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Biomedical subjects

Samuel Ryu

Publications and source records attributed to Samuel Ryu.

18 recordsLinked to original sources
PubMed2007

Partial volume tolerance of the spinal cord and complications of single-dose radiosurgery.

BACKGROUND: Spine radiosurgery causes a rapid dose fall-off within the spinal cord. The tolerance of partial volume of the spinal cord may determine the extent of clinical application. The study analyzed the partial volume tolerance of the human spinal cord to single fraction radiosurgery. METHODS: A total of 230 lesions with spine metastases in 177 patients were treated with radiosurgery with single fraction of 8 to 18 Gy, prescribed to the 90% isodose line that encompassed the target volume. Spinal cord volume was defined as 6 mm above and below the radiosurgery target volume. Spinal cord dose was calculated from the radiation dose/spinal cord volume histogram and correlated with clinical/neurological status and radiographic studies. Median follow-up was 6.4 months (range, 0.5-49 months). The 1-year survival rate was 49%. RESULTS: The average spinal cord volume defined at the treated spinal segment was 5.9 +/- 2.2 mL. The average dose to the 10% spinal cord volume was 9.8 +/- 1.5 Gy, calculated from the dose-volume histogram in the group of 18 Gy prescribed dose. The spinal cord volume that received higher than 80% of the prescribed dose was 0.07 +/- 0.10 mL, which represented 1.3 +/- 1.8% of the cord volume. Among the 86 patients who survived longer than 1 year there was 1 case of radiation-induced cord injury after 13 months of radiosurgery. There were no other cases of spinal cord sequelae. CONCLUSIONS: Whereas the maximum spinal cord tolerance to single-dose radiation is not known, partial volume tolerance of the human spinal cord is at least 10 Gy to 10% of the spinal cord volume defined as 6 mm above and below the radiosurgery target.

Adolescent↗
PubMed2006

Mitigation of radiation-induced optic neuropathy in rats by ACE inhibitor ramipril: importance of ramipril dose and treatment time.

PURPOSE: Radiation-induced optic nerve damage was reduced by ramipril, a prodrug angiotensin-converting enzyme inhibitor (ACEI). This study was to determine the optimum dose and administration time of ramipril for mitigating radiation-induced optic neuropathy. MATERIALS AND METHOD: Adult Fischer 344 male rats were treated with a single dose radiation 30 Gy by using radiosurgical technique. After irradiation, the animals were randomly assigned into groups of different ramipril doses and administration time; control (no treatment), radiation alone, radiation+ramipril in different doses and starting times of drug. Ramipril was given 0.5-1.5 mg/kg/day and AT1R blocker Losartan 20 mg/kg/day in drinking water for 180 days. Functional endpoint with visual evoked potential (VEP) and anatomical endpoint with gross and histological analysis with immunohistochemical (IHC) stain were used. RESULTS: Normal VEP measurements in un-irradiated rats were 46.2+/-7.9 ms. There was no change of VEP value until 4 months, but was lengthened to 188.1+/-58.7 ms at 6 months after radiation. By ramipril treatment with the dose of 1.5 mg starting at 2 weeks after radiation, VEP was significantly shortened to 105.7+/-88.5 ms at 6 months. Gross and microscopic structure of the irradiated optic nerve was well preserved in the ramipril-treated group. CONCLUSION: Ramipril can mitigate the radiation-induced optic nerve damage and preserve the functional integrity of the nerve. The results support early treatment with a high dose of ramipril after radiation.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2006

Postoperative radiosurgery for malignant spinal tumors.

OBJECTIVE: Although, as a primary therapy, radiosurgery for spinal tumors is becoming more common in clinical practice and is associated with encouraging clinical results, we wanted to evaluate outcomes after radiosurgery in a series of postoperative patients. METHODS: We examined the medical records of 18 postoperative patients who received radiosurgical treatment to their residual spinal tumors: metastatic carcinoma (10), sarcoma (3), multiple myeloma/plasmacytoma (4), and giant cell tumor (1). Marginal radiosurgical doses ranged from 6 to 16 Gy (mean, 11.4 Gy) prescribed to the 90% isodose line. All regions of the spine received treatment: 2 cervical, 15 thoracic, and 1 lumbosacral. The volume of irradiated spinal elements receiving 30, 50, and 80% of the total dose ranged from 0.51 to 11.05, 0.19 to 6.34, and 0.06 to 1.73 cm, respectively. Treatment sessions (i.e., patient in to patient out of the room) varied between 20 and 40 minutes. Follow-up ranged from 4 to 36 months (median, 7 mo). RESULTS: Even though significant doses of radiation were delivered to all regions of the spinal cord and nerve roots coincidentally involved in the treatments, only one patient in this series developed progressive symptoms possibly attributable to a toxic effect of the radiosurgery. Of those patients initially presenting with neurological deficits, 92% either remained neurologically stable or improved. CONCLUSION: Our observations suggest that radiosurgery as prescribed in this series of postoperative patients with residual spinal tumor is well-tolerated and associated with little to no significant morbidity.

Adult↗
PubMed2005

Dosimetric study using different leaf-width MLCs for treatment planning of dynamic conformal arcs and intensity-modulated radiosurgery.

This paper systematically studied the dosimetric difference between a 3 mm micro multileaf collimator (MLC), a 5 mm MLC, and a 10 mm MLC for stereotactic radiosurgery using the Brainscan treatment planning system. Thirty-four cases treated with the dynamic conformal arcs technique and 20 cases treated with the intensity modulated radiosurgery/fractionated radiotherapy (IMRS/ IMRT) technique were retrospectively studied. The conformity index, the percentage target coverage, and the dose-volume histogram (DVH) for organs-at-risk (OARs) were used for dosimetric analysis and comparison for different treatment techniques, target volumes, and treatment sites. For the dynamic conformal arcs technique, there were statistically significant differences in the conformity indices between different leaf-width MLCs. The ratio of the conformity indices between different MLCs depended on the target volume. The average conformity index ratios between the 5 mm MLC and the 3 mm MLC were 1.37+/-0.09, 1.12+/-0.04, 1.08+/-0.02 and 1.04+/-0.01, respectively, for patients with the target volume (V) in groups: (1) V< 1 cm3, (2) 1 cm3 < V< 8 cm3, (3) 8 cm3 < V< 27 cm3, and (4) V> 27 CC. The average conformity index ratios between the 10 and 3 mm MLCs were 2.00+/-0.33, 1.45+/-0.09, 1.28+/-0.09, and 1.18+/-0.05 for patients in these four volume groups, respectively. No statistically significant difference was found for the target coverage among different MLCs. For the IMRS/IMRT technique, the average conformity index and target coverage ratios were 1.01+/-0.05 and 1.00+/-0.02, respectively, between the 5 and 3 mm MLCs, and were 1.04+/-0.07 and 0.97+/-0.02, respectively, between the 10 and 3 mm MLCs. The 3 mm MLC showed slightly better overall OAR DVHs than the 5 and 10 mm MLCs, especially for the cranial site with small-volume OARs defined. The results suggest that for the dynamic conformal arcs technique, the narrower leaf-width MLC provides better dose conformity than the wider leaf-width MLCs. This advantage decreases when the target volume increases. For the IMRS/IMRT technique, the narrower leaf-width MLC could have better sparing of small OARs than the wider leaf-width MLC.

Body Burden↗
PubMed2004

Novalis radiosurgery for metastatic spine tumors.

It is logical to anticipate that the field of spinal radiosurgery will evolve in a fashion similar to that seen for intracranial radiosurgery. Given the frequency of various pathologic entities that affect the spine, including those that have proven to be largely intractable to surgery, radiation, and chemotherapy (eg, sarcomas), and the serious clinical, economic and quality-of-life consequences of paraplegia, radiosurgery offers new hope as an adjuvant or primary therapy. The meticulous application of well-designed investigations of relevant clinical outcomes will be critical to the appropriate and effective use of this technology.

Humans↗
PubMed2004

Image-guided radiosurgery of head and neck cancers.

OBJECTIVES: Radiosurgery precisely delivers a single high dose or a few fractionated doses of radiation to a localized tumor via the stereotactic approach. Some head and neck sites are suitable for radiosurgery since there is minimal or no organ motion. The clinical studies were carried out to determine the accuracy of stereotactic radiosurgery and to demonstrate the effectiveness of radiosurgery in head and neck cancers. MATERIALS AND METHODS: Thirteen patients were treated with either single-dose or fractionated radiosurgery to the tumor. All patients except one with cancer of the lip had received prior treatments including surgery, radiotherapy, and chemotherapy for the primary cancers. The dose ranged 12 to 18 Gy for single-dose radiosurgery and 30 Gy in 5 or 6 fractions twice a week for fractionated radiosurgery. Tumor localization was achieved via the stereotactic approach. RESULTS: Accuracy of radiosurgery was within 1.5 mm. Despite the recurrent disease from previous heavy treatments, 9 patients (70%) showed a significant response (complete or >50% tumor reduction) to radiosurgery, and 3 patients had stable disease. Complete tumor response was achieved in 6 patients. All patients had excellent pain relief with functional and cosmetic preservation. There was no acute and subacute radiation toxicity detected clinically during the minimal follow-up of 6 months. CONCLUSION: Image-guided radiosurgery is effective in achieving the local tumor control and pain relief. Radiosurgery provided excellent functional and cosmetic preservation with minimal complication. The results indicate the potential of radiosurgery in the treatment of recurrent and selected primary head and neck cancers.

Carcinoma, Squamous Cell↗
PubMed2004

Modification of radiation injury by ramipril, inhibitor of angiotensin-converting enzyme, on optic neuropathy in the rat.

Inhibitors of angiotensin-converting enzyme (ACE) have been used to reduce radiation-induced normal tissue injury. The present study was carried out to determine whether ramipril, one of the inhibitors of ACE, would ameliorate radiation-induced brain damage, using a well-characterized optic neuropathy model in the rat, one of the most critical and radiosensitive structures in the brain. The brains of adult Fischer rats were irradiated stereotactically with 30 Gy using a single collimated beam. Six months after irradiation and 1.5 mg/kg day(-1) ramipril (started 2 weeks after irradiation), rats were assessed for optic nerve damage functionally, using visual evoked potential, and histologically. Results show that ramipril conferred significant modification of radiation injury, since rats receiving radiation alone showed a threefold lengthening in the mean peak latency in the visual evoked potential, whereas 75% of rats receiving radiation followed by ramipril had evoked potentials that resembled those of normal untreated control rats. The histology of irradiated and ramipril-treated optic nerves appeared nearly normal, while there was significant demyelination in both optic nerves of irradiated rats. The study represents the first demonstration of prophylaxis of radiation injury by a carboxyl-containing ACE inhibitor, providing a pharmacological strategy designed to reduce radiation-induced normal tissue damage.

Administration, Oral↗
PubMed2004

Patterns of failure after single-dose radiosurgery for spinal metastasis.

OBJECT: Single-dose radiosurgery for solitary spinal metastases can achieve rapid and durable pain control. This study was conducted to determine the patterns of failure after spinal radiosurgery. METHODS: Forty-nine patients with 61 solitary spinal metastases underwent radiosurgery between May 2001 and May 2003. Single-dose radiosurgery (10-16 Gy) was delivered only to the involved spinal segments. The authors undertook a retrospective review of clinical notes, including patient questionnaires and radiological studies (computerized tomography or magnetic resonance imaging), to analyze patterns of failure following radiosurgery with regard to the pain and tumor control. Complete and partial pain relief was achieved in 85% of the lesions treated. Relapse of pain at the treated site was noted in 7%. Radiologically, lesions progressively metastasized to the immediately adjacent spines in 5%. These patients also had progressive primary and/or other systemic metastatic diseases. CONCLUSIONS: Spine-related pain control/reduction was excellent. Tumor recurrence at the treated segment and progression to the immediately adjacent region were rare. The results support the use of spinal radiosurgery as an effective treatment option for solitary spinal metastasis.

Adult↗
PubMed2004

Image-guided procedures for intensity-modulated spinal radiosurgery. Technical note.

Radiosurgery for brain tumors has been well established in the radiation oncology and neurosurgery fields. Radiosurgery of extracranial tumors such as those involving the spine is, however, still in the early stage because of difficulties in patient immobilization and organ motion. The authors describe an image-guided procedure for intensity-modulated spinal radiosurgery that was developed at Henry Ford Hospital.

Algorithms↗
PubMed2003

Image-guided and intensity-modulated radiosurgery for patients with spinal metastasis.

BACKGROUND: Radiosurgery can deliver a single, large radiation dose to a localized tumor using a stereotactic approach and hence, requires accurate and precise delivery of radiation to the target. Of the extracranial organ targets, the spine is considered a suitable site for radiosurgery, because there is minimal or no breathing-related organ movement. The authors studied spinal radiosurgery in patients with spinal metastases to determine its accuracy and precision. METHODS: The spinal radiosurgery program was based on an image-guided and intensity-modulated, shaped-beam radiosurgical unit. It is equipped with micromultileaf collimators for beam shaping and radiation intensity modulation and with a noninvasive, frameless positioning device that uses infrared, passive marker technology together with corroborative image fusion of the digitally reconstructed image from computed tomography (CT) simulation and orthogonal X-ray imagery at the treatment position. These images were compared with the port films that were taken at the time of treatment to determine the accuracy of the isocenter position. Clinical feasibility was tested in 10 patients who had spinal metastasis with or without spinal cord compression. The patients were treated with fractionated external beam radiotherapy followed by single-dose radiosurgery as a boost (6-8 grays) to the most involved portion of the spine or to the site of spinal cord compression. RESULTS: The accuracy for the isocenter was within 1.36 mm +/- 0.11 mm, as measured by image fusion of the digitally reconstructed image from CT simulation and the port film. Clinically, the majority of patients had prompt pain relief within 2-4 weeks of treatment. Complete and partial recovery of motor function also was achieved in patients with spinal cord compression. The radiation dose to the spinal cord was minimal. The maximum dose of radiation to the anterior edge of the spinal cord within a transverse section, on average, was 50% of the prescribed dose. There was no acute radiation toxicity detected clinically during the mean follow-up of 6 months. CONCLUSIONS: Image-guided, shaped-beam spinal radiosurgery is accurate and precise. Rapid clinical improvement of pain and neurologic function also may be achieved. The results indicate the potential of spinal radiosurgery in the treatment of patients with spinal metastasis, especially those with solitary sites of spine involvement, to increase the prospects of long-term palliation.

Feasibility Studies↗
PubMed2003

Arsenic trioxide enhances radiation response of 9L glioma in the rat brain.

Arsenic trioxide (ATO) at low doses induces leukemia cells to undergo apoptosis and at higher doses causes blood flow to solid tumors to shut down. To determine whether a potential synergistic interaction exists between ATO at the non-toxic dose level in the rat and radiation, the present study was carried out with orthotopic 9L malignant gliomas growing in the brains of rats. Animals died within 50 days of treatment when 12-day-old 9L gliomas growing in the brain of Fischer rats were treated with either the drug alone (8 mg/kg) or radiation alone (25 Gy). In contrast, the overall tumor cure rate exceeded 50% at a follow-up time of 120 days after the combined treatment with radiation and ATO. Long-term surviving animals showed no clinical or disproportionately enhanced histopathological changes in the brain parenchyma. Early changes in tumor physiology showed that the vascular leakage of FITC-dextran conjugates was apparent within 8 h of drug administration. Last, the use of diffusion magnetic resonance imaging as an early surrogate marker of therapeutic efficacy corroborated the effects of drug with and without radiation on brain histology and animal survival.

Animals↗
PubMed2002

Radiosurgical treatment for Ewing's sarcoma of the lumbar spine: case report.

STUDY DESIGN: Case report. OBJECTIVES: The objective of this study was to document the long-term follow-up of a single case. SUMMARY OF BACKGROUND DATA: Radiosurgery is potentially a useful therapeutic option for spinal tumors. The authors present the unusual case of a patient with recurrent extraosseous Ewing's sarcoma of the lumbar spine, who experienced excellent clinical, radiographic, and oncologic response without complications after treatment with dedicated Novalis Shaped Beam Radiosurgery (Brain Lab, Inc.). METHODS: Observational. RESULTS: We observed excellent clinical and oncologic control at 1-year posttreatment. CONCLUSION: Radiosurgery may be a valuable treatment option for recurrent spinal tumors.

Bone Neoplasms↗
PubMed2002

Pronounced radiosensitization of cultured human cancer cells by COX inhibitor under acidic microenvironment.

PURPOSE: To demonstrate the influence of pH on the cytotoxicity and radiosensitization by COX (cyclooxygenase) -1 and -2 inhibitors using established human cancer cells in culture. METHODS AND MATERIALS: Nonselective COX inhibitor, ibuprofen (IB), and selective COX-2 inhibitor, SC-236, were used to determine the cytotoxicity and radiosensitization at varying pH of culture media. Human colon carcinoma cell line (HT-29) was exposed to the drug alone and in combination with radiation at different pH of the cell culture media. The end point was clonogenic ability of the single-plated cells after the treatment. RESULTS: Cytotoxicity and radiosensitization of IB increased with higher drug concentration and longer exposure time. The most significant radiosensitization was seen with IB (1.5 mM) for 2-h treatment at pH 6.7 before irradiation. The dose-modifying factor as defined by the ratio of radiation doses required to achieve the same effect on cell survival was 1.8 at 10% survival level. In contrast, SC-236 (50 microM for 2-8 h) showed no pH-dependent cytotoxicity. There was modest increase in the cell killing at lower doses of radiation. CONCLUSION: An acidic pH was an important factor affecting the increased cytotoxicity and radiosensitization by ibuprofen. Radiation response was enhanced at shoulder portion of the cell survival curve by selective COX-2 inhibitor.

Cell Survival↗
PubMed2002

Dosimetric characteristics of Novalis shaped beam surgery unit.

The dosimetric characteristics of a new dedicated radiosurgical treatment unit are systematically measured in terms of its percent depth dose, beam profile, and relative scatter factor. High-resolution diode detector, mini-ion-chamber detector, and conventional Kodak XV films are used to measure dosimetric data for a range of field sizes from 6x6 mm to 100x100 mm. The effects of collimator size, micro-multileaf collimator shape, and detector type on the dosimetric data are investigated. Results indicate that, with careful design, accurate dosimetric data could be acquired using either a dedicated diode detector or a mini-ion-chamber detector, and film detector. Special attention is required when measuring dosimetric data for small field sizes such as 6x6 mm.

Equipment Failure Analysis↗
PubMed2002

A technique of intensity-modulated radiosurgery (IMRS) for spinal tumors.

This study is to demonstrate the feasibility of spinal radiosurgery using an image-guided intensity-modulated radiosurgical (IMRS) procedure. A dedicated Novalis shaped beam surgery unit equipped with a built-in micro-multileaf collimator (mMLC) with a single 6 MV photon beam was used. Each patient was simulated in the supine position using an AcQsim CT simulator with infrared sensitive markers for localization. A variety of different treatment plans were developed, but the most common plan was the use of seven coplanar intensity-modulated beams to minimize radiation to critical organs such as the spinal cord and kidneys. An automatic localization device based on infrared and video cameras was used to guide the initial patient setup. Two keV x-ray imaging systems were used to identify potential deviations from the planned isocenter. A total of 25 patients with spinal tumors have been treated using this procedure with a single prescription dose ranging from 6 to 12 Gy. The final verification images indicated that the average isocenter deviation from the planned isocenter was within 2 mm. The phantom verification of isocenter doses indicated that the average deviation of measured isocenter doses from the planned isocenter doses for all patients treated with intensity-modulated beams was less than 2%. Film dose measurement in a phantom study demonstrated good agreement of above 50% isodose lines between the planned and measured results. Preliminary experience shows that precision delivery of high dose radiation could be administered to the planned target volume while the dose to the critical organs is kept within tolerable limits.

Computer Simulation↗
PubMed2002

Noninvasive detection of radiation-induced optic neuropathy by manganese-enhanced MRI.

Available imaging techniques have a limited ability to detect radiation-induced injury of the normal brain. In particular, there is no noninvasive method available for detection of structural or functional neuronal damage induced by radiation. This study was designed to determine whether MRI enhanced using the neuronal track tracer MnCl(2) can detect radiation-induced optic neuropathy. A single dose of radiation (35 Gy) was delivered to produce optic neuropathy in Fischer 344 rats by using a stereotactic method with a 6-mm dorsoventral secondary collimator. At 6 months after irradiation, MRI was performed in 1-mm sections using a 7-T magnetic field with the neuronal tracer MnCl(2) injected into the vitreous of the eye 24 h prior to imaging. The rats were then killed humanely for a histological study with hematoxylin and eosin, glial fibrillary acidic protein (Gfap) for the detection of astrocytic activity, Luxol Fast Blue/Periodic Acid Schiff (LFB/PAS) for the detection of myelinization status, and Bielschowski silver stain for axon status. In nonirradiated control animals, T1-weighted MRI with manganese vitreous injection revealed an optic nerve track that was brightly enhanced from the orbit to the optic chiasm. In the irradiated animals, there was clear evidence of the damage at the optic chiasm and optic nerves, with loss of axon and demyelinization within the site of irradiation upon histological examination. T1-weighted MRI with manganese vitreous injection showed an enhancing optic nerve posterior to the orbit. However, this enhancement disappeared at the site of irradiation. The area of loss of manganese contrast on the MRI scan correlated well with the area of histological abnormality showing axonal degeneration and demyelinization. Radiation-induced optic neuropathy was thus detected noninvasively by MRI with the antegrade neuronal tracer manganese, which exhibited negative contrast enhancement by causing loss of signal. This study represents the first demonstration of MR imaging of radiation-induced neuronal damage and could provide a means to explore the biological and functional integrity of neuronal pathways.

Animals↗
PubMedDate not supplied

The evolving role of stereotactic radiosurgery and stereotactic radiation therapy for patients with spine tumors.

Traditional management strategies for patients with spinal tumors have undergone considerable changes during the last 15 years. Significant improvements in digital imaging, computer processing, and treatment planning have provided the basis for the application of stereotactic techniques, now the standard of care for intracranial pathology, to spinal pathology. In addition, certain of these improvements have also allowed us to progress from frame-based to frameless systems which now act to accurately assure the delivery of high doses of radiation to a precisely defined target volume while sparing injury to adjacent normal tissues. In this article we will describe the evolution from yesterday's standards for radiation therapy to the current state of the art for the treatment of patients with spinal tumors. This presentation will include a discussion of radiation dosing and toxicity, the overall process of extracranial radiation delivery, and the current state of the art regarding Cyberknife, Novalis, and tomotherapy. Additional discussion relating current research protocols and future directions for the management of benign tumors of the spine will also be presented.

Humans↗