Elsevier

Radiotherapy and Oncology

Volume 97, Issue 3, December 2010, Pages 425-430
Radiotherapy and Oncology

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

https://doi.org/10.1016/j.radonc.2010.09.006Get rights and content

Abstract

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 dosimetric 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.

Section snippets

Materials and methods

Beginning in November 2005, patients at the University of Florida (UF) with early-stage NSCLC were treated on an Institutional Review Board-approved protocol with xSBRT to a total dose of 48 Gy delivered in 4 fractions of 12 Gy. Eight patients on this study with peripherally located stage I NSCLC were identified for retrospective treatment planning with pSBRT, including 3 patients with T1N0Mx (maximum tumor diameters, 1.9 cm, 2.1 cm, and 2.4 cm) and 5 patients with T2N0Mx (maximum tumor diameters,

Results

Table 1 describes the target volumes and coverage for the eight cases. The median PTV treated was 77 cm3 (range, 38–138 cm3) and the CTV was 47 cm3 (range, 20–92 cm3). As expected, CTV coverage was comparable (median CTV D99% = 48.6 Gy vs 48 CGE with xSBRT and pSBRT, respectively), while PTV coverage was marginally worse with pSBRT (median PTV D95% = 48 Gy vs 46.5 CGE with xSBRT and pSBRT, respectively). Table 2 shows the dosimetric end points for the specified critical organs at risk for the xSBRT plans

Discussion

Surgery has been the “gold standard” of treatment for patients with early-stage NSCLC. SBRT, however, offers medically inoperable patients with early-stage NSCLC a less invasive treatment approach with local-control rates comparable to those observed with surgical resection [23]. Because the efficacy of SBRT appears to be comparable to surgery, even medically operable patients are considering SBRT in lieu of lobectomy and this approach is currently being tested by the RTOG.

Although significant

Conclusion

Based on our SBRT treatment approach, we found that 3D-CPT significantly reduced the radiation dose to the ipsilateral lung, total lung, heart, esophagus, trachea, and ipsilateral bronchus. This reduction may translate into a clinically important reduction in side effects from SBRT and is the rationale for our present phase I/II study of using 3D-CPT for patients with early-stage NSCLC.

Conflicts of interest statement

The authors have no conflicts of interests to declare.

Role of the funding source

The authors have no source of funding to declare.

Acknowledgements

The authors would like to thank the editorial staff at the University of Florida, Department of Radiation Oncology for helping to edit and prepare the manuscript.

References (33)

Cited by (60)

  • Multi-Institutional Retrospective Analysis of the Outcomes of Proton Beam Therapy for Patients With 1 to 3 Pulmonary Oligometastases From Various Primary Cancers

    2021, Advances in Radiation Oncology
    Citation Excerpt :

    The LPF of our series, which was comparable to those observed in the x-ray SBRT series, may be attributed to the use of relatively high-dose delivery with curative intent. Additionally, the physical features of PBT, which is characterized by dose delivery with a Bragg peak, had a potential effect on the absence of grade ≥3 pneumonitis,5,6 although the passive scattering method was employed in all the PBTs of our series. To investigate the prognostic factors for LPF, we performed UVA and 3 sets of MVAs: using all the parameters, all the parameters except BED10, and all the parameters except dose per fraction, because dose per fraction and BED10 are potentially correlated (correlation coefficient 0.69, P < .001).

View all citing articles on Scopus
View full text