Focal dose escalation using FDG-PET-guided intensity-modulated radiation therapy boost for postoperative local recurrent rectal cancer: a planning study with comparison of DVH and NTCP

[18F]FDG-PET-Based Personalized Radiotherapy Dose Prescription

PET imaging with 2'-deoxy-2'-[18F]fluoro-D-glucose ([18F]FDG) has become one of the pillars in the management of malignant diseases. It has proven value in diagnostic workup, treatment policy, follow-up, and as prognosticator for outcome. [18F]FDG is widely available and standards have been developed for PET acquisition protocols and quantitative analyses. More recently, [18F]FDG-PET is also starting to be appreciated as a decision aid for treatment personalization. This review focuses on the potential of [18F]FDG-PET for individualized radiotherapy dose prescription. This includes dose painting, gradient dose prescription, and [18F]FDG-PET guided response-adapted dose prescription. The current status, progress, and future expectations of these developments for various tumor types are discussed.

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.

Is It Time to Introduce PET/CT in Rectal Cancer Guidelines?

At the moment, international guidelines for rectal cancer suggest to consider F-FDG PET/CT scan in a few conditions: (1) at disease presentation in case of suspected or proven metastatic synchronous adenocarcinoma with potentially curable M1 disease; (2) in the recurrence workup for serial carcinoembryonic antigen level elevation; (3) in the recurrence workup with metachronous metastases documented by CT, MRI, or biopsy; (4) in case of strong contraindication to IV contrast agent administration; and (5) to evaluate an equivocal finding on a contrast-enhanced CT or MRI. PET/CT is not indicated in the follow-up or surveillance of rectal cancer. On the other hand, an attentive evaluation of the literature shows that PET/CT may also be used in some circumstances with significant levels of diagnostic accuracy. This review article aims to emphasize differences between current international guidelines and scientific literature in the role of PET/CT in rectal cancer.

PET imaging in adaptive radiotherapy of gastrointestinal tumors

INTRODUCTION

Radiotherapy is a cornerstone in the multimodality treatment of several gastrointestinal (GI) tumors. Positron-emission tomography (PET) has an established role in the diagnosis, response assessment and (re-)staging of these tumors. Nevertheless, the value of PET in adaptive radiotherapy remains unclear. This review focuses on the role of PET in adaptive radiotherapy, i.e. during the treatment course and in the delineation process.

EVIDENCE ACQUISITION

The MEDLINE database was searched for the terms ("Radiotherapy"[Mesh] AND "Positron-Emission Tomography"[Mesh] AND one of the site-specific keywords, yielding a total of 1710 articles. After abstract selection, 27 papers were identified for esophageal neoplasms, 1 for gastric neoplasms, 9 for pancreatic neoplasms, 6 for liver neoplasms, 1 for biliary tract neoplasms, none for colonic neoplasms, 15 for rectal neoplasms and 12 for anus neoplasms.

EVIDENCE SYNTHESIS

The use of PET for truly adaptive radiotherapy during treatment for GI tumors has barely been investigated, in contrast to the potential of the PET-defined metabolic tumor volume for optimization of the target volume. The optimized target definition seems useful for treatment individualization such as focal boosting strategies in esophageal, pancreatic and anorectal cancer. Nevertheless, for all GI tumors, further investigation is needed.

CONCLUSIONS

In general, too little data are available to conclude on the role of PET imaging during radiotherapy for ART strategies in GI cancer. On the other hand, based on the available evidence, the use of biological imaging for target volume adaptation seems promising and could pave the road towards individualized treatment strategies.

PET/CT imaging-guided dose painting in radiation therapy

Application of functional imaging to radiotherapy (RT) is a rapidly expanding field with the development of new modalities and techniques. Functional imaging of PET in conjunction with RT provides new avenues towards the clinical application of dose painting - a new RT strategy delivering optimized dose redistribution according to the functional imaging information to further improve tumour control. Two prototypical strategies of dose painting are reviewed: dose painting by contours (DPBC) and dose painting by numbers (DPBN). DPBN set a linear correlation of the boost dose and image intensity of this same voxel while homogeneous dose is given to the subvolume contoured by a threshold created in PET images in DPBC. Both comply with strict organs at risk (OAR) constraints and are alternatives for boosting subvolumes in clinical practice. This review focuses on the rationale, target validation, dose prescription verification and evaluation and recent clinical achievements in the field of integrating PET imaging into RT treatment planning. Further research is necessary in order to investigate unresolved problems in its routine clinical application thoroughly.

FDG PET/CT for rectal carcinoma radiotherapy treatment planning: comparison of functional volume delineation algorithms and clinical challenges

PET/CT imaging could improve delineation of rectal carcinoma gross tumor volume (GTV) and reduce interobserver variability. The objective of this work was to compare various functional volume delineation algorithms. We enrolled 31 consecutive patients with locally advanced rectal carcinoma. The FDG PET/CT and the high dose CT (CTRT) were performed in the radiation treatment position. For each patient, the anatomical GTVRT was delineated based on the CTRT and compared to six different functional/metabolic GTVPET derived from two automatic segmentation approaches (FLAB and a gradient-based method); a relative threshold (45% of the SUVmax) and an absolute threshold (SUV > 2.5), using two different commercially available software (Philips EBW4 and Segami OASIS). The spatial sizes and shapes of all volumes were compared using the conformity index (CI). All the delineated metabolic tumor volumes (MTVs) were significantly different. The MTVs were as follows (mean ± SD): GTVRT (40.6 ± 31.28ml); FLAB (21.36± 16.34 ml); the gradient-based method (18.97± 16.83ml); OASIS 45% (15.89 ± 12.68 ml); Philips 45% (14.52 ± 10.91 ml); OASIS 2.5 (41.6 2 ± 33.26 ml); Philips 2.5 (40 ± 31.27 ml). CI between these various volumes ranged from 0.40 to 0.90. The mean CI between the different MTVs and the GTVCT was < 0.4. Finally, the DICOM transfer of MTVs led to additional volume variations. In conclusion, we observed large and statistically significant variations in tumor volume delineation according to the segmentation algorithms and the software products. The manipulation of PET/CT images and MTVs, such as the DICOM transfer to the Radiation Oncology Department, induced additional volume variations.

Tumor heterogeneity and permeability as measured on the CT component of PET/CT predict survival in patients with non-small cell lung cancer

PURPOSE

We prospectively examined the role of tumor textural heterogeneity on positron emission tomography/computed tomography (PET/CT) in predicting survival compared with other clinical and imaging parameters in patients with non-small cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

The feasibility study consisted of 56 assessed consecutive patients with NSCLC (32 males, 24 females; mean age 67 ± 9.7 years) who underwent combined fluorodeoxyglucose (FDG) PET/CT. The validation study population consisted of 66 prospectively recruited consecutive consenting patients with NSCLC (37 males, 29 females; mean age, 67.5 ± 7.8 years) who successfully underwent combined FDG PET/CT-dynamic contrast-enhanced (DCE) CT. Images were used to derive tumoral PET/CT textural heterogeneity, DCE CT permeability, and FDG uptake (SUVmax). The mean follow-up periods were 22.6 ± 13.3 months and 28.5± 13.2 months for the feasibility and validation studies, respectively. Optimum threshold was determined for clinical stage and each of the above biomarkers (where available) from the feasibility study population. Kaplan-Meier analysis was used to assess the ability of the biomarkers to predict survival in the validation study. Cox regression determined survival factor independence.

RESULTS

Univariate analysis revealed that tumor CT-derived heterogeneity (P < 0.001), PET-derived heterogeneity (P = 0.003), CT-derived permeability (P = 0.002), and stage (P < 0.001) were all significant survival predictors. The thresholds used in this study were derived from a previously conducted feasibility study. Tumor SUVmax did not predict survival. Using multivariable analysis, tumor CT textural heterogeneity (P = 0.021), stage (P = 0.001), and permeability (P < 0.001) were independent survival predictors. These predictors were independent of patient treatment.

CONCLUSIONS

Tumor stage and CT-derived textural heterogeneity were the best predictors of survival in NSCLC. The use of CT-derived textural heterogeneity should assist the management of many patients with NSCLC.

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.

Toward the non-surgical management of locally advanced rectal cancer

Neoadjuvant short-course radiotherapy and long-course chemoradiation (CRT) reduce local recurrence rates when compared to surgery alone and remain widely accepted as standard of care for patients with locally advanced rectal cancer. However, surgery is not without complications and a non-surgical approach in carefully selected patients warrants evaluation. A pathological complete response to CRT is associated with a significant improvement in survival and it has been suggested that a longer time interval between the completion of CRT and surgery increases tumor downstaging. Intensification of neoadjuvant treatment regimens to increase tumor downstaging has been evaluated in a number of clinical trials and more recently the introduction of neoadjuvant chemotherapy prior to CRT has demonstrated high rates of radiological tumor regression. Careful selection of patients using high-resolution MRI may allow a non-surgical approach in a subgroup of patients achieving a complete response to neoadjuvant therapies after an adequate time period. Clearly this needs prospective evaluation within a clinical trial setting, incorporating modern imaging techniques, and tissue biomarkers to allow accurate prediction and assessment of response.

A phase I trial of S-1 with concurrent radiotherapy in patients with locally recurrent rectal cancer

BACKGROUND

The purpose of this phase I trial of S-1 chemotherapy in combination with pelvic radiotherapy for locally recurrent rectal cancer was to determine the maximum tolerated dose (MTD), recommended dose (RD), and dose-limiting toxicity (DLT) of S-1.

METHODS

We enrolled 9 patients between April 2005 and March 2009. Radiotherapy (total dose, 60 Gy in 30 fractions) was given to the gross local recurrent tumor and pelvic nodal metastases using three-dimensional radiotherapy planning. We administered oral S-1 twice a day on days 1-14 and 22-35 during radiotherapy. The dose of S-1 was initially 60 mg/m(2)/day and was increased to determine the MTD and RD for this regimen.

RESULTS

DLT appeared at dose level 2 (70 mg/m(2)/day) in 2 patients, who experienced grade 3 enterocolitis and consequently required suspension of S-1 administration for longer than 2 weeks. Hematological toxicity was mild and reversible. At the initial evaluation, complete regression and partial regression were seen in 1 patient (11%) and 2 patients (22%), respectively.

CONCLUSION

This phase I trial of S-1 chemotherapy with pelvic radiotherapy for locally recurrent rectal cancer revealed that the MTD for S-1 was 70 mg/m(2)/day and the RD was 60 mg/m(2)/day.

Individualization of cancer treatment from radiotherapy perspective

Radiotherapy is today used in about 50% of all cancer patients, often in multidisciplinary approaches. With major advance in radiotherapy techniques, increasing knowledge on tumor genetics and biology and the continuous introduction of specifically targeted drugs into combined radio-oncological treatment schedules, individualization of radiotherapy is of high priority to further improve treatment outcomes, i.e. to increase long-term tumor cure and/or to reduce chronic treatment toxicity. This review gives an overview on the importance of predictive biomarkers for the field of radiation oncology. The current status of knowledge on potential biomarkers of tumor hypoxia, tumor cell metabolism, DNA repair, cancer stem cells and biomarkers for combining radiotherapy with inhibition of the epidermal growth factor receptor using monoclonal antibodies is described.

Molecular imaging-based dose painting: a novel paradigm for radiation therapy prescription

Dose painting is the prescription of a nonuniform radiation dose distribution to the target volume based on functional or molecular images shown to indicate the local risk of relapse. Two prototypical strategies for implementing this novel paradigm in radiation oncology are reviewed: subvolume boosting and dose painting by numbers. Subvolume boosting involves the selection of a "target within the target," defined by image segmentation on the basis of the quantitative information in the image or morphologically, and this is related to image-based target volume selection and delineation. Dose painting by numbers is a voxel-level prescription of dose based on a mathematical transformation of the image intensity of individual pixels. The quantitative use of images to decide both where and how to delivery radiation therapy in an individual case is also called theragnostic imaging. Dose painting targets are imaging surrogates for cellular or microenvironmental phenotypes associated with poor radioresponsiveness. In this review, the focus is on the following positron emission tomography tracers: FDG and choline as surrogates for tumor burden, fluorothymidine as a surrogate for proliferation (or cellular growth fraction) and hypoxia-sensitive tracers, including [(18)F] fluoromisonidazole, EF3, EF5, and (64)Cu-labeled copper(II) diacetyl-di(N(4)-methylthiosemicarbazone) as surrogates of cellular hypoxia. Research advances supporting the clinicobiological rationale for dose painting are reviewed as are studies of the technical feasibility of optimizing and delivering realistic dose painted radiation therapy plans. Challenges and research priorities in this exciting research field are defined and a possible design for a randomized clinical trial of dose painting is presented.

Positron emission tomography for benign and malignant disease

Functional imaging using radiolabeled probes that specifically bind and accumulate in target tissues has improved the sensitivity and specificity of conventional imaging. Fluorodeoxyglucose (FDG)-positron emission tomography (PET) has shown improved diagnostic accuracy in differentiating benign from malignant lesions in the setting of solitary pulmonary nodules. FDG-PET has become useful in preoperative staging of patients with lung cancer, and is being tested with many other malignancies for its ability to change patient management. This article provides an overview of the current status of FDG-PET and presents the challenges of moving toward routine use.

["Dose-painting": myth or reality?]

"Dose-painting" radiotherapy allows for a heterogeneous delivery of radiation within the tumour volume by targeting radioresistant areas defined by functional imaging. Within gross tumour volume, it is possible to define one or more target volumes based on biology (biological target volume [BTV]) and to apply a strategy of intensity modulated radiation therapy (IMRT) that will deliver a higher dose to these regions. In this review of the literature, we will highlight the biological elements responsible for radioresistance, and how to image them, then we will detail the radiotherapy techniques necessary for this approach, before presenting clinical results in various situations (head and neck tumours, prostate, brain tumours, etc.). Despite many difficulties that make dose-painting IMRT unusable in routine nowadays, biology-guided radiation therapy represents one of the major pathways of development of radiotherapy in the coming years.