title: Comparison between Clinically Used Irregular Fields Shielded by Cerrobend and Standard Lead Blocks.
abstract: BACKGROUND
  In radiation therapy centers across Iran, protection of normal tissues is usually accomplished by either Cerrobend or lead block shielding. In this study, the influence of these two shielding methods on central axis dose distribution of photon beam a Cobalt unit was investigated in clinical conditions.
  
  
  METHODS
  All measurements were performed for 60Co γ-ray beams and the Cerrobend blocks were fabricated by commercial Cerrobend materials. Standard lead block shields belonged to Cobalt unit. Data was collected through a calibrated ionization chamber, relative dosimetry systems and a TLD dosimetery.
  
  
  RESULTS
  Results of the percent depth dose (PDD) measurements at depths of 0.5, 1, 5, 10, 15 and 20 cm for 23 different field sizes of patients with head and neck cancer showed no significant differences between lead and Cerrobend shielding methods. Measurement results of absolute dosimetry in depths of 1.5, 3, 5, 7, 10 and 12 cm also showed no significant differences between these two shielding methods. The same results were obtained by TLD dosimetry on patient skin.
  
  
  CONCLUSIONS
  Use of melt shielding methods is a very easy and fast shield-making technique with no differences in PDD, absolute and skin dose between lead and Cerrobend block shielding methods.
authors.affiliation: Professor of Medical Physics, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: A R
authors.initials: AR
authors.lastname: Farajollahi
authors.affiliation: Professor of Medical Physics, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
authors.forename: F
authors.initials: F
authors.lastname: Bouzarjomehri
authors.affiliation: MSc of Medical Physics, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: M
authors.initials: M
authors.lastname: Kiani
keywords: Cerrobend; Dosimetry; Lead block; Radiation therapy; Shield; TLD dosimetry