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ORIGINAL ARTICLE
Year : 2019  |  Volume : 18  |  Issue : 4  |  Page : 361-365

Using positron-emission tomography–computed tomography for predicting radiotherapy-induced tumor regression in carcinoma esophagus in an Indian population


1 Department of Radiation Oncology, Command Hospital (CC), Lucknow, Uttar Pradesh, India
2 Department of Malignant Disease Treatment Centre, Command Hospital (SC), Pune, Maharashtra, India
3 Department of Nuclear Medicine, Command Hospital (SC), Pune, Maharashtra, India
4 Department of Pathology, Command Hospital (SC), Pune, Maharashtra, India

Date of Submission14-Dec-2018
Date of Acceptance11-Apr-2019
Date of Web Publication18-Dec-2019

Correspondence Address:
Dr. Niharika Bisht
Command Hospital(SC), Pune-411040, Maharashtra
India
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DOI: 10.4103/wjnm.WJNM_114_18

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   Abstract 


Carcinoma esophagus is a common malignancy of the Indian subcontinent. The role of positron-emission tomography–computed tomography (PET-CT) in the assessment of response to radiotherapy has been widely studied and accepted. However, its precise use as a predictive tool for actual histopathological response to radiotherapy needs further evaluation, especially in an Indian population. The aim of this study was to identify a quantum of metabolic response on PET-CT that can also predict for a good pathological response. Forty-four patients of carcinoma esophagus treated with neoadjuvant chemoradiotherapy followed by surgery were included in the study. All patients underwent a PET-CT before starting treatment as well as at 4–6 weeks after completion of radiotherapy. The percentage change in pre and posttreatment maximum standardized uptake value (SUVmax) value (ΔSUV%) of the primary tumor was correlated against histopathological tumor regression grade (TRG) as per the Mandard's system. Seventy-five percent of the patients with a significant metabolic response, i.e., a ΔSUV% of 60% or more, also had a good pathological response to treatment. Thus, by considering a ΔSUV% of 60%, we could predict for a good pathological response (TRG of 1 or 2) to chemoradiotherapy in our patient set with a sensitivity of 95.45% and a specificity of 72.72%.

Keywords: Carcinoma esophagus, positron-emission tomography–computed tomography, radiotherapy


How to cite this article:
Singh S, Bisht N, Sarin A, Kumar AA, Gupta S, Kapoor A, Mishra PS. Using positron-emission tomography–computed tomography for predicting radiotherapy-induced tumor regression in carcinoma esophagus in an Indian population. World J Nucl Med 2019;18:361-5

How to cite this URL:
Singh S, Bisht N, Sarin A, Kumar AA, Gupta S, Kapoor A, Mishra PS. Using positron-emission tomography–computed tomography for predicting radiotherapy-induced tumor regression in carcinoma esophagus in an Indian population. World J Nucl Med [serial online] 2019 [cited 2020 Jan 28];18:361-5. Available from: http://www.wjnm.org/text.asp?2019/18/4/361/273446




   Introduction Top


Carcinoma esophagus is the eighth most common cancer in the world with a very poor survival (overall ratio of mortality to incidence of 0.88).[1] In the cancer registry of Pune district in India, it is the fifth most common cancer overall.[2] The standard of care for the management of locally advanced disease remains multimodality therapy with neoadjuvant chemoradiotherapy followed by surgery. Although the magnitude of benefit with neoadjuvant therapy remains unclear, several studies have shown the prognostic significance of pathological response and histopathological tumor regression after neoadjuvant therapy in both squamous carcinoma and adenocarcinoma of the esophagus in terms of improved disease-free survival (DFS) and overall survival (OS) in patients with pathological complete response (pCR) compared to patients with partial or no pathological response.[3],[4],[5],[6] The rate of R0 resections is also seen to be the highest in the subset of patients with pathological response in these studies (94%–100% in responders vs. 64%–88% in nonresponders).[5],[6] Postoperative tumor stage has also been shown to be the best predictor of survival outcome in patients of carcinoma esophagus and gastroesophageal junction who have undergone preoperative chemoradiotherapy followed by surgery.[7] Although several tumor regression grading systems have been proposed, the three-tier system proposed by Wu et al. has been reported to have an excellent interobserver agreement in grading the residual tumor in patients of esophageal carcinoma.[8]

Positron-emission tomography–computed tomography (PET-CT) has also been used extensively in the assessment of treatment response, and the prognostic significance of metabolic response postneoadjuvant chemoradiotherapy in patients of locally advanced carcinoma esophagus has been established in several studies.[9],[10],[11],[12],[13] However, there still remains uncertainty about the timing of the PET-CT scan after chemoradiation (2–6 weeks),[11],[14] as well as the reduction in the maximum standardized uptake value (SUVmax) that should be considered significant (varies from 35% to 80% in studies)[11],[14],[15],[16] in terms of predicting pathological response.

Aim

It was our endeavor in this study to try to identify a quantifiable degree of metabolic response seen on 18F-fluoro-2-deoxyglucose positron-emission tomography–computed tomography (18-FDG PET-CT) in patients of carcinoma esophagus treated with neoadjuvant chemoradiotherapy that may be predictive or indicative of histopathological response seen postradical surgery in an Indian population.


   Materials and Methods Top


This was a retrospective analysis of patients of locally advanced carcinoma esophagus treated with neoadjuvant chemoradiotherapy followed by surgery. After requisite approval from the departmental ethical committee, medical records of all patients of carcinoma esophagus (squamous or adenocarcinoma) treated with curative intent at a tertiary cancer hospital between January 2015 and June 2017 were retrieved and analyzed. Only patients who were treated with neoadjuvant chemoradiotherapy followed by radical surgery were selected. All patients were planned on a Nucletron conventional simulator using conventional two-dimensional planning techniques and were treated on a Theratron 780E telecobalt machine. All patients received a dose of 4500 cGy in 25 fractions at 180 cGy per fraction. The concurrent chemotherapy regimens used were paclitaxel + carboplatin, cisplatin + 5-fluorouracil, cisplatin + capecitabine, or cisplatin alone. Four patients received radiotherapy alone due to expected poor tolerance to concurrent chemotherapy either due to an existing comorbidity or due to a poor performance status.

It was mandatory for the patient to have undergone a whole-body PET-CT scan before starting (PET1) and at 4–6 weeks after completing (PET2) radiotherapy to be included in the study. The percentage change in SUVmax for the primary lesion between PET1 and PET2 was calculated for all patients and was termed ΔSUV%. All patients with 60% or more reduction in SUVmax of the primary lesion between PET1 and PET2, i.e., a ΔSUV% of 60% or more, were defined as having a good metabolic response (GMR). The value of 60% for ΔSUV% was decided upon after a thorough and extensive literature review which showed the range of reduction in SUVmax before and after radiotherapy in carcinoma esophagus to vary between 35% and 80%.[11],[14],[15],[16] The various parameters considered in the study are defined in [Table 1].
Table1: Parameters used in the study

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On the basis of tumor regression grade (TRG) reported in the final histopathology report, the patients were classified into good pathological responders (GPRs) and poor pathological responders (PPRs). The Mandard's system[17] [Table 2] was used for reporting TRG. Patients with TRG score of 1 or 2 were included in the GPR group and those with TRG score of 3, 4, or 5 were placed in the PPR group. The list of patients in the GMR group and those in the GPR group was compared, and the concordance between the two lists was analyzed to see whether a correlation existed between the ΔSUV% and the histopathological response.
Table2: Mandard's system for reporting tumor regression grade

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   Results Top


A total of 60 patients of carcinoma esophagus (excluding cervical esophagus) were treated between January 2015 and June 2017 in the radiotherapy department of our hospital. The ratio of males to females was 37:23. Fifty-two of the cases were squamous carcinoma, whereas only 8 were adenocarcinoma despite the preponderance of lower esophageal disease. There were 14 cases with upper third of the esophagus involved, 19 with middle third of the esophagus, and 21 with lower third of the esophagus and esophagogastric junction involvement. In 6 cases, more than one subsite of the esophagus was involved, and the origin of the primary was not discernible.

Six patients were metastatic and were offered palliative radiotherapy only. Two patients were referred after surgery and received postoperative radiotherapy, whereas 4 patients were treated with definitive chemoradiotherapy. A total of 48 patients were treated with neoadjuvant radiotherapy. Of these, one patient did not complete treatment and 3 were lost to follow-up. Thus, a total of 44 patients were available for the analysis and were included in the study.

The mean pretreatment SUVmax was 12.79 (5.8 to 25.25) and mean posttreatment SUVmax was 6.90 (12.2 to 0.0). The mean ΔSUV% was 54% (100% to 0%). Nearly 63.63% (28/44) of patients who underwent surgery showed a GMR. The percentage of patients who showed GPR was 47.72% (21/44). [Figure 1] shows pre- and postradiotherapy PET-CT image of a patient who experienced a GMR.
Figure 1: Pre- and postchemoradiotherapy positron-emission tomography–computed tomography scans showing complete metabolic response in a patient of carcinoma of the upper thoracic esophagus

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All the 21 patients with a GPR had also shown a GMR; however, 7 (25%) patients with a GMR did not show a GPR. There was one case who did not show a GMR but had a very good response on histopathology with a TRG of 1.

A summary of the results is given in [Table 3].
Table3: Asummary of the study observations

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   Discussion Top


Although a vast number and variety of Western studies have been carried out on the use of PET-CT for response assessment and prognostication in esophageal cancer treated with chemoradiotherapy, the majority of cases in these studies are adenocarcinomas. In India and other Asian countries, squamous cell carcinomas tend to be the dominant histology,[18] as was seen in our study as well. The utility of FDG PET-CT should be re-examined in our patient population due to this variation in histology as 18-FDG has been shown to have differential uptake in squamous and adenocarcinomas.[19]

By correlating metabolic response as seen on serial PET scans with the final histopathological response to chemoradiotherapy, it may be possible to not only prognosticate patients accurately but also identify patients likely to have a complete response to neoadjuvant therapy and avoid radical surgery.

In our study, 64% of the patients had a significant metabolic response to chemoradiotherapy (≥60% reduction in SUVmax). Among these patients with significant metabolic response, 75% (21/27) had a TRG of 1 or 2 indicating good pathological response [Figure 2] and possible better prognosis (OS or DFS) compared to those who did not have a good pathological response. This is similar to what is previously published in the literature.[9],[10],[11],[12],[13]
Figure 2: Venn diagram showing a 75% overlap between patients who showed a good metabolic response and those who also had a good pathological response

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In the remaining 25% though, the GMR did not translate into a good pathological response and their TRG varied from 3 to 5. The possible explanations for this lack of correlation between metabolic and histologic responses are as follows:

  • Decreased FDG uptake after irradiation is mainly due to the reduced number of metabolically active tumor cells. However, a decrease of FDG PET does not always predict a good response because FDG can differentiate metabolically active cells from dead cells but cannot differentiate biologically viable from metabolically active cells[20]
  • Variable 18-FDG uptake in residual hypoxic or necrotic tumor cells[21]
  • Possible accelerated repopulation of residual tumor cells between time of second PET scan and surgery
  • Respiratory motion artifact is greatest at the level of the diaphragm and can lead to misregistration of PET and CT images,[22] resulting in variation in the calculated SUVmax of up to 30%–50%.


Thus, by considering a ΔSUV% of 60%, we could predict for a good pathological response (TRG of 1 or 2) to chemoradiotherapy in our patient set with a sensitivity of 95.45% and a specificity of 72.72%. For the above cutoff of 60%, the positive predictive value for a GPR was 77.77% and the negative predictive value was 94.11%.

There was one patient who did not show a significant metabolic response but had a good pathological response. Radiation-induced local inflammation probably contributed toward preventing an adequate fall in SUVmax to be included in the GMR group. This is an established phenomenon[22] and should always remain a differential in a patient who has improved clinically but has a poor response on PET-CT.


   Conclusion Top


Thus, our study was able to show that in an Indian population set, PET-CT can be a useful tool in identifying patients of carcinoma esophagus who are likely to respond to treatment and have potentially improved survival postchemoradiotherapy. However, the modality is far from infallible or error free, and the methodology requires further refinement. The subject certainly merits further research in the form of prospective studies and new innovations like more specific radionuclides for PET scans.

Fallacies

The authors concede that the study does suffer from certain fallacies. These are listed below:

  • The study is a retrospective analysis
  • There is variation in the radiotherapy and chemotherapy schedules used between patients
  • The timing of the PET-CT scans is not uniform for all patients and varies between 4 and 6 weeks in the postneoadjuvant period
  • The results are not statistically significant
  • Lack of follow-up to determine whether the metabolic and PET response actually translated into OS or DFS benefit.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Ferlay J, Soerjomataram I, Ervik M, Dikshit R, Eser S, Mathers C, et al. GLOBOCAN 2012 v1.0, Cancer Incidence and Mortality Worldwide: IARC Cancer Base No. 11. Lyon, France: International Agency for Research on Cancer; 2013. Available from: http://www.globocan.iarc.frz. [Last accessed on 2017 Nov 05].  Back to cited text no. 1
    
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Schneider PM, Baldus SE, Metzger R, Kocher M, Bongartz R, Bollschweiler E, et al. Histomorphologic tumor regression and lymph node metastases determine prognosis following neoadjuvant radiochemotherapy for esophageal cancer: Implications for response classification. Ann Surg 2005;242:684-92.  Back to cited text no. 4
    
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Meredith KL, Weber JM, Turaga KK, Siegel EM, McLoughlin J, Hoffe S, et al. Pathologic response after neoadjuvant therapy is the major determinant of survival in patients with esophageal cancer. Ann Surg Oncol 2010;17:1159-67.  Back to cited text no. 6
    
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Cerfolio RJ, Bryant AS, Talati AA, Eloubeidi MA, Cerfolio RM, Winokur TS, et al. Change in maximum standardized uptake value on repeat positron emission tomography after chemoradiotherapy in patients with esophageal cancer identifies complete responders. J Thorac Cardiovasc Surg 2009;137:605-9.  Back to cited text no. 10
    
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Flamen P, Van Cutsem E, Lerut A, Cambier JP, Haustermans K, Bormans G, et al. Positron emission tomography for assessment of the response to induction radiochemotherapy in locally advanced oesophageal cancer. Ann Oncol 2002;13:361-8.  Back to cited text no. 12
    
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Downey RJ, Akhurst T, Ilson D, Ginsberg R, Bains MS, Gonen M, et al. Whole body 18FDG-PET and the response of esophageal cancer to induction therapy: Results of a prospective trial. J Clin Oncol 2003;21:428-32.  Back to cited text no. 13
    
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Levine EA, Farmer MR, Clark P, Mishra G, Ho C, Geisinger KR, et al. Predictive value of 18-fluoro-deoxy-glucose-positron emission tomography (18F-FDG-PET) in the identification of responders to chemoradiation therapy for the treatment of locally advanced esophageal cancer. Ann Surg 2006;243:472-8.  Back to cited text no. 15
    
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Lordick F, Ott K, Krause BJ, Weber WA, Becker K, Stein HJ, et al. PET to assess early metabolic response and to guide treatment of adenocarcinoma of the oesophagogastric junction: The MUNICON phase II trial. Lancet Oncol 2007;8:797-805.  Back to cited text no. 16
    
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Mandard AM, Dalibard F, Mandard JC, Marnay J, Henry-Amar M, Petiot JF, et al. Pathologic assessment of tumor regression after preoperative chemoradiotherapy of esophageal carcinoma. Clinicopathologic correlations. Cancer 1994;73:2680-6.  Back to cited text no. 17
    
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Samarasam I. Esophageal cancer in India: Current status and future perspectives. Int J Adv Med Health Res 2017;4:5-10.  Back to cited text no. 18
  [Full text]  
19.
Imperiale A, Cimarelli S, Brigand C, Faure G, Karcher G, Rohr S, et al. Does the association of 18F-FDG uptake intensity and lesion topography reveal histological phenotype and tumor differentiation in esophageal cancer? Hell J Nucl Med 2011;14:239-42.  Back to cited text no. 19
    
20.
Chang JM, Lee HJ, Goo JM, Lee HY, Lee JJ, Chung JK, et al. False positive and false negative FDG-PET scans in various thoracic diseases. Korean J Radiol 2006;7:57-69.  Back to cited text no. 20
    
21.
Mees G, Dierckx R, Vangestel C, Van de Wiele C. Molecular imaging of hypoxia with radiolabelled agents. Eur J Nucl Med Mol Imaging 2009;36:1674-86.  Back to cited text no. 21
    
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Bruzzi JF, Munden RF, Truong MT, Marom EM, Sabloff BS, Gladish GW, et al. PET/CT of esophageal cancer: Its role in clinical management. Radiographics 2007;27:1635-52.  Back to cited text no. 22
    


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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