Sampling techniques for the evaluation of treatment plans

Xq, Lu; Lm, Chin

doi:10.1118/1.597096

Cited by 28 publications

(20 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For a fast calculation of specific treatment plan parameters ͑e.g., the DVH or TCP/NTCP values͒ it was proposed to calculate only a small subset of the dose points inside a region of interest. 3,4 A speedup of the complete dose calculation is possible with the help of certain approximations. The crude method is to cut the pencil beams at a certain radial distance, say 15 mm, i.e., all elements beyond 15 mm radius are ignored.…”

Section: Introductionmentioning

confidence: 99%

Acceleration of intensity‐modulated radiotherapy dose calculation by importance sampling of the calculation matrices

et al. 2002

View full text Add to dashboard Cite

In inverse planning for intensity-modulated radiotherapy, the dose calculation is a crucial element limiting both the maximum achievable plan quality and the speed of the optimization process. One way to integrate accurate dose calculation algorithms into inverse planning is to precalculate the dose contribution of each beam element to each voxel for unit fluence. These precalculated values are stored in a big dose calculation matrix. Then the dose calculation during the iterative optimization process consists merely of matrix look-up and multiplication with the actual fluence values. However, because the dose calculation matrix can become very large, this ansatz requires a lot of computer memory and is still very time consuming, making it not practical for clinical routine without further modifications. In this work we present a new method to significantly reduce the number of entries in the dose calculation matrix. The method utilizes the fact that a photon pencil beam has a rapid radial dose falloff, and has very small dose values for the most part. In this low-dose part of the pencil beam, the dose contribution to a voxel is only integrated into the dose calculation matrix with a certain probability. Normalization with the reciprocal of this probability preserves the total energy, even though many matrix elements are omitted. Three probability distributions were tested to find the most accurate one for a given memory size. The sampling method is compared with the use of a fully filled matrix and with the well-known method of just cutting off the pencil beam at a certain lateral distance. A clinical example of a head and neck case is presented. It turns out that a sampled dose calculation matrix with only 1/3 of the entries of the fully filled matrix does not sacrifice the quality of the resulting plans, whereby the cutoff method results in a suboptimal treatment plan.

show abstract

Section: Introductionmentioning

confidence: 99%

Acceleration of intensity‐modulated radiotherapy dose calculation by importance sampling of the calculation matrices

et al. 2002

View full text Add to dashboard Cite

show abstract

“…They were more highly concentrated within the targets and the critical structures of interest and satisfied the accepted guidelines [48][49][50][51][52]. For each structure, we presented numbers of points used in sampling and computed the mean distances to the nearest neighbor point.…”

Section: Test Casesmentioning

confidence: 98%

Intensity modulated radiation therapy with field rotation—a time-varying fractionation study

Dink

Langer

Rardin

et al. 2012

Health Care Manag Sci

View full text Add to dashboard Cite

This paper proposes a novel mathematical approach to the beam selection problem in intensity modulated radiation therapy (IMRT) planning. The approach allows more beams to be used over the course of therapy while limiting the number of beams required in any one session. In the proposed field rotation method, several sets of beams are interchanged throughout the treatment to allow a wider selection of beam angles than would be possible with fixed beam orientations. The choice of beamlet intensities and the number of identical fractions for each set are determined by a mixed integer linear program that controls jointly for the distribution per fraction and the cumulative dose distribution delivered to targets and critical structures. Trials showed the method allowed substantial increases in the dose objective and/or sparing of normal tissues while maintaining cumulative and fraction size limits. Trials for a head and neck site showed gains of 25%-35% in the objective (average tumor dose) and for a thoracic site gains were 7%-13%, depending on how strict the fraction size limits were set. The objective did not rise for a prostate site significantly, but the tolerance limits on normal tissues could be strengthened with the use of multiple beam sets.

show abstract

“…The resulting dose distribution can be approximated by a mean dose with a small deviation characterized by a normal distribution. The determination of a volume dose histogram is done by sampling the volume of interest using a random seed method or, alternatively, a grid-method, 7,8 and determine the volume that a given dose level encompasses.…”

Section: Theorymentioning

confidence: 99%

Decomposition analysis of differential dose volume histograms

Heuvel

2006

Medical Physics

View full text Add to dashboard Cite

Dose volume histograms are a common tool to assess the value of a treatment plan for various forms of radiation therapy treatment. The purpose of this work is to introduce, validate, and apply a set of tools to analyze differential dose volume histograms by decomposing them into physically and clinically meaningful normal distributions. A weighted sum of the decomposed normal distributions (e.g., weighted dose) is proposed as a new measure of target dose, rather than the more unstable point dose. The method and its theory are presented and validated using simulated distributions. Additional validation is performed by analyzing simple four field box techniques encompassing a predefined target, using different treatment energies inside a water phantom. Furthermore, two clinical situations are analyzed using this methodology to illustrate practical usefulness. A comparison of a treatment plan for a breast patient using a tangential field setup with wedges is compared to a comparable geometry using dose compensators. Finally, a normal tissue complication probability (NTCP) calculation is refined using this decomposition. The NTCP calculation is performed on a liver as organ at risk in a treatment of a mesothelioma patient with involvement of the right lung. The comparison of the wedged breast treatment versus the compensator technique yields comparable classical dose parameters (e.g., conformity index approximately = 1 and equal dose at the ICRU dose point). The methodology proposed here shows a 4% difference in weighted dose outlining the difference in treatment using a single parameter instead of at least two in a classical analysis (e.g., mean dose, and maximal dose, or total dose variance). NTCP-calculations for the mesothelioma case are generated automatically and show a 3% decrease with respect to the classical calculation. The decrease is slightly dependant on the fractionation and on the alpha/beta-value utilized. In conclusion, this method is able to distinguish clinically important differences between treatment plans using a single parameter. This methodology shows promise as an objective tool for analyzing NTCP and doses in larger studies, as the only information needed is the dose volume histogram.

show abstract

Sampling techniques for the evaluation of treatment plans

Cited by 28 publications

References 0 publications

Acceleration of intensity‐modulated radiotherapy dose calculation by importance sampling of the calculation matrices

Acceleration of intensity‐modulated radiotherapy dose calculation by importance sampling of the calculation matrices

Intensity modulated radiation therapy with field rotation—a time-varying fractionation study

Decomposition analysis of differential dose volume histograms

Contact Info

Product

Resources

About