Biomedical subjects

Gordon A Watson

Publications and source records attributed to Gordon A Watson.

5 recordsLinked to original sources

PubMed2006

Extraneural metastatic medulloblastoma in an adult.

Medulloblastoma is a rare malignancy in adults, accounting for approximately 1% of all primary brain tumors. Extraneural metastases have been reported in 10-30% of cases and most commonly involve bone; rarely lymph nodes, visceral organs and bone marrow may be involved with disease. We report here our experience with a 26 year-old woman with medulloblastoma treated with gross total resection followed by radiation therapy to her craniospinal axis. She subsequently developed widespread metastatic disease involving bone exclusive of the calvarium and spine for which multi-agent salvage chemotherapy was utilized with initial good clinical response. She later relapsed within the lymph nodes and soft tissues of the pelvis and eventually suffered a local recurrence within the posterior fossa. The treatment of medulloblastoma, particularly salvage therapy following disease recurrence, is reviewed.

Adult↗

PubMed2005

Dynamic collimator optimization compared with fixed collimator angle in arc-based stereotactic radiotherapy: a dosimetric analysis.

OBJECT: The purpose of this study was to determine the effect of static and dynamic collimator optimization when using a micromultileaf collimator (mMLC) in dynamic-arc stereotactic radiosurgery (SRS) by evaluating the dose to healthy peritumoral tissue. METHODS: Thirty patients previously treated for intracranial lesions with the BrainLAB mMLC underwent retrospective replanning. Three collimator optimization strategies were compared for a simulated SRS treatment plan, as follows: Strategy 1, static collimation fixed at 90 degrees throughout arcs; Strategy 2, static collimator settings optimized for each arc; and Strategy 3, dynamic collimator settings optimized every 10 degrees throughout treatment arcs. Dose-volume histograms for a 0.7-cm shell of healthy peritumoral tissue were quantitatively compared. Collimator optimization schemes (Strategies 2 and 3) significantly decreased the volume of peritumoral tissue that is irradiated when compared with static collimation at 90 degrees (Strategy 1). The volume was reduced by 40.6% for Strategy 2 (95% confidence interval [CI] +/- 11) and by 47.1% for Strategy 3 (95% CI +/- 8.1) at the 95% isodose; by 28.4% for Strategy 2 (95% CI +/- 4.9) and 39.1% for Strategy 3 (95% CI +/- 6) at the 90% isodose; and by 18.2% for Strategy 2 (95% CI +/- 8.1) and 25.4% for Strategy 3 (95% CI +/- 7.1) at the 80% isodose. Serial collimator optimization throughout the treatment arcs (Strategy 3) reduced the mean volume of peritumoral tissue irradiated when compared with static collimator optimization (Strategy 2), by 16.1% (95% CI +/- 1.5) at 95% isodose, by 11.7% (95% CI +/- 1) at 90% isodose, and by 8.2% (95% CI +/- 1.2) at 80% isodose regions. In specific cases, linear or polynomial functions were formulated to optimize collimator settings dynamically throughout treatment arcs. CONCLUSIONS: Dynamic collimator optimization during arc-based SRS decreases the volume of healthy peritumoral tissue treated with high doses of radiation and appears to be an effective method of improving target conformality. This study is the first step toward determination of a smoothing function algorithm to allow for true dynamic collimation during SRS.

Brain Neoplasms↗

PubMed2005

Nasopharyngeal carcinoma with axillary node involvement as a component of failure following chemoradiotherapy.

We describe the treatment course and imaging correlations in a patient with a unique case of undifferentiated nasopharyngeal carcinoma with axillary lymph node involvement as a component of failure following chemoradiotherapy. To our knowledge, this is the only such case reported in the literature. A preliminary diagnosis ofaxillary node involvement was based on both positron-emission tomography and computed tomography; these findings were subsequently confirmed by pathologic review following dissection of the node. This case represents a rare presentation of a recurrent nasopharyngeal carcinoma and illustrates the importance of a comprehensive physical examination and correlation with imaging modalities when following these patients over time.

Axilla↗

PubMed2004

Basic principles of radiobiology, radiotherapy, and radiosurgery.

This article reviews the basic principles of radiobiology and the application thereof to the treatment of metastatic spine tumors. The most important concepts of dose fractionation and the concept of biologically effective dose as well as spinal cord tolerance to single and multiple doses of radiotherapy are emphasized. Basic principles of treatment planning for radiotherapy and radiosurgery are outlined.

Humans↗

PubMed2004

Radiation and intensity-modulated radiotherapy for metastatic spine tumors.

Although promising, many questions remain regarding spinal IMRT. The challenge of patient immobilization must be surmounted before a radiation facility can safely offer spinal IMRT. At many institutions, the increased expense and time requirements from physicists, therapists, and physicians preclude the routine use of IMRT for spinal lesions. Finally, there are no randomized data comparing the safety or efficacy of IMRTwith more conventional means of spinal radiation. Nonetheless, IMRT is one of the most important recent technologic advancements in radiation therapy. For complex treatment problems, such as spinal tumors, in which the surrounding organs at risk traditionally place significant constraints on the prescription dose, IMRT has great potential to provide the ideal solution.

Humans↗