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1.
Z Med Phys ; 30(4): 315-324, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32576410

RESUMO

PURPOSE: To approximate dose-volume histogram (DVH) based quality indicators in volumetric modulated arc therapy (VMAT) planning using multi-criteria optimization (MCO) with a low number of composite optimization parameters. METHODS: The solution space for VMAT optimization with a low number of composite optimization parameters is approximated by trilinear dose inter- polation and prediction of dose-volume-histogram (DVH) based plan quality indicator values. To assess the approximation quality a diverse dataset of 44 cranial and 18 spine patient geometries was chosen. Optimization results are governed by three composite parameters focusing on target-organ-at-risk- (OAR)-trade-off, overall healthy tissue sparing, and delivery/quality assurance complexity. 21,266 optimized dose distributions were pre-calculated and the numerical values for a choice of 10 DVH points, referred to as plan quality indicators, were stored to serve as ground truth. Using a subset of 8 and 27 pre-calculated optimization results, dose distributions for unknown parameter values were approximated by trilinear interpolation. The resulting quality indicator values were compared to the previously obtained exact solutions. RESULTS: The magnitude of the deviation between exact and approximated values varied largely with respect to patient geometry and the criterion under investigation. Approximation with 27 pre-calculated results yielded lower deviations than approximation with 8 results, at the cost of a higher pre-calculation workload. CONCLUSIONS: Solution space approximation via trilinear dose interpolation in VMAT treatment planning governed by composite optimization parameters is possible without further knowledge of the internal implementation of the underlying optimizer. Maximum average deviations between approxi- mation and actual values of characteristic dose quality indicators below 1% (cranial) and 8% (spine) allow for a quick qualitative assessment of the possible solution landscape.


Assuntos
Doses de Radiação , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada , Algoritmos , Humanos , Indicadores de Qualidade em Assistência à Saúde , Dosagem Radioterapêutica
2.
J Biophotonics ; 5(11-12): 903-11, 2012 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-22930653

RESUMO

Laser-accelerated particles are a promising option for radiation therapy of cancer by potentially combining a compact, cost-efficient treatment unit with the physical advantages of charged particle beams. To design such a treatment unit we consider different dose delivery schemes and analyze the necessary devices in the required particle beam line for each case. Furthermore, we point out that laser-driven treatment units may be ideal tools for motion adaptation during radiotherapy. Reasons for this are the potential of a flexible gantry and the time structure of the beam with high particle numbers in ultrashort bunches. One challenge that needs to be addressed is the secondary radiation produced in several beam line elements.


Assuntos
Lasers , Radioterapia de Intensidade Modulada/métodos , Aceleração , Humanos , Movimento , Neoplasias/radioterapia , Segurança do Paciente , Radioterapia de Intensidade Modulada/efeitos adversos , Radioterapia de Intensidade Modulada/instrumentação
3.
Z Med Phys ; 22(1): 21-8, 2012 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-21723105

RESUMO

In this work a prioritized optimization algorithm is adapted and applied to treatment planning for intensity modulated proton therapy (IMPT). Originally, this algorithm was developed for intensity modulated radiation therapy (IMRT) with photons. Prioritized optimization converts the clinical hierarchy of treatment goals into an effective optimization scheme for treatment planning. It presents an alternative to conventional methods that combine all optimization goals into a single optimization run with a weighted sum of all planning aims in the objective function. The highest order goal in the first step is to achieve a homogeneous dose distribution of the prescribed dose in the tumour. In subsequent steps the dose to organs at risk (OARs) is minimized dependent upon their clinical priority, whereby the results of previous steps are turned into hard constraints. The large number of degrees of freedom through the additional energy modulation of protons enables a better protection of OARs under the perpetuation of the prescribed dose in the planning target volume (PTV). The solution space of subsequent optimization steps can be extended by introducing a slip factor. This slip factor allows a slight deterioration of the homogeneity in the PTV compared to previous steps and entails much better results in IMRT planning. To investigate the relevance and necessity of the slip factor in IMPT, prioritized optimization with various slip factors is applied to a clinical patient case with a head and neck tumour. It emerges that in IMPT the slip factor has much less impact than in IMRT through the great number of degrees of freedom. Hence, prioritized optimization is particularly well suited for proton therapy planning.


Assuntos
Algoritmos , Neoplasias/radioterapia , Terapia com Prótons , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/métodos , Encéfalo/efeitos da radiação , Tronco Encefálico/efeitos da radiação , Humanos , Órgãos em Risco , Neoplasias Otorrinolaringológicas/radioterapia , Glândula Parótida/efeitos da radiação , Lesões por Radiação/prevenção & controle , Proteção Radiológica/métodos , Dosagem Radioterapêutica
4.
J Appl Clin Med Phys ; 12(4): 3596, 2011 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-22089018

RESUMO

Intensity-modulated radiation therapy (IMRT) requires more beam-on time than normal open field treatment. Consequently, the machines wear out and need more spare parts. A helical tomotherapy treatment unit needs a periodical tungsten target replacement, which is a time consuming event. To be able to predict the next replacement would be quite valuable. We observed unexpected variations towards the end of the target lifetime in the performed pretreatment measurements for patient plan verification. Thus, we retrospectively analyze the measurements of our quality assurance program. The time dependence of the quotient of two simultaneous dose measurements at different depths within a phantom for a fixed open field irradiation is evaluated. We also assess the time-dependent changes of an IMRT plan measurement and of a relative depth dose curve measurement. Additionally, we performed a Monte Carlo simulation with Geant4 to understand the physical reasons for the measured values. Our measurements show that the dose at a specified depth compared to the dose in shallower regions of the phantom declines towards the end of the target lifetime. This reproducible effect can be due to the lowering of the mean energy of the X-ray spectrum. These results are supported by the measurements of the IMRT plan, as well as the study of the relative depth dose curve. Furthermore, the simulation is consistent with these findings since it provides a possible explanation for the reduction of the mean energy for thinner targets. It could be due to the lowering of low energy photon self-absorption in a worn out and therefore thinner target. We state a threshold value for our measurement at which a target replacement should be initiated. Measurements to observe a change in the energy are good predictors of the need for a target replacement. However, since all results support the softening of the spectrum hypothesis, all depth-dependent setups are viable for analyzing the deterioration of the tungsten target. The suggested measurements and criteria to replace the target can be very helpful for every user of a TomoTherapy machine.


Assuntos
Radioterapia de Intensidade Modulada/métodos , Humanos , Método de Monte Carlo , Garantia da Qualidade dos Cuidados de Saúde , Dosagem Radioterapêutica
5.
Radiat Environ Biophys ; 50(3): 339-44, 2011 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-21556847

RESUMO

A technical set-up for irradiation of subcutaneous tumours in mice with nanosecond-pulsed proton beams or continuous proton beams is described and was successfully used in a first experiment to explore future potential of laser-driven particle beams, which are pulsed due to the acceleration process, for radiation therapy. The chosen concept uses a microbeam approach. By focusing the beam to approximately 100 × 100 µm(2), the necessary fluence of 10(9) protons per cm(2) to deliver a dose of 20 Gy with one-nanosecond shot in the Bragg peak of 23 MeV protons is achieved. Electrical and mechanical beam scanning combines rapid dose delivery with large scan ranges. Aluminium sheets one millimetre in front of the target are used as beam energy degrader, necessary for adjusting the depth-dose profile. The required procedures for treatment planning and dose verification are presented. In a first experiment, 24 tumours in mice were successfully irradiated with 23 MeV protons and a single dose of 20 Gy in pulsed or continuous mode with dose differences between both modes of 10%. So far, no significant difference in tumour growth delay was observed.


Assuntos
Terapia com Prótons , Radioterapia/instrumentação , Animais , Feminino , Camundongos , Método de Monte Carlo , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador , Neoplasias Cutâneas/patologia , Neoplasias Cutâneas/radioterapia
6.
Med Phys ; 37(10): 5330-40, 2010 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-21089768

RESUMO

PURPOSE: Laser plasma acceleration can potentially replace large and expensive cyclotrons or synchrotrons for radiotherapy with protons and ions. On the way toward a clinical implementation, various challenges such as the maximum obtainable energy still remain to be solved. In any case, laser accelerated particles exhibit differences compared to particles from conventional accelerators. They typically have a wide energy spread and the beam is extremely pulsed (i.e., quantized) due to the pulsed nature of the employed lasers. The energy spread leads to depth dose curves that do not show a pristine Bragg peak but a wide high dose area, making precise radiotherapy impossible without an additional energy selection system. Problems with the beam quantization include the limited repetition rate and the number of accelerated particles per laser shot. This number might be too low, which requires a high repetition rate, or it might be too high, which requires an additional fluence selection system to reduce the number of particles. Trying to use laser accelerated particles in a conventional way such as spot scanning leads to long treatment times and a high amount of secondary radiation produced when blocking unwanted particles. METHODS: The authors present methods of beam delivery and treatment planning that are specifically adapted to laser accelerated particles. In general, it is not necessary to fully utilize the energy selection system to create monoenergetic beams for the whole treatment plan. Instead, within wide parts of the target volume, beams with broader energy spectra can be used to simultaneously cover multiple axially adjacent spots of a conventional dose delivery grid as applied in intensity modulated particle therapy. If one laser shot produces too many particles, they can be distributed over a wider area with the help of a scattering foil and a multileaf collimator to cover multiple lateral spot positions at the same time. These methods are called axial and lateral clustering and reduce the number of particles that have to be blocked in the beam delivery system. Furthermore, the optimization routine can be adjusted to reduce the number of dose spots and laser shots. The authors implemented these methods into a research treatment planning system for laser accelerated particles. RESULTS: The authors' proposed methods can decrease the amount of secondary radiation produced when blocking particles with wrong energies or when reducing the total number of particles from one laser shot. Additionally, caused by the efficient use of the beam, the treatment time is reduced considerably. Both improvements can be achieved without extensively changing the quality of the treatment plan since conventional intensity modulated particle therapy usually includes a certain amount of unused degrees of freedom which can be used to adapt to laser specific properties. CONCLUSIONS: The advanced beam delivery and treatment planning methods reduce the need to have a perfect laser-based accelerator reproducing the properties of conventional accelerators that might not be possible without increasing treatment time and secondary radiation to the patient. The authors show how some of the differences to conventional beams can be overcome and efficiently used for radiation treatment.


Assuntos
Íons/uso terapêutico , Lasers , Aceleradores de Partículas , Terapia com Prótons , Planejamento da Radioterapia Assistida por Computador/métodos , Fenômenos Biofísicos , Humanos , Neoplasias/radioterapia , Planejamento da Radioterapia Assistida por Computador/estatística & dados numéricos , Radioterapia Conformacional/estatística & dados numéricos
7.
Z Med Phys ; 20(3): 188-96, 2010.
Artigo em Inglês | MEDLINE | ID: mdl-20832006

RESUMO

As an approach towards more biology-oriented treatment planning for external beam radiation therapy, we present the incorporation of local radiation damage models into three dimensional treatment planning. This allows effect based instead of dose based plan optimization which could potentially better match the biologically relevant tradeoff between target and normal tissues. In particular, our approach facilitates an effective comparison of different fractionation schemes. It is based on the linear quadratic model to describe the biological radiation effect. Effect based optimization was integrated into our inverse treatment planning software KonRad, and we demonstrate the resulting differences between conventional and biological treatment planning. Radiation damage can be analyzed both qualitatively and quantitatively in dependence of the fractionation scheme and tissue specific parameters in a three dimensional voxel based system. As an example the potential advantages as well as the associated risks of hypofractionation for prostate cancer are analyzed and visualized with the help of effective dose volume histograms. Our results suggest a very conservative view regarding alternative fractionation schemes since uncertainties in biological parameters are still too big to make reliable clinical predictions.


Assuntos
Neoplasias de Cabeça e Pescoço/radioterapia , Neoplasias da Próstata/radioterapia , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia/métodos , Fracionamento da Dose de Radiação , Humanos , Modelos Lineares , Masculino , Radioterapia/efeitos adversos , Dosagem Radioterapêutica/normas
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