Evaluation of radiobiological effects in intensity modulated proton therapy: New strategies for inverse treatment planning

Wilkens, Jan J.

doi:10.1118/1.1786191

Cited by 2 publications

(9 citation statements)

References 97 publications

(206 reference statements)

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“…This fit works fine in the LET region below 30 keV/ m, and fortunately this is sufficient since higher LET values are not needed for practical purposes in clinical proton therapy: even in the distal dose falloff of a pristine Bragg peak, the LET will stay below this value due to straggling effects. 16,18,19 This simple model was able to reproduce the basic dependencies of RBE on dose and LET, and the RBE values agreed well with experimental results. Figure 1 shows exemplarily the resulting RBE values for the survival of V79 Chinese hamster cells for two dose levels of 1.5 and 3 Gy, using ␣ 0 = 0.1 Gy −1 , = 0.02 m keV −1 Gy −1 , ␣ r = 0.112 Gy −1 , and ␤ r = 0.0298 Gy −2 .…”

Section: A the Rbe Modelsupporting

confidence: 70%

“…We investigated the effects of a variable RBE for several clinical cases with IMPT scanning techniques. 19 Due to the limited space in this paper, here we will just present one example. We chose a patient with a carcinoma of the prostate, since proton therapy is clinically applied to these tumors.…”

Section: Resultsmentioning

confidence: 99%

“…To investigate the off-axis behavior, lateral LET distributions for different field sizes were obtained by Monte Carlo simulations. 19,25 It was found that the LET is constant within the field and increases at the field border ͑Fig. 3͒ because there are more scattered protons with higher stop- ping powers.…”

Section: B the Let Modelmentioning

confidence: 99%

“…This is done in close analogy to the "path length scaling" known from dose calculations: For a single beam, the LET at a given voxel in the CT cube can be obtained from the LET in water by substituting the depth with the water equivalent depth, i.e., the radiological path length. 19,25 The latter is computed by a raytracing algorithm through the CT cube, which does not need additional computation time since it has to be done for the dose calculation anyway.…”

Section: B the Let Modelmentioning

confidence: 99%

“…As the RBE depends on dose, LET, and tissue type, one approach could be to aim not only for a homogeneous dose, but also for a homogeneous LET distribution in the PTV, 19 as this would automatically yield a homogeneous biological effect ͑RBEϫ dose͒. The advantage of this approach would be that there are only physical parameters ͑dose and LET͒ involved in the objective function, i.e., no tissue dependent biological parameters have to be determined.…”

Section: New Objective Functionsmentioning

confidence: 99%

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Optimization of radiobiological effects in intensity modulated proton therapy

Wilkens

Oelfke

2005

Med. Phys.

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Today, inverse treatment planning for intensity modulated proton therapy (IMPT) usually employs a constant relative biological effectiveness (RBE). In this paper, the potential clinical relevance of RBE variations for scanning techniques in IMPT is investigated, and a new strategy to include the RBE into the inverse planning process is presented. Three-dimensional RBE distributions are calculated based on a phenomenological model that describes the RBE as a function of dose, linear energy transfer (LET) and tissue type in the framework of the linear-quadratic model. This RBE model is integrated into the optimization loop of inverse planning by using a modified version of the standard quadratic objective function, where the physical dose is replaced by the biological effect. This system for "biological optimization" was implemented into a research version of the inverse planning software KonRad and allows the direct optimization of the product of RBE and physical dose. Several treatment plans for a prostate case are presented, which compare the biological with the conventional physical dose optimization for IMPT scanning techniques, in particular distal edge tracking (DET) and the full three-dimensional (3D) modulation of beam spots. Mainly due to their different LET distributions, the RBE effects for these two techniques are quite different: while the RBE distribution was more or less homogeneous in the planning target volume (PTV) for 3D modulation, considerable RBE variations within the PTV were observed for DET. These unfavorable effects could be compensated for by employing the new biological objective function, which led to a more homogeneous distribution of the product of RBE and physical dose in the PTV. The computation time increased by a factor of 2 compared to the optimization of the physical dose. In conclusion, the proposed method allows the simultaneous multifield optimization of the biological effect in a reasonable time, and is therefore well suited for studying the influence of a variable RBE in IMPT as well as for minimizing potentially adverse effects.

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Section: A the Rbe Modelsupporting

confidence: 70%

Section: Resultsmentioning

confidence: 99%

Section: B the Let Modelmentioning

confidence: 99%

Section: B the Let Modelmentioning

confidence: 99%

Section: New Objective Functionsmentioning

confidence: 99%

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Optimization of radiobiological effects in intensity modulated proton therapy

Wilkens

Oelfke

2005

Med. Phys.

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Investigating the robustness of ion beam therapy treatment plans to uncertainties in biological treatment parameters

et al. 2012

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Uncertainties in determining clinically used relative biological effectiveness (RBE) values for ion beam therapy carry the risk of absolute and relative misestimations of RBE-weighted doses for clinical scenarios. This study assesses the consequences of hypothetical misestimations of input parameters to the RBE modelling for carbon ion treatment plans by a variational approach. The impact of the variations on resulting cell survival and RBE values is evaluated as a function of the remaining ion range. In addition, the sensitivity to misestimations in RBE modelling is compared for single fields and two opposed fields using differing optimization criteria. It is demonstrated for single treatment fields that moderate variations (up to ±50%) of representative nominal input parameters for four tumours result mainly in a misestimation of the RBE-weighted dose in the planning target volume (PTV) by a constant factor and only smaller RBE-weighted dose gradients. Ensuring a more uniform radiation quality in the PTV eases the clinical importance of uncertainties in the radiobiological treatment parameters, as for such a condition uncertainties tend to result only in a systematic misestimation of RBE-weighted dose in the PTV by a constant factor. Two opposed carbon ion fields with a constant RBE in the PTV are found to result in rather robust conditions. Treatments using two ion species may be used to achieve a constant RBE in the PTV irrespective of the size and depth of the spread-out Bragg peak.

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Evaluation of radiobiological effects in intensity modulated proton therapy: New strategies for inverse treatment planning

Cited by 2 publications

References 97 publications

Optimization of radiobiological effects in intensity modulated proton therapy

Optimization of radiobiological effects in intensity modulated proton therapy

Investigating the robustness of ion beam therapy treatment plans to uncertainties in biological treatment parameters

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