ELSEVIER
Early experience with PET/CT scan in the evaluation of pediatric abdominal neoplasms James J. Murphy*, Mansour Tawfeeq, Brett Chang, Helen Nadel
Department of Pediatric Surgery, British Columbia Children’s Hospital, Vancouver, British Columbia, Canada V6H 3V4 Department of Pediatric Radiology, British Columbia Children’s Hospital, Vancouver, British Columbia, Canada V6H 3V4
Received 25 August 2008; accepted 29 August 2008
Key words:
PET scan; PET/CT scan; Oncology; Pediatric abdominal neoplasms
Abstract
Purpose: Positron emission tomography/computerized tomography (PET/CT) scan provides both functional and anatomical information in a single diagnostic test. It has the potential to be a valuable tool in the evaluation of pediatric abdominal tumors. The goal of this study is to report our early experience with this technology.
Methods: Children who underwent PET/CT scan in the workup for abdominal neoplasms between July 2005 and January 2008 were identified. Retrospective review of all radiologic studies, operative notes, and pathologic reports was undertaken.
Results: A total of 36 patients were collected. These included Burkitt’s lymphoma (8), neuroblastoma (7), rhabdomyosarcoma (6), ovarian tumor (3), Wilms’ tumor (2), hepatocellular carcinoma (2), paraganglioma (1), germ cell tumor (1), undifferentiated sarcoma (1), renal primitive neuroectodermal tumor (1), gastrointestinal stromal tumor (1), adrenocortical carcinoma (1), inflammatory pseudotumor (1), and adrenal adenoma (1). All neoplasms were fluorodeoxyglucose (FDG) were avid. Our experience identified several potential uses for PET/CT scan in this group of patients. These include (1) preoperative staging, (2) selection of appropriate site for biopsy, (3) identification of occult metastatic disease, (4) follow-up for residual or recurrent disease, and (5) assessment of response to chemotherapy. It can also be valuable when the standard diagnostic studies are equivocal or conflicting.
Conclusions: Preliminary data indicate that PET/CT is a promising tool in the evaluation of pediatric abdominal malignancies. The delineation of the exact role of this diagnostic modality will require additional experience.
@ 2008 Elsevier Inc. All rights reserved.
Presented at the 41st annual meeting of the Pacific Association of Pediatric Surgeons, Jackson Lodge, Grand Teton National Park, Wyoming, June 29-July 3, 2008.
* Corresponding author. Department of Pediatric Surgery, British Columbia Children’s Hospital, Vancouver, British Columbia, Canada V6H 3V4.
E-mail address: jmurphy@cw.bc.ca (J.J. Murphy).
Positron emission tomography (PET) technology was developed in 1973 by UCLA researcher Michael E. Phelps [1]. It was initially used in neurology, oncology, and cardiology research.
Fluorodeoxyglucose (FDG) is a glucose analogue that concentrates in areas of active metabolic activity. F (fluorine)18-FDG has become one of the main radiopharma- ceuticals used for functional assessment in oncology since being approved by the Food and Drug Administration in 2000.
The computerized tomography (CT) has been the gold standard test in the evaluation of many malignancies because of the precise anatomical detail it provides. Unfortunately, it does not provide any functional assessment of the tumor. Adjuncts such as meta-iodobenzylguanidine (MIBG) scan in neuroblastoma and gallium scan in lymphoma have been used for that purpose.
The development of a combined PET/CT scanner by Townsend et al [2] in 2000 allows a combination of functional assessment along with fine anatomical detail that has never been available in a single diagnostic modality.
1. Methods
Children who underwent FDG PET/CT in the workup of abdominal neoplasms between July 2005 and January 2008 were identified. Retrospective review of the radiology reports, operative notes, and pathology reports was under- taken. Institutional review board approval was obtained. Information obtained from radiology reports included preoperative or postoperative timing of the study, location of primary tumor as well as the presence of metastatic disease. Avidity of the primary as well as metastatic disease for FDG was recorded. Comparison with standard imaging
techniques such as ultrasound, CT scan, and magnetic resonance imaging (MRI) was made to determine if PET CT scan provided additional information. Preoperative and postoperative scans as well as preadjuvant and postadjuvant therapy (chemotherapy and radiation therapy) scans were compared to assess response to therapy. Operative reports were correlated to preoperative radiologic imaging. In cases where pathology was available, histologic evaluation of the specimen was correlated with FDG avidity.
1.1. Imaging protocol
The administered intravenous dose of FDG was based on 0.14 mCi/kg, minimum of 1 mCi and maximum of 15 mCi. Our uptake period was 60 minutes. To reduce physiologic metabolic fat uptake, the patients were warmed with warm blankets preinjection and in the uptake period. A single PET/ CT scan on an LSO Biograph 16-slice scanner (Siemens Medical, Malvern, Pa., USA) was acquired that sufficed for attenuation correction and diagnostic evaluation. Acquisition parameters for CT were optimized for as low dose as rea- sonably achievable. If the examination was a follow-up study, a low-dose CT with acquisition parameters of 80 kilovolt (peak) and 40 to 60 mA was obtained. All examinations were
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performed with CT dose modulation. This low-dose technique would provide an estimated effective dose of approximately 7 to 9 millisievert (mSV) to the patient. Most CT scans were obtained after the intravenous injection of non-ionic contrast material in a dose of 2 mL/kg up to a maximum of 100 mL. Portal venous opacification was obtained with injection time of 50 seconds with scanning beginning at the end of the injection period at 50 seconds. No oral bowel contrast was used. Imaging was obtained craniocaudal for both the CT and the PET portions of the study. Scanning was performed with the patient breathing quietly for both the PET and CT. The CT images were then reconstructed in 3-mm slice
thickness coned to body contour. The PET and CT studies were displayed and reviewed in multiple planes for both fused and unfused images. All imaging was reviewed by our pediatric radiologist who is dual qualified in diagnostic radiology and nuclear medicine.
2. Results
A total of 36 patients were collected. These included Burkitt’s lymphoma (8), neuroblastoma (7), rhabdomyosar- coma (6): abdominal wall, biliary, prostatic [2], paraspinal, and paratesticular), ovarian tumor (3): dysgerminoma [2],
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granulosa cell tumor [1]), Wilms’ tumor (2), hepatocellular carcinoma (2), undifferentiated sarcoma (1): postradiother- apy for neuroblastoma), metastatic germ cell tumor (1), gastrointestinal stromal tumor (1), adrenocortical carcinoma (1), renal primitive neuroectodermal tumor (PNET) (1), paraganglioma (1), gastric inflammatory pseudotumor (1), and adrenal adenoma (1). A total of 51 PET CT scans (23 preoperatively and 28 postoperatively) were performed.
Fluorodeoxyglucose avidity (FDG) was demonstrated in each of these 36 abdominal solid tumors, both at the primary site as well as in the areas of metastatic disease (Figs. 1-3, 5, 6). The FDG avidity appears to decrease with effective
chemotherapy. Fig. 1 (top) demonstrates the FDG avidity of a very large renal PNET before chemotherapy. Fig. 1 (bottom) shows nearly complete resolution of the FDG avidity after 4 courses of chemotherapy. The lesion was completely resected and pathologic evaluation showed only necrotic tumor with no viable residual PNET.
PET/CT is valuable in demonstrating occult metastatic tumor at unsuspected sites. Figs. 2 and 3 show a child with a recurrent anaplastic Wilms’ tumor. Routine screening ultrasound suggested a small pelvic recurrence. The PET/ CT showed multiple areas of recurrent metastatic disease throughout the abdominal cavity. At laparotomy, she had 5
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different sites of disease, each of which was identified on the PET/CT scan. Figs. 3 and 4 demonstrate tumor in the greater omentum that was seen in the left upper quadrant on PET/CT scan.
PET/CT is also useful in cases where the standard diagnostic studies are equivocal or conflicting. Fig. 5
demonstrates a patient with a recurrent abdominal mass after chemotherapy and radiation therapy for a neuroblastoma. The patient’s initial tumor was MIBG avid, whereas the recurrence was not. PET/CT showed a strongly avid FDG mass with central necrosis. Biopsy demonstrated this to be an undiffer- entiated sarcoma. Unfortunately, he returned with recurrent disease after chemotherapy, and repeat PET/CT showed multiple sites of disease (Fig. 5).
In patients with lymphoma, PET/CT is used for staging as well as to assess residual soft tissue mass after treatment. In two cases with FDG avid nodal disease after completion of therapy, surgical biopsy demonstrated residual active disease. Several patients with a residual soft tissue mass and a negative PET/CT post therapy have been observed without biopsy. No disease recurrence has occurred in that group. Ultrasound and/or magnetic resonance imaging has shown gradual resolution of the residual mass in each case. Laparotomy and biopsy was avoided in these patients. Fig. 6 shows a patient with a gastric Burkitt’s lymphoma. Initial scan demonstrates a highly FDG avid and markedly thickened gastric wall. Follow-up study after completion of chemotherapy reveals a slightly thickened gastric wall with no FDG avidity. This patient has been observed with no further therapy or biopsy.
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In neuroblastoma, FDG avidity appears to diminish with maturation of the tumor. Our current policy is to only use PET/CT scan in non-MIBG avid tumors or if there is conflicting information from the standard imaging. One of the major advantages of PET/CT over MIBG is that the initiation of imaging is after 60 minutes from FDG administration in comparison to 1 to 2 days after MIBG tracer injection. Unlike MIBG, FDG is not specific for neural crest tumors, but future PET/CT imaging with F18- Dopamine may be more specific. Fluorodeoxyglucose PET/ CT in our neuroblastoma cases has shown a greater number of metastatic lesions as well as more clearly identifying metastatic disease than the standard imaging modalities. As
Table 1 Potential uses of PET/CT in pediatric abdominal neoplasms
1. Preoperative staging
2. Selection of appropriate site for biopsy
3. Identifying occult distant metastases
4. Follow-up for recurrent or residual disease (especially lymphoma)
5. Assessment of response to adjuvant chemotherapy
6. Valuable where standard diagnostic studies are equivocal or conflicting
the technology is refined, it may be helpful in assessing response to therapy.
3. Discussion
The PET scan has been increasingly incorporated into diagnostic and follow-up protocols of adult and pediatric malignancies, especially in lymphomas and sarcomas [3-5]. The PET/CT scan in pediatric sarcoma was found to have a high sensitivity (92%) in the detection of malignant sites, similar to results reported in adult patients [3]. In December 2007, Volker [4] reported one of the few prospective studies using PET scan in pediatric sarcoma. The study included 46 patients (Ewing’s sarcoma [23], rhabdomyosarcoma [11], and osteosarcoma [12]). It showed that PET was superior to conventional imaging modalities in the correct detection of lymph node involvement (sensitivity, 95% vs 25%, respec- tively) and bone manifestations (sensitivity, 90% vs 57%, respectively), whereas CT was more reliable than FDG-PET/ CT scan in depicting lung metastases (sensitivity, 100% vs 25%, respectively).
There is a paucity of literature regarding the use of PET and PET/CT in pediatric abdominal neoplasms. To date, this has been limited to single case reports [6-8], with no large series reported.
The FDG avidity was demonstrated in all abdominal tumors, making it a very sensitive diagnostic modality. This may decrease with effective chemotherapy and/or maturation of the tumor (ie, neuroblastoma). Table 1 summarizes the potential uses of PET/CT scan in this group of patients. Its exact role cannot be delineated until additional experience is obtained.
Sites of normal FDG avidity (adenoids thymus, thyroid, bone marrow, growth plate, brain, myocardium, renal pelvis, ureter and bladder, and metabolic fat uptake) can make the interpretation of the PET alone difficult at times. However, in combination with the CT scan the physiologic activity in anatomically normal areas becomes much less of a problem. Reactive lymphadenopathy and postoperative inflammation can demonstrate mild FDG avidity. These false positive scans can be problematic from a surgical perspective. In our limited experience, FDG avidity was much higher in malignant neoplasms than that seen in inflammatory masses. This may allow more accurate differentiation between the two as the technology is developed and refined. Determina- tion of the exact sensitivity and specificity of PET/CT will require additional experience.
References
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