On the validity of density overrides for VMAT lung SBRT planning

Wiant, D; Vanderstraeten, Caroline; Mäurer, J; Pursley, J; Terrell, J; Sintay, B

doi:10.1118/1.4887778

Cited by 24 publications

(33 citation statements)

References 77 publications

(70 reference statements)

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“…In other density related studies, Wiant et al discovered plans which incorporated a density override region between the ITV and PTV margin [26]. These plans provided more accurate dose modeling and decreased normal lung irradiation for lung SBRT.…”

Section: Discussionmentioning

confidence: 99%

“…Hence, dose generated from a static CT by the TPS cannot be directly compared to the dose measured on moving film (consult Ref [26] for an excellent review of the dose smearing effect and compensation). Film motion was accounted for by convolving the TPS dose using a custom script written in MATLAB developed by Wiant et al [26]. Convolved dose plane distributions were then imported into RIT113 software for gamma analysis.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Technical and dosimetric implications of respiratory induced density variations in a heterogeneous lung phantom

Mohatt

Wiant

et al. 2018

Radiat Oncol

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BackgroundStereotactic Body Radiotherapy (SBRT) is an ablative dose delivery technique which requires the highest levels of precision and accuracy. Modeling dose to a lung treatment volume has remained a complex and challenging endeavor due to target motion and the low density of the surrounding media. When coupled together, these factors give rise to pulmonary induced tissue heterogeneities which can lead to inaccuracies in dose computation. This investigation aims to determine which combination of imaging techniques and computational algorithms best compensates for time dependent lung target displacements.MethodsA Quasar phantom was employed to simulate respiratory motion for target ranges up to 3 cm. 4DCT imaging was used to generate Average Intensity Projection (AIP), Free Breathing (FB), and Maximum Intensity Projection (MIP) image sets. In addition, we introduce and compare a fourth dataset for dose computation based on a novel phase weighted density (PWD) technique. All plans were created using Eclipse version 13.6 treatment planning system and calculated using the Analytical Anisotropic Algorithm and Acuros XB. Dose delivery was performed using Truebeam STx linear accelerator where radiochromic film measurements were accessed using gamma analysis to compare planned versus delivered dose.ResultsIn the most extreme case scenario, the mean CT difference between FB and MIP datasets was found to be greater than 200 HU. The near maximum dose discrepancies between AAA and AXB algorithms were determined to be marginal (< 2.2%), with a greater variability occurring within the near minimum dose regime (< 7%). Radiochromatic film verification demonstrated all AIP and FB based computations exceeded 98% passing rates under conventional radiotherapy tolerances (gamma 3%, 3 mm). Under more stringent SBRT tolerances (gamma 3%, 1 mm), the AIP and FB based treatment plans exhibited higher pass rates (> 85%) when compared to MIP and PWD (< 85%) for AAA computations. For AXB, however, the delivery accuracy for all datasets were greater than 85% (gamma 3%,1 mm), with a corresponding reduction in overall lung irradiation.ConclusionsDespite the substantial density variations between computational datasets over an extensive range of target movement, the dose difference between CT datasets is small and could not be quantified with ion chamber. Radiochromatic film analysis suggests the optimal CT dataset is dependent on the dose algorithm used for evaluation. With AAA, AIP and FB resulted in the best conformance between measured versus calculated dose for target motion ranging up to 3 cm under both conventional and SBRT tolerance criteria. With AXB, pass rates improved for all datasets with the PWD technique demonstrating slightly better conformity over AIP and FB based computations (gamma 3%, 1 mm). As verified in previous studies, our results confirm a clear advantage in delivery accuracy along with a relative decrease in calculated dose to the lung when using Acuros XB over AAA.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Technical and dosimetric implications of respiratory induced density variations in a heterogeneous lung phantom

Mohatt

Wiant

et al. 2018

Radiat Oncol

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“…Plans were optimized as per the methodology by Wiant et al46 where by the ITV excluding the GTV on the free breathing scan was overridden to an intermediate density. This methodology was shown to provide significant improvements over ITV optimization with the analytical anisotropic algorithm of the Eclipse planning system (Varian Oncology Systems, CA, USA).…”

Section: Methodsmentioning

confidence: 99%

“…In such cases when the patient tissue traverses into the region containing air during treatment, the high intensity fluence results in a sharp increase in primary interactions, liberated secondary electron generation, and resultant dose deposition 46, 47…”

Section: Introductionmentioning

confidence: 99%

Robust optimization of VMAT for lung cancer: Dosimetric implications of motion compensation techniques

Archibald-Heeren

Byrne

et al. 2017

J Applied Clin Med Phys

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In inverse planning of lung radiotherapy, techniques are required to ensure dose coverage of target disease in the presence of tumor motion as a result of respiration. A range of published techniques for mitigating motion effects were compared for dose stability across 5 breath cycles of ±2 cm. Techniques included planning target volume (PTV) expansions, internal target volumes with (OITV) and without tissue override (ITV), average dataset scans (ADS), and mini‐max robust optimization. Volumetric arc therapy plans were created on a thorax phantom and verified with chamber and film measurements. Dose stability was compared by DVH analysis in calculations across all geometries. The lung override technique resulted in a substantial lack of dose coverage (−10%) to the tumor in the presence of large motion. PTV, ITV and ADS techniques resulted in substantial (up to 25%) maximum dose increases where solid tissue travelled into low density optimized regions. The results highlight the need for care in optimization of highly heterogeneous where density variations may occur with motion. Robust optimization was shown to provide greater stability in both maximum (<3%) and minimum dose variations (<2%) over all other techniques.

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“…Both the 3D and 4D dose calculations on a deformable phantom agreed with measurements in the GTV, and the differences were observed primarily at the edges of the PTV [22]. That error can be further remedied by intelligent CT density overrides [23]. A somewhat different approach to circumventing the need for DIR in lung was examined by Zhang et al [24].…”

Section: Approximations To Full 4d Calculationsmentioning

confidence: 99%

On the dose to a moving target in stereotactic ablative body radiotherapy to lung tumors

Feygelman

Moros

Zhang

2017

J. Phys.: Conf. Ser.

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On the validity of density overrides for VMAT lung SBRT planning

Cited by 24 publications

References 77 publications

Technical and dosimetric implications of respiratory induced density variations in a heterogeneous lung phantom

Technical and dosimetric implications of respiratory induced density variations in a heterogeneous lung phantom

Robust optimization of VMAT for lung cancer: Dosimetric implications of motion compensation techniques

On the dose to a moving target in stereotactic ablative body radiotherapy to lung tumors

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