Effects of the Bragg peak degradation due to lung tissue in proton therapy of lung cancer patients

Kilian-Simon Baumann,Stefan Lautenschläger,Klemens Zink,Veronika Flatten,Uli Weber,Fabian Eberle,Rita Engenhart-Cabillic

doi:10.1186/s13014-019-1375-0

Abstract

PurposeTo quantify the effects of the Bragg peak degradation due to lung tissue on treatment plans of lung cancer patients with spot scanning proton therapy and to give a conservative approximation of these effects.Methods and materialsTreatment plans of five lung cancer patients (tumors of sizes 2.7–46.4 cm3 at different depths in the lung) were optimized without consideration of the Bragg peak degradation. These treatment plans were recalculated with the Monte Carlo code TOPAS in two scenarios: in a first scenario, the treatment plans were calculated without including the Bragg peak degradation to reproduce the dose distribution predicted by the treatment-planning system (TPS). In a second scenario, the treatment plans were calculated while including the Bragg peak degradation. Subsequently, the plans were compared by means of Dmean, D98% and D2% in the clinical target volume (CTV) and organs at risk (OAR). Furthermore, isodose lines were investigated and a gamma index analysis was performed.ResultsThe Bragg peak degradation leads to a lower dose in the CTV and higher doses in OARs distal to the CTV compared to the prediction from the TPS. The reduction of the mean dose in the CTV was − 5% at maximum and − 2% on average. The deeper a tumor was located in the lung and the smaller its volume the bigger was the effect on the CTV. The enhancement of the mean dose in OARs distal to the CTV was negligible for the cases investigated.ConclusionsEffects of the Bragg peak degradation due to lung tissue were investigated for lung cancer treatment plans in proton therapy. This study confirms that these effects are clinically tolerable to a certain degree in the current clinical context considering the various more critical dose uncertainties due to motion and range uncertainties in proton therapy.

Highlights

Since proposed for radiation therapy, ion beams are of increasing interest in radiation oncology [1, 2]
The Bragg peak degradation leads to a lower dose in the clinical target volume (CTV) and higher doses in organs at risk (OAR) distal to the CTV compared to the prediction from the treatment-planning system (TPS)
The enhancement of the mean dose in OARs distal to the CTV was negligible for the cases investigated

Summary

Introduction

Since proposed for radiation therapy, ion beams are of increasing interest in radiation oncology [1, 2]. In homogeneous materials the dose profile of heavy charged particles such as protons consists of a low dose plateau at small depths followed by the so-called Bragg peak where most of the dose is deposited. The Bragg peak is Baumann et al Radiation Oncology (2019) 14:183 to OARs as much as possible. Both approaches can be considered for the treatment of lung cancer patients with protons. It has been shown in some studies that a dose escalation in the tumor improves local control and survival in non-small cell lung cancer (NSCLC) patients [4]. This is often the case for lung cancer patients due to the possible proximity of OARs like the heart, esophagus, trachea, large blood vessels and the spinal cord [4]

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Conclusion