Patient dose from kilovoltage cone beam computed tomography imaging in radiation therapy

The purpose of this study was to implement full/half bowtie filter models in a commercial treatment planning system (TPS) to calculate kilovoltage (kV) cone‐beam CT (CBCT) doses of Varian On‐Board Imager (OBI) kV X‐ray imaging system. The full/half bowtie filter models were created as compensators in Pinnacle TPS using MATLAB software. The physical profiles of both bowtie filters were imported and hard‐coded in the MATLAB system. Pinnacle scripts were written to import bowtie filter models into Pinnacle treatment plans. Bowtie filter‐free kV X‐ray beam models were commissioned and the bowtie filter models were validated by analyzing the lateral and percent‐depth‐dose (PDD) profiles of anterior/posterior X‐ray beams in water phantoms. A CT dose index (CTDI) phantom was employed to calculate CTDI and weighted CTDI values for pelvis and pelvis‐spotlight CBCT protocols. A five‐year‐old pediatric anthropomorphic phantom was utilized to evaluate absorbed and effective doses (ED) for standard and low‐dose head CBCT protocols. The CBCT dose calculation results were compared to ion chamber (IC) and Monte Carlo (MC) data for the CTDI phantom and MOSFET and MC results for the pediatric phantom, respectively. The differences of lateral and PDD profiles between TPS calculations and IC measurements were within 6%. The CTDI and weighted CTDI values of the TPS were respectively within 0.25 cGy and 0.08 cGy compared to IC measurements. The absorbed doses ranged from 0 to 7.22 cGy for the standard dose CBCT and 0 to 1.56 cGy for the low‐dose CBCT. The ED values were found to be 36‐38 mSv and 7‐8 mSv for the standard and low‐dose CBCT protocols, respectively. This study demonstrated that the established full/half bowtie filter beam models can produce reasonable dose calculation results. Further study is to be performed to evaluate the models in clinical situations.PACS number(s): 87.57.uq

Section: Introductionmentioning

confidence: 99%

Implementation of full/half bowtie filter models in a commercial treatment planning system for kilovoltage cone‐beam CT dose estimations

Kim

Alaei

2016

“…The in‐field and out‐of‐field doses delivered by the kV‐CBCT imaging system have been recently reported in the literature 13 , 16 while, to date, only in‐field dose has been discussed for the MV‐CBCT system 17 , 25 . Morin et al (17) reported the image acquisition dose delivered to patients from MV‐CBCT imaging for 5 and 9 MU protocols on pelvis and head‐and‐neck patients.…”

Section: Introductionmentioning

confidence: 99%

“…Pouliot et al (25) evaluated the image quality of MV‐CBCT using low‐dose, and further demonstrated how the MV‐CBCT system can be applied for patient alignment. For the kV‐CBCT system, Islam et al (13) reported point doses at various depths in a cylindrical water phantom. Ding and Coffey (14) calculated the dose to organs from a kV‐CBCT imaging guidance procedure using the VMCBC algorithm.…”

Section: Introductionmentioning

confidence: 99%

Peripheral dose from megavoltage cone‐beam CT imaging for nasopharyngeal carcinoma image‐guided radiation therapy

Jia

Wang

et al. 2012

The growing use of cone‐beam computed tomography (CBCT) for IGRT has increased concerns over the additional radiation dose to patients. The in‐field dose of IGRT and the peripheral dose (PD) from kilovoltage CBCT (KV‐CBCT) imaging have been well quantified. The purpose of this work is to evaluate the peripheral dose from megavoltage CBCT (MV‐CBCT) imaging for nasopharyngeal carcinoma IGRT, to determine the correlation of peripheral dose with MU protocol and imaging field size, and to estimate out‐of‐field organ‐at‐risk (OAR) dose delivered to patients. Measurements of peripheral MV‐CBCT doses were made with a 0.65 cm3 ionization chamber placed inside in a specially designed phantom at various depths and distances from the imaging field edges. The peripheral dose at reference point inside the phantom was measured with the same ionization chamber to investigate the linearity between MUs used for MV‐CBCT imaging and the PD. The peripheral surface doses at the anterior, lateral, and posterior of the phantom at various distances from the imaging field edge were also measured with thermoluminescent dosimeters (TLDs). Seven nasopharyngeal carcinoma patients were selected and scanned before treatment with head–neck protocol, and the peripheral surface doses were measured with TLDs placed on the anterior, lateral, and posterior surfaces at the axial plane of 15 cm distance from the field edge. The measured peripheral doses data in the phantom were utilized to estimate the peripheral OAR dose. Peripheral dose from MV‐CBCT imaging increased with increasing number of MUs used for imaging protocol and with increasing the imaging field size. The measured peripheral doses in the phantom decreased as distance from the imaging field edges increased. PD also decreased as the depth from the phantom surface increased. For the patient PD measurements, the anterior, lateral, and posterior surface doses of 15 cm distance from the field edge were 2.84×10−2, 1.01×10−2, and 0.78×10−2 cGy/MU, respectively. The lens, thyroid, breast, and ovary and testicle, which are outside the treatment and imaging fields, were estimated to receive peripheral OAR doses from MV‐CBCT imaging of 42.4×10−2, 11.9×10−2, 1.4×10−2, 1.0×10−2, and 0.5×10−2 cGy/MU, respectively. In conclusion, MV‐CBCT generates a peripheral dose beyond the edge of the MV‐CBCT scanning field that is of a similar order of magnitude to the peripheral dose from kV‐CBCT imaging. In clinic, using the smallest number of MUs allowable and reducing MV‐CBCT scanning field size without compromising acquired image quality is an effective method of reducing the peripheral OAR dose received by patients.PACS number: 89

“…( 1 ) However, the full potential of these technologies in radiation treatment can be achieved only if the patient can be positioned accurately and reproducibly during every session of the entire course of treatment delivery. ( 2 ) Mega‐voltage (MV) portal imaging has been widely implemented for the past two decades as patient treatment‐positioning tools. Due to the inherent low‐contrast and two‐dimensional nature of the projection images, the precision of MV portal imaging is limited so far as accurately defining the patient's position.…”

Section: Introductionmentioning

confidence: 99%

“…( 2 ) Radiation therapy patients are already being exposed to very high and localized radiation; therefore, the additional radiation from imaging has an associated risk and should be kept low. ( 8 ) Concerns about the stochastic risk of inducing cancer or genetic defects have already been accounted for in the limits on leakage from the primary therapy beam, which should not exceed 0.2% of the absorbed dose rate on the central axis at the treatment distance.…”

Section: Introductionmentioning

confidence: 99%

A comprehensive study on decreasing the kilovoltage cone‐beam CT dose by reducing the projection number

Lü

Palta

2010

The objective of this study was to evaluate the effect of kilovoltage cone‐beam computed tomography (CBCT) on registration accuracy and image qualities with a reduced number of planar projections used in volumetric imaging reconstruction. The ultimate goal is to evaluate the possibility of reducing the patient dose while maintaining registration accuracy under different projection‐number schemes for various clinical sites. An Elekta Synergy Linear accelerator with an onboard CBCT system was used in this study. The quality of the Elekta XVI cone‐beam three‐dimensional volumetric images reconstructed with a decreasing number of projections was quantitatively evaluated by a Catphan phantom. Subsequently, we tested the registration accuracy of imaging data sets on three rigid anthropomorphic phantoms and three real patient sites under the reduced projection‐number (as low as 1/6th) reconstruction of CBCT data with different rectilinear shifts and rotations. CBCT scan results of the Catphan phantom indicated the CBCT images got noisier when the number of projections was reduced, but their spatial resolution and uniformity were hardly affected. The maximum registration errors under the small amount transformation of the reference CT images were found to be within 0.7 mm translation and 0.3° rotation. However, when the projection number was lower than one‐fourth of the full set with a large amount of transformation of reference CT images, the registration could easily be trapped into local minima solutions for a nonrigid anatomy. We concluded, by using projection‐number reduction strategy under conscientious care, imaging‐guided localization procedure could achieve a lower patient dose without losing the registration accuracy for various clinical sites and situations. A faster scanning time is the main advantage compared to the mA decrease‐based, dose‐reduction method.PACS numbers: 87.57.C‐, 87.57.cf, 87.57.cj, 87.57.cm, 87.57.cp, 87.57.N‐, 87.57.nf, 87.57.nj