Impact of choice of dose calculation algorithm on PTV and OAR doses in lung SBRT
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Five dose calculation algorithms commonly used in lung SBRT planning are evaluated for their dosimetric impact on planning target volume (PTV) and organ-at-risk (OAR) doses.
Methods and materials
Treatment plans for thirty lung SBRT patients were included in this multi-institutional planning study. Lung SBRT plans were initially generated using BrainLab Pencil Beam (PB) convolution algorithm to deliver 50 Gy in 5 fractions to PTV (PB_OP plans). Plans were recalculated using BrainLab Monte Carlo (MC) algorithm with the same beam parameters, field settings, and MUs (MC_NO plans) to investigate accuracy limits of PB plans. Next, these plans were re-optimized via MU scaling in MC algorithm while keeping original beam parameters and settings (MC_OP). Further, with these new MUs, all patient plans were recalculated with Pinnacle collapsed cone convolution superposition (CCC), Eclipse anisotropic analytic algorithm (AAA), and Eclipse Acuros XB (AXB) algorithms, and are referred to as AP_NO, AAA_NO, and AXB_NO plans, respectively. DVH of PTV and OARs were used to calculate dosimetric parameters for comparison with MC_OP plans. Patient plans were compared based on PTV size as well as the location in the lung: island targets, adjacent to the ribs/chest wall, or mixed.
Lung SBRT plans using PB dose algorithm overestimated target doses by 10–20% of prescribed dose and these differences were highlighted mainly in the target periphery/dose-buildup region as seen in Dmin and D90. Compared with MC, both Pinnacle and AAA plans overestimated PTV dose in the penumbra region, whereas Acuros plans were in good agreement with MC plans. PTV dose differences ranged 3–5% among Pinnacle, AAA, and Acuros. In general, Acuros AXB performed well for adjacent and mixed targets near the ribs and chest wall, whereas Pinnacle CCC was favored for island targets. OAR Dmax and lung V20 were better reproduced in Pinnacle, whereas Dmean were comparable among all TPS.
Knowing the strengths and limitations of clinical treatment planning system allows more consistent and accurate dose comparison for patients enrolled in protocol studies.
KeywordsLung SBRT AAA Acuros MC Pinnacle Pencil beam TPS
analytical anisotropic algorithm
collapsed cone convolution
conformality index for 100% prescription dose
minimum dose received by x% of structure volume
% of structure volume receiving at least 20 Gy dose
organ at risk
planning target volume
conformality index for 50% prescription isodose volume
Radiation Therapy Oncology Group
stereotactic body radiotherapy
treatment planning system
Availability of data and materials
Please contact the corresponding author for data requests.
AS and KLC participated in the study design. AS, KLC, JSA, and TSK were involved in data collection and performed the statistical analysis. BE, MMH and EM evaluated and approved clinical plans used for patient treatments. AS, KLC, TSK, and DVR reviewed results and helped draft the manuscript. All authors read and approved the final manuscript.
Compliance with ethical standards
Ethics approval and consent to participate
This study was conducted with the approval of the Institutional Review Board of Loyola University Medical Center (LU #209599).
Consent for publication
Conflict of interest
The authors declare that they have no conflicts of interests.
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