Electron dose distributions caused by the contact-type metallic eye shield: Studies using Monte Carlo and pencil beam algorithms.
A metallic contact eye shield has sometimes been used for eyelid treatment, but dose distribution has never been reported for a patient case. This study aimed to show the shield-incorporated CT-based dose distribution using the Pinnacle system and Monte Carlo (MC) calculation for 3 patient cases. For the artifact-free CT scan, an acrylic shield machined as the same size as that of the tungsten shield was used. For the MC calculation, BEAMnrc and DOSXYZnrc were used for the 6-MeV electron beam of the Varian 21EX, in which information for the tungsten, stainless steel, and aluminum material for the eye shield was used. The same plan was generated on the Pinnacle system and both were compared. The use of the acrylic shield produced clear CT images, enabling delineation of the regions of interest, and yielded CT-based dose calculation for the metallic shield. Both the MC and the Pinnacle systems showed a similar dose distribution downstream of the eye shield, reflecting the blocking effect of the metallic eye shield. The major difference between the MC and the Pinnacle results was the target eyelid dose upstream of the shield such that the Pinnacle system underestimated the dose by 19 to 28% and 11 to 18% for the maximum and the mean doses, respectively. The pattern of dose difference between the MC and the Pinnacle systems was similar to that in the previous phantom study. In conclusion, the metallic eye shield was successfully incorporated into the CT-based planning, and the accurate dose calculation requires MC simulation.
Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea.
Sei-Kwon
SK
Kang
Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea.
Jai-Woong
JW
Yoon
Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea.
Taejin
T
Hwang
Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea.
Soah
S
Park
Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea.
Kwang-Ho
KH
Cheong
Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea.
Tae Jin
TJ
Han
Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea.
Haeyoung
H
Kim
Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea.
Me-Yeon
MY
Lee
Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea. Electronic address: kjkim@hallym.or.kr.
Kyoung Ju
KJ
Kim
Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea.
Hoonsik
H
Bae
D000465:Algorithms; D004583:Electrons / Q000627:therapeutic use*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005135:Eye Protective Devices; D006801:Humans; D008670:Metals / Q000528:radiation effects; D009010:Monte Carlo Method; D011835:Radiation Protection / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity
D008670:Metals
Electron treatment; Eye shield; Monte Carlo; Pinnacle