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At least 19 recordsLinked to original sources
PubMed1991

Role of inhomogeneity corrections in three-dimensional photon treatment planning. Photon Treatment Planning Collaborative Working Group.

The role of inhomogeneity corrections in three-dimensional (3-D) radiation treatment planning (RTP) was one of the issues addressed in a National Cancer Institute sponsored research contract. In eight selected disease sites, plans calculated with and without inhomogeneity corrections were compared. The one-dimensional Effective Path Length (EPL) method was used by all four participating institutions as the standard inhomogeneity correction method. However, the dose calculation algorithms were different, particularly in the treatment of blocking effects near the edge of the field. Evaluation tools such as dose-volume histogram, dose statistics, 3-D display of dose distributions and others were used in the comparison. Dose distributions were significantly altered by inhomogeneity corrections in the treatment plans for the lung tumors, and, to a lesser degree, for the breast and Hodgkin's diseases. Dose distributions for tumors of the head and neck region and in the abdomen were not significantly affected. The results should be regarded as particular to the EPL calculations. A treatment plan for the tumor of the larynx was calculated using both the EPL method and a 3-D scatter ray-trace Delta Volume method. For that particular site, inhomogeneity corrections were less important than correctly accounting for the effects of blockings on the scatter dose. Perturbations of electron transport were not accounted for by any of the methods used and not reflected in those sites where the effects were expected to be important. Fully quantitative evaluation of the role of inhomogeneity corrections in treatment planning requires an as yet unavailable all-encompassing accurate method of dose calculation.

Humans↗
PubMed1991

Three-dimensional dose calculations for radiation treatment planning. Photon Treatment Planning Collaborative Working Group.

We discuss geometric and physical aspects of dose calculational methodologies as developed and implemented in three-dimensional treatment planning systems at four institutions participating in an NCI Contract for the Evaluation of High Energy Photon External Beam Treatment Planning. The geometric aspects include such issues as unconventional beam orientations, 3-D patient geometry, image data requirements, and pathlength calculation in 3-D. The physical aspects deal primarily with the formalisms employed in dose calculations. Exact calculation of dose is impractical due to the complex manner in which radiation interacts with matter. Approximations have to be made which limit the accuracy of dose calculations. For a number of situations of clinical interest, especially for regions where electronic equilibrium does not exist, the accuracy of conventional methods of dose calculations is suspect. New, more accurate methods have been proposed but have not been implemented to date. Three-dimensional dose calculations are very time consuming with currently available general purpose computers. With the development of the next generation of computers and other ancillary hardware and with continuously evolving algorithms, accurate and fast three-dimensional dose calculations should become affordable for the radiotherapy community in the near future.

Humans↗
PubMed1991

State-of-the-art of external photon beam radiation treatment planning. Photon Treatment Planning Collaborative Working Group.

A virtual revolution in computer capability has occurred in the last few years, largely based on rapidly decreasing costs and increasing reliability of digital memory and mass-storage capability. These developments have now made it possible to consider the application of both computer and display technologies to a much broader range of problems in radiation therapy, including planning of treatment, dose computation, and treatment verification. Several methods of three-dimensional dose computations in heterogeneous media capable of 3% accuracy are likely to be available, but significant work still remains, particularly for high energy x-rays where electron transport, and possibly pair production, need to be considered. Innovative display and planning techniques, as well as plan evaluation schemes, are emerging and show great promise for the future. No doubt these advances will lead to substantially improved treatment planning systems in the next few years. However, it must be emphasized that for many of these applications a tremendous software and hardware development effort is required.

Computer Graphics↗
PubMed1997

Decision theoretic steering and genetic algorithm optimization: application to stereotactic radiosurgery treatment planning.

Treatment planning for stereotactic radiosurgery and fractionated radiotherapy is currently a labor intensive, operator-dependent process. Many degrees of freedom exist to make rigorous optimization intractable except by computationally intelligent techniques. The quality of a given plan is determined by an aggregate of clinical objectives, most of which are subject to competing tradeoffs. In this work, we present an autonomous scheme that couples decision theoretic guidance with a genetic algorithm for optimization. Ordinal ranking among a population of viable treatment plans is based on a generalized distance metric, which promotes a decreasing hyperfrontier of the efficient solution set. The solution set is driven toward efficiency by the genetic algorithm, which uses the tournament selection mechanism based on the ordinal ranking. Goals and satisficing conditions can be defined to signal the ultimate and the minimum achievement levels in a given objective. A conventionally challenging case in radiosurgery was used to demonstrate the practical utility and the problem-solving power of the decision theoretic genetic algorithm. Treatment plans with one isocenter and four isocenters were derived under the autonomous scheme and compared to the actual treatment plan manually optimized by the expert planner. Quality assessment based on dose-volume histograms and normal tissue complication probabilities suggested that computational optimization could be driven to offer varying degrees of dosimetric improvement over a human-guided optimization effort. Furthermore, it was possible to achieve a high degree of isodose conformity to the target volume in computational optimization by increasing the degree of freedom in the treatment parameters. The time taken to derive an efficient planning solution was comparable and usually shorter than in the manual planning process, and can be scaled down almost linearly with the number of processors. Overall, the autonomous genetic algorithm scheme was found to be powerful and versatile as a computationally intelligent counterpart to human-guided strategies in treatment optimization for stereotactic radiosurgery and radiotherapy.

Algorithms↗
PubMed1981

Treatment objectives and treatment planning.

Treatment planning is perhaps the most challenging aspect of orthodontic treatment. Each patient is an individual and must be treated as such. A conscientious clinician must avoid casting every patient into stereotyped treatment. This article has attempted to present one way to aid and guide the clinician in the methodical thought process necessary in making treatment decisions. An accurate diagnosis and a rational treatment plan are the essential criteria for the achievement of the three major goals of treatment: esthetics, function, and stability.

Dental Arch↗
PubMed2001

Modelling the dosimetric consequences of organ motion at CT imaging on radiotherapy treatment planning.

Treatment planning algorithms usually assume that the correct or at least the mean organ position is derived from the CT imaging procedure, and that this position is reproduced throughout the treatment. In reality a mobile organ is unlikely to be in its exact mean position at the time of imaging, causing the treatment to be planned with an organ off-set from its assumed mean position. This introduces an extra 'CT uncertainty' into the treatment. A Monte Carlo (MC) model is used to simulate organ translations at imaging and evaluate the effect of this uncertainty (above the treatment delivery uncertainties) on the dose distribution. An underdose by 4 Gy in a 60 Gy treatment is calculated in the penumbral region of a single-field dose distribution as a result of the CT uncertainty. The effect is reduced to less then 0.5 Gy when the organ position at planning is derived as the average from multiple pretreatment CT scans. It is shown that a convolution method can be applied to predict the effect of CT uncertainty on the dose distribution for a patient population. Additionally, a variation kernel for a convolution method is derived that incorporates uncertainty at both imaging and treatment.

Algorithms↗
PubMed2003

Nontumor integral dose variation in conventional radiotherapy treatment planning.

Treatment planning involves selecting delivery parameters that distribute the dose to nontumor tissue in such a way as to minimize the risk of complications. This work studied the relationship between nontumor integral dose (NTID), the fractional energy deposited in nontumor tissue, and a variety of delivery parameters for three clinical cases: nasopharynx, pancreas, and prostate. Integral dose for an organ of uniform density is simply the product of the organ density, volume, and mean dose. For each case, conventional plans were generated with 2, 4, 8, 12 and 36 equally spaced beams. All plans were normalized to the same tumor mean dose (< 3%), which is equivalent to the same tumor integral dose. For the pancreas and prostate cases, the patients were assumed to be uniform density. For the nasopharynx case, bones and air cavities were outlined and each assigned a uniform non-unit density. With four or more beams and clinical margin values, the variation in NTID was < 1% as a function of number of beams. With eight or more beams, the variation was < 0.2%. Reducing the beam margin decreased the NTID because less normal tissue was irradiated. However, the effect of the number of beams on NTID was independent of margin size. Higher energy beams reduced the NTID, as expected, and the effect was independent of the number of beams. With four or more beams, variation in beam direction changed NTID by less than 1.5%. Changing beam weights changed NTID by < 2% for plans with four to eight beams. For the body sites studied, the majority of energy was deposited in nontumor tissue, ranging from 72% in the nasopharynx case to 97% for the prostate case. The NTID decreased with increasing tumor size for similar anatomic sizes and increased with increasing size of anatomical region for similar tumor size. Finally, the effect of heterogeneity-corrected doses on the NTID was found to be < 3% for the nasopharynx case. These data support the hypothesis that the NTID is approximately independent of beam orientation or relative weighting when many beams are used. Optimization, therefore, can only find the best distribution of dose; it cannot reduce the energy imparted. NTID may be useful in establishing an upper bound on the quality of plan that can be achieved by optimization.

Dose-Response Relationship, Radiation↗
PubMed1985

The imaging revolution and radiation oncology: use of CT, ultrasound, and NMR for localization, treatment planning and treatment delivery.

The explosion of new imaging technologies such as X ray computed tomography (CT), ultrasound (US), positron emission tomography (PET), and nuclear magnetic resonance imaging (NMR) has forced a major change in radiation therapy treatment planning philosophy and procedures. Modern computer technology has been wedded to these new imaging modalities, making possible sophisticated radiation therapy treatment planning using both the detailed anatomical and density information that is made available by CT and the other imaging modalities. This has forced a revolution in the way treatments are planned, with the result that actual beam configurations are typically both more complex and more carefully tailored to the desired target volume. This increase in precision and accuracy will presumably improve the results of radiation therapy.

Breast Neoplasms↗
PubMed1999

Surgical versus orthodontic correction for Class II patients: age and severity in treatment planning and treatment outcome.

Treatment options for Class II malocclusion include orthognathic surgery. Treatment choices are particularly difficult for young patients because of the uncertainty regarding future growth. Surgical treatment has generally been considered necessary for older patients with more severe Class II problems. The treatment records of more than 500 patients with Class II malocclusion were reviewed. Patients were grouped according to their initial treatment plan (surgery or orthodontics) and treatment outcome (overjet [OJ] reduced to < 4 mm or not). Discriminant function analyses using data from the patient's pretreatment cephalogram were used to determine whether age, in combination with malocclusion severity, could predict the choice of treatment, and whether a simple set of pretreatment variables could predict the success or failure of OJ reduction. The derived equations were tested in a similar group of growing Class II children. Although the data showed clinicians use patient's age in determining treatment choice, age did not seem to be associated with treatment outcome. The majority of the variability that determined the success or failure of OJ reduction was not explained by patient's age or malocclusion severity. These findings suggest other factors, including psychosocial variables, need to be explored if we are to gain a better understanding of why treatments succeed or fail.

Adolescent↗
PubMed1991

Evaluation of high energy photon external beam treatment planning: project summary. Photon Treatment Planning Collaborative Working Group.

A three-year project for the "Evaluation of High Energy Photon External Beam Treatment Planning," sponsored by the National Cancer Institute, is summarized. The participants in this project were determined on a competitive basis and included staff from four institutions: Massachusetts General Hospital; Memorial Sloan-Kettering Cancer Center; the University of Pennsylvania; and Mallinckrodt Institute of Radiation. This project built on the developments in three-dimensional anatomical and dose distribution reconstruction at these institutions and on the clinical guidance at these centers for quantitative evaluation of treatment plans. Protocols for acceptance of patients with lesions at eight different sites were developed and utilized. The technical methodology for interchange of treatment planning tapes, specifications for computerized tomography sections and their reconstruction, and the employment of dose-volume histograms of target regions and specified normal tissues and organs were all developed. Data were accumulated for tumor control probabilities (TCP) and for normal tissue complication probabilities (NTCP) for use in treatment plan design and evaluation. Several treatment parameters were studied as influenced by the availability of three-dimensional treatment planning and specific conclusions were reached.

Humans↗
PubMed2005

Immediate implant placement: diagnosis, treatment planning and treatment steps/or successful outcomes.

Diagnosis and treatment planning are key factors in achieving successful outcomes after placing and restoring implants placed immediately after tooth extraction. The efficacy of immediate implant placement has been established and shown to be predictable if reasonable guidelines are followed. Some or all of the following suggestions, depending on individual circumstances should be considered when evaluating a patient for dental implants: thorough medical and dental histories, clinical photographs, study casts, periapical and panogram radiographs, as well as a linear tomography or computerized tomography of the proposed implant sites. Reasons for tooth extraction include, but are not limited to, insufficient crown to root ratios, remaining root length, periodontal attachment levels, periodontal health of teeth adjacent to the proposed implant sites, unrestorable caries, root fractures with large endodontic posts, root resorption, teeth with deep furcation invasions being considered as abutments for fixed partial dentures, and questionable teeth in need of endodontic retreatment. Teeth requiring root amputations, hemisections or advanced periodontal procedures may have a questionable prognosis, and patients should be given the implant option before these procedures are implemented. Similarly, nonvital teeth, fractured at the gingival margin with roots shorter than 13 mm should be considered for the implant option. This review will describe the steps for immediate implant placement at the time of extraction as well as the "gap" and socket preservation.

Animals↗
PubMed1994

Consideration of time-dose-patterns in 3D treatment planning. An approach towards 4D treatment planning.

PURPOSE: The rendering of the 3D dose distribution together with anatomical information and the volumes of interest (VoI) is essential to get a visual impression of the treatment plan and to find modifications for the optimization of the dose distribution. The integration of biological effects into the 3D treatment planning is of interest for the assessment of different time-dose patterns. MATERIALS AND METHODS: One way of taking into account biological data is to relate the physical dose in critical structures to the corresponding tolerance dose. For that purpose the applied time-dose pattern has to be converted into the standard fractionation scheme being the basis of the tolerance dose. Generally any model can be used for these calculations. Here a modified incomplete repair model is used to calculate the relative biological dose distribution (RBD). The visualization of these biologically isoeffective dose distributions can be performed in the same manner as the physical dose so that the physical and biological dose distributions can by displayed side by side. As this is equivalent to introducing the time as a fourth dimension into 3D treatment planning this is called 4D treatment planning. RESULTS: From 3D dose matrices the biologically isoeffective dose distributions are calculated for the organs at risk. The changes introduced by different time-dose patterns are displayed using the same technique as for rendering 3D treatment plans. The visualisation of the three-dimensional biological dose distributions is shown by means of a patient with an oesophagus carcinoma. The RBD related to the tolerance dose of the organs at risk is displayed for different time-dose fractionations. CONCLUSION: The RBD distribution on a 3D treatment plan can be displayed in the same mode as the physical dose distribution. This offers additionally valuable information in a 3D treatment planning process about the dose to critical organs and the influence of different time-dose patterns.

Color↗
PubMed2006

Validation of a model to evaluate the role of radiographs in the diagnosis and treatment planning of periodontal diseases.

OBJECTIVES: The purposes of this study were (i) to see if an indirect method of design (paper patients) could be developed for study of change affected by radiographs on diagnostic outcome and planned treatment of periodontal patients and (ii) to investigate the effect of the nature of clinical examination on the value of radiographs in reaching a periodontal diagnosis. Paper cases could allow the design of examiner blind studies where repeatability could be assessed. METHODS: 201 patients were assigned to one of four groups and clinically assessed according to group specifications. Radiographs were taken. Periodontal diagnoses and treatment plans were drawn up for each patient with and without radiographic information (real patient). Simulated paper transcriptions were made for each subject and diagnoses and treatment plans were again drawn up (paper patient). RESULTS: For many diagnoses and treatment options assessments were similar for real and paper patients. There was substantial agreement between periodontal diagnoses reached from real and paper assessments (kappa=0.68). Greater differences were seen for extractions and periodontal surgery. Paper assessments better replicated real assessments when more thorough clinical examinations were undertaken. The relatively time efficient Group 2 clinical assessment appeared to perform similarly to the extensive Group 4 clinical assessment. CONCLUSIONS: The model described may be useful for simulating real patients for studies of this nature. The Group 2 assessment appeared to give sufficient clinical information for patient management and may be an appropriate choice for initial diagnosis and treatment planning of periodontal patients.

Anti-Bacterial Agents↗
PubMed1991

Significance of prone positioning in planning treatment for esophageal cancer.

The treatment of esophageal cancer is made difficult by the close proximity of the esophagus to the spinal cord and the requirement to treat the esophageal target volume to doses greater than or equal to 60 Gy while limiting the spinal cord dose to less than or equal to 46 Gy. By placing the patient in the prone position, the esophagus can be displaced away from the spinal cord. We explored the results of this commonly used technique on 16 patients who have undergone simulation in both supine and prone positions. Both AP and lateral orthogonal radiographs were obtained in both positions. The distance between contrast material in the esophagus and spinal cord was noted in at least four transverse planes through the thoracic esophagus on each of the 16 patients. These four transverse planes were located at 3 cm above the carina, at the carina, 3 cm below the carina and 6 cm below the carina. The mean displacement (+/- 1 SD) of the esophagus away from the spinal cord when the patient was in the prone position compared to supine at each of these levels was 1.3 (+/- 0.8) cm, 1.8 (+/- 0.9) cm, 1.8 (+/- 1.0) cm, and 1.9 (+/- 1.1) cm. The range of displacement for all 64 displacement determinations was 0 to 4.2 cm with a mean of 1.7 cm. To evaluate further the consequences of prone positioning on treatment planning and doses received to target volumes and critical structures, we performed 3-dimensional treatment planning with a patient in both prone and supine positions. The requirements were to achieve a tumor volume dose of 60 Gy while keeping the spinal cord dose below 46 Gy. Two types of conventional treatment plans were examined in prone and supine positions. A 6-field plan consisted of delivery of 40 Gy through a large 3-field beam arrangement followed by delivery of 20 Gy through a similar 3-field cone down. An 8-field plan involved the delivery of 30 Gy through AP/PA beams followed by a 3-field beam arrangement to 40 Gy and a subsequent 3-field cone-down for the final 20 Gy. Comparison of dose volume histograms revealed that the 6-field plan spared relatively more heart whereas the 8-field plan spared relatively more lung. Regarding the primary consideration of coverage of target volume with avoidance of spinal cord, prone positioning was superior to supine positioning whether 6- or 8-field arrangements were used.

Esophageal Neoplasms↗
PubMed2002

Treatment planning for molecular targeted radionuclide therapy.

Molecular targeted radionuclide therapy promises to expand the usefulness of radiation to successfully treat widespread cancer. The unique properties of radioactive tags make it possible to plan treatments by predicting the radiation absorbed dose to both tumors and normal organs, using a pre-treatment test dose of radiopharmaceutical. This requires a combination of quantitative, high-resolution, radiation-detection hardware and computerized dose-estimation software, and would ideally include biological dose-response data in order to translate radiation absorbed dose into biological effects. Data derived from conventional (external beam) radiation therapy suggests that accurate assessment of the radiation absorbed dose in dose-limiting normal organs could substantially improve the observed clinical response for current agents used in a myeloablative regimen, enabling higher levels of tumor control at lower tumor-to-normal tissue therapeutic indices. Treatment planning based on current radiation detection and simulations technology is sufficient to impact on clinical response. The incorporation of new imaging methods, combined with patient-specific radiation transport simulations, promises to provide unprecedented levels of resolution and quantitative accuracy, which are likely to increase the impact of treatment planning in targeted radionuclide therapy.

Antigens, Neoplasm↗
PubMed2006

Dosimetric feasibility of cone-beam CT-based treatment planning compared to CT-based treatment planning.

PURPOSE: Cone-beam computed tomography (CBCT) images are currently used for positioning verification. However, it is yet unknown whether CBCT could be used in dose calculation for replanning in adaptive radiation therapy. This study investigates the dosimetric feasibility of CBCT-based treatment planning. METHODS AND MATERIALS: Hounsfield unit (HU) values and profiles of Catphan, homogeneous/inhomogeneous phantoms, and various tissue regions of patients in CBCT images were compared to those in CT. The dosimetric consequence of the HU variation was investigated by comparing CBCT-based treatment plans to conventional CT-based plans for both phantoms and patients. RESULTS: The maximum HU difference between CBCT and CT of Catphan was 34 HU in the Teflon. The differences in other materials were less than 10 HU. The profiles for the homogeneous phantoms in CBCT displayed reduced HU values up to 150 HU in the peripheral regions compared to those in CT. The scatter and artifacts in CBCT became severe surrounding inhomogeneous tissues with reduced HU values up to 200 HU. The MU/cGy differences were less than 1% for most phantom cases. The isodose distributions between CBCT-based and CT-based plans agreed very well. However, the discrepancy was larger when CBCT was scanned without a bowtie filter than with bowtie filter. Also, up to 3% dosimetric error was observed in the plans for the inhomogeneous phantom. In the patient studies, the discrepancies of isodose lines between CT-based and CBCT-based plans, both 3D and IMRT, were less than 2 mm. Again, larger discrepancy occurred for the lung cancer patients. CONCLUSION: This study demonstrated the feasibility of CBCT-based treatment planning. CBCT-based treatment plans were dosimetrically comparable to CT-based treatment plans. Dosimetric data in the inhomogeneous tissue regions should be carefully validated.

Brain Neoplasms↗
PubMed2000

TBI treatment planning using the ADAC pinnacle treatment planning system.

The use of total-body irradiation (TBI) for the purpose of bone marrow transplant is an established procedure at many institutions. In our institution, the TBI monitor unit (MU) calculation starts with the calibration done at the same conditions of the treatment source-axis distance (SAD) = 350 cm for the field size of 40 x 40 cm at a depth of 10 cm). The dose rate in the central axis of the beam at this distance is measured in cGy/MU. A tissue phantom ratio table obtained in the condition of treatment together with off-axis factors is used in the MU calculation for each particular patient. The treatment is done with the patient lying on his/her back and the beam is delivered using right-to-left lateral beams. Due to different thickness' of the patient, a lead compensator is built to compensate for the different parts of the body. Eighteen or 10-MV x-ray photons are used in the TBI treatment, and a 1-cm-thick lucite plate is placed near the patient to increase the dose to the surface. In vivo dosimetry using diodes is done to verify the calculations. The Rando-Phantom was computed-tomography scanned from the head to the abdomen with 1-cm-thick slices covering 70 cm of the phantom. This simulated the TBI treatment and correlated the calculations done by the ADAC treatment planning system to film measurements at the pelvis and lung levels. These results agreed within 5% of the measured dose. The use of the upper arms to reduce the dose to the lungs and optimization of dose using special compensators has been studied using the treatment planning system. Use of the multileaf collimator to compensate the dose received by the patient has been explored in this paper.

Humans↗