An investigation into factors affecting electron density calibration for a megavoltage cone‐beam CT system

Hughes, Jessica R.; Holloway, Lois; Quinn, Alexandra; Fielding, Andrew

doi:10.1120/jacmp.v13i5.3271

Cited by 12 publications

(10 citation statements)

References 29 publications

(50 reference statements)

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“…Dose calculations using MV CBCT images are feasible (1,2) . However, consistently converting CT numbers to electron density can be difficult (3–6) . Previous research studies reported a gamma index of 98% for 3% and 3 mm criteria that described dose calculation accuracy on MV CBCT for head‐and‐neck cases, using in‐house developed image correction filters (7) .…”

Section: Introductionmentioning

confidence: 99%

Feasibility of MV CBCT‐based treatment planning for urgent radiation therapy: dosimetric accuracy of MV CBCT‐based dose calculations

Held

Sneed

Fogh

et al. 2015

J Applied Clin Med Phys

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Unlike scheduled radiotherapy treatments, treatment planning time and resources are limited for emergency treatments. Consequently, plans are often simple 2D image‐based treatments that lag behind technical capabilities available for nonurgent radiotherapy. We have developed a novel integrated urgent workflow that uses onboard MV CBCT imaging for patient simulation to improve planning accuracy and reduce the total time for urgent treatments. This study evaluates both MV CBCT dose planning accuracy and novel urgent workflow feasibility for a variety of anatomic sites. We sought to limit local mean dose differences to less than 5% compared to conventional CT simulation. To improve dose calculation accuracy, we created separate Hounsfield unit–to–density calibration curves for regular and extended field‐of‐view (FOV) MV CBCTs. We evaluated dose calculation accuracy on phantoms and four clinical anatomical sites (brain, thorax/spine, pelvis, and extremities). Plans were created for each case and dose was calculated on both the CT and MV CBCT. All steps (simulation, planning, setup verification, QA, and dose delivery) were performed in one 30 min session using phantoms. The monitor units (MU) for each plan were compared and dose distribution agreement was evaluated using mean dose difference over the entire volume and gamma index on the central 2D axial plane. All whole‐brain dose distributions gave gamma passing rates higher than 95% for 2%/2 mm criteria, and pelvic sites ranged between 90% and 98% for 3%/3 mm criteria. However, thoracic spine treatments produced gamma passing rates as low as 47% for 3%/3 mm criteria. Our novel MV CBCT‐based dose planning and delivery approach was feasible and time‐efficient for the majority of cases. Limited MV CBCT FOV precluded workflow use for pelvic sites of larger patients and resulted in image clearance issues when tumor position was far off midline. The agreement of calculated MU on CT and MV CBCT was acceptable for all treatment sites.PACS numbers: 87.55.D‐, 87.57.Q‐

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Section: Introductionmentioning

confidence: 99%

Feasibility of MV CBCT‐based treatment planning for urgent radiation therapy: dosimetric accuracy of MV CBCT‐based dose calculations

Held

Sneed

Fogh

et al. 2015

J Applied Clin Med Phys

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“…[1] pCT-kVCBCT Calibration curves have been observed to be very stable over a period of eight consecutive weeks. [23] Various image correction methods have been used, and dose variations observed to be in the range −0.23-0.69% of pCT doses.…”

Section: Introductionmentioning

confidence: 99%

“…CBCT has been used to perform dose-of-the day computations but was dependant on dedicated research software for image registration. [ 1 2 3 4 ] CATPhan and CIRS phantoms have been confined to Quality Assurance purposes, therefore, the possibility of using those phantoms as part of dosimetric calculations have been overlooked.…”

Section: Introductionmentioning

confidence: 99%

“…Studies have shown an almost perfect correlation of 0.999 between CBCT and Planning CT (pCT), where dosimetric calculations were performed on linear accelerators with monitor units (MU) between 5 and 60. [ 1 ] pCT-kVCBCT Calibration curves have been observed to be very stable over a period of eight consecutive weeks. [ 2 3 ] Various image correction methods have been used, and dose variations observed to be in the range −0.23-0.69% of pCT doses.…”

Section: Introductionmentioning

confidence: 99%

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Assessment of the dosimetric accuracies of CATPhan 504 and CIRS 062 using kV-CBCT for performing direct calculations

Annkah¹,

Rosenberg²,

Hindocha³

et al. 2014

J Med Phys

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The dosimetric accuracies of CATPhan 504 and CIRS 062 have been evaluated using the kV-CBCT of Varian TrueBeam linac and Eclipse TPS. The assessment was done using the kV-CBCT as a standalone tool for dosimetric calculations towards Adaptive replanning. Dosimetric calculations were made without altering the HU-ED curves of the planning computed tomography (CT) scanner that is used by the Eclipse TPS. All computations were done using the images and dataset from kV-CBCT while maintaining the HU-ED calibration curve of the planning CT (pCT), assuming pCT was used for the initial treatment plan. Results showed that the CIRS phantom produces doses within ±5% of the CT-based plan while CATPhan 504 produces a variation of ±14% of the CT-based plan.

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“…8 Additionally, the increased interest in the use of MVCT data for treatment planning requires knowledge of the electron density of the tissues and checking how the structures of different densities are delineated by different observers. 10 …”

Section: Introductionmentioning

confidence: 99%

Influence of the type of imaging on the delineation process during the treatment planning

Jackowiak

Bąk

Kowalik

et al. 2015

Reports of Practical Oncology & Radiotherapy

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a b s t r a c tAim: The aim of this study was to compare the intra-and interobserver contouring variability for structures with density of organ at risk in two types of tomography: kilovoltage computed tomography (KVCT) versus megavoltage computed tomography (MVCT). The intraand interobserver differences were examined on both types of tomography for structures which simulate human tissue or organs. Materials and methods:Six structures with density of the liver, bone, trachea, lung, soft tissue and muscle were created and used. For the measurements, the special water phantom with all structures was designed. To evaluate interobserver variability, five observers delineated the structures in both types of computed tomography (CT).Results: Intraobserver variability was in the range of 1-14% and was the largest for the liver. (51.86 vs. 67.97), the volume on MVCT was smaller than KVCT. The statistically significant differences between observers were observed for structures with density of the liver, bone and soft tissue on KVCT and for the liver, lung and soft tissue on MVCT. For the structures with density of the trachea and muscles, there were no significant differences for both types of tomography.Conclusions: During the contouring process the interobserver and intraobserver contouring uncertainty was larger on MVCT, especially for structures with HU near 80, compared with KVCT.

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An investigation into factors affecting electron density calibration for a megavoltage cone‐beam CT system

Cited by 12 publications

References 29 publications

Feasibility of MV CBCT‐based treatment planning for urgent radiation therapy: dosimetric accuracy of MV CBCT‐based dose calculations

Feasibility of MV CBCT‐based treatment planning for urgent radiation therapy: dosimetric accuracy of MV CBCT‐based dose calculations

Assessment of the dosimetric accuracies of CATPhan 504 and CIRS 062 using kV-CBCT for performing direct calculations

Influence of the type of imaging on the delineation process during the treatment planning

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