Accumulation of N-Isopropyl-p(123I)iodoamphetamine on Single-Photon Emission Computed Tomography Between Immunosuppressed and Non-immunosuppressed Patients With Primary Central Nervous System Lymphoma

Introduction Primary central nervous system lymphoma (PCNSL) is a rare type of malignant tumor. Due to the rapidly progressive nature of PCNSL, early diagnosis is important, and imaging plays a key role in this process. In particular, N-isopropyl-p(123I)iodoamphetamine (¹²³I-IMP) single-photon emission computed tomography (SPECT) is useful for PCNSL diagnosis because it shows a high accumulation, which distinguishes the lesion from other brain tumors. Recently, PCNSL has been increasingly observed in immunosuppressed patients, including those who have undergone organ transplantation and those who are receiving treatment for acquired immunodeficiency syndrome. These conditions may alter the tumor microenvironment, thereby potentially influencing ¹²³I-IMP accumulation. The current study aimed to validate how immunosuppression affects the diagnostic imaging of PCNSL using ¹²³I-IMP SPECT. Materials and methods This study included 12 patients diagnosed with PCNSL based on surgical specimens, all of whom underwent early and delayed ¹²³I-IMP SPECT imaging. The patients were divided into the immunosuppressed and non-immunosuppressed groups. The immunosuppressed group consisted of three patients who received steroids or immunosuppressants after kidney transplantation. Seven tumors from the three patients in the immunosuppressed group and nine tumors from the nine patients in the non-immunosuppressed group were compared. Early and delayed SPECT images were obtained, and the regions of interest were defined by fusing SPECT with magnetic resonance imaging. The tumor-to-cerebellum (T/C) ratio was calculated, and statistical analysis was performed using the Mann-Whitney U test. Results The immunosuppressed group had a significantly lower T/C ratio on the early ¹²³I-IMP SPECT images than the non-immunosuppressed group (0.57 ± 0.14 vs 0.83 ± 0.14, p < 0.01). The immunosuppressed group also had a significantly lower accumulation on the delayed images than the non-immunosuppressed group (0.84 ± 0.16 vs. 1.22 ± 0.10, p < 0.001). The T/C ratio showed a statistically significant increase from the early to delayed images in both the immunosuppressed and non-immunosuppressed groups (p < 0.01, p < 0.001). Conclusions The immunosuppressed group had a significantly lower ¹²³I-IMP accumulation in the early and delayed images than the non-immunosuppressed group. Based on this finding, an immunosuppressed state strongly influences the ¹²³I-IMP uptake in PCNSL. Thus, the presence or absence of an immunosuppressed state should be considered when diagnosing PCNSL using ¹²³I-IMP SPECT.