Still equivalent for dose calculation in the Monte Carlo era? A comparison of free breathing and average intensity projection <scp>CT</scp> datasets for lung <scp>SBRT</scp> using three generations of dose calculation algorithms

Zvolanek, Kristina M.; Ma, Ruimei; Zhou, Chun; Liang, Xiaoying; Wang, Shuo; Verma, Vivek; Zhu, Xiaofeng; Driewer, J; Lin, Chi; Zhen, Weining; Wahl, Andrew O.; Zhou, Sumin; Zheng, Dandan

doi:10.1002/mp.12193

Cited by 20 publications

(35 citation statements)

References 48 publications

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“…The dose errors observed in this study for Type‐A and Type‐B algorithms are in agreement with numerous previous studies 7, 9, 14, 15. Both algorithms overestimated the target peripheral or “cold spot” indices such as D95% and Dmin, and the magnitude of the overestimation varied widely from case to case.…”

Section: Discussionsupporting

confidence: 91%

“…The simulation and contouring process was as previously described 15. Briefly, patients were simulated with a free‐breathing 3D CT followed by a 4D CT.…”

Section: Methodsmentioning

confidence: 99%

“…For the Type‐A study, a dynamic conformal arc (DCA) plan as previously described and an IMRT plan were created for each patient using a pencil beam algorithm with equivalent path length heterogeneity correction in iPlan v4.5 (Brainlab AG, Feldkirchen, Germany) 15. Both DCA and IMRT plans used a 360° geometry, with a full arc for DCA and seven equal angularly spaced beams for IMRT.…”

Section: Methodsmentioning

confidence: 99%

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Does intensity modulation increase target dose calculation errors of conventional algorithms for lung SBRT?

Zheng

Verma

Wang

et al. 2018

J Applied Clin Med Phys

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PurposeConventional dose algorithms (Type A and Type B) for lung SBRT can display considerable target dose errors compared to Type‐C algorithms. Intensity‐modulated techniques (IMRT/VMAT) are increasingly being utilized for lung SBRT. Therefore, our study aimed to assess whether intensity modulation increased target dose calculation errors by conventional algorithms over conformal techniques.MethodsTwenty lung SBRT patients were parallely planned with both IMRT and dynamic conformal arc (DCA) techniques using a Type‐A algorithm, and another 20 patients were parallely planned with IMRT, VMAT, and DCA using a Type‐B algorithm. All 100 plans were recalculated with Type‐C algorithms using identical beam and monitor unit settings, with the Type‐A/Type‐B algorithm dose errors defined using Type‐C recalculation as the ground truth. Target dose errors for PTV and GTV were calculated for a variety of dosimetric end points. Using Wilcoxon signed‐rank tests (p < 0.05 for statistical significance), target dose errors were compared between corresponding IMRT/VMAT and DCA plans for the two conventional algorithms. The levels of intensity modulation were also evaluated using the ratios of MUs in the IMRT/VMAT plans to those in the corresponding DCA plans. Linear regression was used to study the correlation between intensity modulation and relative dose error magnitudes.ResultsOverall, larger errors were found for the Type‐A algorithm than for the Type‐B algorithm. However, the IMRT/VMAT plans were not found to have statistically larger dose errors from their corresponding DCA plans. Linear regression did not identify a significant correlation between the intensity modulation level and the relative dose error.ConclusionIntensity modulation did not appear to increase target dose calculation errors for lung SBRT plans calculated with conventional algorithms.

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Section: Discussionsupporting

confidence: 91%

“…The simulation and contouring process was as previously described 15. Briefly, patients were simulated with a free‐breathing 3D CT followed by a 4D CT.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Does intensity modulation increase target dose calculation errors of conventional algorithms for lung SBRT?

Zheng

Verma

Wang

et al. 2018

J Applied Clin Med Phys

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“…These results are in contrast with our current study where neither AAA nor AXB algorithms predicted a dose error at isocenter to be greater than 2% over a target density variation spanning a delta on the order of 200 HU. More recently, in a 20 patient study conducted by Zvolanek et al treatment plans based on FB image sets were compared with AIP plans calculated for PBC, AAA, AXB and Voxel Monte Carlo (VMC) algorithms [27]. Even though their computations were done using multiple treatment planning systems, they found dose-differences to be small for Type C computations, so concluded FB and AIP image sets were essentially clinically equivalent.…”

Section: Discussionmentioning

confidence: 99%

“…To date, a limited number of studies have been conducted to compare different image generated datasets [22–27]. However, no systematic study exists to determine which is better for dose computation.…”

Section: Introductionmentioning

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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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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A comprehensive evaluation of advanced dose calculation algorithms for brain stereotactic radiosurgery

Yoon,

Jung,

Tanny

et al. 2023

J Applied Clin Med Phys

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PurposeAccurate dose calculation is important in both target and low dose normal tissue regions for brain stereotactic radiosurgery (SRS). In this study, we aim to evaluate the dosimetric accuracy of the two advanced dose calculation algorithms for brain SRS.MethodsRetrospective clinical case study and phantom study were performed. For the clinical study, 138 SRS patient plans (443 targets) were generated using BrainLab Elements Voxel Monte Carlo (VMC). To evaluate the dose calculation accuracy, the plans were exported into Eclipse and recalculated with Acuros XB (AXB) algorithm with identical beam parameters. The calculated dose at the target center (Dref), dose to 95% target volume (D95), and the average dose to target (Dmean) were compared. Also, the distance from the skull was analyzed. For the phantom study, a cylindrical phantom and a head phantom were used, and the delivered dose was measured by an ion chamber and EBT3 film, respectively, at various locations. The measurement was compared with the calculated doses from VMC and AXB.ResultsIn clinical cases, VMC dose calculations tended to be higher than AXB. It was found that the difference in Dref showed > 5% in some cases for smaller volumes < 0.3 cm3. Dmean and D95 differences were also higher for small targets. No obvious trend was found between the dose difference and the distance from the skull. In phantom studies, VMC dose was also higher than AXB for smaller targets, and VMC showed better agreement with the measurements than AXB for both point dose and high dose spread.ConclusionThe two advanced calculation algorithms were extensively compared. For brain SRS, AXB sometimes calculates a noticeable lower target dose for small targets than VMC, and VMC tends to have a slightly closer agreement with measurements than AXB.

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Still equivalent for dose calculation in the Monte Carlo era? A comparison of free breathing and average intensity projection CT datasets for lung SBRT using three generations of dose calculation algorithms

Cited by 20 publications

References 48 publications

Does intensity modulation increase target dose calculation errors of conventional algorithms for lung SBRT?

Does intensity modulation increase target dose calculation errors of conventional algorithms for lung SBRT?

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

A comprehensive evaluation of advanced dose calculation algorithms for brain stereotactic radiosurgery

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