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

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.

Calculation of the Beam-Modulation Effect of the Lung in Carbon Ion and Proton Therapy With Deterministic Pencil Beam Algorithms

“…This effect is clearly more pronounced for carbon ions than for protons, as the sharper the initial BP the stronger the modulation effect. The modulation effect is generally negligible in proton treatments, as compared to the other dose delivery and treatment uncertainties related to protons, which confirms the work of Baumann et al [10]. Among such uncertainties are particle range uncertainties, patient setup errors, interfractional anatomy changes (e.g., weight loss, tumor shrinkage, etc.)…”

“…Our conclusion is that the lung modulation effect is not very severe for proton treatment planning. This is in agreement with other findings [10,11]. We focus on the carbon ions plans for further analysis due to the larger modulation effect observed for this particle type relative to protons.…”

“…Then, the voxels of VOI lung (within a user-defined density range ρ range from ρ min to ρ max ) are selected and defined as the voxels to be modulated. The modulation power P mod as defined prior is a good estimation for the strength of the lung modulation effect [4,6,[8][9][10] and given as a second user-defined input parameter:…”

“…It was shown that the underdosage of the target volume, due to the BP degradation, increases with an increasing depth of the tumor in lung and a decreasing tumor volume. In a further study by the same group [10] the effects were investigated on proton treatment plans of lung cancer patients. It was found that the maximum underdosage of the target volume due to the BP degradation was in the order of 5% while the average underdosage was roughly 2%.…”

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

“…Following publication of the original article [1], we have been notified that the below text parts of the Discussion chapter should be changed. Currently the text is as follows:…”