Double-scattered proton-based stereotactic body radiotherapy for stage I lung cancer: A dosimetric comparison with photon-based stereotactic body radiotherapy

Purpose: Stereotactic body radiotherapy (SBRT) has gained popularity in the treatment of early-stage non-small-cell lung cancer (NSCLC) because of its ability to deliver conformal radiation doses to small targets. However, photon-based SBRT (xSBRT) is associated with significant grade 3+ toxicities. In this study, we compare xSBRT treatment plans with proton-based SBRT (pSBRT) to determine whether dose to normal structures could be reduced if SBRT was delivered with protons. Materials and methods: Eight patients with medically inoperable, peripherally located stage I NSCLC were treated with xSBRT to 48 Gy in 4 12-Gy fractions. These patients were retrospectively re-planned using the same treatment volumes with 3-dimensional conformal double-scatter proton therapy. A Wilcoxon paired test compared dosimetrit parameters between the plans for each patient. Results: Compared with xSBRT there was a dosimetric improvement with pSBRT for these volumes: lung V5 (median difference [MD] = 10.4%, p = 0.01); V10 (MD = 6.4%, p = 0.01); V20 (MD = 2.1%, p = 0.01): V40 (MD = 1.5%, p = 0.05); and mean lung dose (MD = 2.17 Gy, p = 0.01). There were also benefits (p = <0.05) in D0.1cm3 and D5cm3 with pSBRT to the heart, esophagus, and bronchus. Conclusions: In a dosimetric comparison between photon and proton-based SBRT, protons resulted in lower doses to critical organs at risk and a smaller volume of non-targeted normal lung exposed to radiation (V5, V10, V20, and V40). The clinical significance and relevance of these dosimetric improvements remain unknown. (C) 2010 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 97 (2010) 425-430