The role of dual-time combined 18-fluorodeoxyglucose positron emission tomography and computed tomography in the staging and restaging workup of locally advanced rectal cancer, treated with preoperative chemoradiation therapy and radical surgery

Non-operative management for locally advanced rectal cancer: critical review and future perspective

SUMMARY Over the last few decades we have observed important advances in diagnostic imaging, surgery, pathology and multimodal treatments for rectal cancer, as well as increased efforts to reduce treatment-related toxicities and preserve quality of life for curatively treated patients. Neoadjuvant short-course radiotherapy and long-course chemoradiotherapy followed by total mesorectal excision remain widely accepted as the standard of care for patients with locally advanced rectal cancer. However, a carefully selected group of patients achieving a complete response to neoadjuvant chemoradiotherapy may be spared the effects of surgery and achieve satisfactory oncologic outcomes with a ‘wait-and-see’ strategy. Although supported by the results of previous studies, this intriguing paradigm shift needs prospective evaluation within a clinical trial setting and a more accurate prediction and assessment of response by means of tumor biomarkers and diagnostic imaging.

The role of sequential 18(F) -FDG PET/CT in predicting tumour response after preoperative chemoradiation for rectal cancer

AIM

The aim of this study was to investigate the potential of sequential positron emission tomography (PET)/CT standardized uptake value (SUV)/metabolic area variation in predicting the pathological response to preoperative chemoradiotherapy (CRT) for rectal cancer.

METHOD

Fifty-three patients diagnosed with clinical T3-4 and/or N+ rectal cancer were enrolled. All patients received CRT followed by radical surgery after 6-8 weeks. A PET/CT scan was performed before (PET/CT1) initiation of treatment and a second scan (PET/CT2) was performed within 1 week after the completion of CRT. Thirty-five of 53 patients also underwent a third (PET/CT3) scan within 1 week before surgery. Maximal SUV within the tumour (SUVmax), average SUV within the tumour (SUVmean), metabolic tumour volume (MV), total lesion glycolysis (TLG) and response indices (∆%, i.e. the percentage difference between two different PET/CT scans for SUVmax, SUVmean, MV and TLG) were calculated. The different metabolic parameters were analysed and correlated with the tumour regression grade (TRG) score.

RESULTS

When patients were regrouped as responders (TRG 3-4) and nonresponders (TRG 0-2), significant differences were observed in the percentage differences between PET/CT1 and PET/CT3 for MV (∆%MV(1-3); 91.08% vs 75.43%) and for TLG (∆%TLG(1-3); 94.00% vs 82.02%). As demonstrated by receiver-operating characteristics analysis, ∆%MV(1-3) and ∆%TLG(1-3) both had a strong capability to discriminate between responders and nonresponders. Patients classified as having a pathological complete response (pCR) and a non-pCR showed significant differences in the percentage difference between PET/CT1 and PET/CT3 in SUVmax (∆% SUVmax(1-3); 69.17% vs 57.77%), SUVmean (∆% SUVmean(1-3); 44.20% vs 30.19%), ∆%MV(1-3) (90.93% vs 80.30%) and ∆%TLG(1-3) (94.22% vs 85.63%). ∆%TLG (1-3) was a more powerful discriminator than the others.

CONCLUSION

Differences in the SUV/metabolic area with 18F-fluorodeoxyglucose (18(F) -FDG) PET/CT have the potential to predict a response to preoperative CRT for rectal cancer.

ACR Appropriateness Criteria pretreatment staging of colorectal cancer

Because virtually all patients with colonic cancer will undergo some form of surgical therapy, the role of preoperative imaging is directed at determining the presence or absence of synchronous carcinomas or adenomas and local or distant metastases. In contrast, preoperative staging for rectal carcinoma has significant therapeutic implications and will direct the use of radiation therapy, surgical excision, or chemotherapy. CT of the chest, abdomen, and pelvis is recommended for the initial evaluation for the preoperative assessment of patients with colorectal carcinoma. Although the overall accuracy of CT varies directly with the stage of colorectal carcinoma, CT can accurately assess the presence of metastatic disease. MRI using endorectal coils can accurately assess the depth of bowel wall penetration of rectal carcinomas. Phased-array coils provide additional information about lymph node involvement. Adding diffusion-weighted imaging to conventional MRI yields better diagnostic accuracy than conventional MRI alone. Transrectal ultrasound can distinguish layers within the rectal wall and provides accurate assessment of the depth of tumor penetration and perirectal spread, and PET and PET/CT have been shown to alter therapy in almost one-third of patients with advanced primary rectal cancer. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed every 2 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances in which evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

Fifteen different 18F-FDG PET/CT qualitative and quantitative parameters investigated as pathological response predictors of locally advanced rectal cancer treated by neoadjuvant chemoradiation therapy

PURPOSE

The aim of this study was to correlate qualitative visual response and various PET quantification factors with the tumour regression grade (TRG) classification of pathological response to neoadjuvant chemoradiotherapy (CRT) proposed by Mandard.

METHODS

Included in this retrospective study were 69 consecutive patients with locally advanced rectal cancer (LARC). FDG PET/CT scans were performed at staging and after CRT (mean 6.7 weeks). Tumour SUVmax and its related arithmetic and percentage decrease (response index, RI) were calculated. Qualitative analysis was performed by visual response assessment (VRA), PERCIST 1.0 and response cut-off classification based on a new definition of residual disease. Metabolic tumour volume (MTV) was calculated using a 40 % SUVmax threshold, and the total lesion glycolysis (TLG) both before and after CRT and their arithmetic and percentage change were also calculated. We split the patients into responders (TRG 1 or 2) and nonresponders (TRG 3-5).

RESULTS

SUVmax MTV and TLG after CRT, RI, ΔMTV% and ΔTLG% parameters were significantly correlated with pathological treatment response (p < 0.01) with a ROC curve cut-off values of 5.1, 2.1 cm(3), 23.4 cm(3), 61.8 %, 81.4 % and 94.2 %, respectively. SUVmax after CRT had the highest ROC AUC (0.846), with a sensitivity of 86 % and a specificity of 80 %. VRA and response cut-off classification were also significantly predictive of TRG response (VRA with the best accuracy: sensitivity 86 % and specificity 55 %). In contrast, assessment using PERCIST was not significantly correlated with TRG.

CONCLUSION

FDG PET/CT can accurately stratify patients with LARC preoperatively, independently of the method chosen to interpret the images. Among many PET parameters, some of which are not immediately obtainable, the most commonly used in clinical practice (SUVmax after CRT and VRA) showed the best accuracy in predicting TRG.

Management of distal rectal cancer: results from a national survey

Owing to the complexity of distal rectal cancer its management requires a multidisciplinary approach. The diagnosis and the response after neoadjuvant chemoradiotherapy are not easy to assess and therefore the surgical approach is heterogeneous. The purpose of this survey is to evaluate the experiences of members of the Italian Society of Surgery in diagnosis and treatment strategies for rectal cancer and compare it with international practice. A questionnaire was devised comprising 18 questions with 11 sub-items making a total of 29 questions and submitted online to all the 2,500 members of the SIC starting from July 2010. The survey was completed in June 2011. The overall response rate was 17.8 % (444). The majority of the Italian surgeons' responses were in line with the international consensus reflecting the complex management of distal rectal cancer. Other opinions, especially those on staging, diverge from the common view of MRI being the gold standard in the assessment of loco-regional diffusion of the disease and on the superiority of FDG PET-CT versus CT for systemic staging. The timing for the re-staging and for surgery following neoadjuvant chemoradiotherapy does not reflect the international opinion. Italian surgeons are also exposed to the common difficulties encountered internationally in the management of distal rectal cancer. Probably, the implementation of an Italian rectal cancer registry and of many national and international multicentre studies may improve the management of rectal cancer in Italy.

Is the standardized uptake value of FDG-PET/CT predictive of pathological complete response in locally advanced rectal cancer treated with capecitabine-based neoadjuvant chemoradiation?

OBJECTIVES

Our aim was to assess FDG-PET/CT as a surrogate biomarker of the pathological complete response in locally advanced rectal cancer treated with neoadjuvant chemoradiation.

METHODS

T3-4 and/or N+ rectal cancer patients were treated prospectively with capecitabine-based chemoradiation and total mesorectal excision 7-8 weeks later. FDG-PET/CT uptake was obtained at baseline, after 2 weeks, and 6 weeks following treatment completion, calculating the maximum standardized uptake value (SUV) and percentage difference to identify the early and late metabolic 'response index'.

RESULTS

Thirty-one patients were treated from January 2009 to January 2012 at the Istituto Nazionale dei Tumori of Milan. One patient was excluded due to surgery refusal. The pathological complete response rate was 30%. Early FDG-PET/CT was performed in 24 consenting patients and failed to show predictive utility. On the contrary, significant differences in late SUV value and response index were observed between complete and noncomplete pathological responders (p = 0.0006 and 0.03). In multivariate analysis including most relevant SUV parameters, none of them was independently associated with a pathological complete response. With receiver operating characteristic curve analysis, a late SUV threshold <5.4 had 81% sensitivity and 100% specificity, with 90% overall accuracy.

CONCLUSIONS

We evidenced a possible predictive role of late FDG-PET/CT for the assessment of pathological response in locally advanced rectal cancer following neoadjuvant chemoradiation.

The predictive role of sequential FDG-PET/CT in response of locally advanced rectal cancer to neoadjuvant chemoradiation

PURPOSE

This study prospectively assessed the value of sequential fluorine-18-fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) scans for predicting the response of locally advanced rectal cancer to neoadjuvant chemoradiation.

METHODS

Fifty consecutive patients with locally advanced rectal cancer were enrolled. The treatment consisted of concurrent chemoradiation, which included preoperative 5-fluorouracil-based chemotherapy and pelvic radiation (4500 to 5040 cGy); this was followed 8 weeks later (median: 55 d) by surgery with a curative intent. All the patients underwent FDG-PET/CT before and 5 weeks later (median: 35 d) after the completion of chemoradiation. We evaluated the measurements of the FDG uptake [maximum standardized uptake values (SUV(max))] and the percentage of SUV(max) difference [(response index (RI)] between the prechemoradiation and postchemoradiation FDG-PET/CT scans.

RESULTS

After chemoradiation, 32 of 50 patients (64%) were classified as responders according to the tumor regression grade, which is based on the ratio of fibrosis to residual cancer (tumor regression grade 3-4). For all the patients, the mean prechemoradiation SUV(max) was 14.8, and this was significantly higher than the mean SUV(max) value of 6.1 at postchemoradiation (P< 0.001). The mean RI was significantly higher in the responders than that in the nonresponder patients (62.6% vs. 31.2%, P = 0.001). The following parameters were obtained using a RI cutoff of 53.0% for defining a response to therapy: 75.0% sensitivity, 73.2% specificity, 82.8% positive predictive value, and 61.9% negative predictive value.

CONCLUSIONS

The FDG-PET/CT parameters, and especially the RI, may be best for assessing the neoadjuvant chemoradiation response of locally advanced rectal cancer and these values can potentially assist physicians for planning the optimal treatment.

18F-FDG-PET evaluation of treatment response to neo-adjuvant therapy in patients with locally advanced rectal cancer: a meta-analysis

The purpose of this meta-analysis was to evaluate the utility of positron emission tomography (PET) using fluor-18-deoxyglucose (FDG) to predict the response of rectal cancer to neo-adjuvant therapy. All previously published studies on the role of FDG-PET in predicting the response of rectal cancer to neo-adjuvant therapy were collected. Pooled sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated using statistical software. A total of 28 studies, comprising 1,204 patients with rectal cancer, were included in the meta-analysis. Pooled sensitivity, specificity, PPV and NPV for FDG-PET predicting the response to therapy was 78% [95% confidence interval (CI): 75-82%], 66% (95% CI: 62-69%), 70% (95% CI; 66-73%) and 75% (95% CI: 71-0.79%), respectively. The included studies were of a relatively high methodological quality according to the QUADAS (quality assessment of studies of diagnostic accuracy included in systematic reviews) criteria. Based on the subgroup analyses, there was no significant difference between the response index, the standardized uptake value and the visual response score in predicting the therapy response. However, the accuracy of the group that underwent PET scanning during therapy showed significantly higher values (sensitivity 86% and specificity 80%) than the group that was scanned after completion of the therapy. Therefore, FDG-PET is valuable for predicting the response of rectal carcinoma to neo-adjuvant therapy, and early evaluation of response during the therapy may be more promising. However, additional studies using prospective clinical trials will be required to assess the clinical benefit of this strategy.

Optimal timing for assessment of tumor response to neoadjuvant chemoradiation in patients with rectal cancer: do all patients benefit from waiting longer than 6 weeks?

PURPOSE

To estimate the metabolic activity of rectal cancers at 6 and 12 weeks after completion of chemoradiation therapy (CRT) by 2-[fluorine-18] fluoro-2-deoxy-d-glucose-labeled positron emission tomography/computed tomography ([(18)FDG]PET/CT) imaging and correlate with response to CRT.

METHODS AND MATERIALS

Patients with cT2-4N0-2M0 distal rectal adenocarcinoma treated with long-course neoadjuvant CRT (54 Gy, 5-fluouracil-based) were prospectively studied (ClinicalTrials.org identifier NCT00254683). All patients underwent 3 PET/CT studies (at baseline and 6 and 12 weeks from CRT completion). Clinical assessment was at 12 weeks. Maximal standard uptake value (SUVmax) of the primary tumor was measured and recorded at each PET/CT study after 1 h (early) and 3 h (late) from (18)FDG injection. Patients with an increase in early SUVmax between 6 and 12 weeks were considered "bad" responders and the others as "good" responders.

RESULTS

Ninety-one patients were included; 46 patients (51%) were "bad" responders, whereas 45 (49%) patients were "good" responders. "Bad" responders were less likely to develop complete clinical response (6.5% vs. 37.8%, respectively; P=.001), less likely to develop significant histological tumor regression (complete or near-complete pathological response; 16% vs. 45%, respectively; P=.008) and exhibited greater final tumor dimension (4.3 cm vs. 3.3 cm; P=.03). Decrease between early (1 h) and late (3 h) SUVmax at 6-week PET/CT was a significant predictor of "good" response (accuracy of 67%).

CONCLUSIONS

Patients who developed an increase in SUVmax after 6 weeks were less likely to develop significant tumor downstaging. Early-late SUVmax variation at 6-week PET/CT may help identify these patients and allow tailored selection of CRT-surgery intervals for individual patients.

Shifting concepts in rectal cancer management: a review of contemporary primary rectal cancer treatment strategies

The management of rectal cancer has transformed over the last 3 decades and continues to evolve. Some of these changes parallel progress made with other cancers: refinement of surgical technique to improve organ preservation, selective use of neoadjuvant (and adjuvant) therapy, and emergence of criteria suggesting a role for individually tailored therapy. Other changes are driven by fairly unique issues including functional considerations, rectal anatomic features, and surgical technical issues. Further complexity is due to the variety of staging modalities (each with its own limitations), neoadjuvant treatment alternatives, and competing strategies for sequencing multimodal treatment even for nonmetastatic disease. Importantly, observations of tumor response made in the era of neoadjuvant therapy are reshaping some traditionally held concepts about tumor behavior. Frameworks for prioritizing and integrating complex data can help to formulate treatment plans for patients.

Response prediction in the multimodality therapy of locally advanced rectal cancer

SUMMARY Neoadjuvant therapies have been established in the multimodality treatment of locally advanced rectal cancer. Radiation with concurrent 5-fluorouracil-based chemotherapy followed by surgical resection is considered to be the standard of care in advanced rectal cancer. However, recent studies revealed that patients with complete histopathologic response seem to benefit most from neoadjuvant therapies. Consequently, predictive markers to allow individualization of multimodality therapy in locally advanced rectal cancer are mostly required to identify those who will benefit the most. Unfortunately, there is still an immense lack of factors for response assessment in patients with rectal cancer undergoing multimodality treatment. While conventional diagnostic tools lack sufficient accuracy to provide information for response assessment, newer techniques such as [18F]-fluorodeoxyglucose-PET and diffusion-weighted MRI show promising results. In addition, studies on molecular factors for response assessment in rectal cancer are encouraging but still do not provide a reliable instrument for utilization in clinical practice.

F-18 FDG PET/CT in rectal carcinoma: where are we now?

This short review aims at summarizing the available data pertaining to the usefulness of F-18 FDG PET/CT in rectal cancer. It is specifically focused on the emerging role of F-18 FDG PET/CT in assessing the response to neoadjuvant combined radiochemotherapy in locally advanced rectal cancer. It also probes the possibility of finding standardized PET/CT parameters that are capable of differentiating responders from nonresponders in whom therapeutic approach could be modified.

Accuracy of positron emission tomography/computed tomography and clinical assessment in the detection of complete rectal tumor regression after neoadjuvant chemoradiation: long-term results of a prospective trial (National Clinical Trial 00254683)

BACKGROUND

Neoadjuvant chemoradiation (CRT) therapy may result in significant tumor regression in patients with rectal cancer. Patients who develop complete tumor regression have been managed by treatment strategies that are alternatives to standard total mesorectal excision. Therefore, assessment of tumor response with positron emission tomography/computed tomography (PET/CT) after neoadjuvant treatment may offer relevant information for the selection of patients to receive alternative treatment strategies.

METHODS

Patients with clinical T2 (cT2) through cT4NxM0 rectal adenocarcinoma were included prospectively. Neoadjuvant therapy consisted of 54 grays of radiation and 5-fluorouracil-based chemotherapy. Baseline PET/CT studies were obtained before CRT followed by PET/CT studies at 6 weeks and 12 weeks after the completion of CRT. Clinical assessment was performed at 12 weeks after CRT completion. PET/CT results were compared with clinical and pathologic data.

RESULTS

In total, 99 patients were included in the study. Twenty-three patients were complete responders (16 had a complete clinical response, and 7 had a complete pathologic response). The PET/CT response evaluation at 12 weeks indicated that 18 patients had a complete response, and 81 patients had an incomplete response. There were 5 false-negative and 10 false-positive PET/CT results. PET/CT for the detection of residual cancer had 93% sensitivity, 53% specificity, a 73% negative predictive value, an 87% positive predictive value, and 85% accuracy. Clinical assessment alone resulted in an accuracy of 91%. PET/CT information may have detected misdiagnoses made by clinical assessment alone, improving overall accuracy to 96%.

CONCLUSIONS

Assessment of tumor response at 12 weeks after CRT completion with PET/CT imaging may provide a useful additional tool with good overall accuracy for the selection of patients who may avoid unnecessary radical resection after achieving a complete clinical response. Cancer 2012;3501-3511. © 2011 American Cancer Society.

Locally advanced rectal cancer: a comparison of management strategies

Traditionally, there has been a high local recurrence rate in rectal cancer and 10-40% of patients require a permanent stoma. Both short-course preoperative radiotherapy (SCPRT) and long-course preoperative chemoradiation (CRT) are used to reduce the risk of local recurrence and enable a curative resection. Total mesorectal excision has reduced the rate of local recurrence (even without radiotherapy) to below 10%, but has highlighted a high risk of metastatic disease in 30-40% of patients. Current trials suggest that in resectable cancers, where the preoperative magnetic resonance imaging (MRI) suggests the circumferential resection margin (CRM) is not potentially involved, then SCPRT and CRT are equivalent in terms of outcomes such as local recurrence, disease-free survival (DFS) and overall survival (OS). For patients with more advanced disease, where the CRM is breached or threatened according to the MRI, the integration of more active chemotherapy and biological agents into chemoradiation is an attractive strategy because of the high risk of metastases. However, in none of the trials published in the last decade has chemoradiation impacted on DFS or OS. We examine the strategies of neoadjuvant, concurrent, consolidation (after chemoradiation and before surgery) and postoperative adjuvant chemotherapy with cytotoxic agents, and the integration of biological agents for future potential strategies of treatment. We also compare the trials and compare the different strategies of long-course preoperative radiotherapy and SCPRT; the intensification of preoperative radiation and chemoradiation with dose escalation of external beam radiotherapy, using brachytherapy, intra-operative radiotherapy, hyperfractionation, and various available techniques such as intensity-modulated radiotherapy. We recommend examining dose escalation of radiotherapy to the primary tumour where MRI predicts a threatened CRM. Of the potential treatment strategies involving cytotoxic agents, such as neoadjuvant, concurrent, consolidation and postoperative adjuvant chemotherapy, the most promising would appear to be consolidation chemotherapy following chemoradiation in locally advanced disease, and neoadjuvant chemotherapy in MRI-selected patients who do not require radiation. Improvement in the quality of surgery is also an important future goal.

Value of diffusion-weighted imaging in the detection of viable tumour after neoadjuvant chemoradiation therapy in patients with locally advanced rectal cancer: comparison with T2 weighted and PET/CT imaging

OBJECTIVES

To evaluate the added value of diffusion-weighted imaging (DWI) in combination with T(2) weighted imaging (T2WI) compared with T2WI alone or positron emission tomography (PET)/CT for detecting viable tumour after neoadjuvant chemoradiation therapy (CRT) in patients with locally advanced rectal cancer.

METHODS

50 consecutive patients with locally advanced rectal cancer (≥T3 or lymph node positive) who underwent neoadjuvant CRT and subsequent surgery were enrolled in this retrospective study. All patients underwent 3.0 T rectal MRI and PET/CT after completing CRT. For qualitative analysis, two radiologists independently reviewed T2WI alone and DWI with T2WI over a 1-month interval. One nuclear medicine physician reviewed PET/CT images using a five-point scale. Diagnostic accuracy, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for detecting viable tumour were assessed. For quantitative analysis, the apparent diffusion coefficients (ADCs) of the lesions were measured and compared between the viable tumour group and non-viable tumour groups.

RESULTS

For detecting viable tumours, DWI with T2WI improved diagnostic accuracies (Reviewer 1 detected 90%; Reviewer 2, 86%) over T2WI alone (Reviewer 1 detected 76%, p=0.5; Reviewer 2, 64%, p=0.013) or PET/CT (48%, p<0.001). The sensitivity of DWI with T2WI (Reviewer 1 detected 98%; Reviewer 2, 91%) was significantly higher than those of T2WI alone (Reviewer 1 detected 77%; Reviewer 2, 64%) or PET-CT (43%, p<0.05). Only for Reviewer 2 was the NPV of DWI with T2WI (43%) significantly different from that of PET/CT (17%, p<0.05). The specificities and PPVs of DWI with T2WI were not improved over those of T2WI alone or of PET/CT (both p>0.05). The mean ADC of the viable tumour group (0.93 × 10(-3) mm(2) sc(-1)) was significantly lower than that of the non-viable tumour group (1.55 × 10(-3) mm(2) sc(-1), p<0.0001).

CONCLUSION

Adding DWI to T2WI is helpful for detecting viable tumours after neoadjuvant CRT compared with T2WI alone or PET/CT in patients with locally advanced rectal cancer.

Development and external validation of a predictive model for pathological complete response of rectal cancer patients including sequential PET-CT imaging

PURPOSE

To develop and validate an accurate predictive model and a nomogram for pathologic complete response (pCR) after chemoradiotherapy (CRT) for rectal cancer based on clinical and sequential PET-CT data. Accurate prediction could enable more individualised surgical approaches, including less extensive resection or even a wait-and-see policy.

METHODS AND MATERIALS

Population based databases from 953 patients were collected from four different institutes and divided into three groups: clinical factors (training: 677 patients, validation: 85 patients), pre-CRT PET-CT (training: 114 patients, validation: 37 patients) and post-CRT PET-CT (training: 107 patients, validation: 55 patients). A pCR was defined as ypT0N0 reported by pathology after surgery. The data were analysed using a linear multivariate classification model (support vector machine), and the model's performance was evaluated using the area under the curve (AUC) of the receiver operating characteristic (ROC) curve.

RESULTS

The occurrence rate of pCR in the datasets was between 15% and 31%. The model based on clinical variables (AUC(train)=0.61±0.03, AUC(validation)=0.69±0.08) resulted in the following predictors: cT- and cN-stage and tumour length. Addition of pre-CRT PET data did not result in a significantly higher performance (AUC(train)=0.68±0.08, AUC(validation)=0.68±0.10) and revealed maximal radioactive isotope uptake (SUV(max)) and tumour location as extra predictors. The best model achieved was based on the addition of post-CRT PET-data (AUC(train)=0.83±0.05, AUC(validation)=0.86±0.05) and included the following predictors: tumour length, post-CRT SUV(max) and relative change of SUV(max). This model performed significantly better than the clinical model (p(train)<0.001, p(validation)=0.056).

CONCLUSIONS

The model and the nomogram developed based on clinical and sequential PET-CT data can accurately predict pCR, and can be used as a decision support tool for surgery after prospective validation.

Prospective study on the FDG-PET/CT predictive and prognostic values in patients treated with neoadjuvant chemoradiation therapy and radical surgery for locally advanced rectal cancer

BACKGROUND

2-[fluorine-18]fluoro-2-deoxy-D-glucose-positron emission tomography/computed tomography (FDG-PET/CT) was carried out before and after neoadjuvant chemoradiotherapy (NCRT) followed by radical surgery for locally advanced rectal cancer (LARC). The aim of this study was to define its predictive and prognostic values.

PATIENTS AND METHODS

Patients with cT3-T4 N-/+ carcinoma of medium/low rectum received daily 5-fluorouracil-based chemotherapy infusion and radiation therapy on 6-week period followed by surgery 7-8 weeks later. Tumour metabolic activity, expressed as maximum standardised uptake value (SUV-1 = at baseline and SUV-2 = pre-surgery), was calculated in the most active tumour site. Predictive and prognostic values of SUV-1, SUV-2 and Δ-SUV (percentage change of SUV-1 - SUV-2) were analysed towards pathological response (pR) in the surgical specimen and disease recurrence, respectively.

RESULTS

Eighty consecutive patients entered the study. SUV-1, SUV-2 and Δ-SUV appeared singly correlated with pR, but not one of them resulted an independent predictive factor at multivariate analysis. After a median follow-up of 44 months, 13 patients (16.2%) presented local and/or distant recurrence. SUV-2 ≤5 was associated with lower incidence of disease recurrence and resulted prognostic factor at multivariate analysis.

CONCLUSIONS

Dual-time FDG-PET/CT in patients with LARC treated with NCRT and radical surgery supplies limited predictive information. However, an optimal metabolic response appears associated with a favourable patient outcome.

The use of FDG-PET to target tumors by radiotherapy

Fluorodeoxyglucose positron emission tomography (FDG-PET) plays an increasingly important role in radiotherapy, beyond staging and selection of patients. Especially for non-small cell lung cancer, FDG-PET has, in the majority of the patients, led to the safe decrease of radiotherapy volumes, enabling radiation dose escalation and, experimentally, redistribution of radiation doses within the tumor. In limited-disease small cell lung cancer, the role of FDG-PET is emerging. For primary brain tumors, PET based on amino acid tracers is currently the best choice, including high-grade glioma. This is especially true for low-grade gliomas, where most data are available for the use of (11)C-MET (methionine) in radiation treatment planning. For esophageal cancer, the main advantage of FDG-PET is the detection of otherwise unrecognized lymph node metastases. In Hodgkin's disease, FDG-PET is essential for involved-node irradiation and leads to decreased irradiation volumes while also decreasing geographic miss. FDG-PET's major role in the treatment of cervical cancer with radiation lies in the detection of para-aortic nodes that can be encompassed in radiation fields. Besides for staging purposes, FDG-PET is not recommended for routine radiotherapy delineation purposes. It should be emphasized that using PET is only safe when adhering to strictly standardized protocols.

Target Volume Delineation for Preoperative Radiotherapy of Rectal Cancer: Inter-Observer Variability and Potential Impact of FDG-PET/CT Imaging

To analyze the inter-observer variability and the potential impact of 18F-fluorodeoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) imaging for target volume delineation in preoperative radiotherapy of rectal cancer. Gross tumor volume (GTV) and clinical target volume (CTV) in 2 cases of rectal cancer were contoured by 10 radiation oncologists, 5 on CT and 5 on PET/CT images. Resulting volumes were analyzed by coefficient of variation (CV) and concordance index (CI). Mean GTV was 120 cc±20.4 cc in case A and 119 cc ± 35.7 cc in case B. Mean CTV was 723 cc ± 147.5 cc in case A and 739 cc ± 195.6 cc in case B. CV was lower and CI was similar or higher across the observers contouring GTV on PET/CT. CTV variability was less influenced by the use of PET/CT. PET/CT may allow reducing inter-observer variability in GTV delineation.