The use of biologically related model (Eclipse) for the intensity-modulated radiation therapy planning of nasopharyngeal carcinomas.

PURPOSE:Intensity-modulated radiation therapy (IMRT) is the most common treatment technique for nasopharyngeal carcinoma (NPC). Physical quantities such as dose/dose-volume parameters are used conventionally for IMRT optimization. The use of biological related models has been proposed and can be a new trend. This work was to assess the performance of the biologically based IMRT optimization model installed in a popular commercial treatment planning system (Eclipse) as compared to its dose/dose volume optimization model when employed in the clinical environment for NPC cases. METHODS:Ten patients of early stage NPC and ten of advanced stage NPC were selected for this study. IMRT plans optimized using biological related approach (BBTP) were compared to their corresponding plans optimized using the dose/dose volume based approach (DVTP). Plan evaluation was performed using both biological indices and physical dose indices such as tumor control probability (TCP), normal tissue complication probability (NTCP), target coverage, conformity, dose homogeneity and doses to organs at risk. The comparison results of the more complex advanced stage cases were reported separately from those of the simpler early stage cases. RESULTS:The target coverage and conformity were comparable between the two approaches, with BBTP plans producing more hot spots. For the primary targets, BBTP plans produced comparable TCP for the early stage cases and higher TCP for the advanced stage cases. BBTP plans reduced the volume of parotid glands receiving doses of above 40 Gy compared to DVTP plans. The NTCP of parotid glands produced by BBTP were 8.0 ± 5.8 and 7.9 ± 8.7 for early and advanced stage cases, respectively, while those of DVTP were 21.3 ± 8.3 and 24.4 ± 12.8, respectively. There were no significant differences in the NTCP values between the two approaches for the serial organs. CONCLUSIONS:Our results showed that the BBTP approach could be a potential alternative approach to the DVTP approach for NPC

A Review on the Use of Grid-Based Boltzmann Equation Solvers for Dose Calculation in External Photon Beam Treatment Planning

Deterministic linear Boltzmann transport equation (D-LBTE) solvers have recently been developed, and one of the latest available software codes, Acuros XB, has been implemented in a commercial treatment planning system for radiotherapy photon beam dose calculation. One of the major limitations of most commercially available model-based algorithms for photon dose calculation is the ability to account for the effect of electron transport. This induces some errors in patient dose calculations, especially near heterogeneous interfaces between low and high density media such as tissue/lung interfaces. D-LBTE solvers have a high potential of producing accurate dose distributions in and near heterogeneous media in the human body. Extensive previous investigations have proved that D-LBTE solvers were able to produce comparable dose calculation accuracy as Monte Carlo methods with a reasonable speed good enough for clinical use. The current paper reviews the dosimetric evaluations of D-LBTE solvers for external beam photon radiotherapy. This content summarizes and discusses dosimetric validations for D-LBTE solvers in both homogeneous and heterogeneous media under different circumstances and also the clinical impact on various diseases due to the conversion of dose calculation from a conventional convolution/superposition algorithm to a recently released D-LBTE solver

Comparison of the dose volume histograms between BBTP and DVTP plans for various targets including (a) PTV₇₀, (b) PTV₆₀, (c) PTV₅₄ and various OARs including (d) brain stem, (e) spinal cord, (f) parotid of a typical early stage NPC patient.

<p>Comparison of the dose volume histograms between BBTP and DVTP plans for various targets including (a) PTV₇₀, (b) PTV₆₀, (c) PTV₅₄ and various OARs including (d) brain stem, (e) spinal cord, (f) parotid of a typical early stage NPC patient.</p

Details of optional constraints available for targets and OARs.

<p>*For A<1, higher weighting will be given to low doses so as to avoid the occurrence of cold spots. For A>1, higher weighting will be given to high doses so as to avoid the occurrence of hot spots. For A = 1, equal weighting is given to cold and hot spots.</p><p>Details of optional constraints available for targets and OARs.</p

Summary of biological and physical evaluation results for OARs averaged over 10 early stage NPC patients.

†<p>The symbol “*” indicates that the mean difference between the pair was proved to be statistically significant with a p-value ≤0.05 and the symbol “∼” indicates statistically insignificant result.</p><p>Summary of biological and physical evaluation results for OARs averaged over 10 early stage NPC patients.</p

The biological functions and additional constraints that are selected for optimization of the NPC patient plans.

<p>The biological functions and additional constraints that are selected for optimization of the NPC patient plans.</p

One of the axial computed tomography (CT) slices comparing the isodose curves between the BBTP plan and the DVTP plan of a typical NPC patient.

<p>One of the axial computed tomography (CT) slices comparing the isodose curves between the BBTP plan and the DVTP plan of a typical NPC patient.</p

Constraints to OARs.

<p>Constraints to OARs.</p

Summary of biological and physical evaluation results for OARs averaged over 10 advanced stage NPC patients.

†<p>The symbol “*” indicates that the mean difference between the pair was proved to be statistically significant with a p-value ≤0.05 and the symbol “∼” indicates statistically insignificant result.</p><p>Summary of biological and physical evaluation results for OARs averaged over 10 advanced stage NPC patients.</p