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Showing 10 results for Linear Accelerator
M. Hajizadeh Saffar, M.r. Ghavamnasiri, H. Gholamhosseinian,
Volume 2, Issue 2 (9-2004)
Abstract
Background: In radiotherapy, wedge filters are used for optimizing the tumor dose distribution in patients. The attenuation in beam intensity due to the presence of wedge filter is compensated by means of a wedge factor measured at the central axis of the beam. The field size, depth and SSD dependence of wedge factor have been assessed for 9MV radiations of Neptun PC linear accelerator. Materials and Methods: Wedge factors (WF) at different SSD, field size (FS) and depth (d) in water were measured for 8 steel wedges with different sizes and angles of 15, 30, 45, and 60 degree. Experimental data were obtained using Neptun 10PC, Linac 9MV X-ray machine, a 3D water phantom, dosimeters and an electrometer. To study the effect of field size on WF, the wedge factor was measured for square field sizes from 5 ´ 5 to 20 ´ 20 cm, with 1 cm increment intervals for all wedges and, at the depth of 10 cm, SSD of 100 cm with monitor unit (MU) of 80. Effects of depth on WF were studied by measurement in various depths from 3-19cm for all wedge angles at SSD of 100cm, field size of 10 ´ 10cm and 80 MU irradiation. Effects of SSD on WF were investigated by a variation of SSD from 90-110cm with 5cm increment intervals while the dosimeter was set at depth of 10cm and field size of 10 ´ 10cm were irradiated for 80MU. Results: Linear dependence of WF with field size and depth of measurements were confirmed with 95% certainty. Shapiro-Wilk test, showed that the residual data of the regression tests have normal distributions (P>0.05). There was also found no linear relationship between WF and SSD (P>0.05). Conclusion: WF has linear dependence with field size and depth of measurements, but the rate of variations are less than 2.2% per 10cm variation in field size and less than 1.3% per 10 cm variation in depth of measurements, therefore, correction of WF for field size and depth of
treatments in clinical trials is negligible. Iran . J. Radiat. Res., 2004 2 (2): 53-58
M.t. Bahreyni Toossi, A.r. Khoshbin Khoshnazar,
Volume 2, Issue 3 (12-2004)
Abstract
Background: A set of hardware stereotactic radiosurgery is designed and constructed. The scope of this article is to describe how we have designed and developed stereotactic collimation assembly for a 9 MV Neptun 10 PC linac. Materials and methods: One collimator holder and six collimators were made, with their
radiation field diameter between 12.5 mm to 25 mm at isocenter level. Beam data, such as depth dose percent, off axis ratio and output factor of the collimators were measured. Isocentric
accuracy and dose delivery, accuracy tests were also performed using locally made isocentric alignment control device, target simulator and plexiglass phantom. Results: Average isocenter shifts resulting from gantry and couch motion were respectively 1.5 mm and 2 mm. Simulating a stereotactic radiosurgery with the help of a plexiglass phantom showed less than one percent radiation leakage to critical organs such as eyes and thyroid. Conclusion: Stereotactic collimation assembly in conjunction with the rest of constructed equipments can be employed to set up SRS treatment, provided safety and to compensate operations are taken into account. Iran . J. Radiat. Res., 2004 2 (3): 135-140
Dr A. Mesbahi,
Volume 4, Issue 1 (6-2006)
Abstract
Background: Monte Carlo (MC) modeling of a linear accelerator is a prerequisite for Monte Carlo dose calculations in external beam radiotherapy. In this study, a simple and efficient model was developed for Elekta SL-25 linear accelerator using MCNP4C Monte Carlo code
Materials and methods: The head of Elekta SL-25 linac was simulated for 6 and 18 MV photon beams using MCNP4C MC code. Energy spectra and fluence distribution of photons crossing the phase space plane were calculated. A simple point source model was developed based on calculated photon spectra and spatial distribution. Using this model, percent depth doses (PDDs) and beam profiles were calculated for different field sizes. The results of MC calculations were compared with measurements.
Results: There was a good agreement between MC calculations and measurement for descending part of PDD curves. But, comparing calculated PDDs with measurement showed up to 10% differences for build up region of PDD curves for both energies. For beam profiles, there was 2% difference in flat region and up to 15% difference was seen for out of field region. These results were acceptable according to recommended criteria. Although, using our model the run time was decreased 24 times in comparison to original full Monte Carlo method.
Conclusion: Our study showed that our model is accurate and effective for MC calculations in radiotherapy treatment planning. Also, it substantially lowers MC runtime for radiotherapy purposes.
Dr F. Bouzarjomehri, T. Bayat, M.h. Dashti R, J. Ghisari, N. Abdoli,
Volume 4, Issue 2 (9-2006)
Abstract
ABSTRACT
Introduction: Recently uses of
medium and high energy x-rays has been increased in Iran and radiotherapy
centers along with a variety of accelerators have been installed in some
provinces. In the other hand there is no sufficient skill in designing and
making radiotherapy treatment rooms. This study was conducted to evaluate the
efficacy of different mixtures of barite concrete for shielding the radiotherapy
rooms. In this way we emphasized on determining the size and amount of barite
aggregations to achieve the maximum radiation attenuation which leads to
minimizing wall thickness in treatment room.
Materials and Methods: To
increase concrete density, the barite aggregation was added to concrete.
Different size variations of barite aggregates mixed with different water/cement
ratio were examined. The dimension of cubic concrete specimens for compression
strength test was 15×15×15 cm. The rectangular barite concrete blocks with
different compressions as used for strength test with cross section of 10×10 cm
and thicknesses from 5 to 40 cm were used for radiation attenuation test. For
this test concrete specimens were irradiated by gamma beam of 60Co
(Phoenix Theratron). The transmission radiation through the blocks was measured
by a Farmer ionization chamber (FC65P) in Yazd radiotherapy center.
Results: Our findings showed
that in all specimens the highest mean compression strength was related to the
specimens with equal ratio of fine to coarse barite aggregates but the lowest
HVL was obtained from mixtures with fine to coarse ratio of 35/65. The concrete
sample with a 0.45 water/cement ratio, 350 kg/m3 cement and equal
amounts of fine and coarse barite sands had nearly minimum half value layer(HVL)
and maximum compression strength, so this sample was considered as the best
barite concrete sample.
Conclusion: Since HVL of the
barite concrete specimens with the same compression strength is markedly lower
than the conventional concrete and we have a plenty barite mines in our country
it is recommended to use barite concrete with the best mixture condition based
on our findings for shielding the radiotherapy rooms.
M. Najafi, Dr. Mohammad Reza Deevband, A.a. Yousefi Diba, A. Amin Moghaddam,
Volume 13, Issue 4 (10-2015)
Abstract
Background: Radiation therapy uses high-energy radiation to kill cancer cells. Photoneutron contamination and induced radioactivity of high energy therapeutic photon beams are considered as the main source of occupational exposure to radiation therapists who works with linear accelerators operating above 10 MV. Materials and Methods: The gamma dose rates were measured after termination of different treatment approaches using 15 MV photons and room entry times for each approach was determined. Based on the results of this study, the annual dose of radiation therapists was estimated. Results: The highest dose rate that measured in the treatment room was belonged to 3-field pelvic approach which was equal to 5 ± 1.1 µSv/h. The radiation therapist's room entry times were determined between 3 to 10 minutes and the annual dose was estimated up to 5.9 mSv/y. Conclusion: Although the estimated annual dose is less than the internationally permitted value, the undesirable dose to radiation workers could be reduced through considering recommended room entry times.
S.r. Mahdavi, M.r. Ay, Phd M. Zabihzadeh, M. Allahverdi, M. Shahriari, M. Hoseini-Ghahfarokhi,
Volume 17, Issue 1 (1-2019)
Abstract
Background: During intensity modulated radiation therapy (IMRT) technique, theoretically, presence of flattening filter (FF) across the beamline of clinical linear accelerator (linac) is not essential to obtain uniform lateral profiles due to intensity modulation of photon beams by multileaf collimators (MLCs). The aim of this study was to investigate the dosimetrical properties of 18 MV photon beam-Varian linac with and without FF. Materials and Methods: All dose measurements were performed on 18 MV, FF mode-Varian 2100C/D linac. The FF and flattening filter free (FFF) modes of linac were modeled by MCNPX 2.4. code. The photon and contaminant electrons spectra, dose rate, present depth doses (PDD), lateral dose profiles, total and collimator scatter factors and out of field doses were calculated and compared with and without FF. Results: Removing the FF increased the photon and contaminant electron fluences by factors of 5.48 and 3.94 for a 5 × 5 cm2 field size, respectively. The surface dose increased up to 155%. The flatness of dose profile was disturbed and deteriorated with increase of field size. Despite the dependence of the total scattering factor on field size, the variation of collimator scattering factors was neglected. The out-of-field dose decreased about 81.5 % for a 5 × 5 cm2 field size. Conclusion: Removing FF from the linac head increases the dose rate and decreases the out-of-field dose, but the increased skin dose and deteriorated flatness of lateral dose profile are the main disadvantages of the FFF mode.
Ms.c., K.r. Rajesh, R. Ganapathi Raman Ganapathi Raman, M.m. Musthafa, C.v. Midhun, N. Joseph,
Volume 18, Issue 1 (1-2020)
Abstract
Background: Photoneutrons are produced during the radiotherapy treatment, when high energy X rays interacts with structures of the head of the linear accelerator (linac). The present day TPS are not taking into account the photo-neutron dose and the biological effects associated with it. The late induction of cancer and recurrence of the disease in old cancer patients are being frequently reported. Materials and Methods: Patients undergoing radiotherapy treatment with 15 MV X rays from a Siemens Primus Plus linear accelerator was considered for the study. In the present work, photoneutron spectrum from the linac head is measured using CR 39 SSNTD and the corresponding dose is calculated using Geant4. The composite photoneutron spectrum from the linac head and the corresponding dose was calculated using the kerma evaluation method in a human equivalent tissue phantom. The repeated calculation outcomes and the covariance error analysis in the nuclear data give consistency and an accuracy of 2 % in the results. Results: The result shows that significant amount of photoneutron dose was deposited during radiotherapy treatment when high energy X rays are used. The photoneutron production from the patient itself is yet another major issue which will cause out off field dose. Conclusion: This work gives importance in considering the photoneutron dose during radiotherapy planning and protection. This extra dose might be a factor that contributes to the induction of cancer and also to the recurrence of cancer to previously cured patients.
Ph.d., S. Khoudri, Z. Chaoui,
Volume 20, Issue 3 (7-2022)
Abstract
Background: For various practical reasons in radiotherapy practice, it is very advantageous to have linear accelerators dosimetrically matched. The present work assesses the extent of beam matching by investigating the similarity of dosimetric data from three Clinac-iX accelerators in photons (6, 18 MV) and electrons (6, 9, 12, 16 and 20 MeV) mode. Materials and Methods: The following study is based on detailed comparisons of measured and determined parameters such as percent depth doses (PDDs), cross-plane beam profiles, flatness, symmetry, penumbra and dosimetric leaf gap, MLCT interleaf transmission factor, quality index, Relative output factor, in addition of depth R50, therapeutic range R90 and particle range Rp of electron beam. Results: The current measured data, for both photons and electrons, exhibited satisfactory degree of agreement among the three Clinac-iX. For 6 MV and 18 MV photons energies the maximum deviation of percentage depth does not exceed 0.4 %. For electron depth dose measurements (dmax, R50, R90, Rp) the results revealed a maximum deviation of 0.54 mm for all electron energies and applicators. As a direct clinical application, a left breast and prostate cancer cases were planned on the three Clinac-iX machines and compared for their dose volume histograms. Conclusion: In clinical applications, the patient’s treatment can be shifted from one Clinac-iX to another without reducing the treatment quality in the case of periodic preventive maintenance or interruption of the functioning of the Clinacs; the treatment can be preserved without having to replan.
M. Zabihzadeh, Dr. Z. Sedaghat, H. Shahbazian,
Volume 21, Issue 2 (4-2023)
Abstract
Background: Producing the ideal therapeutic electron beams from a clinical linear accelerator (Linac), is crucial to optimize dose delivery in radiotherapy. The aim of this study was to investigate the properties of electron beams with and without the scattering foil. Materials and Methods: Varian Linac 2100CD head was simulated by means of MCNPX-2.7 program. After validation with measured data, scattering foils were removed and then different dosimetric properties of 6 and 9 MeV electron beams such as depth dose percentage, dose profile, range, surface dose, dose rate and photon contamination were calculated and compared for field sizes ranging from 0.25×0.25 to 10×10 cm2 in three states with primary and secondary scattering foil (SF), without primary scattering foil (PSFF) and without primary and secondary scattering foil (SFF). Results: By removing the scattering foils, dose rates and surface doses were increased more than 25 times in 0.25×0.25 cm2 field, and in the bigger fields, it was less in 10×10 cm2 field, almost 4 times and the photon contamination is reduced by 20% times in 0.25×0.25 cm2 field. Also, Adjacent organs receive a lower dose, Because the dose profile curve was shrieked, it was almost 1cm in field 2×2 cm2 and less than 1cm in other fields. The dose profile flatness was diminished in scattering foil-free (SFF) mode which is not crucial for the small fields. Conclusion: Removing scattering foil improves dosimetric properties of electron beams specially to treat the superficial tumors and for the small field radiotherapy.
S. Okahira, Ph.d., Y. Tanabe, T. Sasaki, A. Yamane, T. Nakayama, A. Osaka, Y. Fuji,
Volume 22, Issue 3 (7-2024)
Abstract
Background: The successful installation of linear accelerators (LINACs) depends on operator skill and experience, and its optimization can be further improved using vendor commissioning support. To facilitate the introduction of LINAC, Elekta provides commissioning support through Accelerated Go Live (AGL) using representative beam data. This study aimed to evaluate the effective commissioning of LINAC-assisted AGL complemented by additional measurements conducted by a user. Materials and Methods: Output doses were measured within a field size of > 3 cm2 using a single chamber with AGL and within a field size of > 2 cm2 using three types of optimal chambers based on the field size adopted by the user. In all cases, the differences between the measured and calculated output doses were maintained at < 2%. Results: The accuracy of couch modeling was evaluated by measuring arc irradiation for three different field sizes, with the electron density value assigned as a dose difference of <2% between the measured and calculated values at 2% for all energies and field size of >3 cm2. Additionally, imaging scan parameters for cone beam computed tomography were optimized to reduce the radiation dose, in comparison to the initial vendor settings, by referencing IEC 60601-2-44 standards and examining results from neighboring facilities. Conclusions: AGL proved to be effective as a temporary check, but additional commissioning efforts by the user were necessary for a more thorough evaluation and more appropriate initiation, aligning with established clinical practices.
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