ORIGINAL ARTICLE 
Annals of Nuclear Medicine Vol. 15, No. 4, 329-335 2001 
99mTc-MIBI SPECT in small cell lung cancer patients before chemotherapy and after unresponsive chemotherapy 
Yuka YAMAMOTO,* Yoshihiro NISHIYAMA,* Kotaro FUKUNAGA,* Katashi SATOH,* Jiro FUJITA** and Motoomi OHKAWA* 
*Department of Radiology, Kagawa Medical University **First Department of Internal Medicine, Kagawa Medical University 
We evaluated the accumulation of 99mTc-MIBI in small cell lung cancer patients before chemotherapy and after unresponsive chemotherapy. The pre-chemotherapeutic group included 22 newly diagnosed patients. These patients underwent a 99mTc-MIBI SPECT study before starting chemotherapy. After chemotherapy, based on changes in tumor size, three different patterns of response (complete remission: CR, partial remission: PR and no change: NC) were defined. The post-chemotherapeutic group included I I patients after chemotherapy who did not respond to chemotherapy. These patients underwent a 99mTc-MIBI SPECT study after completion of chemotherapy. SPECT images were acquired 15 min (early) and 2 hr (delayed) after injection of 99mTc-MIBI. With a region of interest technique, the early ratio, delayed ratio and retention index were calculated. Early and delayed ratios in pre-chemotherapeutic patients were significantly higher than those in post-chemotherapeutic patients. There were no significant differences between the pre-chemotherapeutic and post-chemotherapeutic patients in the retention index. In the pre-chemotherapeutic patients, early and delayed ratios for the CR and PR groups were significantly higher than those for the NC group. There were no significant differences in the retention index with respect to the tumor response 99mTc-MIBI might be useful for evaluating the tumor chemosensitivity in patients with small cell lung cancer. 
Key words: 99mTc-MIBI, small cell lung cancer, chemotherapy 
INTRODUCTION 
THE PRIMARY THERAPEUTIC METHOD for small cell lung cancer is chemotherapy, but the ability of tumors to develop resistance to chemotherapeutic agents is one of the greatest barriers to successful treatment of human cancers. Therefore, the development of effective therapeutic regimens for these resistant neoplasms is an urgent problem in cancer chemotherapy. Nuclear medicine imaging techniques may be applicable to the evaluation of therapeutic efficacy and the 
Received December 13, 2000, revision accepted April 18, 2001. For reprint contact: Yuka Yamamoto, M.D., Department of Radiology, Kagawa Medical University, 1 750-1 Ikenobe, Miki-cho, Kita-gun, Kagawa 76l-0793. JAPAN. E-mail: yuka@kms.ac,jp 
prediction of therapeutic response in cancer. Non-cardiac uses of 99mTc-MIBI (hexakis 2-methoxy isobutyl-isonitrile), such as visualization of lung cancer, have also been investigated. 1-3 Multidrug resistance (MDR) in tumor cells has been correlated with overexpression of MDR1 gene coding for P-glycoprotein (Pgp), a plasma-membrane protein that functions as an energy-dependent transporter of cytotoxic lipophilic agents.4 99mTc-MIBI can be excluded from cytosol against its concentration gradient as a suitable transport substrate by Pgp.5 In this study we evaluated the accumulation of 99mTc-MIBI in small cell lung cancer patients before chemotherapy and after unresponsive chemotherapy. 
MATERIALS AND METHODS 
Patients Thirty-three patients (26 men and 7 women; age range 39-78 yrs) with pre-chemotherapeutic and post-chemotherapeutic small cell lung cancer were investigated. Diagnosis was made by histopathologic analysis of sputum, computed tomography (CT)-guided needle biopsy or endoscopic samples. The pre-chemotherapeutic group included 22 patients newly diagnosed before chemotherapy. These patients underwent a 99mTc-MIBI single photon emission computed tomography (SPECT) study before starting chemotherapy. After the SPECT study, these patients received multidrug chemotherapy regimens consisting of cyclophosphamide, doxorubicin, vincristine, etoposide, cisplatin, mitomycin-C and vindesine. Response to chemotherapy was evaluated by using dimensional criteria: the tumor size was measured on a CT scan performed before the start and within 2-4 weeks after the last chemotherapy. Based on the General Rule for Clinical and Pathological Record of Lung Cancer 6 three different patterns of response were defined: complete remission (CR) (no evidence of disease), partial remission (PR) (50-99% reduction in tumor size) and no change (NC) (less than 50% decrease or increase in tumor size). The post-chemotherapeutic group included 11 patients after completion of chemotherapy consisting of cyclophosphamide, doxorubicin, vincristine (CAV) and etoposide and cisplatin (VP) every 4 weeks for at least four times and who did not respond to chemotherapy (NC). These patients underwent a 99mTc-MIBI SPECT study after completion of chemotherapy. The tumor size on CT ranged from 1.5 to 6.0 cm for pre-chemotherapeutic patients and 1.5 to 5.0 cm for post-chemotherapeutic patients. There were no significant differences among the two groups in tumor size. All patients provided written Informed consent in agreement with the regulations of the university hospital ethical committee. 
SPECT Imaging
SPECT imaging was performed with a large field-of-view gamma camera, with high resolution and a parallel-hole collimator (Picker Prism 2000; Picker International, Cleveland, OH). This camera was interfaced to a dedicated computer (ODYSSEY; Picker International). Doses of 600 MBq 99mTc-MIBI were injected intravenously. Early SPECT acquisition was performed 15 min after the injection of the radioisotope, whereas delayed SPECT images were acquired 2 hr after injection. For SPECT images of the chest, 72 projections were obtained with a 64 x 64 matrix for 45 sec/view in a step-and-shoot mode. With a dual head camera, the total actual acquisition time was 27 min. Image reconstruction was performed by filtered backprojection with a ramp filter. Transverse, coronal and sagittal sections were reconstructed. The system was 7 mm FWHM, and the slice thickness was 10 mm. Attenuation correction was not performed. 
Data Analysis
SPECT images were compared with chest CT and two nuclear medicine physicians (Y.Y., Y.N.) evaluated accumulation in lung tumors. For all patients studied, the transverse slices were evaluated first, followed by the coronal and sagittal views. Semiquantitative analysis of the abnormal uptake of 99mTc-MIBI was performed by drawing identical regions of interest (ROIs) over the tumor uptake and contralateral lung tissue areas on one transverse section that demonstrated the lesion most clearly on both early and delayed scans (Fig.1). The mean ROI values (total counts/total pixels) were measured, and the tumor-to-normal (T/N) ratios were obtained. We called the T/N ratio of early image the early ratio and the T/N ratio of delayed image the delayed ratio. To semiquantitatively evaluate the degree of retention in the lesion, the retention index was calculated with the following formula: (delayed ratio - early ratio) x 100/early ratio 7 The T/N ratio and retention index were expressed as the mean +- S.D. Comparison of pre-chemotherapeutic and post-chemotherapeutic patients for each parameter on 99mTc-MIBI SPECT was performed with the Mann-Whitney U-test. Comparison between CR, PR and NC groups of each parameter on 99mTc-MIBI SPECT was performed with one-factor analysis of variance followed by the post-hoc test. Results were considered significant when p < 0.05. 
RESULTS 
The early ratio was 2.48 +- 0.92 in pre-chemotherapeutic patients and 1.86 +- 0.47 in post-chemotherapeutic patients and this difference was significant (p = 0.0427) (Fig. 2). The delayed ratio was 2.48 +- 1.00 in pre-chemotherapeutic patients and 1.65 +- 0.34 in post-chemotherapeutlc patients and this difference also was significant (p = 0.0059) (Fig. 3). The retention index was 0.66 +- 19.23_ in pre-chemotherapeutic patients and -9.55 +- 11.46 in post-chemotherapeutic patients and there was no significant difference between the two groups (Fig. 4). In pre-chemotherapeutic patients, after chemotherapy 6 patients experienced CR, 9 PR and 7 NC. The early ratio was 3.00 +- 0.94 in the CR group, 2.79 +- 0.74 in the PR group and 1.63 +- 0.50 in the NC group. Figure 5 shows that the early ratios for CR and PR groups were significantly higher (p = 0.0034 and p = 0.0056, respectively) than that of the NC group. The delayed ratio was 3.42 +- 1.04 in the CR group, 2.62 +- 0.53 in the PR group and 1.49 +- 0.38 in the NC group. Figure 6 shows that the delayed ratios for the CR and PR groups were also significantly higher (p = 0.0001 and p = 0.0032, respectively) than that of the NC group. The retention index was 14.66 +- 15.38 in the CR group, -3.94 +- 1 2.76 in the PR group and -5.42 +- 24.68 in the NC group, and there was no significant difference among the three groups (Fig. 7). Radiological findings in two typical cases are shown in Figures 8 and 9.
DISCUSSION 
Use of 201Tl-chloride SPECT is attracting attention for the detection of lung cancer 7 The mechanism of 201Tl-chloride uptake in the cell has been reported to be related to the sodium-potassium adenosine triphosphate pump system.8,9 Since the late 1980s, there has been an increasing number of studies describing 99mTc-MIBI uptake in several tumors, including lung tumors.1-3,10-14 The mechanism of 99mTc-MIBI uptake is different from that of 201Tl-chloride. It has been shown that 99mTc-MIBI is attached to a low molecular weight protein in the lysosomes. The cationic charge and lipophilicity of 99mTc-MIBI, the mitochondrial and plasma membrane potentials of the tumor cell and the cellular mitochondrial content may play a significant role in the tumor uptake of this agent.15 Since malignant tumors maintain a more negative transmembrane potential due to their increased metabolic requirements, this has been postulated to cause increased accumulation of 99mTc-MIBI in malignant tumors. The uptake of 99mTc-MIBI may be also caused by indirect phenomena, such as increased tumor blood flow and capillary permeability.2 A close relationship between 99mTc-MIBI uptake and tumor neoangiogenesis has been observed in other types of neoplasm.16 The mechanism of the chemotherapy effect is not clear. The results of chemotherapy may be conditioned by several factors; in particular, blood flow and vascularity of the tumor affect the bioavailability of the drug and its concentration in extracellular fluids in the neoplastic tissue.17 On the other hand, oxidative metabolism, viability and MDR gene expression infiuence the sensitivity of neoplastic cells to the drugs.18-21 Recently many studies have found that 99mTc-MIBI is a suitable transport substrate of the Pgp efflux pump. The degree of overexpression of Pgp determines resistance to certain chemotherapeutic drugs such as anthracyclines, vinca alkaloids, epipodophyllotoxin, colchicine and actlnomycin D.5,22-26 This indicates that 99mTc-MIBI uptake by neoplastic cells is related to certain factors (histological: blood flow and vascularity; biological and biochemical: cellular metabolism and viability, and expression of MDR) that affect the pharmacological action of the drugs and the results of chemotherapy. Therefore, the degree of 99mTc-MIBI uptake by the tumor can be assumed to be the result of different balances among these factors and it may be considered as a non-invasive in vivo tool to assess the chemosensitivity of the neoplastic mass. It has been suggested that determination of Pgp levels in patients at diagnosis or relapse may play a major role in the design of future treatment protocols 27 but various investigations have revealed only low levels of MDR1 expression in patients with lung cancer, including both small and non-small cell lung cancers 28.29 99mTc-MIBI uptake in a tumor does not necessarily indicate that a cancer is sensitive to drugs associated with MDR, because there are many other mechanisms for resistance to multiple drugs, such as multidrug resistance associated protein, enhanced glutathione S-transferase, altered topoisomerase II, enhanced DNA repair and low levels of cytochrome p-450 reductase.30,31 patients with small cell lung cancer with higher uptakes of 99mTc-MIBI were more likely to respond to chemotherapy than those with lower uptake 32 One case report also showed that absence of 99mTc-MIBI uptake was associated with failure of chemotherapy.33 These studies showed that the degree of 99mTc-MIBI uptake in small cell lung cancer correlated with response to chemotherapy. The information derived from 99mTc-MIBI imaging might be used in the prediction of the course of cancer by identifying patients who will not respond to conventional chemotherapy and could guide the design of the most effective therapy protocols. Our results suggest that the assessment of 99mTc-MIBI uptake may discriminate between different degrees of response to chemotherapy in pre-chemotherapeutic patients. Reduced T/N ratios were found in post-chemotherapeutic patients compared with those in pre-chemotherapeutic patients. A less favorable balance between the above factors-in particular, metabolic activity, vascularization and Pgp expression-may result in reduced 99mTc-MIBI uptake and chemoresistance in post-chemotherapeutic patients 99mTc-MIBI scintigraphy may be utilized to monitor acquired drug resistance induced by chemotherapy, but there was a considerable overlap of 99mTc-MIBI uptake among subjects. We did not have sufficient numbers of patients with small cell lung cancer to arrive at a statistically meaningful conclusion. Further work in this area, including the factor of chemoresistance, needs to be conducted. 
CONCLUSION 
99mTc-MIBI uptake of small cell lung cancer without response to chemotherapy was lower than that of newly diagnosed small cell lung cancer. Before chemotherapy, small cell lung cancer with a higher 99mTc-MIBI uptake was more likely to respond to chemotherapy than that with a lower uptake. 99mTc-MIBI might be useful for evaluating the tumor chemosensitivity in patients with small cell lung cancer. 
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