International Journal of Radiation Research
Volume:7 Issue: 4, Oct 2009

In Helical Tomotherapy (HT), the scaling factor (SF) is the time in seconds that each leaf viewing a target would need to be open to deliver the prescribed dose. The SF is patient-specific and is used to calculate the rotational period of the gantry, and the total treatment time (TTT) of the HT. The SF is generally difficult to estimate. Currently, it takes about one hour to fully optimize a prostate HT plan and to calculate the corresponding TTT. The aim of this study is to develop a method for estimation of the SF directly using a patient-specific approximating function. The SFs of ten randomly selected patients were used to build the approximation model. For the entire group of patients the PTV1 ranged from 57 to 396 cm3 for PTV1 margins from 2 to 10 mm. The discrete data for every patient is represented by an individual function, SF=f (k× PTV1). The values of the function were rescaled to a special unit which represents the target volume irradiated with the prescribed dose per second. The values were normalized with two “geometric” parameters, namely, the target-to-target and the body-to-body ratios. After the normalization, the function for every patient was ordered in the file by the volume of the prostate and seminal vesicles. For prostate HT planning, it was found that the planning target volume (PTV1) has a higher impact on the SF values than the size of the patient''s bodies. The function SF=f (k×PTV1) was found smooth and continuous over the given interval. The rescaled and normalized functions for all patients were represented as delimiters of a 2D field. The method proposed for determination of the SF and TTT for HT prostate planning covers PTV1 of four margins and a volume of prostate and seminal vesicles ranging from 42.8 to 161 cm3. Using these approximations, the TTTs for a second group of patients were determined in several minutes with deviation ranging from −2.8% to +7.1% compared to that of the TTTs calculated using the HT planning system. Iran. J.

Genistein is a soya isoflavone, which is found naturally in legumes, such as soybeans and chickpeas. Radiation–induced free radicals in turn impair the antioxidative defense mechanism, leading to an increased membrane lipid peroxidation that results in damage of the membrane bound enzyme and may lead to damage or death of cell. Hence, the lipid peroxidation is a good biomarker of damage occurs due to radiation and the inhibition of lipid peroxidation is suggestive of radioprotective action. Glutathione has been shown to protect cells against oxidative stress by reacting with peroxides and hydroperoxides and determines the inherent radiosensitivity of cells. For experimentation, healthy Swiss Albino male mice of 6 -8 weeks old were selected from inbred colony. Genistein was dissolved in dimethyl sulfoxide and then prepared different concentration solutions so that the volume administered intraperitoneally was 0.5 ml. Lipid peroxidation was estimated by the method of Ohkawa and GSH was estimated by the method of Moron. The intraperitoneal administration of optimum dose (200 mg/kg body weight) of Genistein before 24 hrs and 15 minutes of irradiation (8 Gy at a dose rate of 1.02 Gy/min) reverted the increase in lipid peroxidation (by 18.01% ± 3.05) and decrease of Glutathione (by 62.05% ± 21.58) caused by irradiation in liver of Swiss albino mice. Statistically analyzed survival data produced a dose reduction factor (DRF) = 1.24. The results indicate that Genistein against radiation effect may pave way to the formulation of medicine in radiotherapy for normal tissue and possible against radiomimetic drug induced toxicity.

In nuclear medicine application often it is required to use computational methods for evaluation of organ absorbed dose. Monte Carlo simulation and phantoms have been used in many works before. The shape, size and volume in organs are varied, and this variation will produce error in dose calculation if no correction is applied. A computational framework for constructing individual phantom for dosimetry was performed on five liver CT scan data sets of Japanese normal individuals. The Zubal phantom was used as an original phantom to be adjusted by each individual data set. This registration was done by Spherical Harmonics (SH) and Thin-Plate Spline methods. Hausdorff distance was calculated for each case. Result of Hausdorff distance for five individual phantoms showed that before registration ranged from 140.9 to 192.1, and after registration it changed to 52.5 to 76.7. This was caused by index similarity ranged from %56.4 to %70.3. A new and automatic three-dimensional (3D) phantom construction approach was suggested for individual internal dosimetry simulation via Spherical Harmonics (SH) and Thin-Plate Spline methods. The results showed that the individual comparable phantom can be calculated with acceptable accuracy using geometric registration. This method could be used for race-specific statistical phantom modeling with major application in nuclear medicine for absorbed dose calculation.

Natural Radioactivity, though natural requires concentration monitoring, especially for the health/ environmental checks of the populace. The activity concentrations of 40K, 238U and 232Th in the waters from wells with depths ranging between 141.0 - 214.0 feet were randomly sampled and determined from 20 locations in Ago-Iwoye town in South Western, Nigeria. The activity concentrations obtained were in the ranges of (9.9-50.9)Bq/kg with mean value of (25.1± 10.7) Bq/kg for 40K, (BDL-15.0) Bq/kg with mean value of (1.2 ± 3.2) Bq/kg for 238U and (BDL-6.2) Bq/kg with mean value of (1.6 ± 1.7) Bq/kg for 232Th. According to the results obtained for the activity concentrations from 20 well water samples in Ago Iwoye, Southwestern, Nigeria it was observed that the v40K, 238U and 232Th values were still within the tolerance level indicating minimal radiological health burden on the human populace and the environment.

Glioblastoma is the most common and most malignant cancer of central nervous system. Targeted radiotherapy is an effective method toward its treatment. Iododeoxyuridine (IUdR) is a halogenated thymidine analogue known to be effective as a radiosensitizer in human cancer therapy. In this study we have evaluated the combination effects of 2-Methoxyestradiol, an inhibitor of hypoxia inducible factor 1α (HIF-1α) and Methoxyaminem, an inhibitor of base excision repair (BER) pathway on radiosensitization of IUdR in glioblastoma spheroid culture. The cytotoxic damages of DNA in U87MG cell line were compared using colony formation assay. Experiments were performed in large spheroids with a diameter of approximately 350μm. Evaluation of the effects of IUdR with 2ME2 and MX pretreatment on spheroid cultured cell followed by ionizing irradiation showed more enhancemented (p≤0.001) IUdR induced-radiosensitization. These results introduced a key role for 2ME2 in IUdR related studies. Pretreatment of tumor cells with IUdR, MX and 2ME2 before irradiation enhances tumor radiosensitization and may improve therapeutic index for IUdR and 2ME2.

Iodine brachytherapy sources with low photon energies have been widely used in treating cancerous tumors. Dosimetric parameters of brachytherapy sources should be determined according to AAPM TG-43U1 recommendations before clinical use. Monte Carlo codes are reliable tools in calculation of these parameters for brachytherapy sources. Dosimetric parameters (dose rate constant, radial dose function, and anisotropy function) of two I-125 brachytherapy sources (models LS-1 and Intersource) were calculated with MCNP4C Monte Carlo code following task group #43 (TG-43U1) recommendations of American Assossiation of Physicists in Medicine. The simulations were done inside a spherical water phantom because of its tissue equivalent properties. The Monte Carlo simulations for radial dose function were performed at distances ranging from 0.25 to 10 cm from the source center. The anisotropy functions F(r, θ), for both sources, were calculated at distances of 1, 2, 3, 5 and 7 cm from the source center for angles ranging from 15 to 90 degree. The results of the Monte Carlo simulation indicated a dose rate constant of 0.952 cGyh -1U-1 and 0.986 cGyh -1U-1 for models LS-1 and Intersource, respectively. The tabulated data and fifth order polynomial coefficients for radial dose functions along the source are described in this paper. The results indicated that the anisotropy in dose distribution increased along the source axis. The obtained results were in good agreement with measurements and calculations of other investigators, using other Monte Carlo codes.

The presence of a wedge filter in the beam trajectory can modify the beam quality and cause some changes in the dosimetry parameters which are usually difficult to be measured directly and accurately. In this study the MCNP-4C Monte Carlo code was used to simulate the 9 MV photon beam generated by a linear accelerator. Upon getting a good agreement between the Monte Carlo simulated and measured dose distribution in open fields, the model was used to simulate the physical wedges. The steel wedges with angles from 15º-60º were modeled and the primary and the secondary photon beams were calculated. The beam profiles and wedges factors were calculated for each wedge. The output factors were determined for 45 wedge. The calculated data were compared with the measured values of the same parameters. The results showed that the use of wedges reduced the fluencies of the primary and scattered photons and also increased the average energy of the primary and the scattered photons. The agreement between the calculated and the measured data was better than 2% for all wedges. The results also showed that as the wedge angle increased, the electron contamination of photon beam decreased. The presence of a wedge in a 9 MV photon beam alters the primary and the scattered components generated by a linear accelerator. The simulated linac machine and its associated data can be used to predict the dose distribution in other complex fields.

Owing to its favourable decay characteristics 177Lu [T1/2= 6.71 d, Eβ(max)= 497 keV] is an attractive radionuclide for various therapeutic applications. Ethylene diamine tatramethylene phosphonate (EDTMP) is one of the most widely used ligands which form stable complexes with various radionuclides and all the complexes. Enriched 176Lu2O3 was dissolved in 0.1 N HCl and evaporated several times and 176LuCl3 target was irradiated at 2.6×1013 n.Cm- 2.S-1 thermal neutron flux for 14 days.177LuCl3 was dissolved in 1N HCl. EDTMP was dissolved in double distilled water at pH=7.5-8.5 and freeze-dried kits was radiolabeled with 177LuCl3. Distribution studies were done in healthy mice. The yield of 177Lu was (~220 TBq/g; 6000 Ci/g), the radionuclidic purity was ~99%.The radiolabeling yield of EDTMP kits at 37°C after 30 min and 4 hours was 98±0.5% and after 72 hours was 90±2.1%, the in vitro stability in human serum at 37°C up to 72 hours post radiolabeling was 85±1.8%.The biodistribution studies of 177Lu-EDTMP and 177LuCl3 in normal mice showed skeleton uptake and low soft-tissue concentration. In this study, we produce ~220 TBq/g (6000 Ci/g) of 177Lu by neutron activation of 176Lu in the Tehran Research Reactor. Our results showed 177Lu-EDTMP as a bone-seeking radiopharmaceutical. Due to its suitable nuclear characteristics 177Lu appears to be worthwhile for palliative therapy of bone metastasis.