Stereotactic radiotherapy of intrapulmonary lesions: comparison of different dose calculation algorithms for Oncentra MasterPlan

• Published in: Radiation oncology (London, England) Vol. 10; no. 1; p. 51
• Main Authors: Troeller, Almut, Garny, Sylvia, Pachmann, Sophia, Kantz, Steffi, Gerum, Sabine, Manapov, Farkhad, Ganswindt, Ute, Belka, Claus, Söhn, Matthias
• Format: Journal Article
• Language: English
• Published: London BioMed Central 22.02.2015; BioMed Central Ltd
• Subjects: Algorithms; Biomedical and Life Sciences; Biomedicine; Cancer Research; Care and treatment; Comparative analysis; Diagnosis; Follow-Up Studies; Humans; Imaging; Lung diseases; Lung Neoplasms - pathology; Lung Neoplasms - surgery; Neoplasm Staging; Oncology; Patient outcomes; Prognosis; Radiation Physics; Radiology; Radiosurgery; Radiotherapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy, Intensity-Modulated - methods; Retrospective Studies; Dose calculation algorithms; Lung SBRT; Pencil Beam; Collapsed Cone; Small pulmonary lesions
• ISSN: 1748-717X; 1748-717X
• DOI: 10.1186/s13014-015-0354-3

Background The use of high accuracy dose calculation algorithms, such as Monte Carlo (MC) and Collapsed Cone (CC) determine dose in inhomogeneous tissue more accurately than pencil beam (PB) algorithms. However, prescription protocols based on clinical experience with PB are often used for treatment plans calculated with CC. This may lead to treatment plans with changes in field size (FS) and changes in dose to organs at risk (OAR), especially for small tumor volumes in lung tissue treated with SABR. Methods We re-evaluated 17 3D-conformal treatment plans for small intrapulmonary lesions with a prescription of 60 Gy in fractions of 7.5 Gy to the 80% isodose. All treatment plans were initially calculated in Oncentra MasterPlan® using a PB algorithm and recalculated with CC (CC re-calc ). Furthermore, a CC-based plan with coverage similar to the PB plan (CC cov ) and a CC plan with relaxed coverage criteria (CC clin ), were created. The plans were analyzed in terms of D mean , D min , D max and coverage for GTV, PTV and ITV. Changes in mean lung dose (MLD), V 10Gy and V 20Gy were evaluated for the lungs. The re-planned CC plans were compared to the original PB plans regarding changes in total monitor units (MU) and average FS. Results When PB plans were recalculated with CC, the average V 60Gy of GTV, ITV and PTV decreased by 13.2%, 19.9% and 41.4%, respectively. Average D mean decreased by 9% (GTV), 11.6% (ITV) and 14.2% (PTV). D min decreased by 18.5% (GTV), 21.3% (ITV) and 17.5% (PTV). D max declined by 7.5%. PTV coverage correlated with PTV volume (p < 0.001). MLD, V 10Gy , and V 20Gy were significantly reduced in the CC plans. Both, CC cov and CC clin had significantly increased MUs and FS compared to PB. Conclusions Recalculation of PB plans for small lung lesions with CC showed a strong decline in dose and coverage in GTV, ITV and PTV, and declined dose in the lung. Thus, switching from a PB algorithm to CC, while aiming to obtain similar target coverage, can be associated with application of more MU and extension of radiotherapy fields, causing greater OAR exposition.