Uses of 3D planning in addition to creating a good treatment: ongoing studies at MGH/HCL.
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Humans↗
Biomedical subjects
M M Urie
Publications and source records attributed to M M Urie.
Comparative treatment planning: proton vs. x-ray beams against glioblastoma multiforme.
The survival of patients with glioblastoma multiforme is extremely poor, the 5-year survival rate being almost zero. The cause of failure is almost exclusively local progression of tumor, the remainder is due to complications of treatment. Although this tumor is clearly radiation resistant, there is evidence of a dose response relationship. Using a thin slice CT scan of the entire head of a patient with glioblastoma multiforme, 3-dimensional radiation treatment plans were developed for treatment to a dose of 90 cobalt-Gray-equivalent (CGE). Dose distributions using protons were compared to those using x-rays. The results showed advantages for the proton beam technique. Namely the proton plan irradiated less non-target brain than the x-ray plan; this was especially so in the decrease of coverage of deep-seated structures. The volume of non-target brain that received more than 70 CGE was 175 ml for the x-ray plan and 94 ml for the proton plan. This study indicates that for a subpopulation of patients with glioblastoma multiforme, at least 90 CGE could be delivered with proton beam techniques to the target with only small volumes of normal brain structures receiving more than 70 CGE.
Brain Neoplasms↗
3-D comparative study of proton vs. x-ray radiation therapy for rectal cancer.
To assess the usefulness of proton beams for treatment of patients with rectal cancer, we have performed comparative 3D treatment planning for proton beam and x-ray beam therapy. Three common x-ray techniques (AP-PA, 3-field, and 4-field box), a proton beam only plan, and a proton boost plan were compared. The plan which would have been treated without the aid of the 3D planning system was also simulated. Dose distributions were analyzed and dose-volume histograms computed for the target volumes and critical normal tissues. Analyses of these plans demonstrate that the proton beam techniques reduce the volume of small bowel irradiated. This may allow higher doses to be delivered to the tumor, with a probable increase in local control, or a reduction in normal tissue complications probability. All the plans developed with the 3D planning system treated significantly less bowel than the one planned without it.
Aged↗
A dose response analysis of injury to cranial nerves and/or nuclei following proton beam radiation therapy.
The low tolerance of the central nervous system (CNS) limits the radiation dose which can be delivered in the treatment of many patients with brain and head and neck tumors. Although there are many reports concerning the tolerance of the CNS, few have examined individual substructures of the brain and fewer still have had detailed dose information. This study has both. A three dimensional planning system was used to develop the combined proton beam/photon beam treatments for 27 patients with skull-base tumors. The cranial nerves and their related nuclei were delineated on the planning CT scans and the radiation dose to each was determined from three dimensional dose distributions. In the 594 CNS structures (22 structures/patient in 27 patients), there have been 17 structures (in 5 patients) with clinically manifest radiation injury, after a mean follow-up time of 74 months (range 40-110 months). From statistical analyses, dose is found to be a significant predictor of injury. Using logistic regression analysis, we find that, for each cranial nerve, at 60 Cobalt Gray Equivalent (CGE) the complication rate is 1% (0.5-3% with 95% confidence) and that the 5% complication rate occurs at 70 CGE (64-81 CGE with 95% confidence). The slope of the dose response curve (at 50%) is 3.2 (2.2-5.4 with 95% confidence). No significant relationship between dose and latency period for nerve injury was found.
Adolescent↗
The role of uncertainty analysis in treatment planning.
The role of uncertainty analysis in 3-D treatment planning systems was addressed by four institutions which contracted with NCI to evaluate high energy photon external beam treatment planning. Treatment plans were developed at eight disease sites and the effects of uncertainties assessed in a number of experiments. Uncertainties which are patient-site specific included variations in the delineation of target volumes and normal tissues and the effects of positional uncertainties due to physiological motion and setup nonreproducibility. These were found to have a potentially major impact on the doses to the target volumes and to critical normal tissues which could result in significantly altered probabilities of tumor control and normal tissue complications. Other uncertainties, such as the conversion of CT data to electron densities, heterogeneities and dose calculation algorithms' weaknesses, are related to physical processes. The latter was noted to have the greatest potential contribution to uncertainty in some sites. A third category of uncertainty related to the treatment machine, the consequences of compensator misregistration, are exclusive to the site and the treatment portal. Because conventional treatment planning systems have not incorporated uncertainty analysis, tools and techniques had to be devised for this work; further development in this area is needed. Many of the analyses could not have been done without full 3-D capabilities of the planning systems, and it can be anticipated that the availability of uncertainty analysis in these systems which allow nontraditional beam arrangements will be of great value.
Humans↗
Three-dimensional photon treatment planning for Hodgkin's disease.
A multi-institutional study was undertaken using computerized planning systems to develop three-dimensional (3-D) radiotherapy plans for Hodgkin's disease (H.D.). Two patients, the first afflicted with bulky stage II disease and another one with early stage I H.D., were studied. Three main categories of plan were produced for each patient: a) a traditional plan which modelled a conventional mantle treatment on the 3-D system, b) a 3-D standard plan where anterior and posterior fields were designed to cover 3-D target volumes, and c) a 3-D unconstrained plan where innovational techniques were employed. Three-dimensional planning provides information about the dose distribution throughout the large volume irradiated in patients with H.D. that is not available with conventional mantle planning. The use of 3-D techniques resulted in improved tumor coverage, but by allowing for uncertainties such as motion, the doses to normal tissues tended to be higher. The use of unorthodox beam arrangements introduced added complexities, and further increased the lung doses. The most even dose distributions were obtained by incorporating compensating filters into anterior fields. Clinicians showed wide variations in their assessment of the plans, possible reasons for which are addressed in this paper. In addition, calculated probabilities from models of tumor control and normal tissue damage are also presented.
Hodgkin Disease↗
Importance of precise positioning for proton beam therapy in the base of skull and cervical spine.
Using proton beam therapy, high doses have been delivered to chordomas and chondrosarcomas of the base of skull and cervical spine. Dose inhomogeneity to the tumors has been accepted in order to maintain normal tissue tolerances, and detailed attention to patient immobilization and to precise positioning has minimized the margins necessary to ensure these dose constraints. This study examined the contribution of precise positioning to the better dose localization achieved in these treatments. Three patients whose tumors represented different anatomic geometries were studied. Treatment plans were developed which treated as much of the tumor as possible to 74 Cobalt-Gray-Equivalent (CGE) while maintaining the central brain stem and central spinal cord at less than or equal to 48 CGE, the surface of the brain stem, surface of the spinal cord, and optic structures at less than or equal to 60 CGE, and the temporal lobes at less than or equal to 5% likelihood of complication using a biophysical model of normal tissue complication probability. Two positioning accuracies were assumed: 3 mm and 10 mm. Both proton beam plans and 10 MV X ray beam plans were developed with these assumptions and dose constraints. In all cases with the same positioning uncertainties, the proton beam plans delivered more dose to a larger percentage of the tumor volume and the estimated tumor control probability was higher than with the X ray plans. However, without precise positioning both the proton plans and the X ray plans deteriorated, with a 12% to 25% decrease in estimated tumor control probability. In all but one case, the difference between protons with good positioning and poor positioning was greater than the difference between protons and X rays, both with good positioning. Hence in treating these tumors, which are in close proximity to critical normal tissues, attention to immobilization and precise positioning is essential. With good positioning, proton beam therapy permits higher doses to significantly more of the tumor in these sites than do X rays.
Adult↗
Proton therapy for carcinoma of the nasopharynx: a study in comparative treatment planning.
Radiation therapy for nasopharyngeal carcinoma is technically difficult because of the complexity of the regional anatomy and the natural history of the disease. The results of a study are presented showing how detailed diagnostic information available from MRI is helpful in defining the target volume to be irradiated and the critical normal structures. By using 3-dimensional planning techniques, an assessment was made of the relative merits of proton beam therapy and of X ray treatment for patients with early stage and locally advanced carcinoma of the nasopharynx. For both types of patient, the study suggests that the use of protons for the major part of treatment results in a more even distribution of dose to the tumor and an increase of approximately 5 Gy in median tumor dose with substantial reductions in doses to adjacent normal tissues. The superior dose distributions possible with protons should translate into improved local control and reduced morbidity. The difficulties of proton treatment planning for this site are addressed.
Adult↗
Distal penetration of proton beams: the effects of air gaps between compensating bolus and patient.
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Air↗
A computerized rotating laminar radionuclide camera.
We have constructed a radionuclide camera that embodies a unique detector-collimator concept and provides a radically new approach to imaging. The heart of the instrument is a linear array of semiconductor detectors separated by thin tungsten plates that confine the field of view of each detector to one dimension. This collimator design has a higher collection efficiency than the standard parallel-hole collimator but cannot directly produce a two-dimensional image. When multiple measurements are taken as the array rotates through 180 degrees, a computerized image restoration algorithm can then produce two-dimensional images with resolution determined by the width of the detectors. A small prototype camera has produced images with resolution superior to conventional Anger cameras.
Computers↗
Proton beam penumbra: effects of separation between patient and beam modifying devices.
The sharp lateral penumbra of a proton beam is often used to spare sensitive normal structures in treating clinical sites in which the target volume abuts, or even wraps around, these structures. Using Monte Carlo calculations and measurements, the factors which influence the penumbra of the proton beam at the Harvard Cyclotron Laboratory were investigated, with particular emphasis on the effects of separation between the patient and any beam modifying devices. Penumbra broadening, characterized by the distance over which the dose rises from 20% to 80% of the central dose, increases with greater amounts of scatterer introduced into the beam line. The broadening due to separation of the beam modifying devices and the patient is essentially linear with increasing air gap; the rate of increase depends on the details of these devices and on the depth of interest in the patient. For a particular portal, most of the parameters which affect the penumbra width are fixed by the patient's anatomy and the target volume. Only the thickness of the compensating bolus around the aperture edge and any air gap between the patient and the beam modifying devices can vary. Families of curves relating combinations of bolus thickness and air gap that maintain a constant penumbra width have been developed for guidelines during patient setup.
Biophysical Phenomena↗
Variable versus fixed modulation of proton beams for treatments in the cranium.
Dose distributions in the cranium with fixed and with variably modulated proton beams were compared. The variable modulation was designed to tailor the proximal high-dose region of each field to the target volume surface whereas the fixed modulation beams had a constant modulation determined by the greatest extent of the target. Dose-volume histograms of normal tissues were compared, as were the estimated complication probabilities. Twelve patients with chordomas or chondrosarcomas of the base of skull who had been treated to approximately 70 cobalt Gray equivalent (CGE) were evaluated. Dose distributions of the actual treatments were compared to those which would have been delivered had the proton beams been variably modulated; two patients for whom x-ray plans were available were also evaluated. The greatest difference in dose between the variable and fixed modulation proton beams, averaged over all the patients, was 13.8 CGE (8.0-18.0 CGE range). Much of this reduction occurred in the brain, particularly the temporal lobes. In those temporal lobes receiving significant doses, variable modulation reduced the volume receiving more than 54 CGE by 3.0 cc; all temporal lobes had at least a 5 CGE difference to some portion, half had more than 10 CGE and three more than 15 CGE difference to some portion. The optic structures, brainstem and spinal cord received from 1 to 3 CGE less dose with the variability modulated beams. Eight of the parotid glands received more than 20 CGE to more than half their volume with the fixed modulation beams; in these, variable modulation reduced the mean dose by 5.3 CGE. The reduction in integral dose with variable as compared to fixed modulation was in the range 3 to 12%; this gain was considerably less than the gain for uniformly modulated proton beams over x-rays in the two patients for whom x-ray plans were available.
Brain Stem↗