Imaging dose from cone beam computed tomography in radiation therapy

Abstract

Imaging dose in radiation therapy has traditionally been ignored due to its low magnitude and frequency in comparison to therapeutic dose used to treat patients. The advent of modern, volumetric, imaging modalities, often as an integral part of linear accelerators, has facilitated the implementation of image-guided radiation therapy (IGRT), which is often accomplished by daily imaging of patients. Daily imaging results in additional dose delivered to patient that warrants new attention be given to imaging dose. This review summarizes the imaging dose delivered to patients as the result of cone beam computed tomography (CBCT) imaging performed in radiation therapy using current methods and equipment. This review also summarizes methods to calculate the imaging dose, including the use of Monte Carlo (MC) and treatment planning systems (TPS). Peripheral dose from CBCT imaging, dose reduction methods, the use of effective dose in describing imaging dose, and the measurement of CT dose index (CTDI) in CBCT systems are also reviewed.

Optimizing the target detectability of cone beam CT performed in image‐guided radiation therapy for patients of different body sizes

“…Fractionated radiation treatments are usually delivered in 20 fractions to improve patient tolerance, so the total radiation dose from CBCT is a factor of 20 greater than that of a single scan 18. Besides, CBCT doses are distributed to the entire imaging region, not only the target volume 19. Hence, it is necessary to know what the radiation doses are from CBCT and raise awareness of using lower radiation doses.…”

Technical Note: Procedure for the calibration and validation of kilo‐voltage cone‐beam CT models

“…Implementation of dual-energy capabilities in CBCT units is finding application in diagnostics to improve material segmentation and enhance contrast. A model of the kV CBCT unit is required to optimize the imaging device, to simulate and correct for scatter radiations, 1 to optimize single 2 and dual-energy acquisition protocols, to compute the patient imaging dose, 3 and for material decomposition in dual-energy CT.…”

“…Verification of CBCT models has been carried out in different manners in the literature. 3 To validate the x-ray source model, some authors performed half-value layer (HVL) measurements, 1,4 but only the first HVL is commonly checked. In a recent work, 5 the authors proposed an original experimental setup to rapidly characterize x-ray sources by acquiring angular-dependent HVLs and fluence data.…”

Influence of daily imaging on plan quality and normal tissue toxicity for prostate cancer radiotherapy

“…The few other studies to be found that calculated the imaging dose on the planning CT did not systematically evaluate different IGRT scenarios but focussed on kV modalities [18–21]. Alaei et al [20] showed that the dose from daily kV CBCT results in an additional isocenter dose of the order of 30–40 mGy for 35 fractions head and neck and 230–240 mGy for 25 fractions pelvis irradiation.…”

“…This is mainly indebted to the fact that imaging energies are not usually commissioned in the treatment planning system (TPS) and not included in the treatment plan. A few studies have calculated the imaging dose for each patient on the planning CT [17–21], but a systematic evaluation of different imaging scenarios on treatment plan quality is still missing. Furthermore, biological effects have been generally disregarded.…”