Dosimetric impacts of beam-hardening filter removal for the CyberKnife system. (June 2021)

• Record Type: Journal Article
• Authors: Kamomae, Takeshi; Matsunaga, Takuma; Suzuki, Junji; Okudaira, Kuniyasu; Kawabata, Fumitaka; Kato, Yutaka; Oguchi, Hiroshi; Shimizu, Morihito; Sasaki, Motoharu; Takase, Yuki; Kawamura, Mariko; Ohtakara, Kazuhiro; Itoh, Yoshiyuki; Naganawa, Shinji
• Is Part Of: Physica medica. Volume 86(2021)
• Page Start: 98
• Page End: 105
• Publication Date: 2021-06
• Subjects: CyberKnife -- Beam quality correction factor -- Beam-hardening filter -- Monte Carlo simulation; Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2021.05.011
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: Beam quality correction factors for CyberKnife after beam-hardening filter removal. Photon energy fluence spectrum was softened by the removal of beam-hardening filter. No remarkable impact was observed for the beam quality correction factors. Abstract: Purpose: Equipment refurbishment was performed to remove the beam-hardening filter (BHF) from the CyberKnife system (CK). This study aimed to confirm the change in the beam characteristics between the conventional CK (present-BHF CK) and CK after the BHF was removed (absent-BHF CK) and evaluate the impact of BHF removal on the beam quality correction factors k Q . Methods: The experimental measurements of the beam characteristics of the present- and absent-BHF CKs were compared. The CKs were modeled using Monte Carlo simulations (MCs). The energy fluence spectra were calculated using MCs. Finally, k Q were estimated by combining the MC results and analytic calculations based on the TRS-398 and TRS-483 approaches. Results: All gamma values for percent depth doses and beam profiles between each CK were less than 0.5 following the 3%/1 mm criteria. The percentage differences for tissue-phantom ratios at depths of 20 and 10 cm and percentage depth doses at 10 cm between each CK were −1.20% and −0.97%, respectively. The MC results demonstrated that the photon energy fluence spectrum of the absent-BHF CK was softer than that of the present-BHF CK. The k Q values for the absent-BHF CK were in agreement within 0.02% with those for the present-BHF CK. Conclusions: The photon energy fluence spectrum was softened by the removal of BHF. However, no remarkable impact was observed for the measured beam characteristics and k Q . Therefore, the previous findings of the k Q values for the present-BHF CK can be directly used for the absent-BHF CK.