en Radiation Biology Radiation Biology تحقيق بديع Original Research <div style="text-align: justify;">Background: To study attenuation and increased skin dose for the iBEAM Standard couchtop, and attenuation of the BreastSTEP board, for an Elekta Compact 6 MV accelerator. Materials and Methods: Couchtop attenuation were measured for the range of gantry angles 125&deg;-180&deg; and field sizes 5&times;5-20&times;8 cm². H&N extension and the BreastSTEP attenuations measured in an 8&times;8 cm2 field. The couchtop effect on percentage depth-dose (PDD) measured by an EFD diode for field sizes 5&times;5-20&times;20 cm² and compared with that produced by a Co-60 beam passing through a &lsquo;tennis-racket&rsquo; couch insert. A Monte Carlo (MC) model of the couchtop produced to provide more superficial PDDs. (PDDs that are more superficial) Results: Maximum couchtop attenuation (7.6%) measured for the 135&deg; gantry and 5&times;5 cm² field. Couch extension attenuation was 1.5% lower. Adding BreastSTEP increased attenuation by 2.4%. MC attenuation results agreed with measurements to within 0.2%. The couchtop removed the dose buildup effect almost completely and increased the PDD at 0.4 mm depth by 60.6%-74.6%. MC-calculated PDDs at the depth range of skin basal cell layer (0.1-0.4 mm) increased by 55.3%-63.2%. The couch insert in the Co-60 beam increased the dose at 0.4 mm depth by 18.1%. For the same dose prescription at 10 cm depth, the insert in the Co-60 beam produced a skin dose 49.7% lower than the couchtop at 6 MV. Conclusion: These results provide useful practical data on attenuation and skin dose increase applicable to many centres. The accelerator-couchtop combination creates a greater skin dose increase than a tennis-racket insert on a Co-60 unit.</div> Radiotherapy, couch top, beam attenuation, skin dose. 299 309 http://ijrr.com/browse.php?a_code=A-10-1-729&slc_lang=en&sid=1 F. Arianfard 7900319475328460012353 7900319475328460012353 No Department of Radiology & Radiobiology, School of Paramedical Sciences, Shiraz University of Medical Sciences, Shiraz, Iran M.A. Mosleh-Shirazi mosleh_amin@hotmail.com 7900319475328460012354 7900319475328460012354 Yes Physics Unit, Department of Radiotherapy and Oncology, Namazi Hospital, Shiraz University of Medical Sciences, Shiraz, Iran S. Karbasi 7900319475328460012355 7900319475328460012355 No Physics Unit, Department of Radiotherapy and Oncology, Namazi Hospital, Shiraz University of Medical Sciences, Shiraz, Iran S. Mousavi 7900319475328460012356 7900319475328460012356 No Physics Unit, Department of Radiotherapy and Oncology, Namazi Hospital, Shiraz University of Medical Sciences, Shiraz, Iran