Comparison of different dosimetric methods for red marrow absorbed dose calculation in thyroid cancer therapy

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

Objectives:

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.

Methods:

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 whole-body 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.

Results:

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).

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.

Radionuclide therapy: current status and prospects for internal dosimetry in individualized therapeutic planning

The efficacy and toxicity of radionuclide therapy are believed to be directly related to the radiation doses received by target tissues; however, nuclear medicine therapy continues to be based primarily on the administration of empirical activities to patients and less frequently on the use of internal dosimetry for individual therapeutic planning. This review aimed to critically describe the techniques and clinical evidence of dosimetry as a tool for therapeutic planning and the main limitations to its implementation in clinical practice. The present article is a nonsystematic review of voxel-based dosimetry. Clinical evidence pointing to a correlation between the radiation dose and therapeutic response in various diseases, such as thyroid carcinoma, neuroendocrine tumors and prostate cancer, is reviewed. Its limitations include technical aspects related to image acquisition and processing and the lack of randomized clinical trials demonstrating the impact of dosimetry on patient therapy. A more widespread use of dosimetry in therapeutic planning involves the development of user-friendly dosimetric protocols and confirmation that dose estimation implies good efficacy and low treatment-related toxicity.

Red bone marrow dose estimation using several internal dosimetry models for prospective dosimetry-oriented radioiodine therapy

The aim of the present study was to review the available models developed for calculating red bone marrow dose in radioiodine therapy using clinical data. The study includes 18 patients (12 females and six males) with metastatic differentiated thyroid cancer. Radioiodine tracer of 73 ± 16 MBq ¹³¹I was orally administered, followed by blood sampling (2 ml) and whole-body scans (WBSs) done at several time points (2, 6, 24, 48, 72, and ≥ 96 h). Red bone marrow dose was estimated using the OLINDA/EXM 1.0, IDAC-Dose 2.1, and EANM models, the models developed by Shen and co-workers, Keizer and co-workers and Siegel and co-workers, and Traino and co-workers, as well as the single measurement model (SMM). The results were then compared to the standard reference model Revised Sgouros Model (RSM) reported by Wessels and co-workers. The mean dose deviations of the Traino, Siegel, Shen, Keizer, OLINDA/EXM, EANM, SMM, and IDAC-Dose 2.1 models from the RSM were - 17%, - 24%, 6%, - 29%, - 15%, 40%, 48%, and - 8%, respectively. The statistical analysis demonstrated no significant difference between the results obtained with the RSM and with those obtained with the Shen, Traino, OLINDA/EXM, and IDAC-Dose 2.1 models (t test; p_value > 0.05). However, a significant difference was found between RSM doses and those obtained with the EANM, SMM, and Keizer models (t test; p_value < 0.05). The correlation between red marrow dose from the SMM and EANM models was modest (R² = 0.65), while the crossfire dose calculated with the OLINDA/EXM and IDAC-Dose 2.1 models were in good agreement with each other and with the reference model. The findings obtained indicate that most of the dosimetry models can be used for a reliable dosimetry, and the calculated total body doses can be considered as a reliable non-invasive option for a conservative activity planning. In addition, the excellent performance of the IDAC-Dose 2.1 model will be of particular importance for a practical and accurate dosimetry, with the advantages of allowing for the use of realistic advanced phantoms and updated dose fractions, and of providing information about the blood dose contribution to the red bone marrow.

A practical method of I-131 thyroid cancer therapy dose optimization using estimated effective renal clearance

In thyroid cancer patients with renal impairment or other complicating factors, it is important to maximize I-131 therapy efficacy while minimizing bone marrow and lung damage. We developed a web-based calculator based on a modified Benua and Leeper method to calculate the maximum I-131 dose to reduce the risk of these toxicities, based on the effective renal clearance of I-123 as measured from two whole-body I-123 scans, performed at 0 and 24 h post-administration.

Estimating (131)I biokinetics and radiation doses to the red marrow and whole body in thyroid cancer patients: probe detection versus image quantification

OBJECTIVE

To compare the probe detection method with the image quantification method when estimating (131)I biokinetics and radiation doses to the red marrow and whole body in the treatment of thyroid cancer patients.

MATERIALS AND METHODS

Fourteen patients with metastatic thyroid cancer, without metastatic bone involvement, were submitted to therapy planning in order to tailor the therapeutic amount of (131)I to each individual. Whole-body scans and probe measurements were performed at 4, 24, 48, 72, and 96 h after (131)I administration in order to estimate the effective half-life (Teff) and residence time of (131)I in the body.

RESULTS

The mean values for Teff and residence time, respectively, were 19 ± 9 h and 28 ± 12 h for probe detection, compared with 20 ± 13 h and 29 ± 18 h for image quantification. The average dose to the red marrow and whole body, respectively, was 0.061 ± 0.041 mGy/MBq and 0.073 ± 0.040 mGy/MBq for probe detection, compared with 0.066 ± 0.055 mGy/MBq and 0.078 ± 0.056 mGy/MBq for image quantification. Statistical analysis proved that there were no significant differences between the two methods for estimating the Teff (p = 0.801), residence time (p = 0.801), dose to the red marrow (p = 0.708), and dose to the whole body (p = 0.811), even when we considered an optimized approach for calculating doses only at 4 h and 96 h after (131)I administration (p > 0.914).

CONCLUSION

There is full agreement as to the feasibility of using probe detection and image quantification when estimating (131)I biokinetics and red-marrow/whole-body doses. However, because the probe detection method is inefficacious in identifying tumor sites and critical organs during radionuclide therapy and therefore liable to skew adjustment of the amount of (131)I to be administered to patients under such therapy, it should be used with caution.

Prediction of iodine-131 biokinetics and radiation doses from therapy on the basis of tracer studies: an important question for therapy planning in nuclear medicine

OBJECTIVES

This study aimed to present a comparison of iodine-131 (I) biokinetics and radiation doses to red-marrow (rm) and whole-body (wb), following the administration of tracer and therapeutic activities, as a means of confirming whether I clearance and radiation doses for therapy procedures can be predicted by tracer activities.

METHODS

Eleven differentiated thyroid cancer patients were followed after receiving tracer and therapeutic I activity. Whole-body I clearance was estimated using radiation detectors and OLINDA/EXM software was used to calculate radiation doses to rm and wb.

RESULTS AND DISCUSSION

Tracer I activity of 86 (±14) MBq and therapeutic activity of 8.04 (±1.18) GBq were administered to patients, thereby producing an average wb I effective half-time and residence time of, respectively, 13.51 (±4.05) and 23.13 (±5.98) h for tracer activities and 13.32 (±3.38) and 19.63 (±4.77) h for therapy. Radiation doses to rm and wb were, respectively, 0.0467 (±0.0208) and 0.0589 (±0.0207) mGy/MBq in tracer studies and 0.0396 (±0.0169) and 0.0500 (±0.0163) mGy/MBq in therapy. Although the differences were not considered statistically significant between averages, those between the values of effective half-times (P=0.906), residence times (P=0.145), and radiation doses to rm (P=0.393) and to wb (P=0.272), from tracer and therapy procedures, large differences of up to 80% in wb I clearance, and up to 50% in radiation doses were observed when patients were analyzed individually, thus impacting on the total amount of I activity calculated to be safe for application in individual therapy.

CONCLUSION

I biokinetics and radiation doses to rm and wb in therapy procedures are well predicted by diagnostic activities when average values of a group of patients are compared. Nonetheless, when patients are analyzed individually, significant differences may be encountered, thus implying that nuclear medicine therapy-planning requires due consideration of changes in individual patient-body status from initial tracer to final therapy procedures to thus provide appropriate adjustments in therapeutic activities.