title: Assessment of dose error due to nylon mesh of treatment couch.
abstract: OBJECTIVE
  This study aims at the assessment of dose error in patients undergoing radiotherapy due to treatment couch of Co-60 teletherapy unit.
  
  
  METHODS
  In this study beam attenuation due to treatment couch of Co-60 unit was measured in air for different gantry angles and field sizes. Polymethylmethacrylate (PMMA) phantom was used to estimate the effect of depth on attenuation. Impact of couch on surface dose was also evaluated.
  
  
  RESULTS
  Beam attenuation due to couch was in the range of 0.5-28% for different gantry angles with standard field size of 10 × 10 cm(2) with optimum position of metallic cranks. Maximum attenuation (29%) was observed with smallest field size i.e. 5 × 5 cm(2). Beam attenuation has been found higher in phantom as compared to that in air However, no particular trend of attenuation has been noted with varying depth of phantom. A 6% increase in surface dose has also been observed due to couch insertion for normal beam incidence. Maximum error of 80% is also note-worthy for most unfavorable situation of irradiation at 180 degree through the metallic cranks.
  
  
  CONCLUSIONS
  It has been determined that ignoring the treatment couch and its accessories can result in dose error of 0.5-80%, depending on gantry angle, field size and position of couch accessories. Therefore, consideration of dose error due to couch during treatment planning is recommended.
authors.affiliation: Institute of Nuclear Medicine, Oncology and Radiotherapy (INOR), Abbottabad, Pakistan. Electronic address: attiagul@gmail.com.
authors.forename: Attia
authors.initials: A
authors.lastname: Gul
authors.affiliation: Department of Physics, Hazara University, Mansehra, Pakistan.
authors.forename: Mehnaz
authors.initials: M
authors.lastname: Liaquat
authors.affiliation: Department of Physics, Hazara University, Mansehra, Pakistan.
authors.forename: Aneela
authors.initials: A
authors.lastname: Kanwal
authors.affiliation: Institute of Nuclear Medicine, Oncology and Radiotherapy (INOR), Abbottabad, Pakistan.
authors.forename: Nadeem Zia
authors.initials: NZ
authors.lastname: Abbasi
authors.affiliation: Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad, Pakistan.
authors.forename: Muhammad Basim
authors.initials: MB
authors.lastname: Kakakhel
authors.affiliation: Institute of Nuclear Medicine, Oncology and Radiotherapy (INOR), Abbottabad, Pakistan.
authors.forename: Akbar
authors.initials: A
authors.lastname: Ali
mesh_terms: D009757:Nylons; D011829:Radiation Dosage; D011867:Radioisotope Teletherapy / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D061106:Radiotherapy Setup Errors; D012867:Skin / Q000528:radiation effects
chemical_list: D009757:Nylons
keywords: Attenuation; Dose error; Skin dose; Treatment couch