Proton therapy for early-stage non-small cell lung cancer (NSCLC)

Abstract

In the setting of early-stage non-small cell lung cancer (NSCLC), defining the optimal clinical context for proton beam therapy (PBT) is challenging due to the increasing evidence demonstrating high rates of local control and good tolerance of stereotactic ablative body radiation (SABR). Given the relatively small percentage of lung and other critical structures treated with SABR, dosimetric studies comparing the two techniques have typically concluded that there are modest advantages to PBT, typically by reducing the low dose volumes, such as volume of lung receiving 5 Gy. This advantage may be more significant in treating larger tumors, multiple tumors, or central tumors. Most of the published studies are based on passive scattering PBT. Dosimetric benefits are likely to increase when pencil beam scanning/intensity-modulated proton therapy (IMPT) is employed, as has been observed in dosimetric reports in the locally advanced setting. More clinical data is needed regarding the safety and efficacy of stereotactic PBT in comparison to SABR. However, the only randomized trial that has been attempted closed early due to poor accrual, thus demonstrating the difficulty in designing trials in this context that incorporate a relevant and focused scientific question that can be extrapolated to clinical practice, yet also accrue sufficiently. The advent and increased use of advanced image-guided radiation therapy (IGRT) techniques in the context of proton therapy, as well as the widespread implementation of IMPT, will increase the potential benefit of PBT. The next 5-10 years will likely yield more appropriate, feasible studies that will help answer the question of patient selection for this advanced technology.

Keywords: Proton therapy; early stage; non-small cell lung cancer (NSCLC).

Figure 1

Differences in dose distributions between IMRT (A), passive scattering proton plans (B), and IMPT (C). All three plans are conformal and are effective in sparing normal structures, with the IMPT plan demonstrating a modest improvement over the other two. IMRT, intensity-modulated radiotherapy; IMPT, intensity-modulated proton therapy