Red Marrow Absorbed Dose Calculation in Thyroid Cancer Patient Using a Simplified Excel Spreadsheet

Absorbed dose to red marrow (D_rm) can be calculated using blood dosimetry. However, this method is laborious and invasive. Therefore, image-based dosimetry is the method of choice. Nonetheless, the commercial software is expensive. The goal of this work was to develop a simplified excel spreadsheet for image-based radioiodine red marrow dosimetry.

The serial whole-body images (acquired at 2^nd, 6^th, 24^th, 48^th, and 72^th hours) of 29 patients from the routine pretherapeutic dosimetry protocol were retrospectively reanalyzed. 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 terms of absorbed dose coefficient (d_rm)]. For the simplified excel spreadsheet, the wholebody count was obtained from the vendor-supplied software. Then, the TIAC_WB was computed by a fitting time-activity curve using an 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 both methods was done using a non-inferiority test using a paired t-test or the Wilcoxon signed-rank test.

The TIAC_WB showed no significant difference between both methods (p=0.243). 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<0.05).

The dose assessment from a simplified Excel spreadsheet is feasible and relatively low cost compared to the commercial OLINDA/EXM image-based dosimetry software.