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. 2018 Sep;19(5):616-624.
doi: 10.1002/acm2.12426. Epub 2018 Aug 5.

Dosimetric comparison of pencil beam and Monte Carlo algorithms in conformal lung radiotherapy

Yelda Elcim  1 , Bahar Dirican  1 , Omer Yavas  2
Affiliations

Dosimetric comparison of pencil beam and Monte Carlo algorithms in conformal lung radiotherapy

Yelda Elcim et al. J Appl Clin Med Phys. 2018 Sep.

Abstract

Purpose: In this study, lung radiotherapy target volumes as well as critical organs such as the lungs, spinal cord, esophagus, and heart doses calculated using pencil beam (PB) and Monte Carlo (MC) algorithm-based treatment planning systems (TPSs) were compared. The main aim was the evaluation of calculated dose differences between the PB and MC algorithms in a highly heterogeneous medium.

Methods: A total of 6 MV photon energy conformal treatment plans were created for a RANDO lung phantom using one PB algorithm-based Precise Plan Release 2.16 TPS and one MC algorithm-based Monaco TPS. Thermoluminescence dosimeters (TLDs) were placed into appropriate slices within the RANDO phantom and then irradiated with an Elekta-Synergy® Linear Accelerator for dose verification. Doses were calculated for the V5, V10, V20, and mean lung doses (MLDs) in bilateral lungs and D50, D98, D2, and mean doses in the target volume (planning target volume, PTV).

Results: The minimum, maximum, and mean doses of the target volumes and critical organs in two treatment plans were compared using dose volume histograms (DVHs). The mean dose difference between the PB and MC algorithms for the PTV was 0.3%, whereas the differences in V5, V10, V20, and MLD were 12.5%, 15.8%, 14.4%, and 9.1%, respectively. The differences in PTV coverage between the two algorithms were 0.9%, 2.7% and 0.7% for D50, D98 and D2, respectively.

Conclusions: A comparison of the dose data acquired in this study reveals that the MC algorithm calculations are closer to the 60 Gy prescribed dose for PTV, while the difference between the PB and MC algorithms was found to be non-significant. Because of the major difference arising from the dose calculation techniques by TPS that was observed in the MLD with significant medium heterogeneity, we recommend the use of the MC algorithm in such heterogeneous sites.

Keywords: Monte Carlo; algorithm; pencil beam; radiotherapy; treatment planning systems.

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Figures

Figure 1
Figure 1
Image (a) shows a physical view of the lung treatment field, and (b) shows treatment planning views of transverse, sagittal, coronal slices with a DRR image of a RANDO phantom.
Figure 2
Figure 2
(a) RANDO Phantom slice No. 18 of TLD No. 1; (b) Treatment planning images of (a).
Figure 3
Figure 3
(a) RANDO Phantom slice No. 17 of TLD No. 2; (b) Treatment planning image of (a).
Figure 4
Figure 4
(a) RANDO Phantom slice No. 16 of TLD Nos. 3–6; (b) Treatment planning image of (a).
Figure 5
Figure 5
(a) RANDO Phantom slice No. 15 of TLD No. 7; (b) Treatment planning image of (a).
Figure 6
Figure 6
DVHs derived from the PB algorithm with Precise Plan (on the left) and the MC algorithm with a Monaco treatment plan (on the right).
Figure 7
Figure 7
Transverse, sagittal, coronal dose distributions, and DRR views of the PB algorithm Precise Plan Release 2.16.
Figure 8
Figure 8
Transverse, sagittal, coronal dose distributions, and DVH views of the MC algorithm Monaco Version 5.10.
See this image and copyright information in PMC

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