PET-Center, Groningen University Hospital, The Netherlands. Dept. of Urology, Groningen University Hospital, The Netherlands

Transcription

1 CHAPTER 5 VISUALIZATION OF BLADDER CANCER USING 11 C-CHOLINE POSITRON EMISSION TOMOGRAPHY (PET): FIRST CLINICAL EXPERIENCE. I.J. de Jong 1,2, J. Pruim 1, PH. Elsinga 1, M,M.G.J Jongen 1, H.J.A. Mensink 2 and W. Vaalburg 1 1 PET-Center, Groningen University Hospital, The Netherlands 2 Dept. of Urology, Groningen University Hospital, The Netherlands Eur J Nucl Med 2002;29:

2 Chapter 5 ABSTRACT INTRODUCTION Fluorine-18 fluorodeoxyglucose (FDG), the most widely used radiopharmaceutical in positron emission tomography (PET) for oncological purposes, is unsuitable for imaging of bladder cancer due to high excretion into the urine. More specific PET radiopharmaceuticals which are not excreted into urine would be welcome. Carbon- 11 labeled choline (CHOL) is a new radiopharmaceutical potentially useful for tumor imaging and is not excreted into the urine. We prospectively studied the visualization of bladder cancer using CHOL PET. METHODS Eighteen patients with bladder cancer and five healthy volunteers were included. Bladder cancer was first diagnosed by transurethral resection or by biopsy of the tumor. Next, PET images were performed before surgical treatment by cystectomy. The histopathological findings after cystectomy were used as the gold standard. PET images were performed on either an ECAT 951/31 or an ECAT Exact HR+ system. Attenuation-corrected PET images were obtained after injection of 400 MBq CHOL. PET images were analyzed by two independent physicians using visual analysis and calculation of the standardized uptake value (SUV). RESULTS In the normal bladder wall, the uptake of CHOL was low, and the bladder margin was only outlined by minimal urinary radioactivity, if present. In ten patients the tumor was detected correctly by CHOL PET with a SUV of 4.7 ± 3.6 (mean±sd). One false positive CHOL PET scan was seen in a patient with an indwelling catheter for 2 weeks prior to the PET scan. In two patients lymph node metastases were detected by CHOL PET. A micrometastasis < 5 mm was not visualized with CHOL PET. In seven patients, no residual tumor was found after surgery. In six of seven patients CHOL PET imaging was negative. In situ carcinoma, dysplasia and a non invasive urothelial tumor (pta) remained undetected in three of these six patients. Minimal to no urinary tract radioactivity was seen in 22/23 subjects. Non-specific uptake of CHOL was observed in the small bowel, rectum and prostate gland. CONCLUSION CHOL uptake in bladder cancer was avid, visualizing the tumor in the virtually absence of urinary radioactivity. No uptake of CHOL was seen in pre-malignant lesions or in small non-invasive tumors. Our results warrant further research into the value of CHOL PET in the clinical management of patients with bladder cancer. Key words:bladder cancer Choline - Positron emission tomography 56

3 Visualization of bladder cancer using 11 C-Choline PET INTRODUCTION Positron emission tomography (PET) using 18 F-fluoro-2-deoxy-D-glucose (FDG) has been shown to be an accurate technique for tumor detection and staging and for the monitoring of therapy in patients with malignant tumors 1. Clinical experience with FDG-PET in bladder cancer has, however, reveals a major disadvantage of FDG: the excretion of radioactivity into urine causing accumulation of activity in the bladder 2,3. Carbon-11 labeled choline (CHOL) has been reported as a new PET radiopharmaceutical for tumor detection which is not excreted into the urine 4,5. Choline is one of the components of phosphatidylcholine, an essential element of phospholipids in the cell membrane 6. Malignant tumors may show a high proliferation and increased metabolism of cell membrane components which will lead to an increased uptake of choline 7. Recently, CHOL has been reported to be a potential radiopharmaceutical for the imaging of prostate and bladder cancer with PET 4,8. In this study we report on our first clinical experiences in the visualization of bladder cancer with CHOL PET. MATERIALS AND METHODS PATIENTS AND CONTROLS Eighteen consecutive patients with histologically proven bladder cancer and five healthy volunteers were studied. The patients were staged according to cystoscopy, findings of palpation during bimanual examination under anesthesia and transurethral resection or biopsy of the tumor. A computed tomography (CT) or a magnetic resonance imaging (MRI) scan of the abdomen was performed routinely to assess the presence of lymph node metastases and invasion beyond the bladder wall. A CT scan of the lungs was performed routinely to assess pulmonary metastases. To minimize post biopsy effects, all CHOL PET studies were performed at least 2 weeks after the transurethral resection or biopsy. Approval from the Hospital Medical Ethics Committee was obtained. Patients and controls were informed about the purpose and hazards of the study both orally and in writing, and gave their informed consent. RADIOPHARMACEUTICALS CHOL was produced using the Anatech RB-86 robot by the method described by Hara and co-workers 9. In brief, 11 C-methyl iodide, prepared from 11 CO 2, was transferred to a reaction vial at room temperature and trapped in 100 µl dimethylaminoethanol. After reacting at 100 o C for 5 minutes, the precursor was evaporated by a nitrogen flow of 200 ml/min at 110 o C for 10 minutes. CHOL was pro- 57

4 Chapter 5 duced with specific activities > 3700 GBq/mmol. CHOL was dissolved in 4 ml of saline. The solution was isotonic, colorless and sterile, with a radiochemical purity of > 95%. IMAGING PROTOCOL Prior to the PET study, patients were fasted overnight with the exception of water and their usual medication. The PET studies were performed using either an ECAT 951/ 31 or an ECAT Exact HR + PET Camera (Siemens/CTI, Knoxville, USA). These devices have a 56 cm patient aperture and simultaneously acquire 31 planes over a 10.8-cm (ECAT 951), or 63 planes over a 15.2-cm axial field of view (ECAT Exact HR + ). After appropriate positioning, a transmission scan using a 68 Ge/ 68 Ga ring source was performed over three bed positions (10 minutes per position), covering the pelvis and lower part of the abdomen. The upper external iliac spine was used as a reference for the lower limit of the upper bed position. This was immediately followed by intravenous injection of 400 MBq CHOL. Data acquisition was started at 5 minutes after injection. Static emission scanning was performed over the same area for 7 minutes per bed position. IMAGE RECONSTRUCTION AND ANALYSIS Attenuation-corrected images were made using an iterative reconstruction algorithm (ordered subsets expectation maximization). PET images were analyzed by two experienced PET physicians who were blinded to the clinical data, in order to determine the number and distribution of the lesions. The location of each lesion was marked on case record forms and qualitatively scored as;, no uptake; +, low uptake, just above background; ++, intermediate uptake, clearly above background or +++, high uptake. Analysis of the preferential uptake of the radiopharmaceutical in the primary tumor was performed by calculating standardized uptake values (SUVs) from regions of interest (ROIs) obtained from the attenuation-corrected images. The ROIs were visually drawn over the primary tumor using the ROI tool in the standard ECAT software. HISTOLOGICAL EXAMINATION To obtain the diagnosis of invasive bladder cancer, histology was studied on surgical specimens obtained by transurethral resection or biopsy of the tumor. Secondly, after pelvic lymph node dissection and radical cystectomy, the final pathological stage was determined. The surgical specimens were processed according to the standard methods. In brief this included conditioned optimal fixation, the taking of samples of the tumor to be stored in a frozen tissue bank and dissection of the pelvic lymph node specimens. The tissue was embedded in paraffin and mounted on slides. Primary 58

5 Visualization of bladder cancer using 11 C-Choline PET histological diagnosis was made on haematoxylin and eosin (H/E) stained sections with, if necessary, additional immunohistochemical staining to optimize the histological diagnosis. Based on the histological examination the tumor size was determined and the tumor was staged according to the 1997 TNM classification of the International Union Against Cancer (UICC). STATISTICAL ANALYSIS No further statistics were applied owing to the limited number of investigated patients. RESULTS NORMAL DISTRIBUTION OF CHOL In the five healthy volunteers the uptake of CHOL in the bladder was low and equivalent to non-specific uptake of CHOL elsewhere in the pelvic region. The bladder margin was only outlined by the urinary radioactivity if present. Non-specific uptake of CHOL was seen in all patients in the intestines, rectum and prostate gland. VISUALIZATION OF BLADDER CANCER In 11 patients with bladder cancer a residual invasive tumor was found after final surgery. The results on CHOL PET imaging and final histology are shown in Table 1. In 10 of these 11 patients the tumor was visualized by CHOL-PET. The degree of uptake of CHOL in the tumor, measured by SUVs, ranged from 1.5 to 13.0 (mean±sd =4.7±3.6). Lymph node metastases were detected by CHOL PET in two patients, leaving a micrometastasis < 5 mm undetected in one patient. In seven patients with bladder cancer, no residual invasive tumor was found after final surgery ( T0 ). The results on CHOL PET imaging and final histology are shown in table 2. Pre-malignant lesions (dysplasia, in situ carcinoma) were present in three of these patients and in one patient a superficial urothelial carcinoma (pta) was present. In one of the seven patients without residual tumor, a substantial level of urinary radioactivity was seen which interfered with proper evaluation of the uptake of CHOL in the bladder wall. In the remaining six patients CHOL PET was negative, Figure 1 shows the CHOL-PET images of a patient with a pt4ag2n0m0 bladder cancer with infiltration into the prostatic stroma. Figure 2 shows the CHOL PET images of a patient with a pt3g3pn0m0 bladder carcinoma of the left bladder wall. In one patient CHOL PET was false positive, the appearance mimicking a bladder tumor of the right bladder wall and dome (SUV = 5.2) (Fig.3). This patients has had 59

6 Chapter 5 Table 1. Patients, tumor status and PET findings of patients with residual tumor after cystectomy (n=11) Pt. no. Age (yrs) Tumor location TUR/biopsy Clinical stage Cystectomy Visual uptake; tumor Visual uptake; nodes SUV tumor 1 63 Diffuse TxG2 UCC N0, M0 pt4ag2 N Bladder neck pt3g3 UCC N0, M0 pt3g3 pn Ventral, dome pt3g3 UCC N0, M0 pt4ag3 pn Trigone, dorsal pt3g3 UCC N0, M0 pt3g Dome pt2 CS N0, M0 n.p n.a Solitary PT2G3 UCC N0, M0 PT3G3 N Solitary left PT2G3 UCC N0, M0 pt3g3 N0 + - n.a Solitary left PT2G3 UCC N0, M0 pt2g3 pn Solitary left PT2G3 UCC N0, M0 PT3G3 pn0 +++ FP Solitary right PT2G3 UCC N0, M0 pt3g3 pn Dorsal T3G3 UCC N1, M0 pt3g3 N UCC, urothelial cell carcinoma; CS, Carcinosarcoma; FP, false positive; n.a., not available; n.p., not performed Table 2. Patients, tumor status and PET findings of patients without residual tumor after cystectomy (n=7) Pt. no. Age (yr) Tumor location TUR/biopsy Clinical stage Cystectomy Visual uptake; tumor Visual uptake; nodes SUV tumor 1 77 Solitary dome pt1g3 SC N0, M0 PT1a N Solitary right pt1g2 UCC N0, M0 pt0 pn0, CIS Multi focal pt1cg3 UCC N0, M0 pt0 N Solitary right pt2g3 UCC N0, M0 pt0 pn Solitary pt1g2 UCC N0, M0 pt0, dysplasia Solitary dome pt1g3 UCC + CIS N0, M0 pt0 pn0, CIS Solitary left pt1g3 UCC N0, M0 pt0 N0 n.a. - - SC, Squamous cell carcinoma; UCC, urothelial cell carcinoma; CIS, carcinoma in situ; n.a., not available 60

7 Visualization of bladder cancer using 11 C-Choline PET Figure. 1. Attenuation-corrected CHOL PET images of a patient with a pt4ag2 NO MO bladder carcinoma with invasion of the prostate gland. Increased uptake of choline is seen over the entire bladder wall and in the prostate. Figure. 2. Attenuation-corrected CHOL PET images of a patient with a pt3g3 pno MO bladder carcinoma. Increased uptake of choline over the tumor in the left bladder wall. 61

8 Chapter 5 Figure. 3. Attenuation-corrected CHOL PET images of a patient with a pt3g3 pno MO bladder carcinoma of the left wall. Increased uptake of choline is seen over the posterior and right bladder wall (SUV 5.2), but no uptake is seen in the tumor located in the left wall. and an indwelling catheter for 2 weeks prior to the PET study. The primary tumor in the left bladder wall remained unidentified with CHOL PET. DISCUSSION The most commonly used radiopharmaceutical for PET in oncology is FDG. However, FDG has a number of disadvantages, among which excretion into the urine is the most important when dealing with prostate or bladder cancer. To circumvent the problem of radioactivity in the bladder, numerous methods have been advocated. Bladder drainage by Foley catheter, continuous bladder irrigation and hyperhydration with forced diuresis were instituted but they did not solve the problem sufficiently 10,11. More specific PET radiopharmaceuticals which are not primarily excreted into the bladder would be welcome in PET imaging of bladder cancer 12. L-Methyl-[ 11 C]-methionine has been proposed for this purpose. However, the initial results using this radiopharmaceutical were poor, only tumors of more than 1cm in diameter being imaged 13. It was also shown that L-methyl-[ 11 C]-methionine-PET was unsuitable for monitoring of neoadjuvant chemotherapy in bladder cancer

9 Visualization of bladder cancer using 11 C-Choline PET CHOL is a new potential radiopharmaceutical for PET imaging of bladder cancer. Choline, after phosphorylation to phosphatidylcholine, is an essential component of the cell membrane 6. Cancer is associated with cell proliferation and up-regulation of the enzyme choline-kinase (which catalyzes the phosphorylation of choline), providing the rationale for the use of CHOL as a radiopharmaceutical in oncological PET 15. High contents of phosphorylcholine have been demonstrated in for instance breast cancer and cerebral gliomas using phosphorus-31 magnetic resonance spectroscopy imaging 15. In prostate cancer, alterations in choline/citrate ratios were measured using magnetic resonance spectroscopy 16. The intracellular mechanisms by which choline acts have not yet been completely clarified, but a function in cell signal transduction and in apoptosis has been proven 17. CHOL PET has already shown potential for the detection and staging of tumors in areas where FDG lacks sensitivity, such as the brain and the prostate 5,18, although we recently addressed limitations in esophageal cancer 19. Consistent with the initial report 5, we did not find uptake of CHOL in the normal bladder wall. Non-specific uptake was seen in the intestine, the rectum and the prostate gland in men, which did not interfere with the evaluation of the bladder and pelvic lymph nodes. In agreement with the previous reports on CHOL PET 4,5,8 we also observed some excretion of the tracer into the urine in the majority of the patients. In one patient we did see more intense accumulation of radioactivity in the urine. This accumulation may have been due to incomplete tubular re-absorption of the intact tracer as has been proven for 18 F-labelled choline 20, or to enhanced excretion of labeled oxidative metabolites like betaine 21. However, neither mechanism has yet been confirmed, further study of this question is warranted. In this study CHOL PET was effective in visualizing the primary tumor as a hot spot in the bladder. False positive CHOL PET was observed in one patient with an indwelling catheter for 2 weeks prior to the CHOL PET study. This finding is probably related to the inflammatory and proliferative changes in the mucosa of the bladder that are known to result from an indwelling catheter. So far, two choline transport mechanisms have been identified in mammalian cells: an energy dependent choline specific transport and transport by simple diffusion 17,20. Increased uptake of choline in reactive tissue could be explained by simple diffusion to hyperemia of the mucosa of the bladder. Uptake of CHOL in inflammatory tissue could lead to false positive results, as with FDG 22,23. The failure to detect small lesions like dysplasia, in situ carcinoma and superficial urothelial cell carcinoma could be due to the limitations of the resolution of the present generation of PET cameras, which is around 5 mm. Future generations of PET cameras will have intrinsic resolutions of approximately 2 mm. However, as well as the 63

10 Chapter 5 intrinsic resolution of the system, the signal-to-noise ratio (contrast) is of importance in PET imaging. A low contrast will decrease the visibility whereas high contrast can lead to an increase in visibility which may extend beyond the intrinsic resolution. The low uptake of choline in small and in pre-malignant lesions could be a limitation to the clinical application of CHOL PET in bladder cancer. CHOL PET yielded clear images with good contrast at 5 min post injection. The rapid blood clearance of CHOL allows rapid data acquisition which is convenient for the patient. On the other hand, the use of an 11 C-labelled radiopharmaceutical has a practical restriction, related to the short physical half-life of 11 C. This short half-life necessitates the availability of an on-site cyclotron, which may well limit the wide spread use of CHOL in the near future. Theoretically, 18 F-labelled choline should be an alternative to CHOL, but it has been shown that this tracer is excreted into the urine 24, the same limitation as is seen with FDG in bladder cancer. In conclusion, CHOL uptake in bladder cancer was avid, visualizing the tumor in the virtual absence of urinary radioactivity. No uptake of CHOL was seen in pre-malignant lesions or in small non-invasive tumors. These results permit further research on the value of CHOL PET in the clinical management of patients with bladder cancer. REFERENCES 1 Reske SN, Kotzerke J. FDG-PET for clinical use. Results of the 3rd German Interdisciplinary Consensus Conference, Onko-PET III. Eur J Nucl Med. 2001;28: Heicappell R, Muller-Mattheis V, Reinhardt M, Vosberg H, Gerha H, Ackermann R. Staging of pelvic lymph nodes in neoplasms of the bladder and prostate by positron emission tomography with 2-[(18)F]-2-deoxy-D-glucose. Eur Urol 1999:36: Bachor, R, Kotzerke J, Reske SN, Hautmann R. Lymph nde staging of bladder neck carcinoma with positron emission tomography. Urologe A 1999;38: Hara T, Kosaka N, Kishi H. PET imaging of prostate cancer using carbon-11-choline. J Nucl Med 1998;39: Hara, T, Kosada N, Kondo T, Kishi H, Kobori O. Imaging of brain tumor, lung cancer, esophageal cancer, colon cancer, prostate cancer and bladder cancer with (C-11)choline. J Nucl Med 1997;38:250P (abstract) 6 Zeisel SH. Dietary choline: biochemistry, physiology and pharmacology. Annu Rev Nutr 1981;1: Podo F. Tumor phospholipid metabolism. NMR Biomed 1999;12: Kotzerke J, Prang J, Neumaier B, Volkmer B, Guhlman A, Kleinschmidt K, Hautmann R, Reske SN. Experience with carbon-11 choline positron emission tomography in prostate carcinoma. Eur J Nucl Med 2000;27: Hara T, Kosaka N, Yuasa M, Yoshida H: 11 C-choline and 2-[ 18 F]Fluoroethyl-dimethyl-2- oxyethylammonium (choline analog): automated synthesis and tumor imaging. J Labelled Compounds Radiopharm 1997;40:

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