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SUMMARY:Source Head Fluence Modulation in Cobalt-60 Teletherapy: A dosimet
 ric and Monte Carlo study
DTSTART;VALUE=DATE-TIME:20190320T123000Z
DTEND;VALUE=DATE-TIME:20190320T130000Z
DTSTAMP;VALUE=DATE-TIME:20260906T154107Z
UID:indico-contribution-1341@indico.tlabs.ac.za
DESCRIPTION:Speakers: Nhlakanipho Mdziniso (Department of Physics\, Univer
 sity of Eswatini\, Faculty of Science and Engineering)\n**Background and P
 urpose**: Innovations in external beam radiotherapy have been limited to l
 inear accelerators\, yet radiotherapy began with cobalt-60 teletherapy. On
 e such technology is called intensity modulated radiotherapy (IMRT)\, whic
 h can be executed with cobalt-60 teletherapy units to yield dosimetric cha
 racteristics that are comparable with linear accelerator beams. The lower 
 energy and weaker penetration may be negligible in the delivery of efficie
 nt IMRT in cobalt-60 teletherapy especially for head and neck cancers with
  superficial extent. The aim of this study was to investigate the implemen
 tation of step and shoot technology in cobalt-60 teletherapy.\n\n**Materia
 ls and Methods**: A clinical MDS Nordion Equinox 80 unit was used at dose 
 rates of 67.7 ± 7.4 cGy/min and 61.4 ± 3.1 cGy/min. Three intensity maps
  were prescribed with Oncentra 4.3\, and they were verified with GafChromi
 c EBT2 film measurements in a PTW universal IMRT verification phantom. Two
  other measurements were made with GafChromic RTQA2-1010 film whilst a phy
 sical compensator was constructed and placed in the accessory holder. A 0.
 125 cc PTW 31010 Semiflex thimble chamber was used for dose rate constancy
  checks\, and a calibrated Lufft OPUS 20 was used to monitor temperature a
 nd pressure. Images of post-irradiation films were acquired prior to net o
 ptical density readouts and normalised lateral beam profile plots. Two-dim
 ensional gamma index evaluations of the results were made against Monte Ca
 rlo simulations of three source diameters.\n\n**Results and Discussion**: 
 Film calibration curves showed that GafChromic RTQA2-10101 film had a low 
 dose response than GafChromic EBT2 film. Normalised lateral beam profiles 
 generated from film measurements and Monte Carlo simulations output data r
 evealed that step and shoot technology can be executed in cobalt-60 teleth
 erapy by symmetric and asymmetric segmented secondary collimator jaw motio
 n or by using a three-dimensional physical compensator. Gamma passing rate
 s were highest between physical measurements and Monte Carlo simulations o
 f a 1.5 cm diameter source when using 3 mm\, 3 % and 5 mm\, 5 % criteria. 
 Furthermore\, radiochromic film can be a viable tool for dose verification
  and quality assurance measurements in resultant beam fluence maps.\n\n**C
 onclusions and Future Recommendations**: Sharply defined beam intensities 
 can be achieved in cobalt-60 teletherapy by a shift to small source diamet
 ers\, as revealed by the results of Monte Carlo simulations for the smalle
 st source diameter. Effort is needed to extend this study to the use of mu
 ltileaf collimation for more complex beam intensity.\n\nhttps://indico.tla
 bs.ac.za/event/82/contributions/1341/
LOCATION:J Block Auditorium
URL:https://indico.tlabs.ac.za/event/82/contributions/1341/
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