Stereotactic, Single-Dose Irradiation of Lung Tumors: A Comparison of Absolute Dose and Dose Distribution Between Pencil Beam and Monte Carlo Algorithms Based on Actual Patient CT Scans

• Published in: International journal of radiation oncology, biology, physics Vol. 78; no. 3; pp. 955 - 963
• Main Authors: Chen, Huixiao, Lohr, Frank, Fritz, Peter, Wenz, Frederik, Dobler, Barbara, Lorenz, Friedlieb, Mühlnickel, Werner
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.11.2010; Elsevier
• Subjects: ALGORITHMS; Biological and medical sciences; BODY; CALCULATION METHODS; Carcinoma, Non-Small-Cell Lung - diagnostic imaging; Carcinoma, Non-Small-Cell Lung - pathology; Carcinoma, Non-Small-Cell Lung - surgery; CAT SCANNING; COMPUTERIZED TOMOGRAPHY; DIAGNOSTIC TECHNIQUES; DISEASES; Diseases of the respiratory system; DOSES; Hematology, Oncology and Palliative Medicine; Humans; Lung - anatomy & histology; Lung - diagnostic imaging; Lung Neoplasms - diagnostic imaging; Lung Neoplasms - pathology; Lung Neoplasms - surgery; Lung tumor; LUNGS; MATHEMATICAL LOGIC; Medical sciences; MEDICINE; Monte Carlo; MONTE CARLO METHOD; NEOPLASMS; NUCLEAR MEDICINE; ORGANS; Pencil beam; Phantoms, Imaging; PLANNING; Pneumology; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; Radiography; RADIOLOGY; RADIOLOGY AND NUCLEAR MEDICINE; Radiometry - methods; Radiosurgery - instrumentation; Radiosurgery - methods; RADIOTHERAPY; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects); RESPIRATORY SYSTEM; Stereotactic body radiotherapy (SBRT); THERAPY; TOMOGRAPHY; Tumor Burden; Tumors of the respiratory system and mediastinum; Stereotactic body radiotherapy (SBRT); Pencil beam; Monte Carlo; Lung tumor; Dose repartition; Human; Lung disease; Radiodiagnosis; Respiratory disease; Lung cancer; Radiosurgery; Stereotaxia; Malignant tumor; Radiotherapy; Algorithm; Treatment; Irradiation; Medical imagery; Bronchus disease; Computerized axial tomography; Treatment planning; Comparative study; Cancer; Test object
• ISSN: 0360-3016; 1879-355X; 1879-355X
• DOI: 10.1016/j.ijrobp.2009.08.012

Dose calculation based on pencil beam (PB) algorithms has its shortcomings predicting dose in tissue heterogeneities. The aim of this study was to compare dose distributions of clinically applied non–intensity-modulated radiotherapy 15-MV plans for stereotactic body radiotherapy between voxel Monte Carlo (XVMC) calculation and PB calculation for lung lesions. To validate XVMC, one treatment plan was verified in an inhomogeneous thorax phantom with EDR2 film (Eastman Kodak, Rochester, NY). Both measured and calculated (PB and XVMC) dose distributions were compared regarding profiles and isodoses. Then, 35 lung plans originally created for clinical treatment by PB calculation with the Eclipse planning system (Varian Medical Systems, Palo Alto, CA) were recalculated by XVMC (investigational implementation in PrecisePLAN [Elekta AB, Stockholm, Sweden]). Clinically relevant dose–volume parameters for target and lung tissue were compared and analyzed statistically. The XVMC calculation agreed well with film measurements (<1% difference in lateral profile), whereas the deviation between PB calculation and film measurements was up to +15%. On analysis of 35 clinical cases, the mean dose, minimal dose and coverage dose value for 95% volume of gross tumor volume were 1.14 ± 1.72 Gy, 1.68 ± 1.47 Gy, and 1.24 ± 1.04 Gy lower by XVMC compared with PB, respectively (prescription dose, 30 Gy). The volume covered by the 9 Gy isodose of lung was 2.73% ± 3.12% higher when calculated by XVMC compared with PB. The largest differences were observed for small lesions circumferentially encompassed by lung tissue. Pencil beam dose calculation overestimates dose to the tumor and underestimates lung volumes exposed to a given dose consistently for 15-MV photons. The degree of difference between XVMC and PB is tumor size and location dependent. Therefore XVMC calculation is helpful to further optimize treatment planning.