Calculation of water equivalent thickness of materials of arbitrary density, elemental composition and thickness in proton beam irradiation

Zhang, Rui; Newhauser, Wayne D.

doi:10.1088/0031-9155/54/6/001

Cited by 86 publications

(88 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…22 If equivalent WEPL values are calculated for CT ref and CBCT images, we assume an approximate equivalence between the proton dose distributions. In this study, WEPL was calculated using uniform step-based ray tracing 23 in conjunction with proton stopping power ratio approximation 24 as follows:…”

Section: F Calculation Of Weplmentioning

confidence: 99%

Proton dose calculation on scatter‐corrected CBCT image: Feasibility study for adaptive proton therapy

et al. 2015

View full text Add to dashboard Cite

Purpose: To demonstrate the feasibility of proton dose calculation on scatter-corrected cone-beam computed tomographic (CBCT) images for the purpose of adaptive proton therapy. Methods: CBCT projection images were acquired from anthropomorphic phantoms and a prostate patient using an on-board imaging system of an Elekta infinity linear accelerator. Two previously introduced techniques were used to correct the scattered x-rays in the raw projection images: uniform scatter correction (CBCT us ) and a priori CT-based scatter correction (CBCT ap ). CBCT images were reconstructed using a standard FDK algorithm and GPU-based reconstruction toolkit. Soft tissue ROI-based HU shifting was used to improve HU accuracy of the uncorrected CBCT images and CBCT us , while no HU change was applied to the CBCT ap . The degree of equivalence of the corrected CBCT images with respect to the reference CT image (CT ref ) was evaluated by using angular profiles of water equivalent path length (WEPL) and passively scattered proton treatment plans. The CBCT ap was further evaluated in more realistic scenarios such as rectal filling and weight loss to assess the effect of mismatched prior information on the corrected images. Results: The uncorrected CBCT and CBCT us images demonstrated substantial WEPL discrepancies (7.3 ± 5.3 mm and 11.1 ± 6.6 mm, respectively) with respect to the CT ref , while the CBCT ap images showed substantially reduced WEPL errors (2.4 ± 2.0 mm). Similarly, the CBCT ap -based treatment plans demonstrated a high pass rate (96.0% ± 2.5% in 2 mm/2% criteria) in a 3D gamma analysis. Conclusions: A priori CT-based scatter correction technique was shown to be promising for adaptive proton therapy, as it achieved equivalent proton dose distributions and water equivalent path lengths compared to those of a reference CT in a selection of anthropomorphic phantoms. C 2015 American Association of Physicists in Medicine. [http://dx

show abstract

Section: F Calculation Of Weplmentioning

confidence: 99%

Proton dose calculation on scatter‐corrected CBCT image: Feasibility study for adaptive proton therapy

et al. 2015

View full text Add to dashboard Cite

show abstract

“…The linear stopping power ratio also relates the physical thickness of a material to its water-equivalent thickness (WET). Numerical and analytical methods have been developed to calculate the WET of arbitrary materials (Newhauser et al, 2007; Zhang & Newhauser, 2009) and measurements of WET can be used to determine the linear stopping power ratio (Sánchez-Parcerisa, Gemmel, Jäkel, Parodi, & Rietzel, 2012; Zhang, Taddei, Fitzek, & Newhauser, 2010). …”

Section: Introductionmentioning

confidence: 99%

Calculations and measurements of the scintillator-to-water stopping power ratio of liquid scintillators for use in proton radiotherapy

Ingram

Robertson

Beddar

2015

Nuclear Instruments and Methods in Physics Research Section A:

View full text Add to dashboard Cite

Liquid scintillators are a promising detector for high-resolution three-dimensional proton therapy dosimetry. Because the scintillator comprises both the active volume of the detector and the phantom material, an ideal scintillator will exhibit water equivalence in its radiological properties. One of the most fundamental of these is the scintillator’s stopping power. The objective of this study was to compare calculations and measurements of scintillator-to-water stopping power ratios to evaluate the suitability of the liquid scintillators BC-531 and OptiPhase HiSafe 3 for proton dosimetry. We also measured the relative scintillation output of the two scintillators. Both calculations and measurements show that the linear stopping power of OptiPhase is significantly closer to water than that of BC-531. BC-531 has a somewhat higher scintillation output. OptiPhase can be mixed with water at high concentrations, which further improves its scintillator-to-water stopping power ratio. However, this causes the solution to become cloudy, which has a negative impact on the scintillation output and spatial resolution of the detector. OptiPhase is preferred over BC-531 for proton dosimetry because its density and scintillator-to-water stopping power ratio are more water equivalent.

show abstract

“…Using the stopping power ratio approximation, (21) the WET through one voxel is the product of the relative stopping power (

{RSP}_{i}

) and path length (

t_{i}

) within that voxel. The total WET of the path is the accumulation of the WET from all voxels traversed by the ray:

W E T = true \sum_{i} t_{i} \times R S P_{i}

Polar WET plots were generated for the assessment of anatomic change on proton range.…”

Section: Methodsmentioning

confidence: 99%

Quantitative assessment of anatomical change using a virtual proton depth radiograph for adaptive head and neck proton therapy

Wang

Yin

Zhang

et al. 2016

J Applied Clin Med Phys

View full text Add to dashboard Cite

The aim of this work is to demonstrate the feasibility of using water‐equivalent thickness (WET) and virtual proton depth radiographs (PDRs) of intensity corrected cone‐beam computed tomography (CBCT) to detect anatomical change and patient setup error to trigger adaptive head and neck proton therapy. The planning CT (pCT) and linear accelerator (linac) equipped CBCTs acquired weekly during treatment of a head and neck patient were used in this study. Deformable image registration (DIR) was used to register each CBCT with the pCT and map Hounsfield units (HUs) from the planning CT (pCT) onto the daily CBCT. The deformed pCT is referred as the corrected CBCT (cCBCT). Two dimensional virtual lateral PDRs were generated using a ray‐tracing technique to project the cumulative WET from a virtual source through the cCBCT and the pCT onto a virtual plane. The PDRs were used to identify anatomic regions with large variations in the proton range between the cCBCT and pCT using a threshold of 3 mm relative difference of WET and 3 mm search radius criteria. The relationship between PDR differences and dose distribution is established. Due to weight change and tumor response during treatment, large variations in WETs were observed in the relative PDRs which corresponded spatially with an increase in the number of failing points within the GTV, especially in the pharynx area. Failing points were also evident near the posterior neck due to setup variations. Differences in PDRs correlated spatially to differences in the distal dose distribution in the beam's eye view. Virtual PDRs generated from volumetric data, such as pCTs or CBCTs, are potentially a useful quantitative tool in proton therapy. PDRs and WET analysis may be used to detect anatomical change from baseline during treatment and trigger further analysis in adaptive proton therapy.PACS number(s): 87.55‐x, 87.55.‐D, 87.57.Q‐

show abstract

Calculation of water equivalent thickness of materials of arbitrary density, elemental composition and thickness in proton beam irradiation

Cited by 86 publications

References 21 publications

Proton dose calculation on scatter‐corrected CBCT image: Feasibility study for adaptive proton therapy

Proton dose calculation on scatter‐corrected CBCT image: Feasibility study for adaptive proton therapy

Calculations and measurements of the scintillator-to-water stopping power ratio of liquid scintillators for use in proton radiotherapy

Quantitative assessment of anatomical change using a virtual proton depth radiograph for adaptive head and neck proton therapy

Contact Info

Product

Resources

About