Red Marrow Absorbed Dose Calculation in Thyroid Cancer Patient using A Simplified Excel Spreadsheet

INTRODUCTION: Absorbed dose to red marrow ("D" _"rm" ) can be calculated using blood dosimetry. However, completed blood method is laborious and invasive. Therefore, image-based dosimetry is the method of choice. Nonetheless, commercial software is expensive. The goal of this work was to develop a simplified Excel spreadsheet for image-based radioiodine red marrow dosimetry.
METHODS: The serial whole-body images (acquired at 2, 6, 24, 48, and 72 hours) of 29 patients from the routine pre-therapeutic dosimetry protocol were retrospectively reanalyzed. In routine, the commercial OLINDA/EXM image-based dosimetry software was used to calculate the whole-body time-integrated activity coefficient (〖"TIAC" 〗_"WB" ) and "D" _"rm" (in term of absorbed dose coefficient (d_rm)). For a simplified Excel spreadsheet, the whole-body count was obtained from the vendor supplied software. Then, the 〖"TIAC" 〗_"WB" was computed by fitting time-activity curve using Excel function. S-factor was taken from other publications and scaled according to the patient-specific mass. A comparison of the 〖"TIAC" 〗_"WB" and d_rm from two methods was analyzed using a non-inferiority test based on a paired t-test or the Wilcoxon signed rank test.
RESULTS: The 〖"TIAC" 〗_"WB" showed no significant difference between two methods (p-value 0.243 with a paired t-test). The calculated "d" _"rm" " " from a simplified Excel spreadsheet was assumed to be statistically non-inferior to the commercial OLINDA/EXM image-based dosimetry software with the non-inferiority margin of 0.02 (p-value < 0.05 with the Wilcoxon signed rank test).
DISCUSSION AND CONCLUSION: The dose assessment from a simplified Excel spreadsheet is feasible and relatively low cost compared to the commercial OLINDA/EXM image-based dosimetry software