Medical Internal Radiation Dose Method Research Articles

Evaluating bone marrow dosimetry with the addition of bone marrow structures to the medical internal radiation dose phantom

AbstractBackgroundReliable estimates of radiation dose to bone marrow are critical to understanding the risk of radiation‐induced cancers. Although the medical internal radiation dose phantom is routinely used for dose estimation, bone marrow is not defined in the phantom. Consequently, methods of indirectly estimating bone marrow dose have been implemented based on dose to surrogate volumes or average dose to soft tissue.MethodsIn this study, new bone marrow structures were implemented and evaluated to the medical internal radiation dose phantom in Geant4, offering improved fidelity. The dose equivalent to the bone marrow was calculated across medical, occupational, and space radiation exposure scenarios, and compared with results using prior indirect estimation methods.ConclusionOur results show that bone marrow dose may be overestimated by up to a factor of three when using the traditional methods when compared with the improved fidelity medical internal radiation dose method, specifically at clinical x‐ray energies.

EFFECTIVE DOSE TO ADULT PATIENTS UNDERGOING RENAL SCANS WITH 99MTC (DMSA, DTPA, EC AND MAG3).

Renal scintigraphy plays an important role in the diagnosis of various kidney disorders. This procedure can be performed with different radiopharmaceuticals. The patients undergoing renal scintigraphy receive a radiation dose that should be assessed. In this study, the effective dose of patients due to renal scintigraphy with 99mTc (DMSA, DTPA, EC and MAG3) was calculated for the International Commission on Radiological Protection (ICRP) 110 adult reference phantoms using the Medical Internal Radiation Dose method and the ICRP 60 and 103 tissue weighting factors. The results show that the highest effective dose per unit activity administered is due to 99mTc DMSA. On average, the effective dose per unit activity administered of 99mTc DMSA is almost twice the effective dose per unit activity administered of other radiopharmaceuticals. The effective doses per unit activity administered calculated using the ICRP 103 tissue weighting factors are always lower than that calculated using the ICRP 60 tissue weighting factors and the ICRP 128 data.

Internal dosimetry studies of 177Lu-BBN-GABA-DOTA, as a cancer therapy agent, in human tissues based on animal data

The goal of using radiopharmaceuticals for therapeutic purposes is twofold: first, the most damage to cancer cells and, second, the most negligible dose transfers to healthy tissues. As 177Lu has the potential to cure a wide range of malignancies due to its varied range of beta energies, 177Lu-BBN-GABA-DOTA has been developed for therapeutic applications. In addition, 177Lu-BBN-GABA-DOTA can be over-expressed on gastrin-releasing peptide (GRP) receptors of the prostate, breast, small cell lung cancer, gastric, and colon tumors. The purpose of this study was to calculate the amount of dose absorption in human body organs using medical internal radiation dose (MIRD) and GATE code methods, after animal injection.In this study, the amount of absorbed dose in different organs (spleen, kidney, Lung, Pancreas, Heart, Adrenal, Intestine, Stomach, and Liver) were calculated for 1-MBq accumulation of 177Lu-BBN-GABA-DOTA in source organs (spleen, kidney, Lung, Pancreas, Heart, Adrenal, Intestine, Stomach, and Liver) using Monte Carlo Simulation (GATE code) with Zubal phantom. Moreover, compared with MIRD method, the results of the simulation showed considerable consistency.It was estimated that a 1-MBq administration of 177Lu-BBN-GABA-DOTA to the human body would result in an absorbed dose of 1.07E-02 mGy and 4.97E-02 (MIRD method) and 1.26E-02 mGy and 5.19E-02 (Gate code) in the Pancreas and adrenal 120 h after injection, respectively. The highest and lowest percentage differences between MIRD and Gate results are related to the Pancreas and spleen, respectively. Finally, the results showed that there is a good agreement between MIRD method and Gate code simulation for absorbed dose estimation.

Phase I clinical study of NMB58, a novel positron emission tomography (PET)-myocardial perfusion imaging tracer, conducted to evaluate its safety and pharmacokinetics in Japanese healthy adult males.

NMB58 is a novel positron emission tomography (PET) tracer containing flurpiridaz as an active ingredient and available as a myocardial perfusion imaging tracer that targets mitochondrial complex 1. A phase I clinical study of NMB58 was conducted to evaluate its safety and pharmacokinetics in healthy volunteers. Ten healthy Japanese volunteers received bolus injection of NMB58 (111-167MBq) intravenously and underwent imaging studies at rest on day 1. Of these subjects, 5 (day 2 cohort 1; exercise stress) and 5 (day 2 cohort 2; pharmacological stress) similarly underwent stress imaging studies on day 2. The safety of NMB58 was evaluated through monitoring of signs/symptoms, electrocardiography, vital signs, and laboratory examinations at baseline and several time points during 3days. Sequential whole-body positron emission tomography-computed tomography (PET/CT) scan data were acquired for up to 5-h post-injection, with venous blood and urine samples collected for up to 8-h post-injection. Based on the results of the biodistribution study, the absorbed radiation dose (Rad) was estimated by the Medical Internal Radiation Dose method. On day 1, the kidneys were shown to have the highest Rad, followed by the myocardium. On day 2, the myocardium was shown to have the highest Rad, followed by the kidneys. The mean effective doses (EDs) per unit activity administered were 0.021, 0.017 and 0.021mSv/MBq for overall subjects (day 1), day 2 cohort 1 and day 2 cohort 2, respectively. The estimated exposure dose of NMB58 was similar to or lower than those of radiotracers currently approved for clinical use, including 18F-Fludeoxyglucose. Biodistribution results indicated that NMB58 distributed to the myocardium exhibited high and sustained retention after administration. The cumulative urinary radioactivity excretion rate was shown to be 6.9, 2.3%, and 8.0% of the injected dose in overall subjects (day 1), day 2 cohort 1 and day 2 cohort 2. There were no drug-related adverse events, and the tracer was well tolerated in all subjects. Based on radiation dosimetry, biodistribution, and safety evaluations, NMB58 was found to be a suitable tracer for clinical use in PET myocardial perfusion imaging during exercise or pharmacological stress.

Internal dosimetry studies of 170Tm-EDTMP complex, as a bone pain palliation agent, in human tissues based on animal data

Radiopharmaceuticals with therapeutic applications are designed to deliver high doses of radiation to target organs with minimizing unwanted radiation to healthy tissues. Owing to the potential of targeted radiotherapy to treat a wide range of malignancies, 170Tm -EDTMP was developed for possible therapeutic applications. This study describes absorbed dose prediction of 170Tm-EDTMP in human organs after animal injection which is determined via medical internal radiation dose (MIRD) and MCNP-4C code methods. It was estimated that a 1-MBq administration of 170Tm-EDTMP into the human body would result in an absorbed dose of 37.9 mGy (MIRD method) and 38.02 mGy (MCNP-4C code) in the bone surface after 60 days post injection. Highest and lowest difference between MIRD and MCNP results are for lung and bone surface respectively. Finally, the results show that there is a good agreement between MIRD method and MCNP-4C simulation code for absorbed dose estimation.

Re-evaluation of pediatric 18F-FDG dosimetry: Cristy–Eckerman versus UF/NCI hybrid computational phantoms

Because of the concerns associated with radiation exposure at a young age, there is an increased interest in pediatric absorbed dose estimates for imaging agents. Almost all reported pediatric absorbed dose estimates, however, have been determined using adult pharmacokinetic data with radionuclide S values that take into account the anatomical differences between adults and children based upon the older Cristy–Eckerman (C–E) stylized phantoms. In this work, we use pediatric model-derived pharmacokinetics to compare absorbed dose and effective dose estimates for 18F-FDG in pediatric patients using S values generated from two different geometries of computational phantoms. Time-integrated activity coefficients of 18F-FDG in brain, lungs, heart wall, kidneys and liver, retrospectively, calculated from 35 pediatric patients at the Boston’s Children Hospital were used. The absorbed dose calculation was performed in accordance with the Medical Internal Radiation Dose method using S values generated from the University of Florida/National Cancer Institute (UF/NCI) hybrid phantoms, as well as those from C–E stylized computational phantoms. The effective dose was computed using tissue-weighting factors from ICRP Publication 60 and ICRP Publication 103 for the C–E and UF/NCI, respectively. Substantial differences in the absorbed dose estimates between UF/NCI hybrid pediatric phantoms and the C–E stylized phantoms were found for the lungs, ovaries, red bone marrow and urinary bladder wall. Large discrepancies in the calculated dose values were observed in the bone marrow; ranging between −26% to +199%. The effective doses computed by the UF/NCI hybrid phantom S values were slightly different than those seen using the C–E stylized phantoms with percent differences of −0.7%, 2.9% and 2.5% for a newborn, 1 year old and 5 year old, respectively. Differences in anatomical modeling features among computational phantoms used to perform Monte Carlo-based photon and electron transport simulations for 18F, and very likely for other radionuclides, impact internal organ dosimetry computations for pediatric nuclear medicine studies.

Abstract ID: 160 Advanced personalised 3D dosimetry based on Monte Carlo simulation for Peptide Receptor Radionuclide Therapy

Molecular radiotherapy (MRT) is an effective technique for the treatment of several oncological diseases, based on the delivery of radiation to malignant tissues via the interaction of an agent with molecular sites and receptors [1] . In the clinical practice, the calculation of the absorbed dose is performed using the Medical Internal Radiation Dose (MIRD) scheme, based on pre-calculated transfer functions determined on standard anthropomorphic phantoms. The MIRD scheme assumes that radiopharmaceutical activity is distributed uniformly inside the organs [2] . For this reason, dose calculation is not planned or optimised for patients’ specific characteristics. To increase the efficacy and quality of clinical trials, a detailed and reliable 3D patient specific dosimetry is required. Monte Carlo techniques are shown to provide the most accurate approach for the radiotherapy dose calculation. In this work, we used Raydose Monte Carlo code [3] to provide a patient specific 3D dose distribution in MRT at the voxel level for patients enrolled as part of a clinical trial on Peptide Receptor Radiotherapy (PRRT) with 177Lu and we compared doses to lesions and OARs with standard dose calculations obtained using the MIRD method. One hundred patients were enrolled in a clinical trial in PRRT with an activity prescription of 177Lu-DOTA-Tyr3-octreotide. All patients were scanned five times with a SPECT/CT scanner and both lesions and OARs were drawn manually on fused images. Sequential scans were co-registered using a non-rigid registration algorithm. Raydose 3D dose maps were compared with dose calculations obtained using the OLINDA/EXM software. Preliminary results for the first 20 patients show that mean doses calculated with OLINDA/EXM are significantly higher than mean doses calculated with Raydose. Initial data based on Monte Carlo dose calculations suggest a possible underestimation of the dose to OARs in PRRT treatments. More accurate dose calculation could be used on a patient by patient basis to increase the prescribed activity, maintaining a safe level of toxicity. A complete analysis that includes doses to lesions is in progress.

Assessment of Patient Dose by Positron Emission Tomography (PET) and Medical Internal Dose (MIRD) Methods

Dynamic experiments cannot be observed easy on patients for determination of dosimetry in human PET studies dosimeter studies. In this study, it is aimed to estimate dose amount absorbed by some critical organs (e.g. bladder, lung, thyroid and ovary) by using a developed phantom. The phantom was improved as an original anthropomorphic whole body phantom which has been arranged with dynamic system. Therefore, organ absorbed doses by applying of fluorine-18-fluorodeoxyglucose in PET studies and was observed by using the phantom, while TLD dosimeters were used for determination of internal absorbed doses. In medical physics, the accuracy of absorbed dose resulting from radiopharmaceutical application was determined by the medical internal radiation dose method that depends theoretically on the cumulated activity of the source organs and their mass. The MIRD calculation was also used for the study and comparatively evaluated with the experimental results which were collected by using improved phantom. DOI: 10.12693/APhysPolA.130.90 PACS/topics: 87.57.uk, 87.53.Bn

Determination of Organ Doses in Radioiodine Therapy using Monte Carlo Simulation.

Radioactive iodine treatment is a type of internal radiotherapy that has been used effectively for the treatment of differentiated thyroid cancer after thyroidectomy. The limit of this method is its affects on critical organs, and hence dosimetry is necessary to consider the risk of this treatment. Scope of this work is the measurement of absorbed doses of critical organs by Monte Carlo simulation and comparing the results with other methods of dosimetry such as direct dosimetry and Medical Internal Radiation Dose (MIRD) method. To calculate absorbed doses of vital organs (thyroid, sternum and cervical vertebrae) via Monte Carlo, a mathematical phantom was used. Since iodine 131 (131I) emmits photon and beta particle, *F8 tallies, which give results in MeV were applied and the results were later converted to cGy by dividing by the mass within the cell and multiplying by 1.6E-8. The absorbed dose obtained by Monte Carlo simulations for 100, 150 and 175 mCi administered 131I was found to be 388.0, 427.9 and 444.8 cGy for thyroid, 208.7, 230.1 and 239.3 cGy for sternum and 272.1, 299.9 and 312.1 cGy for cervical vertebrae. The results of Monte Carlo simulation method had no significant difference with the results obtained via direct dosimetry using thermoluminescent dosimeter-100 and MIRD method. Hence, Monte Carlo is a suitable method for dosimetry in radioiodine therapy.

Preliminary dosimetry of (166)Ho-propylene di-amino tetra (methy1enephosphonicacid) for human based on biodistribution data in rats.

Nowadays, radionuclides with high β- particle energies such as (166)Ho are recommended for bone marrow ablation in patients with multiple myeloma. The addition of skeletal targeted radiotherapy to the patients can improve the response rate in phase I and II trials, with promising long-term survival data. In this work, the absorbed dose to each organ of human for (166)Ho-propylene di-amino tetra methy1enephosphonicacid (PDTMP) was evaluated based on biodistribution studies in rats and was compared with (166)Ho-tetraazacyclododecane tetramethylene-phosphonate (DOTMP) as the only clinically used Ho-166 bone marrow ablative agent. In this work, the accumulated activity in animals was extrapolated to the accumulated activity in humans by mass extrapolation method. The absorbed dose to each organ of human for (166)Ho-PDTMP was evaluated by medical internal radiation dose method. In this study, 166 Ho-PDTMP complex was prepared successfully using an in-house synthesized PDTMP ligand and (166)HoCl 3. Radiochemical purity of (166)Ho-PDTMP was checked by instant thin layer chromatography (>99%). The biodistribution of (166)Ho-PDTMP in wild-type rats was checked in animal tissues up to 48 h. All values were expressed as mean ± standard deviation, and the data were compared using Student's t-test. Statistical significance was defined as P < 0.05. The highest absorbed dose for this complex is observed in red marrow with 0.691 mSv/MBq. (166)Ho-PDTMP demonstrated a higher red marrow: Non target organ uptake ratio compared to (166)Ho-DOTMP. The results showed that 166 Ho-PDTMP has considerable characteristics compared to (166)Ho-DOTMP and therefore can be a good candidate for bone marrow ablation.

A comparative study of preliminary dosimetry for human based on distribution data in rats with 111In, 90Y, 153Sm, and 177Lu labeled rituximab

Radio immunotherapy is one of the most important and effective therapies for B-cell non Hoddgkin?s lymphoma treatment. Today, anti CD-20 antibodies labeled with beta emitter radionuclides are used in radio immunotherapy. Various radionuclides for labeling anti CD-20 antibodies have been studied and developed for the treatment and diagnosis of malignancies. This paper describes the preparation, bio-distribution and absorbed dose rate of 111In, 90Y, 177Lu, and 153Sm labeled anti CD-20 antibodies (rituximab) in human organs, after injection to rats. The macro cyclic bifunctional chelating agent, N-succinimidyl-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid (DOTA-NHS) for conjugation to antibody, was used to prepare DOTA-rituximab. The conjugates were purified by molecular filtration, the average number of DOTA conjugated per mAb was calculated and total concentration was determined by spectrophotometric method. Radio-labeling was performed at 40 ?C for 24 hours. After the quality control studies, the final radioactive solution was injected intravenously into rats through their tail vein. The tissue uptakes of each injection were measured. Then we calculated S values for 177Lu and 153Sm by using specific absorbed fractions and data used in the manner of radio-labeled analysis and dosimetry for humans. The absorbed dose rate of each organ was calculated in the specific time by medical internal radiation dose method with linear approximation in the activity measurements.

Quantitative Analysis of 90Y Bremsstrahlung SPECT-CT Images for Application to 3D Patient-Specific Dosimetry

The aim of this study was to evaluate the accuracy of the activity quantification of single-photon emission computed tomography/computed tomography (SPECT-CT) (90)Y-Bremsstrahlung images and to validate the S-voxel method. An anthropomorphic torso phantom with radioactive inserts ((90)Y) was acquired by SPECT-CT. Constant calibration factors (cps/MBq) for the quantification were evaluated, considering different volume, shape, position inside the phantom, activity concentration and background, and distance from detectors. S-voxel values (EGSnrc) were implemented in MATLAB R0086 USA software. Dose comparisons between S-voxel and the conventional Medical Internal Radiation Dose method were repeated in a group of 11 patients administered with (90)Y-DOTATATE. Using the appropriate calibration factors to recover the volume variability, the error about the measurement repeatability and the activity variation was within 4%. The variability of activity quantification, depending on the position in the phantom, detector distance, and background, was <10%, <5%, and <10%, respectively. The absorbed-dose values calculated by OLINDA were in agreement with the mean dose values obtained by the S-voxel method (difference, <10%). The results confirm that, with the hybrid SPECT-CT system, quantitative analysis of SPECT (90)Y-Bremsstrahlung images and the generation of three-dimensional dose distributions are feasible. The improved analysis of Bremsstrahlung images could have a notable clinical impact, allowing to address the dosimetric verification to patients during the course of therapy.

The AAPM/RSNA Physics Tutorial for Residents

The decay of a radioactive nucleus leads to the emission of energy in the form of photons or charged particles. The form and energy of the radiation emitted will depend on the decaying nucleus. Some of the emitted energy will be absorbed by target organs; the ratio of the absorbed energy to the mass of the target is the radiation dose. Charged particles traveling in a medium slow down because of interactions between the electric charge of the particle and that of the orbital electrons and nuclei of the medium. These interactions transfer energy from the charged particle to the orbital electrons and the nuclei of the medium. A photon may be transmitted through a medium or may be attenuated by the medium. Of the four mechanisms by which photons interact with matter, two are important in the energy range of interest in nuclear medicine: the photoelectric effect and Compton scattering. The internal radiation dose from radionuclides used in nuclear medicine can be estimated with the Medical Internal Radiation Dose (MIRD) method. Important aspects of the MIRD method include the concepts of source and target organs, energy emitted per decay, absorbed fraction, S value, cumulated activity, and effective dose equivalent.