Biomedical subjects

B J Salter

Publications and source records attributed to B J Salter.

4 recordsLinked to original sources

PubMed2005

Intensity-modulated radiosurgery for childhood arteriovenous malformations.

PURPOSE: Presentation of intensity-modulated radiosurgery (IMRS) for the treatment of inoperable, complex shaped pediatric arterio-venous malformations AVM. METHOD: Between 03/99 and 11/04, IMRS was delivered to seven children aged six to 18 years. Prescribed minimum doses ranged from 17.5 to 20 Gy (median 18 Gy). Radiosurgery planning and delivery used a serial tomotherapeutic IMRT technique (Peacock IMRT, North American Scientific/Nomos, Cranberry Township, PA) over two to four couch angles. A linear accelerator attached binary multi-leaf collimator was used to generate pencil beams of 10 mm by either 8.5 or 4.0 mm. Treatment planning employed an inverse treatment planning optimization algorithm. Parameters submitted to the treatment planning system were: prescription dose (PD), volume of target allowed to receive less dose (standard 3%), minimum dose (0.5 Gy less than PD), and maximum dose (200% of PD). Planning system specific IMRS target and tissue types were selected to prioritize dose conformality over dose homogeneity. The prescription isodose encompassed at least 95% of the target volume. We calculated conformality (CI) and homogeneity indices (HI) to characterize the quality of IMRS plans, and summarized preliminary clinical outcomes. FINDINGS: Target volumes ranged from 0.71 to 63.02 cm(3) (median 13.8 cm(3), 6/7 AVM larger than 10 cm(3)). Median CI was 1.07 (range 1.05 to 1.7) according to RTOG criteria. Median HI was 1.12 (range 1.09 to 1.23). During limited follow-up (median 32 months, range 5 to 53 months), two AVM completely obliterated at 19 and 22 months, and partial obliteration (>75%) was observed in three cases. No treatment-related side effects, other than acute nausea and temporary headaches interpreted as being associated with changes in cerebral blood distribution, were observed. CONCLUSIONS: IMRS can allow for highly conformal planning and delivery of radiosurgery radiation doses even if pediatric AVM target volumes are large and/or highly complex in shape. This technique has been seen to result in favorable preliminary outcomes, thus supporting future exploration of this technique in pediatric and adult patients.

Adolescent↗

PubMed2001

The TALON removable head frame system for stereotactic radiosurgery/radiotherapy: measurement of the repositioning accuracy.

PURPOSE: To present the TALON removable head frame system as an immobilization device for single-fraction intensity-modulated stereotactic radiosurgery (IMRS) and fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT); and to evaluate the repositioning accuracy by measurement of anatomic landmark coordinates in repeated computed tomography (CT) examinations. METHODS AND MATERIALS: Nine patients treated by fractionated stereotactic intensity-modulated radiotherapy underwent repeated CTs during their treatment courses. We evaluated anatomic landmark coordinates in a total of 26 repeat CT data sets and respective x, y, and z shifts relative to their positions in the nine treatment-planning reference CTs. An iterative optimization algorithm was employed using a root mean square scoring function to determine the best-fit orientation of subsequent sets of anatomic landmark measurements relative to the original image set. This allowed for the calculation of the x, y, and z components of translation of the target isocenter for each repeat CT. In addition to absolute target isocenter translation, the magnitude (sum vector) of isocenter motion and the patient/target rotation about the three principal axes were calculated. RESULTS: Anatomic landmark analysis over a treatment course of 6 weeks revealed a mean target isocenter translation of 0.95 +/- 0.55, 0.58 +/- 0.46, and 0.51 +/- 0.38 mm in x, y, and z directions, respectively. The mean magnitude of isocenter translation was 1.38 +/- 0.48 mm. The 95% confidence interval ([CI], mean translation plus two standard deviations) for repeated isocenter setup accuracy over the 6-week period was 2.34 mm. Average rotations about the x, y, and z axes were 0.41 +/- 0.36, 0.29 +/- 0.25, and 0.18 +/- 0.15 degrees, respectively. Analysis of the accuracy of the first repeated setup control, representative of single-fraction stereotactic radiosurgery situations, resulted in a mean target isocenter translation in the x, y, and z directions of 0.52 +/- 0.38, 0.56 +/- 0.30, and 0.46 +/- 0.25 mm, respectively. The mean magnitude of isocenter translation was 0.99 +/- 0.28 mm. The 95% confidence interval for these radiosurgery situations was 1.55 mm. Average rotations at first repeated setup control about the x, y, and z axes were 0.24 +/- 0.19, 0.19 +/- 0.17, and 0.19 +/- 0.12 degrees, respectively. CONCLUSION: The TALON relocatable head frame was seen to be well suited for immobilization and repositioning of single-fraction stereotactic radiosurgery treatments. Because of its unique removable design, the system was also seen to provide excellent repeat immobilization and alignment for fractionated stereotactic applications. The exceptional accuracy for the single-fraction stereotactic radiosurgical application of the system was seen to deteriorate only slightly over a 6-week fractionated stereotactic treatment course.

Algorithms↗

PubMed2001

NOMOS Peacock IMRT utilizing the Beak post collimation device.

Intensity-modulated radiation therapy (IMRT), an exciting recent development in the field of radiation therapy, is widely anticipated by many to make possible significant improvements in the quality of radiation treatments delivered to patients. The NOMOS Peacock method of delivery, often referred to as serial tomotherapy because of its "slice-wise" treatment of a tumor, has been used since 1994 to treat some 8000+ patients worldwide. This slice-wise method of treatment is known to produce extremely conformal dose distributions due to its ability to specifically match the dose distribution on each slice to the shape of the target volume on that same slice. Based on the belief of this institution, and the NOMOS Corporation, that an increase in the number of treatment slices into which the target is segmented would lead directly to an improvement in three-dimensional (3D) dose conformality, a joint effort was undertaken to develop a new MIMIC collimator treatment mode. Inherent to the original design of the NOMOS MIMIC binary multileaf collimator were 2 treatment modes: a 2-cm mode with a slice thickness of approximately 1.7 cm and a 1-cm mode with a slice thickness of approximately 0.85 cm. As a result of this collaborative effort, a new MIMIC treatment mode has been developed. The method employs a slit collimator, post-collimation device known as the BEAK, enabling the treatment mode referred to as Beak Mode. The device imposes a distal redefinition of the slice thickness, or length, by effectively blocking the full retraction of the MIMIC vanes. The end result is a newly available slice thickness of approximately 4 mm, which is shown in this work to yield significant improvements in dose conformality for 2 representative patients. The comparative analysis of these 2 patient plans includes, in addition to a comparison of isodose distributions, an evaluation of dose-volume histogram (DVH) information, and a comparison of indices of conformality (CI) and homogeneity (HI).

Humans↗

PubMed2001

An oblique arc capable patient positioning system for sequential tomotherapy.

A new patient positioning system has been designed and manufactured, allowing for the accurate delivery of obliquely oriented intensity modulated treatment arcs via a commercially available IMRT system. The ability to deliver such obliquely oriented intensity modulated arcs allows the commercial system to more closely approach a 4pi pencil beam delivery geometry which, in turn, allows for significant improvements in conformality for many tumor geometries. While the IMRT system delivered to this institution in the fall of 1996 was capable of planning for nonparallel plane delivery schemes, it proved incapable of delivering such treatments with acceptable accuracy. Because our early clinical experience revealed that certain patients could benefit significantly from such a delivery scheme we endeavored to design and manufacture an alternative treatment couch/patient positioning system (Xlator) which could overcome the limitations of the vendor supplied system. We present our initial evidence for the benefits of obliquely oriented intensity modulated treatment arcs, along with data demonstrating the inability of the original vendor supplied system to deliver such treatments with acceptable accuracy. The design of our new system is presented, as well as data demonstrating its ability to accurately deliver obliquely oriented intensity-modulated arcs. A detailed comparison of the performance of the Xlator and the vendor-supplied system is presented with regard to match line repeatability and hysteresis. Finally, the ability of the Xlator to deliver multiple couch angle sequential tomotherapy with spatial accuracy necessary to radiosurgical applications is demonstrated via a AAPM Report 54,TG-42 hidden target test. Readers note: The Xlator patient positioning system designed and patented here has recently come to be commercially available, and is currently marketed by the vendor under the name Crane II.

Adult↗