which appears possible using both photon and proton irradiation. Proton plans reduced dose to organs at risk. Integrated peripheral boosts should be considered more frequently in these very advanced tumours.

[The role of cross-sectional imaging in staging of rectal cancer]

The ongoing diversification of treatment strategies for rectal cancer justifies the demand for highly specialized radiological imaging. Currently, numerous studies have underlined the ability of magnetic resonance imaging (MRI) to determine those parameters that are critical for therapeutic decision-making and prognosis in rectal cancer. Computed tomography (CT) does not meet the criteria of a first line diagnostic procedure with regard to local staging but will remain the workhorse in the search for distant metastases. The increasing acceptance of extended MRI-based concepts will, however, improve cost-effectiveness and simplify patient management. Response evaluation and detection of recurrent disease are the major indications for positron emission tomography (PET)/CT, which is currently not routinely recommended.