Development of A Head Docking Device for Linac-based Stereotactic Radiosurgery System to be Installed on Neptun 10 PC Linac

Introduction:  Stereotactic  radiosurgery  is  a  technique  for  the  treatment  of  intracranial  lesions  with  highly  collimated  x-ray  beam.  Linac-based  radiosurgery  is  currently  performed  by  two  techniques:  couch or pedestal mounted. In the first technique, a device is required to affix patient's head to a couch  and  moreover  to  translate  it  accurately.  Structure  of  such  a  device  constructed  by  the  authors  in  addition to the acceptance test which was performed to evaluate the device has been described in this  article.  Materials and Methods:  A head docking device has been designed and constructed according to the  geometry of linac's couch and desired functions. The device is completely made from aluminum and  consists  of  four  major  components:  attachment  bar,  lower  structure  with  four  movements,  upper  structure with two movements equipped with a lock, two handles and a mounting ring for stereotactic  frame. Translating accuracy, mechanical stability and isocentric accuracy were assessed in the frame of  acceptance test.  Results:  Translating  accuracy,  mechanical  stability  and  isocentric  accuracy  within  95%  confidence  intervals were found to be 1, 1.64 and 3.2 mm, respectively.  Discussion and Conclusion: According to AAPM report no.54 recommendation head docking device  should translate head with accuracy of 1 mm, the property which was met by the constructed device.  Moreover  considering  the  measured  isocentric  accuracy,  encompassing  mechanical  stability,  constructed device can confidently be used in stereotactic treatment

A Monte Carlo Simulation of Photon Beam Generated by a Linear Accelerator

ntroduction:  Monte  Carlo  simulation  is  the  most  accurate  method  of  simulating  radiation  transport  and  predicting doses at different points of interest in radiotherapy. A great advantage of the Monte Carlo method  compared  to  the  deterministic  methods  is  the  ability  to  deal  accurately  with  any  complex  geometry.  Its  disadvantage is the extremely long computing time required to obtain a dose distribution with good statistical  accuracy.  Materials and Methods: The MCNP-4C Monte Carlo code was used to simulate a 9 MV photon beam from  a Neptun 10PC linear accelerator. The accelerator was modeled as a complete unit consisting of a target, exit  window, initial collimator, primary collimator, flattening filter, monitor chamber and secondary collimator.  The geometrical details and the composition of each component was either obtained from the manufacturer or  was  directly  measured.  The  simulation  of  the  source  was  performed  in  a  two  step  process.  Initially,  the  electron source was defined. Secondly, the bremsstrahlung energy spectra and the fluence distribution at the  scoring  planes  were  used  to  define  the  photon  source.  The  simulated  electron  beam  energy  followed  a  Gaussian distribution, with FWHM equal to 12% in nominal energy. The used intensity distribution of the  electron beam also followed a Gaussian distribution with a FWHM equal to 0.34 cm. To compute the photon  beam data a 50 × 50 × 40 cm 3  water phantom located at SSD = 100 cm was simulated. The depth dose and  the dose profile curves were calculated for four different field sizes (5×5, 10×10, 20×20 and 30×30 cm 2 ) and  compared against the measured values. The low-energy cut-off for the photons and electrons was 10 and 500  KeV, respectively. The measurements were carried out by using a Scanditronix dose scanning system and a  0.12 cm 3  RK ionization chamber.  Results: To verify the simulated model, the calculated Monte Carlo dose data were compared against the  corresponding measured values. The energy spectra and the angular distribution of the x-ray beam generated  by the Neptun 10PC linac was examined. The result showed an efficiency of about 73% for the production of  bermsstrahlung photon by the target. The agreement between the calculated and the measured depth dose and  the dose profile was generally better than 2% for all the fields.  Discussion and Conclusion: The simulation of the Neptun 10PC linac performed in this work is capable of  computing the depth dose data and the beam profiles in water phantom for all the predefined fields including  5×5, 10×10, 20×20 and 30×30 cm 2 . Therefore, it can be concluded that MCNP-4C is a suitable tool for the  dose calculation in radiotherapy. The simulated linac machine and the resulting data can be used to predict  the dose distribution in all complex fields

Evaluation of the Effects of Different Filters and Helium Bag on the Reduction of Electron Contamination in Photon Beam of Neptun Linac

Introduction:  Skin  sparing  is  one  of  the  most  desirable  characteristics  of  high  energy  photon  beams. However, the photons emerging from the target of linacs are contaminated by secondary  electrons  as  a  result  of  their  interactions  with  air,  collimators,  flattening  filter  and  any  other  objects in their path. This phenomenon tends to increase the skin dose received by the patients. A  practical and simple way to reduce the contribution of electron contamination is to place a sheet of  medium  to  high  Z  material  just  after  the  secondary  collimator.  In  this  study,  filters  having  different thickness and atomic number were applied and their effectiveness on the reduction of  skin dose was evaluated.  Materials and Methods: The filters of different thickness and atomic number were applied. The  percent depth dose values were determined by the direct measurements made in a Scanditronix  water phantom using a PTW 31006 Pin Point chamber having a sensitive volume of 0.015 cm 3 . A  Perspex  filter  holder  was  made  to  be  installed  on  the  accessory  slot.  A  plastic  bag  containing  helium  was  also  made  using  thin  plastic  sheet  to  study  the  effect  of  the  helium  bag  when  it  replaces the air column between the head of the linac and the phantom. All of the measurements  were  carried  out  for  the  three  field  sizes  of  10×10,  20×20  and  25×25  cm 2 .  The  setups  were  adjusted for SSD = 100 cm. The ratio of the surface dose to maximum dose (Ds) was used as the  criterion to determine the optimum filter.   Results: The dosimetry results obtained in the water phantom indicated that a 0.4 mm thick Pb  filter is the most effective one. This filter reduces the Ds for the field sizes of 10×10, 20×20 and  25×25 cm 2  by 5.7, 7.9 and 9.6%, respectively. Also the simultaneous use of the optimum filter and  He bag is more effective than the filter alone. It reduces the Ds by 6.3, 10.1 and 12.3% for the  field sizes of 10×10, 20×20 and 25×25 cm 2 , respectively.  Discussion and Conclusion:  Based on the results of this work it is evident that the contribution  of contaminant electrons to dose from the air column between the head and the phantom is much  smaller than it from the secondary electrons arising from the head of the linac. On the other hand,  the electron contamination originating from the air column is almost independent of the field size.  But  the  surface  dose  arising  from  the  secondary  electrons  produced  by  the  head  of  the  linac  depends on the field size, which is increased by increasing the field size

Skin Dosimetry in Radiotherapy of Breast Cancer: a Comparison between EBT and EBT3 Radiochromic Films

Objective: Radiochromic EBT3 film is a later generation of radiochromic films. The aim of this study is to compare EBT and EBT3 radiochromic films in radiotherapy fields of breast cancer. Methods: A RANDO phantom was irradiated by a 6 MV Siemens Primus linac with medial and lateral fields of radiotherapy of breast cancer. Dosimetry was performed in various points in the fields using EBT and EBT3 films. Films were scanned by a Microtek color scanner. Dose values from two films in corresponding points were compared. Results: In the investigation of calibration, net optical density (NOD) of EBT radiochromic is more than the EBT3 radiochromic film. The highest percentage difference between NODs of two films is related to 0.75 Gy and equals to 14.19%. The lowest value is related to 0.2 Gy dose and is equal to 3.31%. The highest percentage difference between two films on the RANDO phantom in breast cancer fields is 13.51% and the minimum value is equal to 0.33%. Conclusion: From the comparison between the two films, most of the points show differences in dose in the measurements in fields of breast cancer radiotherapy. These differences are attributed to the thickness of the active layers, the overall thickness of the films, and the difference in the calibration fitted functions. The advantage of EBT film over EBT3 is a higher sensitivity; on the other hand EBT3 film allows to use its both sides in the scanning process and it is a new version of this film type

In-vitro Study of Photothermal Anticancer Activity of Carboxylated Multiwalled Carbon Nanotubes

Background and Objective: Multi-walled Carbon Nano Tubes (MWCNTs) as an important element of nanosciences have a remarkable absorption in the region of NIR window (650-900 nm) which can overcome the limitations of deep treatment in photothermal therapy. To disperse MWCNTs in water, it is proposed to attach carboxylated functional group (-COOH) to MWCNTs in order to increase dispersivity in water. Materials and Methods: A stable suspension of MWCNTs-COOH with different concentrations (from 2.5 to 500 μg/ml) was prepared. Then, they were compared for their ability to increase temperature in the presence of 810 nm laser irradiation and through a wide range of radiation time (from 20 to 600 s) and three laser powers (1.5, 2 and 2.5 w). The temperature rise was recorded real time every 20 seconds by a precise thermometer. Results: Absorption spectrum of MWCNTs-COOH suspension was remarkably higher than water in a wavelength range of 200 to 1100 nm. For example, using the concentrations of 2.5 and 80 μg/ml of MWCNTs-COOH suspension caused a temperature elevation 2.35 and 9.23 times compared to water, respectively, upon 10 min laser irradiation and 2.5 w. Moreover, this predominance can be observed for 1.5 and 2 w radiation powers, too. Our findings show that the maximum of temperature increase was obtained at 80 μg/ml concentration of MWCNT-COOH suspension for three powers and through all periods of exposure time. Our results show that the minimum required parameters for a 5°C temperature increase (a 5°C temperature increase causes cell death) were achieved through 2.5 w, 28 μg/ml concentration and 20 second irradiation time in which both concentration and radiation times were relatively low. Conclusion: Our results showed that MWCNTs-COOH can be considered as a potent photothermal agent in targeted therapies. New strategies must be developed to minimize the concentration, irradiation time and radiation power used in experiments

Analysis of Permanent Magnet Demagnetization Effect Outer-rotor Hybrid Excitation Flux Switching Motor

This paper addresses the irreversible permanent magnet (PM) demagnetization analysis of hybrid excitation flux switching motor (HEFSM) with outer-rotor configuration. PM demagnetization cause the PM strength used in the motor significantly reduces and hence contributes less torque performance. The study is focused on thermal analysis and conducted at various temperature up to as high as 180 degrees Celsius which has a tendency to be demagnetized. Therefore, PM demagnetization is among a critical issue and influences the choice of the applied motor. The analysis is carried out based on finite element method (FEM) and percentage of PM demagnetization is then calculated. Finally, based on simulated and calculated results the final design outer-rotor HEFSM has only 0.85 percent PM demagnetization at very high temperature and obviously the is no PM demagnetization at normal operating conditions