Eur J Nucl Med Mol Imaging (2010) 37:319–329 DOI 10.1007/s00259-009-1276-9
ORIGINAL ARTICLE
Role of PET/CT in malignant pediatric lymphoma Raef Riad & Walid Omar & Magdy Kotb & Magdy Hafez & Iman Sidhom & Manal Zamzam & Iman Zaky & Hussein Abdel-Dayem
Received: 10 July 2009 / Accepted: 24 August 2009 / Published online: 15 September 2009 # Springer-Verlag 2009
Abstract Introduction Malignant pediatric lymphoma accounts for 10–15% of all pediatric cancers, (representing 2–3% of all malignancies), with a peak incidence between 5–9 years. Chemotherapy is usually the first and most common mode of treatment. The choice of treatment and prediction of prognosis depend on the histological type of tumor, initial staging, evaluating treatment response, and detection of early recurrence. Conventional imaging modalities have many limitations. PET/CT is more accurate, however so far the literature lacks the results of a large group of patients. Aim of study To report the role of PET/CT in the abovementioned objectives at the newly established Children’s Cancer Hospital in Cairo, Egypt, which is one of the busiest dedicated pediatric oncology centers of such purposes in the world. All findings were proven by histopathology, clinically, and by clinical follow-up.
Patient population A total of 152 patients (35 girls and 117 boys) with histologically proven malignant lymphoma (117 HD, 35 NHL) were included in this study. They were divided into four groups. Group I: 41 patients for initial staging. Group II: 51 patients for evaluating early treatment response after two to three cycles of chemotherapy. Group III: 42 patients for evaluating treatment response 4–8 weeks after the end of their treatment. Group IV: 18 patients evaluated for long-term follow-up. Results of PET/CT were compared with the other conventional imaging modalities (CIM). Results The sensitivity, specificity, accuracy, and positive and negative predictive values of PET/CT and CIM were as follows: In Group I: PET/CT modified staging and treatment in 11 out of 41 cases (26.8%), upstaged 5 (12.2%) patients and down-staged six (14.6%) patients. Group II: 100%, 97.7%, 98%, 85.7%, 100%, respectively, for PET/CT and 83%, 66.6%, 68.6%, 25%, 96.7% for CIM
Supported by grants from The Children’s Cancer Hospital Foundation and the Cancer Institute Friends Association. R. Riad : W. Omar Department of Nuclear Medicine, Children’s Cancer Hospital (CCH), Cairo University, Cairo, Egypt I. Sidhom : M. Zamzam Department of Pediatric Oncology, Children’s Cancer Hospital (CCH), Cairo University, Cairo, Egypt I. Zaky Department of Radio-diagnosis, Children’s Cancer Hospital (CCH), Cairo University, Cairo, Egypt M. Kotb Department of Nuclear Medicine, National Cancer Institute, Cairo, Egypt
M. Hafez Department of Nuclear Medicine, Children’s Cancer Hospital (CCH), Cairo University, Cairo, Egypt H. Abdel-Dayem Department of Radiology, Nuclear Medicine Section, St. Vincent`s Catholic Medical Centers of New York, New York Medical College, Valhalla, NY, USA H. Abdel-Dayem (*) Department of Radiology, New York Medical College, Nuclear Medicine Service, St. Vincent’s Catholic Medical Centers of New York, 170 West 12th Street, Cr. 327, New York, NY 10011, USA e-mail:
[email protected]
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respectively Group III: At the end of chemotherapy 100%, 90.9%, 92.8%, 75%, 100%, respectively, for PET/CT and 55.5%, 57.5%, 57.1%, 26.3%, 82.6% for CIM, respectively. Group IV: For long-term follow-up, all the parameters scored 100% for PET/CT, 100%, 38.4%, 72.2%, 50%, 100% for CIM, respectively. Conclusion PET/CT in pediatric lymphoma is more accurate than CIM. We recommend that it should be the first modality for all purposes in initial staging, evaluating treatment response and follow-up. Keywords Malignant lymphoma . Pediatric lymphoma . Initial staging . Evaluating treatment response . Follow-up malignant lymphoma . F18-FDG PET/CT
Introduction Malignant lymphoma accounts for 10–15% of pediatric cancers, (representing 2–3% of all malignancies). Hodgkin’s disease (HD) represents 40% of lymphomas in children [1, 2]. The Rye pathological classification distinguishes four categories, among which the nodular sclerosis (in adolescents) and the mixed cellularity subtypes (in pre-pubertal children) are the most frequent [3]. Non-Hodgkin’s lymphoma (NHL) represents 60% of pediatric lymphomas and occurs with a peak incidence between the ages of 5 and 9 years [4, 5]. Several histological classifications exist for NHL. The Revised European—American Lymphoma (REAL) classification is among the most widely used and focuses on the distinction between B and T cell neoplasms [6]. The choice of treatment strategy essentially depends on the initial stage, the pathological subtype, and the presence of factors indicating a poor prognosis, such as B symptoms. Therapeutic options include various combinations of chemotherapy and radiotherapy for HD and mainly combinations of chemotherapy for NHL. With good advances in treatment, there is now a general trend to decrease the aggressiveness of the treatments in order to limit the long-term side-effects in these patients with a long life expectancy. Indeed, the overall survival rate is higher than 90% in HD [7] and above 75% in NHL [8]. Conventional imaging methods such as computed tomography (CT), MRI, and ultrasonography (US) are commonly used in the evaluation of pediatric lymphomas, along with physical examination and bone marrow biopsy. Physical examinations are obviously limited by the location of the disease, but are of primary importance for peripheral lymph node staging. All imaging techniques have significant limitations. CT diagnostic criteria are mainly based on size. As a result, CT neither identifies malignant involvement in normal-size lymph nodes nor characterizes enlargement due to other causes. In addition, CT performs rather poorly in detecting spleen and liver involvement. MRI is the procedure
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of choice in assessing bone marrow and central nervous system infiltration, but it is not convenient for the routine imaging of the entire bone marrow. Some of these limitations are most evident in post-treatment evaluation, in which anatomical imaging methods are unable to differentiate residual tumor from fibrosis or to detect early recurrence. 18 F-fluorodeoxyglucose (18F-FDG) is a glucose analogue that provides unique information about glucose metabolism of normal and abnormal tissues, in particular in malignant diseases. Although adult lymphomas have been widely investigated with 18F-FDG positron emission tomography (PET), the literature concerning children is limited and the number of patients studied in reported articles are small [9–17]. Currently, in adult oncology imaging, there is a transition phase from stand-alone PET to PET-computed tomography (CT), with PET-CT most likely becoming the accepted international standard in pediatric cancer imaging as well [40]. We conducted this retrospective study at the newly established Children’s Cancer Hospital in Cairo, Egypt, one of the busiest centers in the world for evaluating the performance of 18F-FDG PET/CT in pediatric lymphomas for the purpose of initial staging, evaluating treatment response early after two to three cycles of chemotherapy, from 3–8 weeks after chemo treatment and for long-term follow-up. We also aimed to compare the 18F-FDG PET/CT results with those of conventional imaging modalities.
Patient population Between January 2008 and March 2009, 152 patients (35 girls and 117 boys) with histologically proven malignant lymphomas received PET/CT at the newly established Children’s Cancer Hospital. A total of 117 had HD and 35 had NHL. Their age ranged from 3 years to 18 years. The clinical stage of disease was evaluated according to the Ann Arbor classification for HD [18] and Murphy classification for NHL [19]. According to the indication for the PET/CT scan, the population was divided into four groups: Group 1: PET/CT was performed at time of diagnosis, as part of the initial staging. This group included 41 patients, (39 HD, two NHL Burkett’s lymphoma). The clinical staging was adopted by the clinicians based on CIM. Six were stage I, 15 were stage II, 12 were stage III, and eight patients were stage IV. Group 2: PET/CT was performed during the treatment to evaluate early response to therapy after two to three courses of chemotherapy. PET/CT was
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performed 12–14 days after the end of two to three courses of chemotherapy just before the due date of the coming course. Fifty-one patients were in this group (45 HD, 6 NHL). Five patients were stage I, 20 were stage II, 18 were stage III and eight were stage IV. Group 3: PET/CT was performed 4–8 weeks (mean 5.7 weeks) after completion of treatment to evaluate the disease status. Forty-two patients are included in this group (29 HD, 13 NHL). Three out of the 42 patients were stage I, eight were stage II, 21 were stage III, and ten were stage IV. Group 4: PET/CT was performed 3–12 months (mean 6.8 months) during follow-up of patients in complete clinical remission. The indication for the PET/CT studies were either systematic surveillance or assessment of residual masses detected on other imaging modalities. A total of 18 patients were included in this group (six HD, 12 NHL).
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Diagnostic quality CT was obtained with 170 mAs and 120 kVp. The radiation exposure dose from low-dose CT was in average 3.37 mGy while that for diagnostic CT was 11.48 mGy. Interpretation PET/CT studies were read by two nuclear medicine consultants independently while CIM were reviewed by consultant radiologist. Data analysis PET/CT results were compared with the findings of the physical examination, CT, MRI, US, and bone marrow biopsy when available. The accuracy of each test was determined based on either pathological correlation (13 patients) or clinical follow-up (139 patients). An IBM compatible PC was used to store and analyze the data and to produce graphic presentation of important results.
PET imaging Results A total of 196 studies were performed on a dedicated PET/ CT scanner (40-slice Siemens true-point). Patients fasted for at least 4–6 h prior to examination. Blood glucose levels were lower than 120 mg/dl. Patient’s weight ranged from 9.5–79 kg with a mean of 35.8 kg. Acquisitions were started 45–60 min after intravenous injection of 3.7 MBq/ kg 18F-FDG. Whole-body scans were acquired in overlapped bed positions usually from mid thigh to base of skull with the arms extended above the head, with 3-min acquisition for each bed position. All patients except six were imaged without sedation. Images were processed using iterative reconstruction. Attenuation correction was applied using CT data according to the manufacturer’s recommended protocol. Semi-quantitative estimation of tumor glucose metabolism by means of SUV (standardized uptake value) was done for all cases. CT acquisition CT was performed either as low-dose CT for attenuation correction and anatomical localization or high-dose CT for diagnostic purposes based on the CT adjusted mA. Oral contrast was given in 48 studies while IV contrast was given in 106 studies according to requirements of each case and the recommendation of the referring physician. An initial scout view was obtained with 35 mAs and 120 kVp, followed by spiral CT at 0.8 s per rotation with 50 mAs (quality reference), 120 kVp, section thickness of 5 mm, and a 4.25-mm interval in low-dose CT.
Group 1: Initial staging (41 patients) PET/CT and conventional imaging methods were concordant in 30 (73.2%) and discordant in remaining 11 patients (26.8) (Table 1). PET/CT upstaged five patients out of the 11 discordant cases and down-staged six patients. Two patients were upstaged from stage I to stage II (confirmed by pathological examination): one patient from stage II to stage III, one patient from stage II to stage IV, in whom CT showed a suspicious parenchymal lesion in the right lung while PET/CT confirmed focal intensely active right pulmonary nodal lesion with maximum SUV 4.2. Follow-up CT confirmed metastatic lymphomatous lesion in the right lung. Another patient was upstaged from stage III to stage IV. In this patient, PET/CT was the only modality to show bone lesions with maximum SUV ranging from 3.8 to 5.1 and mean SUV 4.2 (Fig. 1). In the six patients down staged by PET/CT, one patient from stage II to stage I, three patients from III to II and two patients from stage IV to stage II (Table 1). PET/CT thus modified the staging and treatment options in 11 out of 41 cases (26.8%), upstaging five (12.2%) patients and down-staging six (14.6%) patients. Group 2: Early response to therapy (51 patients) PET/CT and CIM were concordantly negative in 29 (56.8 %) patients out of the 51 of this group and concordantly positive in five (Fig. 2). Discordant was in 17/51 cases (33.3%). PET/
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Table 1 Results of CIM and PET/CT in the 11 discordant cases of the first group for initial staging CIM
PET/CT
Result
1
Rt. Cervical nodes
Upstaging from stage I to II
2
Lt. cervical Lymph node
3
Lt. cervical and mediastinal nodes
4
Mediastinal LN, abnormal suspicious parenchymatous Rt. lung lesion Cervical, supra-clavicular, mediastinal LN & splenic hilar LN
Bilateral cervical, bilateral axillary, mediastinal active LNs Bilateral cervical, axillary, sub-carinal active LN. Lt. cervical, mediastinal as well as gasro-splenic and para-aortic nodes Mediastinal lymph nodes with definite Rt. pulmonary lymphomtous lesion Cervical , supra-clavicular, mediastinal LNs, splenic hilar LNs & multiple active bone lesions. Rt. cervical only Pelvic LN only
5
6 7 8 9 10 11
Rt. cervical & Rt. para-tracheal Cervical, mediastinal, abdominal and pelvic LN,s Cervical, mediastinal, para-aortic nodes Cervical, common iliac, inguinal nodes Bilateral cervical, hepatic & splenic focal lesions Supra-& infra diaphragmatic lesions & hepatic focal lesion
Cervical and mediastinal Common iliac, inguinal nodes Multiple active splenic focal lesions only Infra-diaphragmatic nodes
CT was true-negative in 15 patients out of the 17 discordant findings, which were false-positive in CT. These 15 patients were kept under follow-up for 13 months and proved to be on total remission by all means including follow-up PET/CT. PET/CT was true-positive in one study out of the 17 discordant cases. It showed active uptake over the left inguinal lymph node with maximum SUV 2.94. This node was not reported in the conventional CT due to small size and open biopsy showed lymphomatous infiltration of this excised node (Fig. 3). PET/CT was false-positive in one study of a 5-year-old girl with HD (mixed cellularity) stage II B. She was evaluated after three cycles of induction chemotherapy. CT showed near total resolution of the previously demonstrated cervical and mediastinal nodes while PET/CT showed intense FDG uptake in the bowel wall associated with wall thickening max SUV 4:9 and resolution of the supra-diaphragmatic nodes. Open biopsy showed inflammation of the bowel wall with no evidence of lymphomatous infiltration (Fig. 4). In this group, after two to three courses of chemotherapy, the sensitivity, specificity, accuracy, and positive and negative predictive values of PET/CT were 100%, 97.7%, 98%, 85.7%, 100%, respectively, as compared to 83%, 66.6%, 68.6%, 25%, 96.7% for CIM (Table 2). Group 3: Evaluation of treatment response 3–8 weeks after end of therapy (42 cases) In 17 patients (40.4%), PET/CT were concordantly truenegative compared to CIM (Fig. 5), and concordantly true-
Upstaging from stage I to II Upstaging from stage II to III Upstaging from stage II to IV Upstaging from stage III to IV
Down staging from stage II to I Down staging from stage III to stage II Down staging from stage III to stage II Down staging from stage III to stage II Down staging from IV to II Down staging from IV to II
positive in five (11.9%) patients. One study was false-positive in both PET/CT and CIM. This study was for a patient with HD that showed solitary jugular lymph node involvement in both with maximum SUV 4.23. The patient didn’t receive any treatment. Six months later, PET/CT showed complete resolution of this lesion. On the other hand, PET/CT was discordant with CIM in 19/42 (45.2%) patients. Thirteen of these 19 patients PET/ CT were negative while conventional CT showed residual masses. All were kept under follow-up for 10 months and proved to be in complete remission clinically and by follow-up PET/CT. In four studies, there was complete resolution of the previously detected lesions on the conventional CT while the PET/CT showed residual active uptake at some of the initial sites of involvement and a newly developed bone lesion in one; maximum SUVs ranged from 1.94 to 7.4. These patients, based on clinical assessment, received second-line chemotherapy. Follow-up PET/CT after end of treatment showed complete resolution of the previously reported active lesions. In two of the 19 discordant studies, PET/CT showed false-positive uptake. In one patient, there was active uptake in the large bowel; SUV 3.8 with no detectable lesions in the conventional CT or sonogram. Pathological examination of the surgically excised bowel lesion showed inflammation with no evidence of malignancy (Fig. 6a, b). In the other patient, there was low-grade uptake over small inguinal node that was less than 1 cm in the CT and was considered negative by CT criteria. Follow-up PET/CT after 6 months of follow-up with no treatment showed disappearance of this inguinal node.
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Fig. 1 a, b Baseline PET/CT showed right iliac and right proximal femoral lesions (a) as well as vertebral bony lesion (b, arrows)
In this group, the sensitivity, specificity, accuracy, and positive and negative predictive values of PET/CT were 100%, 90.9%, 92.8%, 75%, 100%, respectively, as compared to 55.5%, 57.5%, 57.1%, 26.3%, and 82.6% for CIM (Table 2). Fig. 2 Results of PET/CT and CIM in early evaluation of chemotherapy response
Group 4: Follow-up (18 patients) Concordance between PET/CT and CIM was found in 13/18 patients (72.2%). Eight were true-negative and five were true-positive in both PET/CT and CIM. Discordance was in
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Fig. 3 PET/CT showed metabolically active disease in Lt. inguinal lymph node with SUV 2.94
5/18 cases (27.7%) in which PET/CT was true negative and confirmed by another follow-up study after 6 months. PET/CT showed 100% sensitivity, specificity, accuracy, and positive and negative predictive values while the CIM showed 100% sensitivity, 38.4% specificity, 72.2% accuracy, 50% PPV, 100% NPV (Table 2).
Discussion 18
F-FDG PET/CT is now considered the most accurate imaging modality in the management of adult lymphomas. Its value has been well documented for initial staging, at mid chemotherapy, after the end of therapy, and for assessing tumor recurrence in the follow-up [15, 17, 20–23]. However, few data are available in the literature about pediatric lymphoma [9–13]. Although one may expect similar 18F-FDG uptake whether the patient is a child or an adult, the situation is different as we are dealing with different populations. The pathological subgroups are different in children and adults; for example, the nodular sclerosis and mixed cellularity subtypes are the most frequent forms of HD in children [1]. NHLs in children also differ from NHLs in adults. In children, they present with high-grade malignancy, fre-
quent extra-nodal sites, and early non-contiguous spread, particularly to the bone marrow and the central nervous system. They are mainly a proliferation of immature lymphoid cells [4]. Regarding treatment, in the past there was great concern about long-term side-effects related to cumulative effects of high-dose chemotherapy and asymmetrical volumes of irradiation [1, 4]. Therapeutic improvements thus entailed reduction of doses and of fields of irradiation, fractionation of the doses, and use of newer chemotherapeutic agents. All of these resulted in diminishing therapy-related morbidity and late effects. Improving the patient’s quality of life still remains a big challenge in pediatric oncology. Surveillance of minimal residual disease is thus of primary importance in following those patients cured with less aggressive treatments. Clinical follow-up is very crucial and has to be supported by other imaging modalities when needed. The choice between these has to be in consideration of saving patients from unnecessary radiation and be as cost-effective as possible. Initial staging Accurate initial staging is of primary importance, especially in children, as over-treatment increases the risk of long-
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Fig. 4 PET/CT showed intense tracer uptake in the wall of the descending colon with suggested wall thickening in the CT images. Biopsy showed inflammatory cells
term side-effects, and advanced stages require an aggressive therapeutic regimen. PET has been reported to affect the initial staging and treatment planning of up to more than 20% of cases [15, 16, 20, 24–27]. Wiehrauch et al. 2002 showed that PET upstaged four out of 22 patients with HD Table 2 Sensitivity, specificity, accuracy, PPV, NPV of PET/CT and CIM of various groups in the study Sensitivity Specificity Accuracy PPV NPV
[28]. Many studies proved that PET is superior to conventional imaging modalities in the initial staging of lymphoma [29–32]. Montravers et al. 2002 reviewed 27 PET studies including 15 studies using a coincidence system in 27 children [13]. They found very encouraging
Early evaluation (Group 2)
Late evaluation (Group 3)
Recurrence (Group 4)
PET/CT (%)
CIM (%)
PET/CT (%)
CIM (%)
PET/CT (%)
CIM (%)
100 97.7 98 85.7 100
83 66.6 68.6 25 96.7
100 90.9 92.8 75 100
55.5 57.5 57.1 26.3 82.6
100 100 100 100 100
100 38.4 72.2 50 100
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Fig. 5 Results of PET/CT and CIM after end of chemotherapy
results in terms of both diagnostic performance and clinical impact. The population included both HD and NHL, and the indications for the study were variable. PET changed the stage of the disease in four out of seven cases, and affected the choice of treatment in one out of seven. Depas et al. 2004 indicated that 18F-FDG PET is an appropriate method for evaluating children with lymphomas, but they also showed that its performance and impact may differ according to the clinical situation [27]. PET modified both the stage and the treatment approach in 10.5% of the patients. Hermann et al. 2005 carried their work on 25 patients with pediatric lymphoma for initial staging comparing FDG PET with conventional CT. They concluded that the staging of childhood lymphoma using FDG PET shows differences compared to CT resulting in a different staging in six of 25 patients [39]. In our study, PET/CT modified the staging and treatment planning in 11 out of 41 cases (26.8%), upstaging five (12.2%) patients and down staging (14.6%) patients. Evaluating response to therapy Morphologic image abnormality is not a reliable indicator of active disease. Residual abnormalities occur in 30–60% after therapy and are usually considered persistent lymphoma, as CT scan cannot differentiate between benign and malignant disease. Only 10–20% of these residual masses seen at completion of therapy are positive for lymphoma on biopsy and 18% of these will eventually relapse. Additionally, distinct subgroups of non-Hodgkin’s lymphoma respond differently to various therapeutic approaches [33, 34]. PET has an important role in evaluating the response to chemotherapy. It is usually performed after completion of therapy. Earlier assessment is becoming popular as a routine part of management in patients with HD and histologically aggressive NHL. Changes in FDG uptake can occur soon after initiation of chemotherapy and precede changes in tumor volume seen on morphological imaging modalities. Few authors correlated between early evaluation of chemotherapy (after 2–3 weeks) with long-term prognosis and survival. Timing in evaluating the response to therapy is debatable. Kostakoglu et al. 2002 showed that progression-free survival is better correlated with PET after
the first cycle of chemotherapy [35]. On the other hand, Friedberg et al. 2003 showed that PET after 3 cycles of chemotherapy has higher predictive value for disease recurrence than PET scanning after completion of therapy [36]. MacManus et al. 2007 has assessed the value of FDG early response assessment with PET in aggressive NHL (predominantly diffuse large B cell lymphoma) and HD. They concluded that PET imaging after two to three cycles of chemotherapy is far superior to CT scan in predicting free survival and is reliable as assessment of response at end of therapy [37]. In 2007, Strobel et al. compared the impact of PET/CT during and after chemotherapy in 40 patients with HD and 30 patients with NHL. PET/CT performed after two to four cycles of chemotherapy in 31/ 40 (82%) with HD demonstrated complete remission, which did not change at the end of therapy by PET/CT findings. The remaining nine patients with HD (18%) had partial remission in PET/CT. For NHL 22/30 (73%) patients had complete remission in PET/CT, which was unchanged in repeated studies at the end of treatment. In the remaining eight patients with NHL, PET/CT during treatment revealed partial remission in seven patients and stable remission in one patient. None of the complete responders progressed until the end of therapy. They concluded that end treatment PET/CT is unnecessary if PET/CT study after two or three cycles of chemotherapy shows complete remission and the clinical course is uncomplicated [38]. Depas et al. 2005 [27] reported specificity of conventional imaging methods to be 56% as compared to 94% specificity for PET in evaluating treatment response. Patients (15/16) with negative PET scan at the end of treatment remained in remission, compared to 9/16 patients for conventional imaging methods. They stated in their study that here was no standardization regarding the timing of the PET evaluations during treatment. It is not known whether studying patients after two to three cycles of chemotherapy will yield results similar to those obtained when performing PET at end of therapy. Similarly, the present study showed that the specificity of PET/CT was 97.7% as compared to 66.6% of conventional radiological methods in early evaluation of treatment response. The same results were found in assessment of response at the end of chemotherapy treatment. The specificity of PET/CT was 90.9% compared to 57.5% for
Eur J Nucl Med Mol Imaging (2010) 37:319–329 Fig. 6 a PET/CT showed intense tracer uptake in the lower abdomen 3 weeks after completion of chemotherapy. b Pathological examination showing suppurative inflammation with no malignant cells
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conventional radiological measures. Although the followup period for the discordant cases that were negative in PET/CT (13 months for group II and 10 months for group IV) is relatively short to judge that PET/CT is right. After coupling PET/CT results with clinical evaluation and follow-up laboratory essay and follow-up CT, we come to great certainty that PET/CT was right at this stage. Long-term follow-up Furthermore, in children, the issue of follow-up became one of particular importance. Although the overall recurrence rate is fairly low, particularly in HD, the general trend to reduce the aggressiveness of the therapeutic regimen may lead to an increase in the number of relapses. The availability of efficient salvage treatments may further justify systematic follow-up of those patients who are at risk of relapse, using an accurate technique. Depas et al. 2005 indicated the ability of PET to detect recurrence after treatment. Fifty-six out of 59 PET studies were negative in the systematic long-term follow-up compared with 39/59 for conventional methods evaluations. PET was falsepositive in 3/59 PET studies. False-positive results were due to muscle uptake, asymmetrical thymus, and atrial myocardial uptake. They reported high specificity of 95% for PET versus 66% for conventional methods in detection of recurrence during long-term follow-up [27]. The results of the current study are comparable to these results as it showed 100% specificity for PET/CT in detection of recurrence versus 38.4% for conventional CT.
Conclusion The current study showed the importance of 18F-FDG PET/ CT as a useful method in the management of pediatric lymphomas. It showed great value in initial staging of lymphomas. PET/CT had significant implications in terms of early assessment of treatment response. PET/CT appears to be highly specific and allows for accurate characterization of residual masses, which are not uncommon in pediatric patients.
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