Papers by Keyword: Radiotherapy

Abstract: External beam radiotherapy is a crucial method in treating cancer as it requires a high level of accuracy in patient positioning. Hence, commercial thermoplastic masks have a significant role during radiotherapy treatment as it is an efficient way of accurately positioning the patient without risking their safety and comfort. However, these commercial masks are expensive due to the use of costly compounds and additives, and several studies have concluded that commercial masks can significantly increase the surface dose. This study examined the effects of various thermoplastic reinforced composites for an alternative economic mask in terms of depth-dose distribution through Monte Carlo simulations in GEANT4 Application for Tomographic Emission (GATE). The simulations were varied by incident beams and their energies, material composition of the phantom, and varying thermoplastic reinforced composites. In general, the results indicated that PCL/PLA (polycaprolactone/polylactic acid), PLA/PU (polylactic acid/polyurethane), PCL/RH (polycaprolactone/rice husk), LDPE/PALF (low-density polyethylene/pineapple leaf fiber), and PP/PALF (polypropylene/pineapple leaf fiber) composites showed relatively accurate dose delivery in the target volume, which the slight difference will accumulate the 5% marginal error in treatment planning systems.

Abstract: We developed the photon counting CT system by using a conventional laboratory X-ray source and a CdTe line sensor. Attenuation coefficients were obtained from the measured CT image data. Our suggested method for deriving the electron density and effective atomic number from the measured attenuation coefficients was tested experimentally. The accuracy of the electron densities and effective atomic numbers are about <5 % (the averages of absolute values are 2.6 % and 3.1 %, respectively) for material of 6< Z and Zeff <13. Our suggested simple method, in which we do not need the exact source X-ray spectrum and detector response function, achieves comparable accuracy to the previous reports.

Abstract: The objective of this study is to recommend optimized shield design from the shielding viewpoint for installation of the Cyclotron, Cyberknife and Linear Acceleration (LINAC) facility at Bangabandhu Sheikh Mujib Medical University (BSMMU) in Dhaka, Bangladesh. The shield design for Cyclotron, Cyberknife and LINAC has been performed considering ICRP-103 (2007) recommendations for occupational and public dose limits. The optimized design parameters for Radiation Shielding Concrete (RSC) with hardened density of 2.35 gm/cm³ are: 254 cm thickness of RSC as primary barrier for LINAC on both side of the source, 198 cm and 178 cm thickness of RSC on parking side and earthen side wall for Cyclotron, a maze wall of thickness 198 cm and 122 cm RSC for Cyclotron and LINAC, 168 cm and 152 cm thickness of RSC from opposite to the maze wall, slab thickness 152 cm excluding a false ceiling of thickness 122 cm with RSC having a functional story height of 503 cm for LINAC, 122 cm and 259 cm slab thickness of RSC for Cyberknife and Cyclotron. The use of RSC in the shield design of wall and roof shows that it limits radiation exposure of staff, patients, visitors and the public to acceptable level, thus optimizing radiation protection.

Abstract: Passive Solid State Nuclear Track Detectors (SSNTDs) are a versatile tool for neutron studies as has been shown long ago and several good quality materials are commercially available. They are useful for charged particle detection in the linear energy transfer (LET) range above the threshold value of ~10 keV μm^-1. Linacs, operating above 6 MeV up to the energy region where radiotherapy is applied usually up to ~25MeV, induce unwanted photo-neutron field; their spectra shows two components due to reaction dynamics based on evaporation and knock-on mechanisms. Neutrons produced by Linacs are often neglected in health application; however, today it has become necessary to assess the effect on patient, staff and radiation workers. Radiation studies using SSNTDs play a major role in this case. Other fields also take advantage of the passive detectors properties; in fact they are employed with success to measure neutron signals relevant for plasma diagnostics as it was demonstrated at the RFX facility as part of the ITER project. The PADC-NTD techniques provide information on external neutron field values around the RFX-installation during pulsed operation. In any case, converter materials, as charged particles from (n, p) and (n, α) reactions, are required to produce neutron fingerprints through latent tracks. These once etched provide information on neutron fluence spatial values. Track histograms are then employed to determine photo-neutron induced damage in materials as well as radiation dose to both patient and professionally exposed workers. The estimated neutron fluence that can be determined by NTM covers a large range of values, the largest being above 10¹⁰ (± 12%) neutrons/cm².

Abstract: Solid-state dosimetry employs highly sensitive semiconductors such as Gallium Nitride (GaN) and Silicon (Si), but they have a common drawback of over response compared to tissues for low-energy scattered photons, which induces inacceptable errors for radiotherapy application. To tackle this issue, we propose a compensation method consisting in using two different materials of dosimetric interest with different atomic numbers. Their responses are denoted as SC1 and SC2. The response ratio SC1/water as a function of the ratio SC1/SC2 exhibits a monotonic curve that can serve as reference to compensate the over-response of SC1. To validate this method, we have studied the dosimetric response of GaN (0.1 mm³) and Si crystals (2.5 mm³) by simulations, using a validated model based on the general cavity theory in a homogeneous water phantom. The dosimetric response of GaN and Si calculated using the model has errors within 2.5% compared to measured data. The local fluence spectra have been obtained by convolution of pencil beam kernel built by Monte Carlo simulations for different clinical irradiation conditions with field size (from 5×5 cm² up to 20×20 cm²) at depth in the phantom (from 2 cm to 25 cm). The obtained results confirm a monotone relationship between GaN/water dose ratio and GaN/Si dose ratio. The reference curve is independent of irradiation conditions (field size, dosimeter position...), and allows determination of compensation value by identification.

Abstract: Star shot analysis is one common and important module in physics quality assurance (QA) which is regularly performed on the radiotherapy machine. A star shot analysis method by image processing is proposed. First, through ROI selection and image binarization, the irrelevant image parts are excluded and the star-shots are highlighted. Then the center and beam branches of the shots are determined by iteration, coordinate transformation, threshold values analysis and image segmentation. Finally, beam center lines and a minimum circle encompassing beam intersections are calculated by mathematic operations. The proposed method is performed on three star shot films and all beam center lines, beam intersections and minimum circles are obtained instantly and showed clearly. The results present good consistency with the commercial verification software and indicate that the proposed method provides the physicist a considerable comparison in physics QA.

Abstract: A new method for the evaluation of radiotherapy 3D polymer gel dosimeters has been developed using ultrasound to assess the significant structural changes that occur following irradiation of the dosimeters. Polymer gel dosimeters were being fabricated using a monomer named 2-Hydroxyl-Ethyl-Meta-Acrylate (HEMA) with the presence of gelatine as a gelling agent. The readymade gel which is the concentration for HEMA fixed at 2, 4 and 5% would then undergo an ultrasonic evaluation to test for the propagation of sound speed through it. In the observation of relationship between the ultrasound propagation speeds as the doses increase (focusing at the cross region from overlapped beams) and concentration of monomer, the propagation speed for all the three polymer gel dosimeter phantoms still varies between 1460 to 1570 m/s which is still in the range of speed of sound for human tissue [. The ultrasonic absorption attenuation coefficient dose sensitivity for polymer gel dosimeters for 2, 4 and 5% of monomer are in the range of 0.02 to 0.6 dB which is equivalent to human tissue. As a comparison, it can be seen that gel phantoms with high concentration of monomer (5%) is more sensitive to the radiation compared to the lower (2% and 4%) concentrations. Regarding the absolute results of mechanical and acoustic properties; the copolymer-in-oil phantom is equivalent with soft tissue.

Abstract: An increasing amount of public interest in environmental monitoring programmes is being focused on the environmental impact of radiation arising from nuclear power operations and the corresponding detection of slight variations in the natural radiation background. The primary objective of individual monitoring for external radiation is to assess, and thus limit, radiation doses to individual workers. Supplementary objectives are to provide information about the trends of these doses and about the conditions in places of work and to give information in the event of accidental exposure. Depending on the kind of radiation hazard, the ICRP recommended maximum permissible dose (MPD) values. These are the maximum dose equivalent values, which are not expected to cause appreciable body injury to a person during his lifetime. Thermoluminescent Dosimetry (TLD) has been developed during 1960-70 for various applications in medicine and industry. TLD, the most advanced and most intensively studied integrating dosimeter system, has now reached the stage at which it may replace or supplement film dosimetry. TLD systems are widely applied to environmental monitoring programmes near nuclear installations. TLD systems with high reproducibility in the milli roentgen dose range are required in order to measure exposures equal to that resulting from an exposure rate of 10μR h-1 during field periods of from several days up to a year. A brief list of applications specific to radiation oncology is given here. In radiation oncology dosimetric accuracy demanded is of the order of 2-5%. TLDs offer a clear solution since their precision meets this criteria. Contents

Abstract: Objective: To compare dose-volume histograms (DVHs) and the dose distribution of three-dimensional conformal radiotherapy(3DCRT),7 fields radiotherapy(7FRT) and intensity-modulated radiotherapy (IMRT) of treatment planning in gastric cancer. Methods: We selected 5 patients with gastric cancer, they were pathologically confirmed stage T3,T4 or N+ gastric cancer. All patients underwent radical gastrectomy. A dosimetry study was carried out on these five patients. For each patient, three kinds of treatment planning were designed with a prescribed dose of 45Gy to 95％of PTV.Many kinds of parameters of these plans in each patient were compared: isodose distributions line、dose-volume histogram(DVH)、V95%、V110%、CI、HI、EI of target volume and the dose of related critical organs. Results: IMRT was superior to 3DCRT and 7F-RT in dose uniformity（p＜0.05）, there was no statistical difference between 3DCRT and 7FRT in CI（p>0.05）.IMRT had better dose conformity than 3DCRT and 7FRT（p＜0.05）, and 3DCRT was better than 7FRT in CI（p＜0.05）.IMRT showed better EI than 3DCRT and 7FRT（p＜0.05）,there was no statistical difference between 3DCRT and 7FRT in EI（p>0.05）.IMRT had advantage at sparing liver compared with 3DCRT and 7FRT（p＜0.05）,7FRT showed better D1/3 of liver than 3DCRT（p＜0.05）,but there was no statistical difference between 3DCRT and 7FRT in Dmean of liver（p>0.05）.IMRT expressed better Dmax of spinal cord than 3DCRT and 7F-RT（p＜0.05）, and 7FRT was better than IMRT in Dmax of spinal cord（p＜0.05）.But the dose received by the both kidneys were not significantly different. Conclusion: IMRT is superior to 3DCRT and 7FRT,and 3DCRT plans showed better CI and Dmax of spinal cord composed to 7FRT,and 7FRT was superior to 3DCRT in D1/3 of liver. IMRT for gastric cancer had physics advantage for clinical application.

Abstract: Mdthod :110 gastric cancer patients were selected from Feb 2004 to Jan 2006, who had complete pathological data and were underwent radical resection. All patients were diagnosed by endoscopy, preoperative histologic diagnosis and exclusion from distant metastasis, using D1 or D2 lymph node dissection, postoperative pathology confirmed stump negative. Univariate analysis was applied on the pathologic information and multivariate analysis was applied based on the univariate analysis. Result :(1)Univariate analysis showed that tumor diameter、histology、vascular invasion、lymphatic vessel invasion and neural invasion were correlated with T/N classification.Multivariate analysis showed that vascular invasion and lymphatic vessel invasion were correlated with T classification and lymphatic vessel invasion was associated with N classification. (2) For T and N stages, lymphatic vessel invasion was strongly related factor. Conclusion: For T and N stages,, lymphatic vessel invasion was strongly relevant factor. For patients with confirmed lymphatic vessel invasion, postoperative adjuvant radiotherapy is suggested.