Usefulness of ^99mTc MAG₃ renogram for monitoring before and after carbon ion radiotherapy in patients with renal cell carcinoma

Introduction: Carbon‐ion radiotherapy (CIRT) for primary renal cell carcinoma (RCC) showed high local control rates (100% at 5 years) even in the inoperable patients. For clinical management after CIRT in RCC patients, evaluation of preserved renal function especially in non-irradiated renal parenchyma is important to assess and monitor the adverse event of renal function. Monitoring using eGFR is convenient and useful after CIRT in RCC, however, it is hard to evaluate the split function of the kidneys. It has been suggested that serial assessment of renal function by measuring tubular extraction with ^99mTc-MAG₃ might permit earlier and more sensitive detection of renal damage. <Patients> A total of 6 patients who had received CIRT for RCC; 3 patients for 66.0Gy/12Fractions and 3 patients for 72.0Gy/12Fractions were enrolled in this study. ^99mTc-MAG3 renogram before, 3-6 months and 12-18 months after CIRT were analyzed. The effective renal plasma flow of both kidneys (total cERPF), peak time (min), T1/2 from the PT (min), C20/max index were calculated and were compared with their eGFR and the adverse events evaluation category of National Cancer Institute’s Common Terminology Criteria for Adverse Events (CTCAE) version 4.0 <Result and Summary> In the analysis using ^99mTc-MAG₃ renogram, it was possible to detect the renal function deterioration of non-irradiated renal parenchyma. In some patients, the ^99mTc-MAG₃ renogram showed renal function deterioration, which it might be not due to CIRT but systemic diseases or kidney diseases. ^99mTc-MAG₃ renogram is considered to be a useful diagnostic tool for the assessment of split renal function in CIRT for RCC. <Teaching Points> 1) ^99mTc-MAG₃ renogram is a useful non-invasive diagnostic tool to evaluate renal function after CIRT in patients with renal cell carcinoma, especially for the assessment of split renal function.2) With the ^99mTc-MAG₃ renogram, it is possible to detect renal function deterioration of non-irradiated renal parenchyma.3) Serial assessment of renal function by measuring tubular extraction with ^99mTc-MAG₃ might permit earlier and more sensitive detection of renal damage after CIRT.

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