Martin S. Weinhous

Stereotactic radiosurgery for lung tumors: Preliminary report of a phase I trial

BACKGROUND Stereotactic radiosurgery is well established for the treatment of intracranial neoplasms but its use for lung tumors is novel. METHODS Twenty-three patients with biopsy-proven lung tumors were recruited into a two-institution, dose-escalation, phase I clinical trial using a frameless stereotactic radiosurgery system (CyberKnife). Fifteen patients had primary lung tumors and 8 had metastatic tumors. The age range was 23 to 87 years (mean, 63 years). After undergoing computed tomography-guided percutaneous placement of two to four small metal fiducials directly into the tumor, patients received 1,500 cGY of radiation in a single fraction using a linear accelerator mounted on a computer-controlled robotic arm. Safety, feasibility, and efficacy were studied. RESULTS Nine patients were treated with a breath-holding technique, and 14 with a respiratory-gating, automated, robotic technique. Tumor size ranged from 1 to 5 cm in maximal diameter. There were four complications related to fiducial placement: three pneumothoraces requiring chest tube insertion and one emphysema exacerbation. There were no grade 3 to 5 radiation-related complications. Follow-up ranged from 1 to 26 months (mean, 7.0 months). Radiographic response was scored as complete in 2 patients, partial in 15, stable in 4, and progressive in 2. Four patients died of non-treatment-related causes at 1, 5, 9, and 11 months after radiation. CONCLUSIONS Single-fraction stereotactic radiosurgery is safe and feasible for the treatment of selected lung tumors. Additional studies are planned to investigate the optimal radiation dose, best motion-suppression technique, and overall treatment efficacy.

Fluoroscopic study of tumor motion due to breathing: Facilitating precise radiation therapy for lung cancer patients

Target motion due to breathing is one of the major obstacles in dose escalation of radiation therapy to some tumors in the thoracoabdominal region. The development of beam gating or target motion tracking techniques provides a possibility to reduce normal tissue volume in a treatment field. Tumor motion monitoring in those techniques plays a crucial role, but has not yet been adequately explored. This paper reports our preliminary investigation on breath introduced tumor motion. Tumor locations and motion properties were determined from digitized fluoroscopic videos acquired during patient simulation. Image distortion due to irregularities in the imaging chain, such as the pincushion distortion, was corrected with a polynomial unwarping method. Temporal Fourier transformation of the fluoroscopic video was introduced to convert the motion information over time to a static view of a motion field, in which regions with different motion ranges can be directly measured. Patient breathing patterns vary from patient to patient and so does the kinematic behavior of individual tumors. In order to evaluate the feasibility for tracking internal target motion with nonionizing-radiation techniques, motion patterns between internal targets and external radio opaque markers placed on patients chest during fluoroscopic video acquisition were compared. For some patients, significant motion phase discrepancies between an internal target and an external marker have been observed. Quantitative measurements are reported. These results will be useful in the design of a motion tracking or gated radiotherapy system.

Error rates in clinical radiotherapy.

PURPOSE Error rates in clinical oncology are undergoing increasing scrutiny. The purpose of this study was to understand error frequency, error patterns, underlying causal links, consequences, and possible prevention strategies in clinical radiotherapy. PATIENTS AND METHODS Treatment information, self-reported error documentation, and retrospective analyses of electronic treatment verification transcripts for 1,925 consecutive patients treated with a total of 93,332 individual radiotherapy fields were reviewed and analyzed. RESULTS A total of 59 separate errors that affected 168 individual treatment fields were detected, which yielded a crude radiation delivery error rate of 0.18%. All 59 errors were judged to be level I (negligible chance of adverse medical outcome) with the most common error category being a minor treatment field block misplacement. A comprehensive quality assurance program and an electronic record-and-verify linear accelerator interlock system seem to have prevented the occurrence of many additional errors. However, nine of the 59 errors were directly related to the use of this system and generally involved the transposition of similar numbers within series of treatment coordinate data-sets. Overall, radiotherapy error rates favorably compare with reported error rates for pharmaceutical administration in large tertiary care hospitals. CONCLUSION When modern automated error-minimization methods are used along with nonpunitive error reporting systems, clinical radiotherapy seems to be highly safe. Formal error analysis studies may allow the rational design of prevention strategies that are attuned to the frequency, seriousness, and antecedent causes of many classes of potential radiotherapy errors.

Dosimetry of a W-188/Re-188 beta line source for endovascular brachytherapy

PURPOSE The objective was to determine the dosimetry of a potential endovascular brachytherapy source consisting of a coiled tungsten wire mounted on the distal end of a drive wire and neutron-activated to contain the parent-daughter nuclides tungsten-188 (188W) and rhenium-188 (188Re). METHODS A coiled tungsten wire 40 mm in length was neutron-activated by double-neutron capture for 78 hours at 1.9 x 10(15) h/cm2/s to contain 925 MBq (25 mCi) of 188W/188Re in equilibrium. The dose-fall off from this source was determined using three independent methods: (a) Thermoluminescence dosimetry with small LiF-100 rods, (b) Gafchromic film dosimetry, and (c) Bang gel dosimetry. In addition, a Monte Carlo simulation was performed to compute the beta-dose. RESULTS Each of the three measurement methods recorded similar values for the dose fall-off within the distances useful for endovascular brachytherapy. The Monte Carlo calculations closely approximated the measured results in the treatment range between 1 and 3 mm and may thus be useful for evaluating changing geometries in the development of catheters and source setups. A 2 min restenosis treatment delivering 20 Gy at a radius of 2 mm would require a source of 1384.8 MBq/cm (37.4 mCi/cm). CONCLUSIONS The dose distribution from a 188W/188Re source is similar to that of a 90Y-source. An added advantage of the 188W/188Re source is that it can be used for at least two months and still provides fast treatment times because of the parent isotopes half-life of 69 days. The additional gamma emission from the source is too small to impose a serious radiological hazard. The high atomic number and density of the source material allows direct fluoroscopic imaging without additional markers.

Intensity-modulated radiotherapy: rethinking basic treatment planning paradigms

is a high likelihood of metabolically and clonogenically active tumor, the treatment plan might be designed to deliver a dose significantly higher than that delivered to a different region within the CTV in which the risk of tumor progression is considered lower. In a similar way, a region of the CTV located immediately adjacent to a critical normal structure might be given a lower target priority rating simply because the risk/benefit equation for this field segment is heavily in favor of normal tissue sparing. The traditional PTV is thus deconstructed into a series of regions of greater or lesser desired treatment intensity. This may lead to grossly inhomogeneous treatment plans, with hot spots (or, more rarely, cold spots) of 20% or more. We must learn how to make best use of these dosimetric inhomoge

Subunity coordinate translation with Fourier transform to achieve efficient and quality three-dimensional medical image interpolation

A new approach to the interpolation of three-dimensional (3D) medical images is presented. Instead of going through the conventional interpolation scheme where the continuous function is first reconstructed from the discrete data set and then resampled, the interpolation is achieved with a subunity coordinate translation technique. The original image is first transformed into the spatial-frequency domain. The phase of the transform is then modified with n-1 linear phase terms in the axial direction to achieve n-1 subunity coordinate translations with a distance 1/n, where n is an interpolation ratio, following the phase shift theorem of Fourier transformation. All the translated images after inverse Fourier transformation are then interspersed in turn into the original image. Since windowing plays an important role in the process, different window functions have been studied and a proper recommendation is provided. The interpolation quality produced with the present method is as good as that with the sampling (sinc) function, while the efficiency, thanks to the fast Fourier transformation, is very much improved. The approach has been validated with both computed tomography (CT) and magnetic resonance (MR) images. The interpolations of 3D CT and MR images are demonstrated.

THE RADIOBIOLOGY AND PHYSICS OF BRACHYTHERAPY

The principles of radiobiology are the same for both EBRT and brachytherapy. Strict spatial limitation of the delivered dose, a function of the inverse square law, is one reason that brachytherapy is attractive. The biologic rationale of LDR implants is maximization of normal tissue repair to enhance the therapeutic ratio. Fractionated HDR treatment schedules have been formulated that provide good biologic approximation of the well-established LDR practices. The HDR approach improves both patient comfort and radiation safety; also, the brief treatment times can permit geometric improvements by transiently displacing sensitive structures.

Successful Conversion from a Linear Accelerator-Based Program to a Gamma Knife Radiosurgery Program: The Cleveland Clinic Experience

From August 1989 to January 1997, 307 treatments in 293 patients were performed with a linear accelerator-based (LINAC) stereotactic radiosurgery system. Because of the program s success, the need for a dedicated radiosurgery unit in Ohio and the desire to treat functional disorders, the Cleveland Clinic Health System (CCHS) obtained the first Gamma Knife in the state of Ohio. Based on the previous volume of patients for radiosurgery, it was estimated that 75-100 patients would be treated during the first year of operation. However, during the first calendar year, 214 treatments were performed on 205 patients, which far exceeded expectations. The success of the CCHS Gamma Knife Center can be attributed to an increase in a number of factors. These included marketing efforts, patient awareness, increased use for functional disorders, physician understanding of radiosurgery, use by qualified nonaffiliated radiation oncologists and neurosurgeons, and outpatient delivery (95% with the Gamma Knife vs <5% with the LINAC). With proper planning, education, and awareness, the opening of a Gamma Knife Center can greatly increase the volume of radiosurgery performed when compared with a LINAC-based program.

Feasibility of human/robot cooperation in image-directed radiation oncology

Image-directed radiation therapy potentially offers significant improvement over current open-loop radiotherapy techniques. Utilizing real-time imaging of tumors, it may be possible to direct a treatment beam to achieve better localization of radiation dose. Since real-time imaging offers relatively poor fidelity, automated analysis of images is formidable. However, experienced physicians may take advantage of visual cues and knowledge of how cancer spreads to infer the location of tumors in partially occluded or otherwise ambiguous scenes. At the Cleveland Clinic, an image-directed radiation treatment system, consisting of a relatively compact linear accelerator manipulated by a 6 degree-of-freedom robot, is in use for treatment of brain tumors. This same system could be applied to teleoperated radiation treatment of non-stationary tumors. To evaluate the prospects for operator-interactive, image-directed therapy, a simulator was constructed to determine the effectiveness of emulated human-in-the-loop treatments. Early performance results based on video recordings of actual lung tumors show that image-directed treatment can offer significant improvements over current practice, motivating development of teleoperated treatment systems.

Physics and basic parameters of brachytherapy

Brachytherapy (short‐distance therapy) is the therapeutic process whereby radioactive sources are placed into very close proximity to target tissue. Radioactive materials were so used beginning shortly after the discovery of radium by Marie and Pierre Curie in 1898. For the purposes of brachytherapy, radioactive materials are those that emit “rays” that can cause ionization (and hence DNA damage and the destruction of target cells). The potentially useful rays include beta, gamma, and other possibilities such as neutrons. Beta rays, properly beta particles, are simply high energy electrons. Gamma rays are high energy photons (part of the electromagnetic spectrum like visible light, but with much higher energy). These particles are produced during the radioactive decay of certain isotopes. The physics of those events and the parameters that apply to the therapeutic use of the isotopes are the primary topics of this report. J. Surg. Oncol. 1997;65:143–150.