Composite Plan Research Articles

SU-FF-T-89: The Effect of Breast Motion On Dose Distribution in Tangential IMRT with Direct Aperture Optimization

Purpose: Inverse planning for breast IMRT can be accomplished with Direct Aperture Optimization (DAO) where the user defines the traditional tangential fields within which the shapes and weights of multiple segments, including an open segment as ‘flash’, are optimized. The purpose of this study is to evaluate the technique and examine the effects of relative weights of the open segments to other segments on the impact of breathing motion. Method and Materials: IMRT plans were generated using DAO inverse planning with manually fixed relative weights of the open segments. To simulate breathing motion, the same set of optimized segments was reapplied with the isocenter shifted up and down by up to 1cm and the resulting dose distributions were added. The quality of both the static plans and the composite plans were compared among different open segment weights. Results: Five cases with varying breast sizes were examined. For the static plans, we found that uniform dose distributions could be generated with relative weights of the open segments in the range of 45–85%. Unacceptable hot spots were produced when the weights of the open segments were larger than 85%. For composite plans simulating breathing motion, the most uniform dose distribution happens when the open segment weights were in the range of 75–85%, below which the dose uniformity degrades. We observed that in the composite plans, for each 1% decrease in the open segment weighting, the volume covered by the 98% dose decreased by approximately 0.06%, independent of breast size. Conclusion: DAO provides a robust and efficient technique for breast IMRT planning. The proper open segment weight was found to be between 75% and 85%, and is not significantly dependent of breast size and laterality. Within this range, high-quality IMRT plans were produced for each case.

Treatment planning with protons for pediatric retinoblastoma, medulloblastoma, and pelvic sarcoma: How do protons compare with other conformal techniques?

To calculate treatment plans and compare the dose distributions and dose-volume histograms (DVHs) for photon three-dimensional conformal radiation therapy (3D-CRT), electron therapy, intensity-modulated radiation therapy (IMRT), and standard (nonintensity modulated) proton therapy in three pediatric disease sites. The tumor volumes from 8 patients (3 retinoblastomas, 2 medulloblastomas, and 3 pelvic sarcomas) were studied retrospectively to compare DVHs from proton therapy with 3D-CRT, electron therapy, and IMRT. In retinoblastoma, several planning techniques were analyzed: A single electron appositional beam was compared with a single 3D-CRT lateral beam, a 3D-CRT anterior beam paired with a lateral beam, IMRT, and protons. In medulloblastoma, three posterior fossa irradiation techniques were analyzed: 3D-CRT, IMRT, and protons. Craniospinal irradiation (which consisted of composite plans of both the posterior fossa and craniospinal components) was also evaluated, primarily comparing spinal irradiation using 3D-CRT electrons, 3D-CRT photons, and protons. Lastly, in pelvic sarcoma, 3D-CRT, IMRT, and proton plans were assessed. In retinoblastoma, protons resulted in the best target coverage combined with the most orbital bone sparing (10% was the mean orbital bone volume irradiated at > or =5 Gy for protons vs. 25% for 3D-CRT electrons, 69% for IMRT, 41% for a single 3D lateral beam, 51% for a 3D anterolateral beam with a lens block, and 65% for a 3D anterolateral beam without a lens block). A single appositional electron field was the next best technique followed by other planning approaches. In medulloblastoma, for posterior fossa and craniospinal irradiation, protons resulted in the least dose to the cochlea (for only posterior fossa irradiation at > or =20 Gy, 34% was the mean cochlear volume irradiated for protons, 87% for IMRT, 89% for 3D-CRT) and hypothalamus-pituitary axis (for only posterior fossa irradiation at > or =10 Gy, 21% was the mean hypothalamus-pituitary volume irradiated for protons, 81% for IMRT, 91% for 3D-CRT); additional dose reductions to the optic chiasm, eyes, vertebrae, mandible, thyroid, lung, kidneys, heart, and liver were seen. Intensity-modulated radiotherapy appeared to be the second best technique for posterior fossa irradiation. For spinal irradiation 3D-CRT electrons were better than 3D-CRT photons in sparing dose to the thyroid, heart, lung, kidney, and liver. With pelvic sarcoma, protons were superior in eliminating any dose to the ovaries (0% of mean ovarian volume was irradiated at > or =2 Gy with protons) and to some extent, the pelvic bones and vertebrae. Intensity-modulated radiotherapy did show more bladder dose reduction than the other techniques in pelvic sarcoma irradiation. In the diseases studied, using various techniques of 3D-CRT, electrons, IMRT, and protons, protons are most optimal in treating retinoblastomas, medulloblastomas (posterior fossa and craniospinal), and pelvic sarcomas. Protons delivered superior target dose coverage and sparing of normal structures. As dose-volume parameters are expected to correlate with acute and late toxicity, proton therapy should receive serious consideration as the preferred technique for the treatment of pediatric tumors.

A methodology for verification of radiotherapy dose calculation

Object. A methodology for dosimetric verification of radiation therapy plans was developed and implemented. Dosimetric accuracy of clinically active intensity-modulated radiotherapy (IMRT) and intensity-modulated radiosurgery (IMRS) programs was assessed using this methodology. Methods. The methodology included several dosimetric tasks that were performed to assess the dosimetric accuracy of a treatment plan. Absolute dosimetry of the composite plan was performed using an ionization chamber. Film dosimetry was performed for each individual field and for the multifield composite plan. Calculated dose distributions and film measurements were compared using software developed for the specific tasks. Two-dimensional maps of gamma index, dose difference, and distance-to-agreement were calculated and displayed. To date, good agreement between measurements and calculations has been observed in 160 clinical IMRT and IMRS plans. The largest observed absolute dose disagreement was −4.79%. The mean absolute dose difference was 0.26%, with a standard deviation of 1.75%. The authors specify a 3% dose difference and 3-mm distance as the scaling acceptability criteria for the gamma index calculations of the film measurement analysis. The planning and delivery system in clinical use has proven consistently to satisfy these criteria. Conclusions. The dosimetric verification methods and the software tools developed were both quantitative and clinically practical. The measurements and the analysis demonstrated that the IMRT and IMRS planning and delivery system in use was sufficiently accurate for highly conformal treatments.

A methodology for verification of radiotherapy dose calculation

Object. A methodology for dosimetric verification of radiation therapy plans was developed and implemented. Dosimetric accuracy of clinically active intensity-modulated radiotherapy (IMRT) and intensity-modulated radiosurgery (IMRS) programs was assessed using this methodology. Methods. The methodology included several dosimetric tasks that were performed to assess the dosimetric accuracy of a treatment plan. Absolute dosimetry of the composite plan was performed using an ionization chamber. Film dosimetry was performed for each individual field and for the multifield composite plan. Calculated dose distributions and film measurements were compared using software developed for the specific tasks. Two-dimensional maps of gamma index, dose difference, and distance-to-agreement were calculated and displayed. To date, good agreement between measurements and calculations has been observed in 160 clinical IMRT and IMRS plans. The largest observed absolute dose disagreement was −4.79%. The mean absolute dose difference was 0.26%, with a standard deviation of 1.75%. The authors specify a 3% dose difference and 3-mm distance as the scaling acceptability criteria for the gamma index calculations of the film measurement analysis. The planning and delivery system in clinical use has proven consistently to satisfy these criteria. Conclusions. The dosimetric verification methods and the software tools developed were both quantitative and clinically practical. The measurements and the analysis demonstrated that the IMRT and IMRS planning and delivery system in use was sufficiently accurate for highly conformal treatments.

Use of surface response methodology for the optimization of the concentration of the sweet orange essential oil of Algeria by wiped film evaporator

The evaluation of the optimum conditions for concentration of the sweet orange essential oil by wiped film evaporator required a planning of experiments. The factors of the selected centered composite plan are the rate of feed, the temperature of the heated fluid and the stirring velocity. The quadratic model obtained required complementary work by simplex method to determine the optimum. The analysis by gas chromatography of the samples revealed a 18.2 times concentrated oxygenated compound in the residue.

Hierarchical combinatorial planning of medical treatment

The paper addresses a problem of constructing a composite plan for a medical treatment on the basis of hierarchical morphological approach, multicriteria ranking, and morphological clique problem. The approach consists of the following phases: (a) hierarchical description of the medical plan; (b) generation of local alternative actions; (c) multicriteria selection of the local actions; and (d) composition of the best local actions into the global composite medical plan. An illustrative numerical example for children asthma describes the problem and solving processes.

Patient specific quality assurance for the delivery of intensity modulated radiotherapy

A patient specific quality assurance program has been developed to facilitate the clinical implementation of intensity modulated radiotherapy (IMRT) delivered using a micro-multileaf collimator. The methodology includes several dosimetric tasks that are performed prior to the treatment of each patient. Film dosimetry is performed for each individual field and for the multifield composite plan. Individual field measurements are performed at a depth of 5 cm in a water equivalent slab phantom; export of dose calculations from the treatment planning system is similarly specified. For the composite distribution, parameters from the patient plan are applied to an IMRT phantom, and film is exposed in an axial orientation. Distributions are compared with the aid of software developed for the specific tasks. The measured and calculated dose distributions can be superimposed and positioned graphically using move, rotate, and mirror tools, as well as by specifying isocenter coordinates and using fiducial marks. Horizontal and vertical profiles are available for analysis. Dose difference, distance-to-agreement, and γ index, the minimum scaled multidimensional distance between a measurement and a calculation point determined in combined dose and physical distance space, are calculated along a specified isodose line and displayed. γ provides an excellent measure of disagreement between measurement and calculation for complex intensity distributions. We specify 3% dose difference and 3 mm distance as our scaling acceptability criteria. Absolute dosimetry for each composite plan is performed using an ionization chamber. To date, excellent agreement between measurements and calculations has been observed. © 2003 American College of Medical Physics. PACS number(s): 87.53.–j, 87.66.–a

Acceleration of dose calculations for intensity-modulated radiotherapy.

The requirements and trade-offs between accuracy and speed for radiotherapy dose computations have been discussed for decades. Inverse planning used for intensity-modulated radiotherapy (IMRT) optimization imposes additional demands on dose calculation since it is an iterative process in which dose calculations might be repeated many (10's to 1000's) of times. This work discusses the accuracy and speed issues as related to IMRT dose calculations. A hybrid dose calculation method which accelerates the optimization process is proposed and applied in which a fast-pencil beam (PB) model is used for initial optimization iterations, followed by superposition/convolution (SC) calculations. Optimization dose results are compared for pure PB optimization, pure SC optimization, and PB optimization followed by SC optimization. Plans were evaluated in terms of isodose coverage, dose-volume histograms, and total dose calculation time for five head and neck cases with diverse locations, sizes, and shapes for tumors and critical structures. Patient plans were designed for nine equispaced beams. For one patient, an additional five-beam configuration was tested. We found that gross features of intensity distributions resulting from all schemes were similar, however there were differences in the fine detail. Differences were small between composite dose distributions optimized with PB and SC methods, yet differences in individual beam dose distributions were quite significant. When the SC method was used to compute dose following optimization with PB method, dose differences were reduced significantly both for composite plans and for individual beams. Substantial overall timesavings were observed, allowing IMRT dose planning to become a more interactive activity.

A Class of Three-Level Experimental Designs for Response Surface Modeling

Most empirically constructed response surface models are based on polynomials containing terms of order 2 or less. Experimental designs involving three equally spaced levels of each factor are popular choices for collecting data to tit such models. Because complete three-level factorial plans require more experimental runs than can usually be accommodated in practice, smaller designs are typically used. The families of three-level designs most often used in this context are the Box–Behnken plans and various forms of the central composite designs. This article introduces a different method for constructing composite designs, motivated by notions of sequential experimentation and the minimax and maximin distance criteria used in spatial modeling. Operational and performance characteristics of some designs constructed by the method are compared to those of competing Box–Behnken and central composite plans.

Composite sampling enhances the confidence of soil microarthropod abundance and species richness estimates

The quantification of abundance and species richness of soil microarthropods is most often severely hindered by extraordinary data variability, highly skewed frequency distributions, many extreme and zero counts, and small sample sizes. We developed a composite sampling technique to enhance the confidence of abundance and species richness estimates. Many soil cores (n ≥ 100) are sampled, animals extracted, the extracts pooled, mixed, and subsamples (aliquots) taken. Compared to the standard (separate sampling units), no microarthropods were lost or mechanically damaged during the compositing procedure. The confidence of abundance estimates was substantially greater in the composite than in the standard, although not for taxa of low abundance (< ≈ 10 3 ind.m −2 ). Moreover, compositing was the superior technique in estimating species richness. The number of sampling units needed to recover a certain number of species with the composite was 70% of the standard method. We conclude that composite sampling is a promising alternative to the standard technique and may help to increase the generally low confidence of microarthropod field data. Finally, potential limitations of composite plans are discussed: a great number of field cores from an unbiased sampling plan have to be composited; comparisons between composites of unequal size should be avoided; all information on the variation among field cores is lost by compositing; parallel measurements of fauna and other variables in the same cores are not possible.

Spinal cord dose from standard head and neck irradiation: implications for three-dimensional treatment planning

Background and purpose: Treatment with traditional standard field arrangements for patients with head and neck cancer rarely causes myelopathy. Often, initial treatment fields are reduced to avoid the spinal cord after 45 Gy has been delivered and the cord dose that is delivered by `off-cord' fields is not calculated. To determine a conservative limit to set for the cord dose for conformally-planned field arrangements, the total spinal cord dose delivered with standard opposed lateral fields was evaluated. Materials and methods: Two types of treatment plans were evaluated for 10 patients enrolled on a parotid-sparing protocol for bilateral head and neck treatment, i.e. (1) standard opposed lateral fields, including large initial fields treating nodal volumes to 45 Gy, off-cord fields for an additional 25 Gy and electron nodal boost fields for an additional 5 Gy and (2) complex 3-D treatment planned field geometries with conformal dose distributions (actual treatment fields). Treatment fields for the protocol conformal plans were arranged so that the maximum cord dose was not to exceed 50 Gy. Dose–volume histograms for both types of planned treatments were analyzed. The maximum and minimum dose to the 1 cm 3 cord volume receiving the highest dose were reported. Results: The maximum dose to the cord from the standard composite plans was on average 52 Gy, with a range of 48.9–55.9 Gy. This consisted of an additional 6.3 Gy (average) from the scatter and block transmission dose from the off-cord lateral fields above the prescribed 45 Gy. For the conformal plans, the maximum dose was on average 49.4 Gy (which is protocol criteria). Discussion and conclusion: The maximum spinal cord dose of 50 Gy set as a dose constraint for 3-D treatment planning for conformal plans is a comparable dose to that given in standard opposed lateral head and neck treatments and has been determined to be a conservative spinal cord dose limit, which we have applied in our clinic.

Comparative analysis of optimal endoglucanase production by Trichoderma reesei and intergeneric fusants of Trichoderma reesei Saccharomyces cerevisiae

Intergeneric fusants of Trichoderma reesei QM 9414/Saccharomyces cerevisiae NCIM 3288 developed in the authors' laboratory can convert cellulosic materials directly to ethanol in a single step process. The production of endoglucanase in this case is a key factor. The production profile of this enzyme by the intergeneric fusants is different from Trichoderma reesei QM 9414 (WT). The production of endoglucanase was studied seperately by Trichoderma reesei (WT) using optimal production medium which was designed as per the combined screening approach of Plackett-Burman followed by a central composite experimental plan and the intergeneric fusants using optimal production medium obtained by Box-Behnken optimization procedure. Dried grass was used as the cellulosic substance whose concentration was kept constant during the statistical optimization procedure. The concentration of dried grass was later varied keeping the other optimized medium constituents constant to find the final optimum medium composition for endoglucanase production.

Conformal radiation treatment of prostate cancer using inversely-planned intensity-modulated photon beams produced with dynamic multileaf collimation

To implement radiotherapy with intensity-modulated beams, based on the inverse method of treatment design and using a multileaf collimation system operating in the dynamic mode. An algorithm, based on the inverse technique, has been integrated into the radiotherapy treatment-planning computer system in our Center. This method of computer-assisted treatment design was used to derive intensity-modulated beams to optimize the boost portion of the treatment plan for a patient with a T1c cancer of the prostate. A dose of 72 Gy (in 40 fractions) was given with a six-field plan, and an additional 9 Gy (in five fractions) with six intensity-modulated beams. The intensity-modulated fields were delivered using dynamic multileaf collimation, that is, individual leaves were in motion during radiation delivery, with the treatment machine operating in the clinical mode. Exhaustive quality assurance measurement and monitoring were carried out to ensure safe and accurate implementation. Dose distribution and dose-volume histogram of the "inverse method" boost plan and of the composite (72 Gy primary + 9 Gy boost) plan were judged clinically acceptable. Compared to a manually designed boost plan, the inverse treatment design gave improved conformality and increased dose homogeneity in the planning target volume. Film and ion chamber dosimetry, performed prior to the first treatment, indicated that each of the six intensity-modulated fields was accurately produced. Thermoluminescent dosimeter (TLD) measurements performed on the patient confirmed that the intended dose was delivered in the treatment. In addition, computer-aided treatment-monitoring programs assured that the multileaf collimator (MLC) position file was executed to the specified precision. In terms of the overall radiation treatment process, there will likely be labor savings in the planning and the treatment phases. We have placed into clinical use an integrated system of conformal radiation treatment that incorporated the inverse method of treatment design and the use of dynamic multileaf collimation to deliver intensity-modulated beams. The system can provide better treatment design, which can be implemented reliably and safely. We are hopeful that improved treatment efficacy will result.

Crystallization mechanisms of calcium phosphate cement for biological uses

Self-setting calcium phosphate cement for dental or surgical applications can be prepared by the addition of a liquid to a mixture of acidic and basic calcium phosphate. After hardening, the final compound becomes hydroxyapatite. Using an orthogonal central composite plan, the main factors which control the setting and the final hardness of the cement were defined and models are proposed. The mechanisms of crystallization, the role of free and linked water, and the nature of the final and intermediate compounds are described.

Massively parallel support for case-based planning

The Caper case-based planner uses the massive parallelism of the Connection Machine to quickly retrieve cases and plans from a large, unindexed memory. The system can retrieve cases and plans based on any feature of the target problem, including abstractions of target features. By controlling which features are part of the retrieval probe and their level of abstraction, a wide range of queries can be issued. The more specific the query, the closer the retrieved cases are to the current problem. Unlike serial planners, Caper can afford to retrieve several plans to achieve different parts of the target problem, and then merge them into a composite plan that solves most of the target goals with less adaptation. We are testing Caper's case-retrieval components in two domains: car assembly and transportation logistics. >

The objective evaluation of alternative treatment plans: II. Score functions

A series of six patients with adenocarcinoma of the prostate, Stages A 2, B 1, or B 2, were planned for treatment using a four-field box technique at 25 MV. Plans were prepared by three techniques: composite, mid-plane, and conformal. The dose distributions at the central plane and at two planes offset by ±2 cm were evaluated by means of score functions which quantify the magnitude of regret for target dose gradient, target over- and under-dose, non-target tissue overdose, and for overdose to the rectum, bladder, and femoral heads. The score functions are normalized to give values in the range from 10 (ideal) to zero (limit of acceptability), with negative values indicating unacceptable deviations from the prescribed dose limits. The scores for off axis conformal plans were found to be essentially the same as for mid-plane plans on the central plane. However, mid-plane planning was shown to be totally inadequate for off-axis planes, where the average target gradient and underdose scores were reduced by 10 units. Composite planning resulted in adequate target coverage on all planes, but at the expense of unacceptable overdose to non-target tissue. The effect of reducing the posterior beam weight to half that of the other three beams was to reduce the target gradient score by 1.6 ± 0.5 units and to increase the rectal score by 0.9 ± 0.3 units.

Power system reliability planning practices in North America

The authors present selected results from a recently completed research project for the Electric Power Research Institute. One component of the project was intended to develop and test methodologies for gathering data on how utility customers value service reliability, as measured by either the cost of outages or the willingness to pay for reliability. Another component of this project involved a survey of current and emerging reliability planning practices in the North American utility industry, especially regarding interest in value-based reliability planning. The results of the survey, including the survey design and methodology, are given. The authors briefly discuss potential applications of interruption costs in generation and composite system reliability planning. >

Study of retention of vitamin B6 in non-traditionally canned foods on using an experimental plan method (short communication).

AbstractIn this work the influence of the non‐traditional canning method, based on a decreased thermosterilization intensity (15–70 min/121°C) combined with ionizing radiation (0,5–9.5 kGy), upon retention of vitamin B6 contained in model samples of pork in its own juice, being stored for a short time (41 days) at a temperature of 20 °C ± 2 °C is studied. In the experiment, a uniform, central, composite plan of the experiment ROUCE‐KOP which belongs to the group of surface‐response methods (RSM — Response Surface Methodology) [1] was employed.

Sampling Plans in Insect Pest Management Based on Wald's Sequential Probability Ratio Test

Equations for the stopping boundaries, and operating characteristic (OC) and average sample number (ASN) functions, of Wald's sequential probability ratio test (SPRT) are presented for the binomial, negative binomial, normal, and Poisson distributions. The effects of errors in Wald's OC and ASN equations due to overshooting the decision boundaries, and errors due to truncating, postponing decisions beyond the first stage, and taking more than one observation at each stage of the decision process are discussed. Monte Carlo procedures are used to show that Wald's equations overestimate the true error probabilities and underestimate the true ASN for a two-decision sampling plan based on the negative binomial distribution. A Monte Carlo procedure for modifying the decision boundaries to yield actual OC and ASN functions approximately equal to the desired ones is presented. Monte Carlo procedures are also used to examine the errors in Wald's OC and ASN functions when used to describe the OC and ASN functions of a composite three-decision sampling plan based on two single SPRT's using the negative binomial distribution. Wald's equations, in general, overestimate the true error probabilities and underestimate the true ASN even more for the three-decision case compared with the two-decision case. Recommendations are given as to the seriousness of the errors inherent in Wald's equations in relation to all of the other errors that are associated with the sampling process, and the choice between Wald's and Monte Carlo OC and ASN functions to describe the properties of a sampling plan.

Multistage Multiattribute Acceptance Sampling in Serial Production Systems

Abstract A multistage Bayesian acceptance sampling model for a serial production process, which incorporates multiple-type defects that may occur in each stage of the process is proposed. A subproblem heuristic to solve for near optimal multistage multiattribute acceptance sampling plans is also developed. The performance and sampling characteristics of the multistage model and the solution heuristic are illustrated and compared to a set of independent single stage plans and a final stage composite plan, showing considerable differences.