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Patient dose from kilovoltage cone beam computed tomography imaging in radiation therapy
Author(s) -
Islam Mohammad K.,
Purdie Thomas G.,
Norrlinger Bernhard D.,
Alasti Hamideh,
Moseley Douglas J.,
Sharpe Michael B.,
Siewerdsen Jeffrey H.,
Jaffray David A.
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2198169
Subject(s) - imaging phantom , image guided radiation therapy , cone beam computed tomography , linear particle accelerator , nuclear medicine , dosimetry , medical imaging , dose profile , rotation (mathematics) , image quality , isocenter , beam (structure) , physics , medical physics , optics , medicine , computed tomography , computer science , radiology , artificial intelligence , image (mathematics)
Kilovoltage cone‐beam computerized tomography (kV‐CBCT) systems integrated into the gantry of linear accelerators can be used to acquire high‐resolution volumetric images of the patient in the treatment position. Using on‐line software and hardware, patient position can be determined accurately with a high degree of precision and, subsequently, set‐up parameters can be adjusted to deliver the intended treatment. While the patient dose due to a single volumetric imaging acquisition is small compared to the therapy dose, repeated and daily image guidance procedures can lead to substantial dose to normal tissue. The dosimetric properties of a clinical CBCT system have been studied on an Elekta linear accelerator ( Synergy ®RP, XVI system) and additional measurements performed on a laboratory system with identical geometry. Dose measurements were performed with an ion chamber and MOSFET detectors at the center, periphery, and surface of 30 and 16‐cm‐diam cylindrical shaped water phantoms, as a function of x‐ray energy and longitudinal field‐of‐view (FOV) settings of 5,10,15, and 26 cm . The measurements were performed for full 360 ° CBCT acquisition as well as for half‐rotation scans for 120 kVp beams using the 30‐cm‐diam phantom. The dose at the center and surface of the body phantom were determined to be 1.6 and 2.3 cGy for a typical imaging protocol, using full rotation scan, with a technique setting of 120 kVp and 660 mAs . The results of our measurements have been presented in terms of a dose conversion factorf CBCT , expressed in cGy ∕ R . These factors depend on beam quality and phantom size as well as on scan geometry and can be utilized to estimate dose for any arbitrary mAs setting and reference exposure rate of the x‐ray tube at standard distance. The results demonstrate the opportunity to manipulate the scanning parameters to reduce the dose to the patient by employing lower energy (kVp) beams, smaller FOV, or by using half‐rotation scan.