Patient CT Data Research Articles

Navigated Control: Ein neues Konzept für die Computer-Assistierte-HNO-Chirurgie

This work conceived and evaluates a mechatronical system for ORL-surgery by example of a Shaver for Functional Endoscopic Sinus Surgery controlled by navigation. The Shaver is automatically on/off-regulated depending on the current position in relation to the planned working space. This working space is defined on the basis of the individual CT data. Within this area the Shaver reacts to the signal of the surgeon (foot pedal). If the Shaver leaves the working space, an interruption of the drive regulation to the Shaver takes place. The evaluation of the planning software based on 32 patient CT-data sets. The registration accuracy in a anatomical model was examined on 451 measurements of endonasal attached titanium screws. The conversions of the working space were evaluated at 5 different technical models. The average time for segmenting the working space was found at 4.23 minutes per case. An average registration accuracy of the Shaver of 1.08 mm resulted. The pre-defined cavity was to be cleared away without restrictions. The preoperative determined work-space was converted by 3.1 mm over all levels. The study proves the feasibility of a mechatronical assistant system by the example of the navigate-controlled Shaver in paranasal sinus surgery. Contrary to conventional CAS solutions redundancy and cognitive discharge of the surgeon are considered in this conception. We see numerous applications according to the explained principle for power-control of instruments in ORL-surgery in the future such as drilling, high frequency surgery or laser.

Bewertung der Implantatposition von 107 individuellen CTX-Hüftendoprothesenschäften mit EBRA-FCA

The aim of this study was to assess the ratio of correct and malpositioned stems in a THR population with custom-made stems. Furthermore, any relation of the extent of deviation from the exact stem position and defined patient variables was evaluated. Preoperatively, in three-dimensional virtual reality, CTX-individual hip stems were positioned in femora reconstructed from the individual patient's CT data until a stable cortical fit was achieved. Postoperative femoral stem position was measured with EBRA-FCA (EinzelBildRontgenAnalyse-Femoral Component Analysis). Differences of planned and actual depth of stem position were calculated for 107 CTX-custom-made hip stems implanted at one institution. Compared to preoperative planning 59 hip stems were placed too high, while 16 were placed exactly to within one millimeter and 32 were positioned too low. Deviations of postoperative stem position from preoperative planning did not correlate with previous femoral osteotomy found in one-third of femora or femoral anteversion exceeding 25 degrees as present in two-thirds of patients. In 71 % the intraoperative stem position did match the preoperative CTX-implant fitting into virtual patient femora. 29 % of implanted stems were malpositioned, i. e., deviations were greater plus or minus 5 mm to preoperative computer planning. None of the examined variables such as body mass index, previous femoral osteotomy, surgical approach, abnormal anteversion angle served as a predictive value for CTX-stem position in this cohort.

Dosimetric evaluation of MRI-based treatment planning for prostate cancer**The materials in this paper have been presented in part at the San Diego 2003 AAPM.

The purpose of this study is to evaluate the dosimetric accuracy of MRI-based treatment planning for prostate cancer using a commercial radiotherapy treatment planning system. Three-dimensional conformal plans for 15 prostate patients were generated using the AcQPlan system. For each patient, dose distributions were calculated using patient CT data with and without heterogeneity correction, and using patient MRI data without heterogeneity correction. MR images were post-processed using the gradient distortion correction (GDC) software. The distortion corrected MR images were fused to the corresponding CT for each patient for target and structure delineation. The femoral heads were delineated based on CT. Other anatomic structures relevant to the treatment (i.e., prostate, seminal vesicles, lymph notes, rectum and bladder) were delineated based on MRI. The external contours were drawn separately on CT and MRI. The same internal contours were used in the dose calculation using CT- and MRI-based geometries by directly transferring them between MRI and CT as needed. Treatment plans were evaluated based on maximum dose, isodose distributions and dose–volume histograms. The results confirm previous investigations that there is no clinically significant dose difference between CT-based prostate plans with and without heterogeneity correction. The difference in the target dose between CT- and MRI-based plans using homogeneous geometry was within 2.5%. Our results suggest that MRI-based treatment planning is suitable for radiotherapy of prostate cancer.

738 poster A Monte Carlo-based tool for proton dose verification on patient CT data

738 poster A Monte Carlo-based tool for proton dose verification on patient CT data

Adaptation of GEANT4 to Monte Carlo dose calculations based on CT data

The GEANT4 Monte Carlo code provides many powerful functions for conducting particle transport simulations with great reliability and flexibility. However, as a general purpose Monte Carlo code, not all the functions were specifically designed and fully optimized for applications in radiation therapy. One of the primary issues is the computational efficiency, which is especially critical when patient CT data have to be imported into the simulation model. In this paper we summarize the relevant aspects of the GEANT4 tracking and geometry algorithms and introduce our work on using the code to conduct dose calculations based on CT data. The emphasis is focused on modifications of the GEANT4 source code to meet the requirements for fast dose calculations. The major features include a quick voxel search algorithm, fast volume optimization, and the dynamic assignment of material density. These features are ready to be used for tracking the primary types of particles employed in radiation therapy such as photons, electrons, and heavy charged particles. Recalculation of a proton therapy treatment plan generated by a commercial treatment planning program for a paranasal sinus case is presented as an example.

Quantitative measurement of regional tumor response to therapy

We have validated the use of a 3D deformable image registration algorithm in mapping the motion of a phantom lung tumor. We then applied the method to measure regional intra-tumor response in lung cancer patients treated with induction chemotherapy followed by concurrent chemoradiation. Numerous methods have been developed to quantify global tumor response to therapy. We describe for the first time a method to quantify response within radiographically defined intra-tumor sub-populations. A deformable image registration algorithm using a 3D optical flow method was developed to obtain a displacement vector between each voxel in a pair of related CT scans. The algorithm was validated by mapping the displacement of each voxel in a phantom lung tumor CT scan to a corresponding CT scan with a known 1.2cm and 2.4cm displacement. We then applied this method to a series of four recent lung cancer patients treated on a phase III protocol with two cycles of carboplatin-taxol based chemotherapy followed by concurrent chemoradiation with weekly carboplatin-taxol. Each patient obtained a high resolution spiral CT scan prior to treatment, after induction chemotherapy and after chemoradiation. A total of 32 tumor sub-populations were identified by dividing each pre-treatment tumor volume into octants. Each voxel of the pre-treatment scan was then independently mapped to the post-chemotherapy and post-radiation CT scans. The volume of the mapped tumor sub-populations were then compared to the pre-treatment CT scan as a measure of regional tumor response to each therapy. The measured displacement of the phantom lung tumor voxels was 1.20 and 2.40 cm with a full-width at tenth maximum of 0.008 and 0.006 cm respectively. The maximum error in voxel displacement was 1 mm. In the patient CT data sets, the mapped voxels of the intra-tumor regions were visualized on each of the post-treatment scans as represented in the color overlays of the CT scans in the figure. From this representative course it is evident that significant differences in response to therapy can be measured within tumor sub-populations. Although one tumor responded uniformly with less than 10% difference between octants, the other tumors responded with greater than 20% variation between the maximally and minimally responding octants. In one case, the residual volume in the maximally and minimally responding octants were 6.7% and 75.7% respectively. The residual tumor volume in each octant ranged from 26.7% to 86.9% with a mean of 59.2% after induction chemotherapy compared with a range of 6.7% to 75.7% with a mean of 39.8% after concurrent chemoradiation. A pair-wise comparison of the response to chemotherapy and concurrent chemoradiation in each of the 32 octants measured revealed no correlation between response to chemotherapy and response to concurrent chemoradiation with a correlation coefficient of r = 0.40. We have validated a new method of mapping voxel motion between related CT scans. We then successfully applied this technique to measure regional intra-tumor response to therapy. One tumor appeared to respond uniformly, while others responded with significant regional heterogeneity suggesting the existence of tumor sub-populations with a range of therapeutic sensitivity. Finally, despite the prevailing belief that response to chemotherapy predicts for response to radiation, the magnitude of this response was not correlated within sub-populations of the tumor in our study.

Designing cranial implants in a haptic augmented reality environment

Medical sculptors and neurosurgeons create virtual 3D cranial models based on patient CT data superimposed over their hands as if they were sculpting physical models.

Comparison between a conventional treatment energy and 50 MV photons for the treatment of lung tumours

Radiation therapy in the thoracic region is difficult due to the presence of many dose-limiting structures and the large density differences that affect the dose distribution. Conventional irradiation techniques use low-energy photon beams to avoid build-up effects superficially in the tumour and increased lateral scattering of the beams. For deep-seated tumours higher beam energies could have lung-sparing properties that would enable dose escalation.A comparison was made for a conventional low photon energy (6 MV) and 50 MV photons for the treatment of a lung tumour. A representative patient geometry was selected, consisting of a small tumour semi-enclosed in lung tissue. Treatment plans were designed using a commercial 3D-pencil beam treatment planning system. The treatment beams designed in the TPS were simulated with the Monte Carlo code EGS4/BEAM and the dose distribution in the phantom created from the patients CT-data was calculated using MCDOSE with identical beam geometry for both energies.The intrinsic difference between the two photon energies implies a sparing effect of lung that can be utilized for dose escalation. For a treatment with two beams the mean total dose to the tumour could be increased by 5.3% for 50 MV, corresponding to 3.2 Gy for a prescription dose of 60 Gy, with the same complication probability for the treated lung as for 6 MV.In conclusion, high-energy beams have qualities that can be taken advantage of for irradiation of lung tumours. Optimum solutions would probably require the use of both high- and low-energy beams.

Radiation doses to infants and adults undergoing head CT examinations.

For routine noncontrast CT examinations of the head, we compared the radiation doses of infant patients aged no more than two years old, with those of "adults" defined as any patient whose weight was greater than 40 kg. Data were obtained for 23 infants, and an equal number of "adults," who underwent CT head examinations between May 1997 and March 1998. Patient CT data acquired included the x-ray tube potential (kVp), mAs, section thickness, and total number of sections. For radiation dosimetry purposes, the head was modeled as a uniform cylinder of water using patient size data obtained from a representative cross-sectional image. CT techniques and patient size data permitted the computation of the mean section doses in the head region, total energy imparted, and the corresponding effective doses. All CT scans were performed at 120 kVp, with an average current-exposure time product of 271 +/- 73 and 340 +/- 0 mAs for infants and "adults," respectively. The radius of the water cylinder used to model the patient head increased from 58 mm for 4 kg newborns to 70 mm for 8 kg infants. For "adults," there was little correlation between the weight of the patient and the mean water equivalent radius of 88 mm (r2 = 0.14). Mean section doses were 44.4 +/- 11.1 mGy for infants, and 44.2 +/- 1.5 mGy for "adults." The energy imparted to infants correlated with patient weight (r2= 0.35) much more than did that of "adults" (r2= 0.02). The average infant energy imparted (66.4 +/- 28.7 mJ) was approximately half the value obtained for "adults" (140 +/- 10 mJ). The average effective dose to the infants (7.6 +/- 3.1 mSv), however, was approximately six times higher than that for "adults" (1.3 +/- 0.1 mSv). There was no significant correlation between patient effective dose and patient mass for either the infant (r2 = 0.12) or the "adult" group of patients (r2= 0.02). Infant doses varied much more than "adult" doses, primarily because of a wider range of x-ray technique factors selected and secondarily due to the variation in infant head size. The observed variability in the computed radiation dose parameters indicates that it should be possible to reduce infant doses routinely in head CT examinations without any adverse effect on diagnostic imaging performance. For such routine head CT scans, the average dose reduction for infants weighing between 4 and 8 kg would be expected to range between 40% and 60%.

Simulation of postoperative 3D facial morphology using a physics-based head model

We propose a prototype of a facial surgery simulation system for surgical planning and the prediction of facial deformation. We use a physics-based human head model. Our head model has a 3D hierarchical structure that consists of soft tissue and the skull, constructed from the exact 3D CT patient data. Anatomic points measured on X-ray images from both frontal and side views are used to fire the model to the patient's head. The purposes of this research is to analyze the relationship between changes of mandibular position and facial morphology after orthognathic surgery, and to simulate the exact postoperative 3D facial shape. In the experiment, we used our model to predict the facial shape after surgery for patients with mandibular prognathism. Comparing the simulation results and the actual facial images after the surgery shows that the proposed method is practical.

A two-step algorithm for predicting portal dose images in arbitrary detectors.

Recently, portal imaging systems have been successfully demonstrated in dosimetric treatment verification applications, where measured and predicted images are quantitatively compared. To advance this approach to dosimetric verification, a two-step model which predicts dose deposition in arbitrary portal image detectors is presented. The algorithm requires patient CT data, source-detector distance, and knowledge of the incident beam fluence. The first step predicts the fluence entering a portal imaging detector located behind the patient. Primary fluence is obtained through ray-tracing techniques, while scatter fluence prediction requires a library of Monte Carlo-generated scatter fluence kernels. These kernels allow prediction of basic radiation transport parameters characterizing the scattered photons, including fluence and mean energy. The second step of the algorithm involves a superposition of Monte Carlo-generated pencil beam kernels, describing dose deposition in a specific detector, with the predicted incident fluence. This process is performed separately for primary and scatter fluence, and yields a predicted dose image. A small but noticeable improvement in prediction is obtained by explicitly modeling the off-axis energy spectrum softening due to the flattening filter. The algorithm is tested on a slab phantom and a simple lung phantom (6 MV). Furthermore, an anthropomorphic phantom is utilized for a simulated lung treatment (6 MV), and simulated pelvis treatment (23 MV). Data were collected over a range of air gaps (10-80 cm). Detectors incorporating both low and high atomic number buildup are used to measure portal image profiles. Agreement between predicted and measured portal dose is better than 3% in areas of low dose gradient (<30%/cm) for all phantoms, air gaps, beam energies, and detector configurations tested here. It is concluded that this portal dose prediction algorithm is fast, accurate, allows separation of primary and scatter dose, and can model arbitrary detectors.

Optimizing radiotherapy of orbital and paraorbital tumors: intensity-modulated X-ray beams vs. intensity-modulated proton beams

Purpose: This study presents a dosimetric optimization effort aiming to compare intensity-modulated (IM) X-rays and IM protons in 4 different orbital and paraorbital tumors. These are most challenging targets for standard radiotherapy due to their close relationship with the eyes and related structures. Methods and Materials: A primary orbital lymphoma, an optic nerve meningioma, a sphenoidal ridge meningioma protruding into the orbit, and a pediatric parameningeal paraorbital rhabdomyosarcoma were selected for the purpose of this study. Planning target volumes (PTVs) and organs at risk (OAR) were defined in each patient CT data set for each tumor site. IM X-ray and IM proton three-dimensional treatment plans were implemented. The following total tumor doses were prescribed: 30 Gy for the orbital lymphoma, 54 Gy for both meningiomas, and 50.4 Gy for the rhabdomyosarcoma case. Dose-volume histograms (DVHs) were obtained for all targets and OAR with both treatment techniques. DVHs were used to predict normal tissue complication probabilities (NTCPs) for the OAR in the vicinity of the tumor. Results: The PTV coverage was optimal and equally homogeneous with both IM X-rays and IM proton plans in the 4 tumor sites. DVHs for most OAR were better with IM proton beams especially in the low- to mid-dose range region. The integral nontarget dose was lower with IM protons in every case (factor ranging from 1.5 to 1.9). However, predicted NTCPs (for severe late effects) were equally low for both treatment techniques in every tumor site. Conclusion: Although IM proton plans optimally decreased the dose to the OAR in all tumor sites, both optimized X-ray and proton beams equally succeeded to reduce severe-toxicity prediction risks to less than 5% while optimally treating the PTV.

Volume rendering quantification algorithm for reconstruction of CT volume-rendered structures: Part I. Cerebral arteriovenous malformations.

Volume rendering is a visualization technique that has important applications in diagnostic radiology and in radiotherapy but has not achieved widespread use due, in part, to the lack of volumetric analysis tools for comparison of volume rendering to conventional visualization techniques. The volume rendering quantification algorithm (VRQA), a technique for three-dimensional (3-D) reconstruction of a structure identified on six principal volume-rendered views, is introduced and described. VRQA involves three major steps: 1) preprocessing of the partial surfaces constructed from each of six volume-rendered images; 2) merging these processed partial surfaces to define the boundaries of a volume; and 3) computation of the volume of the structure from this boundary information. After testing on phantoms, VRQA was applied to CT data of patients with cerebral arteriovenous malformations (AVM's). Because volumetric visualization of the cerebral AVM is relatively insensitive to operator dependencies, such as the choice of opacity transfer function, and because precise volumetric definition of the AVM is necessary for radiosurgical treatment planning, it is representative of a class of structures that is ideal for testing and calibration of VRQA. AVM volumes obtained using VRQA are intermediate to those obtained using axial contouring and those obtained using CT-correlated biplanar angiography (two routinely used visualization techniques for treatment planning for AVM's). Applications and potential expansions of VRQA are discussed.

Simulating lower extremity nerve blocks with virtual reality

Regional anesthesia offers many potential benefits to patients, and provides a gratifying aspect of practice to anesthesiologists. Unfortunately, these techniques are often avoided because practitioners lack familiarity with the procedures. Current methods of teaching regional anesthesia require the clinician to learn while performing actual procedures on patients. This approach poses a barrier to learning because it can create anxiety among student, teacher, and patient. We have developed a method of simulating regional anesthesia with the goal of allowing physicians to gain technical familiarity with these procedures before actual patient contact. Our approach involves the visual presentation of a patient using virtual reality that is created from CT-scan data and presented in stereo through a head-mounted display. The sense of touch and needle resistance is simulated with a PHANToM servo-controlled force transduction device. The system provides satisfactory realism to allow the user to suspend disbelief, and accept the environment as representing a patient upon whom a regional anesthetic procedure can be performed. Because the simulation is derived from patient CT data and biomechanical testing of tissue properties, actual patient characteristics may be modeled. Procedures can be rehearsed and alternative approaches attempted before actual patient contact. By using virtual reality, this approach reduces the space, expense, and inflexibility of a mannequin-based simulator. Early experience with the system suggests that physicians find this tool useful in learning the anatomy and technical approach to regional anesthesia.

In vivo dosimetry with a liquid‐filled electronic portal imaging device

The thesis describes the use of a liquid‐filled electronic portal imaging device, EPID, for in vivo dosimetry, i.e., for the verification of transmission, exit, and midplane dose. First, the application of the EPID to measure the transmission dose, i.e., the dose behind the patient, was investigated under various clinical conditions. For this purpose corrections for the nonlinear response of the EPID with dose and the effects of photon scatter in the EPID were performed. Next, a convolution model was developed to convert transmission dose images to exit and midplane dose distributions in the patient. Patient inhomogeneities are taken into account by using the radiological path length through the patient, which is derived from the measured transmission dose, i.e., without using patient data (CT). Finally, the accuracy of EPID exit and midplane dose measurements was determined for several homogeneous and inhomogeneous phantoms in open and wedged beams and for a few patients treated for larynx, breast, lung and prostate cancer. It was found that for most phantoms exit and midplane doses agree within 2% (1 s.d.) with ionization chamber measurements. EPID midplane dose measurements during patient treatment generally agreed within 2.5% with 3D treatment planning calculations. Occasionally larger differences were observed due to differences between the actual patient anatomy during treatment and the patient CT data, used for treatment planning. It is concluded that transmission dosimetry with a liquid‐filled EPID can be used to determine the 2D exit and midplane dose for several treatment sites in clinical practice and to quantify the influence of anatomical changes on the dose delivery.

Frame Slippage Verification in Stereotactic Radiosurgery

Purpose: To develop a method for detecting frame slippage in stereotactic radiosurgery by interactively matching in three dimensions Digitally Reconstructed Radiographs (DRRs) to portal images. Methods and Materials: DRRs are superimposed over orthogonal edge-detected portal image pairs obtained prior to treatment. By interactively manipulating the CT data in three dimensions (rotations and translations) new DRRs are generated and overlaid with the orthogonal portal images. This method of matching is able to account for ambiguities due to rotations and translations outside of the imaging plane. The matching procedure is performed with anatomical structures, and is used in tandem with a fiducial marker array attached to the stereotactic frame. The method is evaluated using portal images simulated from patient CT data and then tested using a radiographic head phantom. Results: For simulation tests a mean radial alignment error of 0.82 mm was obtained with the 3D matching method compared to a mean error of 3.52 mm when using conventional matching techniques. For the head phantom tests the mean alignment displacement error for each of the stereotactic coordinates was found to be Δx = 0.95 mm, Δy = 1.06 mm, Δz = 0.99 mm, with a mean error radial of 1.94 mm (SD = 0.61 mm). Conclusion: Results indicate that the accuracy of the system is appropriate for stereotactic radiosurgery, and is therefore an effective tool for verification of frame slippage.

A CT-aided PC-based physical treatment planning of TBI: a method for dose calculation

Background and purpose: As for conventional radiotherapy, one of the basic requirements in Total Body Irradiation (TBI) is to know accurately the dose delivered to the entire body. Both the dosimetry and the treatment planning need to be improved. Physical, technical and dosimetrical aspects of TBI have been widely discussed in the literature. However, to our knowledge, no planning systems specifically designed for TBI are commercially available. This article describes a CT-aided PC-based planning system (TBI- Plansys) and its dose calculation algorithm, which applies scatter and inhomogeneity corrections, developed for the TBI technique currently in use at our centre (AP/PA irradiation with patient positioned on his side). Material and method: A description of the material and method followed in the dosimetrical procedure is included as it constitutes the basis of the proposed dose calculation algorithm (more than 2D). A Windows programming environment has been used to develop the software. Results: TBI- Plansys uses patient CT data and indicates absolute and relative dose distributions along midline (at reference points), the transversal axis at the specification point and on transverse sections. The system also calculates the appropriate thicknesses of bolus and shielding to modify undesired dose distributions. TBI- Plansys has been checked against two other well-established systems (beam-zone method and our in vivo semiconductor probe-based system). The checks showed good accuracy with dose differences less than 1% and 3% for homogeneous and inhomogeneous tissues, respectively. Conclusions: CT calculations by TBI- Plansys allow us to detect undesired distributions which may go unnoticed by calculations at only some specific points. The system has shown clear advantages for routine clinical use as it generates more detailed and accurate information than manual calculations and diminishes the time requirements.

Initial results for automated computational modeling of patient-specific electromagnetic hyperthermia.

Developments in finite-difference time-domain (FD-TD) computational modeling of Maxwell's equations, super-computer technology, and computed tomography (CT) imagery open the possibility of accurate numerical simulation of electromagnetic (EM) wave interactions with specific, complex, biological tissue structures. One application of this technology is in the area of treatment planning for EM hyperthermia. In this paper, we report the first highly automated CT image segmentation and interpolation scheme applied to model patient-specific EM hyperthermia. This novel system is based on sophisticated tools from the artificial intelligence, computer vision, and computer graphics disciplines. It permits CT-based patient-specific hyperthermia models to be constructed without tedious manual contouring on digitizing pads or CRT screens. The system permits in principle near real-time assistance in hyperthermia treatment planning. We apply this system to interpret actual patient CT data, reconstructing a 3-D model of the human thigh from a collection of 29 serial CT images at 10 mm intervals. Then, using FD-TD, we obtain 2-D and 3-D models of EM hyperthermia of this thigh due to a waveguide applicator. We find that different results are obtained from the 2-D and 3-D models, and conclude that full 3-D tissue models are required for future clinical usage.

Differential-pencil-beam dose calculations for charged particles.

The use of a convolution or differential-pencil-beam (DPB) algorithm has been studied for charged-particle dose calculations as a means of more accurately modeling the effects of multiple scattering. Such effects are not reflected in current charged-particle dose calculations since these calculations rely on depth-dose data measured in homogeneous water-equivalent phantoms and use ray-tracing techniques to calculate the water-equivalent pathlength from patient CT data. In this study, isodose plots were generated from three-dimensional dose calculations using Monte Carlo, DPB, and standard ray-tracing methods for a 4-cm modulated 150-MeV proton beam incident on both homogenous and heterogeneous phantoms. To simulate therapy conditions with charged particles, these studies included cases where compensating boluses were introduced to modify the particle range across the treatment field. Results indicate that multiple-scattering effects, including increased penumbral width as a function of beam penetration and the "smearing" of isodose distributions downstream from complex heterogeneities, are well modeled by the DPB algorithm. The DPB algoirthm may also be used to obtain more useful estimates of the dose uncertainty in regions near the end of the beam's range downstream from complex heterogeneities than can be derived from standard ray-tracing calculations.

Three dimensional electron beam treatment planning evaluation for post op radiotherapy of the chest wall

A multi-institutional collaborative working group (CWG) has conducted a study to evaluate electron beam three dimensional treatment planning for post-operative radiotherapy of the chest wall. This included defining criteria for target volume, dose uniformity, the use of bolus and the requirements for incorporating tissue inhomogeneities in treatment planning. Patients for this particular disease site were selected so that they would provide the opportunity to study the following treatment planning challenges: (1) sloping surface topography, (2) underlying inhomogeneities (lung), (3) varying thickness of chest wall over lung, (4) field matching techniques, (5) bolus effects on dose distribution and (6) electron arc dosimetry studies. Patients entered into this study had histology of invasive carcinoma of the breast (all subtypes) and were clinical stage T3 and T4 breast cancer (postmastectomy). Patients with positive margins and inflammatory breast were excluded. Patient CT data sets were obtained under protocol conditions. This provided a contiguous set of CT slices 10 mm thick from 5 cm superior to the sternal notch to 5 cm inferior to the xyphoid. The protocol called for a dose of 4500 cGy to the supraclavicular volume, 5000 cGy to the internal mammary volume and the postmastectomy chest wall. Critical structures evaluated included the lung, heart, and skin. Plans were done with a lD, 2D, and 3D dose calculation algorithm with the patient CT data sets modified to be water equivalent and then the plans were recalculated using the CT tissue data. Finally, a best 3D plan was developed using non-standard beam arrangements, e.g. non-coplanar beams and any and all 3D planning tools available. Plans were then evaluated under a criteria established by the CWG and compared to calculated tumor control probability and normal tissue complication probabilities. Full details of the study for this particular site will be presented.