Abstract
In this work we compare doses from imaging procedures performed on today's state‐of‐the‐art integrated imaging systems using a reference radiochromic film dosimetry system. Skin dose and dose profile measurements from different imaging systems were performed using radiochromic films at different anatomical sites on a humanoid RANDO phantom. EBT3 film was used to measure imaging doses from a TomoTherapy MVCT system, while XRQA2 film was used for dose measurements from kilovoltage imaging systems (CBCT on 21eX and TrueBeam Varian linear accelerators and CyberKnife stereoscopic orthogonal imagers). Maximum measured imaging doses in cGy at head, thorax, and pelvis regions were respectively 0.50, 1.01, and 4.91 for CBCT on 21eX, 0.38, 0.84, and 3.15 for CBCT on TrueBeam, 4.33, 3.86, and 6.50 for CyberKnife imagers, and 3.84, 1.90, and 2.09 for TomoTherapy MVCT. In addition, we have shown how an improved calibration system of XRQA2 film can achieve dose uncertainty level of better than 2% for doses above 0.25 cGy. In addition to simulation‐based studies in literature, this study provides the radiation oncology team with data necessary to aid in their decision about imaging frequency for image‐guided radiation therapy protocols.PACS number: 87.53.Bn, 87.55.Qr, 87.56.Fc
Highlights
IntroductionImage-guided radiotherapy (IGRT) has become standard of care in advanced highly conformal radiotherapy techniques, mainly because of advantages it offers in improving target localization by minimizing errors in patient positioning prior to treatment delivery.[1,2,3] the increased imaging sessions associated with IGRT posed questions about the amount of concomitant dose burden.[4,5] The American Association of Physicists in Medicine (AAPM) Task Group 75 has differentiated between the management of imaging dose from IGRT and doses received from diagnostic radiology exams because IGRT doses could be optimized within treatment regimen.[6,7] The importance of imaging dose management in IGRT stems from concepts such as ALARA (as low as reasonably achievable), but it constitutes a risk of stochastic effects outside the primary treatment area which is in parallel to risks arising from linear accelerator head leakage and scatter.[4]
Image-guided radiotherapy (IGRT) systems In this study, we compare four different IGRT imaging systems used in contemporary radiotherapy: cone-beam computed tomography (CBCT) system mounted on Varian 21eX and TrueBeam clinical linear accelerators (Varian, Palo Alto, CA) as a part of On-Board Imaging (OBI) system; TomoTherapy Hi·ART (Accuray Inc., Sunnyvale, CA) fan beam megavoltage computed tomography (MVCT); and 2D kV stereoscopic orthogonal imagers on CyberKnife treatment unit (Accuray Inc.)
on-board imaging (OBI) system installed on TrueBeam shows further decrease in surface dose due to addition of Titanium into bowtie filters, while mAs setting for both OBI versions remained the same
Summary
Image-guided radiotherapy (IGRT) has become standard of care in advanced highly conformal radiotherapy techniques, mainly because of advantages it offers in improving target localization by minimizing errors in patient positioning prior to treatment delivery.[1,2,3] the increased imaging sessions associated with IGRT posed questions about the amount of concomitant dose burden.[4,5] The American Association of Physicists in Medicine (AAPM) Task Group 75 has differentiated between the management of imaging dose from IGRT and doses received from diagnostic radiology exams because IGRT doses could be optimized within treatment regimen.[6,7] The importance of imaging dose management in IGRT stems from concepts such as ALARA (as low as reasonably achievable), but it constitutes a risk of stochastic effects outside the primary treatment area which is in parallel to risks arising from linear accelerator head leakage and scatter.[4]. Tomic et al[15,16] used XRQA GAFCHROMIC film model calibrated in terms of air kerma in air to measure on-board imaging (OBI) CBCT imaging dose profiles and surface doses for head and neck, thorax, and pelvis of a humanoid RANDO phantom. They have shown that, for typical kV CBCT beam qualities, simple mass-energy absorption coefficient ratios water-to-air can approximate the dose conversion from measured by film air kerma in air at the surface to a dose to water at the phantom surface, following the AAPM TG-61 protocol.[23] Giaddui et al[21]. The dosimetric properties of these films were tested widely in the literature in terms of absorption spectra,(24) postirradiation waiting time,(24,25) scanning mode and exposure to light,(25,26) high temperature behavior,(25) performance in water,(27) depth dose measurements,(28) and energy dependence.[29,30]
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