Design of a generally applicable abdominal shield for reducing fetal dose during radiotherapy of common malignancies in pregnant patients

Background: In most cancer cases, the treatment choice for a pregnant patient is radiotherapy. In these patients, the abdomen is usually not exposed; therefore fetus exposure is due to peripheral dose (PD). The purpose of this study was to estimate the fetal dose (the maximum PD in each pregnancy stage) for modalities available and to fabricate and evaluate a generally applicable fetal shield. Materials and Methods: PD values were measured for brain, breast and mediastinum irradiation in a whole body anthropomorphic phantom using a NE 2571 ionization chamber. An external shield was then designed to reduce the fetal dose to the standard dose limit, 5 mSv. Results: The range of PD values as a function of distance from the field's edge were as follows 1) 9.4-259 cGy for Mantel field; 2) 6.5-95 cGy for chest wall irradiation with 10 MeV electrons, 3) 8.5-52.5 cGy for tangential field with Co-60 and 4) 4.8-7.8 cGy for brain radiotherapy with 9 MV photon. PD values for the same setups using the fetal shield were as follows: 1) 1.4-22 cGy, 2) 0.5-4 cGy, 3) 1.5-5 cGy and 4) under 1 cGy. Conclusions: The measured PD data sets can be used to estimate fetal dose for specific treatment setups and pregnancy stages. The use of external shield designed in this research reduced the fetal dose effectively to under the threshold (a 70-90% reduction), except for the final stages of pregnancy in Hodgkin's patients. Iran. J. Radiat. Res., 2012; 10(3-4): 151-15

Evaluation of Benzimidazole Resistance in Haemonchus contortus Using Comparative PCR-RFLP Methods

Background: In order to deworm the ruminants especially of sheep in Iran, consumption of benzimi­dazoles has more than 2 decades history and today farmers are using imidazothiazoles, macrocyclic lactones and mostly benzimidazole compounds (BZs) to treat infected farm animals. It has been demonstrated that the most common molecular mechanism leading to BZsresistance in Haemonchus contortus is a single mutation at amino acid 200 (phenylalanine to tyrosine) of the isotype 1 of beta tubulin gene. According to the report of such mutations in Iranian Telador­sagia circumcincta isolates with Restriction Site Created PCR-RFLP, we decided to evaluate the frequency of such mutations in H. contortus in three different geographical areas of Iran.Methodes: A total of 102 collected adult male H. contortus were evaluated with PCR-RFLP (us­ing PSP1406I as restriction enzyme). By means of a second step to compare function of different methods and to increase sensitivity of detection mechanism, a third of samples were examined by another PCR-RFLP method (using TaaI as restriction enzyme) and finally beta tubulin gene of two samples was sequenced.Results: All of samples were detected as BZss homozygote. Finally, beta tubulin gene sequenc­ing of two samples showed no point mutation at codon 200.Conclusion: It seems that BZresistance of H. contortus in Iran is not a serious problem as antici­pated before

Evaluation of Therapeutic Properties of a Low Energy Electron Beam Plus Spoiler for Local Treatment of Mycosis Fungoides: A Monte Carlo Study

Background: When using low-energy electron beams for the treatment of skin lesions, such as Mycosis Fungoides (MF), a beam spoiler is used to decrease electron therapeutic depth (R90) while increasing the surface dose. Objective: The aim of this study was to evaluate the characteristics of a 5 MeV electron beam when using a spoiler for the local treatment of MF skin lesions by Monte Carlo (MC) simulation. Material and Methods: In this experimental study, a Siemens Primus treatment head and an acrylic spoiler, positioned at the end of applicator, were simu-lated using BEAMnrc, an EGSnrc user code. The modelled beam was validated by measurement using MP3-M water tank, Roos parallel plate chamber and Semi flex Chamber-31013 (all from PTW, Freiburg, Germany). For different spoiler thickness-es, dose distributions in water were calculated for 2 field sizes and were compared to those for the corresponding open fields. Results: For a 1.3 cm spoiler, therapeutic range changed from 1.5 cm (open field) to 0.5 cm and 0.4 cm for 10 × 10 cm2 and 20 × 20 cm2 field sizes, respectively. Maximum increase in penumbra width was 2.8 and 3.8 cm for 10 × 10 cm2 and 20 × 20 cm2 field sizes, respectively. Maximum increase in bremsstrahlung contamination was %2 in both field sizes. Conclusion: R90 decreased exponentially with increase in spoiler thickness. The effect of field size on penumbra was much larger for spoiled beam compared to the open beam. The results of this research can be applied to optimize the radiation treatment of MF patients in our hospital

A study of the photoneutron dose equivalent resulting from a Saturne 20 medical linac using Monte Carlo method

High energy linacs have several advantages including lower skin dose and higher dose rate at deep sighted tumors. But, at higher energies photonuclear reactions produce neutron contamination. Photoneutron contamination has been investigated from the early days of modern linacs. However, more studies have become possible using Monte Carlo codes developed in recent years. The aim of this study was to investigate the photoneutron spectrum and dose equivalent produced by an 18 MV Saturne linac at different points of a treatment room and its maze. The MCNP4C code was used to simulate the transport of photoneutrons produced by a typical 18 MV Saturne linac. The treatment room of a radiotherapy facility in which a Saturne 20 linac is installed was modeled. Neutron dose equivalent was calculated and its variations at various distances from the center of the X-ray beam was studied. It was noted that by increasing the distance from the center of the beam, fast neutrons decrease rapidly, but thermal neutrons do not change significantly. In addition, the photoneutron dose equivalent was lower for smaller fields. The fast photoneutrons were not recorded in the maze. It can be concluded that the fast photoneutrons are highly attenuated by concrete barrier, while the slow photoneutrons are increased. In addition, increasing the X-ray field size increases the photoneutron dose equivalent around the treatment room and maze. It seems that the walls play an effective role in increasing the photoneutron dose equivalent

Targeted photothermal therapy of melanoma in C57bl/6 mice using Fe3 O4 @Au core-shell nanoparticles and near-infrared laser

Background: Gold nanoshells can be tuned to absorb a particular wavelength of light. As a result, these tunable nanoparticles (NPs) can efficiently absorb light and convert it to heat. This phenomenon can be used for cancer treatment known as photothermal therapy. In this study, we synthesized Fe3 O4 @Au core-shell NPs, magnetically targeted them towards tumor, and used them for photothermal therapy of cancer. Objective: The main purpose of this research was to synthesize Fe3 O4 @Au coreshell NPs, magnetically target them towards tumor, and use them for photothermal therapy of cancer. Material and Methods: In this experimental study, twenty mice received 2 � 106 B16-F10 melanoma cells subcutaneously. After tumors volume reached 100 mm3,the mice were divided into five groups including a control group, NPs group, laser irradiation group, NPs + laser group and NPs + magnet + laser group. NPs were injected intravenously. After 6 hours, the tumor region was irradiated by laser (808 nm, 2.5 W/cm2, 6 minutes). The tumor volumes were measured every other day. Results: The effective diameter of Fe3 O4 @Au NPs was approximately 37.8 nm. The average tumor volume in control group, NPs group, laser irradiation group, NPs + laser irradiation group and NPs + magnet + laser irradiation group increased to 47.3, 45.3, 32.8, 19.9 and 7.7 times, respectively in 2 weeks. No obvious change in the average body weight for different groups occurred. Conclusion: Results demonstrated that magnetically targeted nano-photothermal therapy of cancer described in this paper holds great promise for the selective destruction of tumors. © 2021, Shriaz University of Medical Sciences. All rights reserved

An intraoral cone system for a Neptun 10PC linear accelerator

Intraoral irradiation, the treatment choice for well defined oral-cavity tumors, is done using intraoral cone (IOC) systems. In this study, an IOC system was developed for a Neptun 10PC linac. Beam parameters necessary to plan an intraoral electron treatment were evaluated for two applicators, a flat and a beveled end. Measurements were performed using a Scanditronix (p-Si) diode field detector in a Scanditronix (RFAplus) 3-D (three-dimensional) water phantom. Percent depth dose distributions, beam profiles, and leakage dose distributions for the developed cone system are presented

TUMOR DOSE ERROR ANALYSIS FOR MEGAVOLTAGE OPEN AND BLOCKED FIELDS USING MEASURED SCATTER CORRECTION FACTORS

Introduction. The most important goal in radiation therapy is treating the tumor while protecting the surrounding healthy tissue. To achieve this goal the difference between prescribed and deliveredtumor dose has to be less than±2 percent. This study evaluated the necessity of using output factors for changing output of a reference field to the output of other field sizes.
 Methods. Scp was measured in water and Se in a narrow cylindrical phantom built in this research for cobalt and 12 MV beams. The separation of Scp to Sc and Sp parts for blocked fields was evaluated by comparing the measured and calculated Scp values for blocked fields.
 Results. Results of this study indicates that if output factors are not used for a 12 MV beam the difference between delivered and prescribed tumor dose is from 13 percent (in largest field) to – 6 percent (in smallest field) ( difference was 8 percent for cobalt beam). The 'method of separating Scp to Se and Sp was verified (maximum difference from measured values was 1.3 percent).
 Discussion. In the method of using phantom field size for selecting Scp, tumor dose was more than prescribed dose from 2.4 percent (for a 27 percent block) to 7.8 percent (for a 90 percent block) for a 12 MV beam (the error increased by block size and proximity of block to the center)

A comparison of the basic photon and electron dosimetry data for Neptun 10PC linear accelerators

. In recent years the similarity of dosimetric characteristics of modern linear accelerators with the same make, model and nominal energy, has become more common. The goal of this study was to quantitatively investigate the reproducibility of the basic photon and electron dosimetry data from Neptun 10PC accelerators across the institutions. In the current study, the photon and electron dosimetry data collected during acceptance and initial commissioning of six Neptun 10PC linear accelerators are analyzed. The dates of original installations of these six machines were evenly spread out over a 5 year period and the series of measurements were conducted during an average of 1-2 months after original installations. All units had identical energies and beam modifiers. For photon beams, the collected data include depth dose data, output factors and beam profile data in water. For electron beams, in addition to depth dose data and output factors, the effective source skin distance for 10 × 10 cm field size is also presented. For most beam parameters the variation (one standard deviation), was less than 1.0% (less than 2% for 2 parameters). A variation of this magnitude is expected to be observed during annual calibration of well-maintained accelerators. In conclusion, this study is presenting a consistent set of data for Neptun 10PC linear accelerators. This consistency implies that for this model, a standard data set of basic photon and electron dosimetry could be established, as a guide for future commissioning, beam modeling and quality assurance purposes

Dosimetric Calculations of a Radioactive Eye Plaque used in Management of Ocular Melanoma Using Monte Carlo Simulations

Introduction & Objective: Brachytherapy using I-125 radioactive seeds in removable episcleral plaques (EP) is often used in treatment of ocular malignant melanoma. Some radioactive seeds are fixed in a gold bowl-shaped plaque. The plaque is sutured to the sclera surface corresponding to the base of the intraocular tumor, allowing for a localized radiation dose delivery to the tumor. Minimum target doses as high as 85Gy are directed at malignant tumor. The aim of this study was to develop a Monte Carlo simulation of an ocular plaque in order to calculate the resulting isodose distributions. Materials & Methods: The MCNP-4C Monte Carlo code is used to simulate the plan of an episcleral plaque treatment. A 20-mm Collaborative Ocular Melanoma Study (COMS) plaque with 3, I-125 seed of model 6711 was used. Resulting dose distributions, including central axis dose and off-axis dose profiles, were calculated in a water phantom with 12mm radius. The calculated dose distributions were compared to the corresponding dose measured by Knuten et al., 2001. Results: Central axis dose calculations represent a rapid dose fall off, which is an important factor in selection of appropriate eye plaque for management of tumors with known dimension. Calculated off-axis dose profiles show decreased dose uniformity at distances close to the plaque. Increasing of distance from the plaque resulted in increasing of the dose uniformity. Conclusion: Monte Carlo simulation of eye plaques can be used as a useful tool in process of design, development and treatment planning of ocular radioactive plaques