Optimized cocktail of 90Y/177Lu for radionuclide therapy of neuroendocrine tumors of various sizes: a simulation study.

BACKGROUND AND OBJECTIVES: There is significant interest and potential in the treatment of neuroendocrine tumors via peptide receptor radionuclide therapy (PRRT) using one or both of 90Y and 177Lu-labeled peptides. Given the presence of different tumor sizes in patients and differing radionuclide dose delivery properties, the present study aims to use Monte Carlo simulations to estimate S-values to spherical tumors of various sizes with 90Y and 177Lu separately and in combination. The goal is to determine ratios of 90Y to 177Lu that result in the largest absorbed doses per decay of the radionuclides and the most suitable dose profiles to treat tumors of specific sizes. MATERIAL AND METHODS: Particle transfer calculations and simulations were performed using the Monte Carlo GATE simulation software. Spherical tumors of different sizes, ranging from 0.5 to 20 mm in radius, were designed. Activities of 177Lu and 90Y, individually and in combination, were homogeneously placed within the total volume of the tumors. We determined the S-values to the tumors, and to the external volume outside of the tumors (cross-dose) which was used to approximate background tissue. The dose profiles were obtained for each of the different tumor sizes, and the uniformity of dose within each tumor was calculated. RESULTS: For all tumor sizes, the self-dose and cross-dose per decay from 90Y were higher than that from 177Lu. We observed that 177Lu had the most uniform dose distribution within tumors with radii less than 5 mm. For tumors greater than 5 mm in radius, a ratio of 25% 90Y to 75% 177Lu resulted in the most uniform doses. When the ratio of 177Lu to 90Y was smaller, the uniformity improved more with increasing tumor size. The cross-dose stayed approximately constant for tumors larger than 15 mm for all ratios of 177Lu to 90Y. Finally, as the size of the tumor increased, differences in the S-values between different ratios of 177Lu to 90Y decreased. CONCLUSION: Our work showed that to achieve a more uniform dose distribution within the tumor, 177Lu alone is more effective for small tumors. For medium and large tumors, a ratio of 90Y to 177Lu with more or less 177Lu, respectively, is recommended.

Assessment Relation of Myocardial Detector Counts and Administered Activity of 99mTc-SestaMIBI in MPI: The Effects of Body Weight, BMI, and Gender.

INTRODUCTION: In myocardial perfusion imaging, reducing the number of photons in images of obese patients causes poor image quality. To solve this problem, we need to inject the tracer according to the patients' weight. Therefore, this study aimed to investigate the relationship between myocardial photon counts with patients' weight, BMI, and gender. MATERIALS AND METHODS: A total of 129 patients underwent myocardial perfusion imaging in a twoday stress-first protocol, but only rest images were included in this study. Multiplication factor was used to determine the amount of radiopharmaceutical activity injected into the patients. For evaluating the effect of gender, the photon counts of 22 female patients were also assessed when the breast tissue was pulled upward (Breast Up). The total myocardial detector counts in the raw images were calculated from the summation of 32 projections. A multiple linear regression test was used to simultaneously examine the effects of weight, BMI, and gender on photon counts. RESULTS: There was no significant relationship between photon counts and patients' weight (p=0.129) and BMI (0.406), but gender had significant effects on photon counts, and myocardial detector counts were found to be higher in males (p=0.00). There was a statistically significant difference between the images of Breast Up and Non-Breast Up, and myocardial detector counts were higher in the Breast Up imaging method (p=0.00). CONCLUSION: Using the bodyweight formula, the image quality was comparable in obese and lean patients, but myocardial detector counts were lower in females, and this formula needs to be adjusted according to the patient's gender.

Evaluation of Dosimetric Parameters for Tumor Therapy with 177Lu and 90Y Radionuclides in Gate Monte Carlo Code.

BACKGROUND: 90Y and 177Lu are two well-known radionuclides used in radionuclide therapy to treat neuroendocrine tumors. OBJECTIVE: This current study aims to evaluate, compare and optimize tumor therapy with 90Y and 177Lu for different volumes of the tumor using the criterion of self-absorbed dose, cross-absorbed dose, absorbed dose profile, absorbed dose uniformity, and dose-volume histogram (DVH) curve using Gate Monte Carlo simulation code. MATERIAL AND METHODS: In our analytical study, Gate Monte Carlo simulation code has been used to model tumors and simulate particle transport. Spherical tumors were modeled from radius 0.5 to 20 mm. Tumors were uniformly designed from water (soft tissue reagent). The full energy spectrum of each radionuclide of 177Lu and 90Y was used in the total volume of tumors with isotropic radiation, homogeneously. Self-absorbed dose, cross-absorbed dose, absorbed dose profile, absorbed dose uniformity, and DVH curve parameters were evaluated. RESULTS: The absorbed dose for 90Y is higher than 177Lu in all tumors (p-value <5%). The uniformity of the absorbed dose for 177Lu is much greater than 90Y. As the tumor size increases, the DVH graph improves for 90Y. CONCLUSION: Based on self-absorbed dose, cross-absorbed dose, absorbed dose uniformity, and DVH diagram, 177Lu and 90Y are appropriate for smaller and larger tumors, respectively. Next, we can evaluate the appropriate cocktail of these radionuclides, in terms of the type of composition, for the treatment of tumors with a specific size.

Implementation of dose point kernel (DPK) for dose optimization of 177Lu/90Y cocktail radionuclides in internal dosimetry.

BACKGROUND: Due to the importance of choosing the applicable dosimetry method in radionuclide therapy, the present study was conducted to investigate the efficiency of the implementation of Dose Point Kernel (DPK) for dose optimization of 177Lu/90Y Cocktail Radionuclides in internal Dosimetry. METHODS: In this study, simulations and calculations of DPK were performed using the GATE/GEANT4 Monte Carlo code. For specific liver dosimetry, the NCAT phantom and convolution algorithm-based Fast Fourier Transform method was used by MATLAB software. RESULTS: The self-dose of 177Lu and 90Y radionuclides in the liver of NCAT phantom were 1.1708E-13, and 4.8420E-11 (Gy/Bq), respectively, and the cross-dose of 177Lu and 90Y radionuclides out of the liver of NCAT phantom were 2.03615E-16, and 0.8422E-13 (Gy/Bq) respectively. Overall results showed that with an increase the value of 90Y with quarter steps in a cocktail, the amount of the self-dose increase 1.5, 6, and 29 times respectively, and with an increase the value of 177Lu in quarter step in a cocktail, the amount of the cross dose decrease 3, 15 and 68 percent respectively. CONCLUSION: Generally, the present results indicate that the calculated DPK functions of 177Lu and 90Y cocktails can play an important role in choosing the best combination of radionuclide to optimize treatment planning in cocktail radionuclide therapy.