Radiation Dose From Cone Beam Computed Tomography for Image-Guided Radiation Therapy

PurposeTo image the abdomen of a patient with a gantry mounted imaging system of a linear accelerator, different cone beam computed tomography (CBCT) protocols are available. The whole‐body dose of a full rotation abdomen CBCT and a half rotation CBCT was compared. In our clinic, both CBCT protocols are used in daily routine work.MethodsWith an adult anthropomorphic Alderson phantom, the whole‐body dose per CBCT scan was measured with thermoluminescence dosimeters. The half rotation CBCT was applied such that the gantry mounted X‐ray source rotated around the right side of the phantom. The 183 measurement locations covered all ICRP recommended critical organs (except the gonads). The effective dose was calculated with the mean organ dose and the corresponding tissue weighting factors. A point‐by‐point dose comparison of both protocols was conducted.ResultsThe effective dose was 5.4 mSv ±5% and 5.0 mSv ±5% (estimated type B 1σ) for the full and the half rotation CBCT respectively. There was no significant difference (α = 0.05) in the effective dose within the precision of the measurement (1σ = 5%). The half rotation CBCT displayed an inhomogeneous dose distribution in a transversal phantom slice in contrast with the full rotation CBCT. In the imaging region, the mean dose was (20.5 ± 3.4) mGy and (19.2 ± 7.4) mGy (measured type A 1σ) for the full and the half rotation CBCT respectively.ConclusionThe half compared to the full rotation CBCT displays a smaller field‐of‐view in a transversal slice and no significant difference in the effective dose. Hence, the full rotation CBCT is favorable compared to the half rotation CBCT. However, by using the half rotation protocol, critical volumes in the patient can be spared compared to the full rotation protocol.

Section: Discussionmentioning

confidence: 90%

“…Some of them evaluated only the CTDI values 3, 9. Kan et al.,10 Cheng et al.,6 and Hälg et al 7. determined the effective dose (ED) for pelvis protocols using the OBI of a Varian linear accelerator.…”

Section: Introductionmentioning

confidence: 99%

Technical note: No increase in effective dose from half compared to full rotation pelvis cone beam CT

Hauri

Hälg

Schneider

2017

“…For the head phantom, the maximum dose values were from 1.5 to 2.0 cGy for 100 kVp and from 2.6 to 3.4 cGy for 120 kVp beams. Kan et al (2) measured organ and effective dose (ED) measurements for the On‐Board Imager (OBI) system (Varian Medical Systems, Palo Alto, CA) by using thermoluminescent dosimeters (TLD) in three different sites. They found that the mean skin doses from standard dose CBCT to head and neck, chest, and pelvis were 6.7, 6.4, and 5.4 cGy per scan, respectively.…”

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 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

“…Commercially available offerings, such as the RANDO (The Phantom Laboratory, Salem, NY) and ATOM (Computerized Imaging Reference Systems, Inc. Norfolk, VA) phantoms, as well as custom phantoms, (1) have seen use with optically stimulated luminescence (OSL), semiconductor, and fiber optic coupled dosimeters in order to measure skin and organ doses from a range of radiographic and therapy procedures 2 , 3 , 4 , 5 , 6 . In order to make physical dose measurements more applicable to the range of clinical patient sizes, it would be beneficial to have phantoms of various body mass indexes (BMI).…”

Section: Introductionmentioning

confidence: 99%

Super‐size me: adipose tissue‐equivalent additions for anthropomorphic phantoms

Fisher

Hintenlang

2014

Physical anthropomorphic phantoms have been utilized for a variety of dosimetric studies across a range of procedures utilizing diagnostic imaging equipment. Unfortunately, these phantoms are often limited to a single reference size, which often may not be representative of the patient population at large. This work set out to develop an adipose tissue‐equivalent substitute material that could be used to create low cost physical additions for existing anthropomorphic phantoms. Using commercially available products, a methodology was developed to accomplish this, and an addition was built to create a 90th percentile by weight phantom from an existing 50th percentile model. This methodology can easily be used to expand the utility of existing anthropomorphic phantoms in order to better represent patients of various body morphologies, and investigate the effects of patient size in diagnostic procedures.PACS numbers: 87.53.Bn, 87.57.qh