Biomedical subjects

Bill J Salter

Publications and source records attributed to Bill J Salter.

10 recordsLinked to original sources

PubMed2006

Image-guided intensity-modulated radiation therapy for gallbladder carcinoma.

PURPOSE: Clinical and technical parameter analysis of patients treated with ultrasound-based image-guided tomotherapeutic IMRT for gallbladder cancer. METHODS AND MATERIALS: Between 8/2001 and 5/2005, 10 patients with primary tumors of the gallbladder were treated by image-guided IMRT to median doses of 59 Gy. To analyze normal tissue radiation exposure reduction using this novel approach, a virtual plan comparison between actually delivered IMRT plans and re-computed plans with identical inverse planning parameters but more conventional PTV safety margins was conducted. RESULTS: Average CTV was 379 cm(3), with a mean initial PTV of 834 cm(3). In 9/10 patients, a boost was delivered to a mean CTV(boost) of 171 cm(3) and average PTV(boost) of 241 cm(3). One patient reported RTOG grade 3 acute toxicity. All other patients exhibited Grade 2 or lower acute toxicity. Preliminary median overall survival was 16.7 months (range 3.2-34.9 months), with 5/10 patients alive at analysis. Virtual plan comparison revealed significant organ-at-risk sparing by the enabled PTV margin reduction. CONCLUSION: Ultrasound-based image-guided IMRT is a feasible mechanism of delivering conformal radiation doses to tumors of the gallbladder with acceptable toxicity. Early outcome data with this novel radiation planning and delivery technique are encouraging and comparable to previously reported literature.

Adenocarcinoma↗

PubMed2006

Stereotactic body radiation therapy for centrally located lung lesions.

Presentation of outcomes of patients treated by stereotactic body radiation therapy (SBRT) for lung lesions located within or touching a 2 cm zone around major airways. Serial tomotherapeutic SBRT has been planned and delivered at our institution since August 2001. Of 108 patients treated for primary and secondary lung tumors, nine harbored tumors (8 metastases, 1 recurrent NSCLC) located in close proximity to carina, right and left main bronchi, right and left upper lobe bronchi, intermedius, right middle lobe, lingular, or right and left lower lobe bronchi. SBRT was delivered to total doses of 36 Gy in 3 fractions (n = 8) or 6 fractions (n = 1), using a serial tomotherapy system (Nomos Peacock). We assessed local tumor control, clinical toxicity, normal tissue imaging changes, and overall survival. Median tumor volume was 26 cm3 (range 1.7 to 135 cm3). Tumor locations were hilar (n = 3), and parenchymal in six cases. Hilar lesions accounted for the three largest tumor volumes in the series. During a median follow-up of 10.6 months (range 2.5 to 41.5 months), all lesions treated were locally controlled as confirmed by CT or CT/PET imaging. Parenchymal imaging changes included focal lung fibrosis and major airway wall thickening. One occurrence of major airway occlusion (right lower lobe bronchus) was observed. This event was diagnosed by chest x-ray at 36 months, following treatment of the second largest hilar lesion in the present series. Based on the outcomes observed in this small sample series, SBRT for centrally located lung lesions appears feasible, was associated with low incidence of toxicities, and provided sustained local tumor control. However, long-term survival may be associated with major airway injury. As long-term follow-up in larger numbers of patients is lacking at this time, exclusion of patients with centrally located lesions may be considered when patients are treated in curative intent.

Airway Obstruction↗

PubMed2006

Monte Carlo characterization of target doses in stereotactic body radiation therapy (SBRT).

To compare finite-size pencil beam/equivalent path-length (FSPB/EPL) and Monte Carlo (MC) SBRT dose computations for serial tomotherapy and to quantitatively assess dose differences between the dose calculation methods. Based on 72 SBRT plans for pulmonary targets, FSPB/EPL, considering the inhomogeneous lung environment, and MC calculations were performed to establish differences between FSPB/EPL predicted dose and MC derived doses. Compared with MC, FSPB/EPL consistently overestimated minimum doses to the clinical target volume and planning target volumes by an average of 18.1+/-7.15% (range 4 to 33.4%), and 21.9+/-10.4% (range 1.2 to 45.5%), respectively. The respective mean target dose differences were 15.5+/-7.4% (2.8-36.4%) and 19.2+/-7.6% (3.6-40.1%). Deviations from MC doses were lesion size and location dependent, with smaller lesions completely embedded into lung parenchyma being most susceptible. Larger lesion in contact with mediastinum and chest wall showed lesser differences. In comparison with MC dose calculation, FSPB/EPL overestimates doses delivered to pulmonary SBRT targets. The observed dose differences may have impact on local tumor control rates, and may deserve consideration when using fast, but less accurate dose calculation methods.

Carcinoma, Non-Small-Cell Lung↗

PubMed2004

Daily ultrasound-based image-guided targeting for radiotherapy of upper abdominal malignancies.

PURPOSE: Development and implementation of a strategy to use a stereotactic ultrasound (US)-based image-guided targeting device (BAT) to align intensity-modulated radiotherapy (IMRT) target volumes accurately in the upper abdomen. Because the outlines of such targets may be poorly visualized by US, we present a method that uses adjacent vascular guidance structures as surrogates for the target position. We assessed the potential for improvement of daily repositioning and the feasibility of daily application. METHODS AND MATERIALS: A total of 62 patients were treated by sequential tomotherapeutic IMRT between October 2000 and June 2003 for cholangiocarcinoma and gallbladder carcinoma (n = 10), hepatocellular carcinoma (n = 10), liver metastases (n = 11), pancreatic carcinoma (n = 20), neuroblastoma (n = 3), and other abdominal and retroperitoneal tumors (n = 8). The target volumes (TVs) and organs at risk were delineated in contrast-enhanced CT data sets. Additionally, vascular guidance structures in close anatomic relation to the TV, or within the TV, were delineated. Throughout the course of IMRT, US BAT images were acquired during daily treatment positioning. In addition to the anatomic structures typically used for US targeting (e.g., the TV and dose-limiting organs at risk), CT contours of guidance structures were superimposed onto the real-time acquired axial and sagittal US images, and target position adjustments, as indicated by the system, were performed accordingly. We report the BAT-derived distribution of shifts in the three principal room axes compared with a skin-mark-based setup, as well as the time required to perform BAT alignment. The capability of the presented method to improve target alignment was assessed in 15 patients by comparing the organ and fiducial position between the respective treatment simulation CT with a control CT study after US targeting in the CT suite. RESULTS: A total of 1,337 BAT alignments were attempted. US images were not useful in 56 setups (4.2%), mainly because of limited visibility due to daily variations in colonic and gastric air. US imaging was facilitated in intrahepatic tumors and asthenic patients. The mean +/- SD shift from the skin mark position was 4.9 +/- 4.35, 6.0 +/- 5.31, and 6.0 +/- 6.7 mm in the x, y, and z direction, respectively. The mean magnitude vector of three-dimensional alignment correction was 11.4 +/- 7.6 mm. The proportion of daily alignments corrected by a magnitude of >10, >15, and >20 mm was 48.9%, 25.1%, and 12.7%, respectively. The magnitude of shifts in the principal directions, as well as the three-dimensional vector of displacement, was statistically significant (test against the zero hypothesis) at p <0.0001. The guidance structures that were the most valuable for identification of the TV position were the branches of the portal vein, hepatic artery, and dilated bile ducts in intrahepatic lesions and the aorta, celiac trunk, superior mesenteric artery, and extrahepatic aspects of the portal vein system in retroperitoneal and extrahepatic lesions. The mean total setup time was 4.6 min. The correlation of BAT targeting with target setup error assessment in the control CT scans in 15 patients revealed setup error reduction in 14 of 15 alignments. The average setup error reduction, assessed as a reduction in the length of setup error three-dimensional magnitude vector, was 54.4% +/- 26.9%, with an observed mean magnitude of residual setup error of 4.6 +/- 3.4 mm. The sole worsening of an initial setup was by a magnitude of <2 mm. US targeting resulted in statistically significant improvements in patient setup (p = 0.03). CONCLUSION: Daily US-guided BAT targeting for patients with upper abdominal tumors was feasible in the vast majority of attempted setups. This method of US-based image-guided tumor targeting has been successfully implemented in clinical routine. The observed improved daily repositioning accuracy might allow for individualized reduction of safety margins and optional dose escalation. Compared with the established application of the BAT device for prostate radiotherapy, in which the target can be directly visualized, the TV in the present study was predominantly positioned relative to guidance vascular structures in close anatomic relation. We perceived an enormous potential in improved and individualized patient positioning for fractionated radiotherapy and also for stereotactic extracranial radiotherapy and radiosurgery, especially for tumors of the liver and pancreas.

Abdominal Neoplasms↗

PubMed2004

Repositioning accuracy of a commercially available thermoplastic mask system.

BACKGROUND AND PURPOSE: To evaluate the repositioning accuracy of a commercially available thermoplastic mask system for single dose radiosurgery treatments and fractionated treatment courses. PATIENTS AND METHODS: The repositioning accuracy of the Raycast-HP mask system (Orfit Industries, Wijnegem, Belgium) was analyzed. Twenty-two patients that were treated by intensity-modulated radiation therapy (IMRT) or intensity modulated radiosurgery (IMRS) for 43 intracranial lesions, underwent repeated CT imaging during their course of treatment, or as a positional control immediately before radiosurgery. We evaluated multiple anatomical landmark coordinates and their respective shifts in consecutive repeated CT-controls. An iterative optimization algorithm allowed for the calculation of the x, y and z-components of translation of the target isocenter(s) for each repeated CT, as well as rotation in the respective CT data sets. In addition to absolute target isocenter translation, the total magnitude vector (i.e. sum-vector) of isocenter motion was calculated along with patient rotations about the three principle axes. RESULTS: Fifty-five control CT datasets were analyzed for the target isocenter's respective position relative to the original treatment planning CT simulation. Mean target isocenter translation was 0.74+/-0.53, 0.75+/-0.60 and 0.93+/-0.78 mm in x, y and z-directions, respectively. Mean rotation about the x, y and z-axes was 0.67+/-0.66, 0.61+/-0.63 and 0.67+/-0.61 degrees, respectively. The respective median and mean magnitude vectors of isocenter translation were 1.28 and 1.59+/-0.84 mm. Analysis of the accuracy of the first setup control, representative of setup accuracy for radiosurgery treatments, compared with setup accuracy throughout a fractionated radiation treatment course were statistically equivalent (P= 0.15) thus indicating no measurable deterioration of setup accuracy throughout the treatment course. CONCLUSIONS: The analyzed Orfit thermoplastic mask system performed favorably compared with other mask immobilization systems for which peer-reviewed repositioning data exist. While the performance of the system for fractionated treatment courses was considered to be excellent, use of this mask system for radiosurgery immobilization in our clinic is subject to additional quality assurance measures to prohibit the delivery of treatments with target dislocations larger than 2 mm. The measured data in the present study should enable the users of this system to assign appropriate margins for the generation of planning target volumes.

Cranial Irradiation↗

PubMed2004

External beam radiation therapy for hepatocellular carcinoma: potential of intensity-modulated and image-guided radiation therapy.

External beam radiotherapy has historically played a minor role in the primary treatment of hepatocellular carcinoma. Although there is evidence for tumor response to external beam radiotherapy and despite the fact that a radiation dose-response relationship has been established, the limited radiation tolerance of the adjacent normal liver has prohibited wider use of radiation therapy in this disease. Recent technological and conceptual developments in the field of radiation therapy-such as intensity-modulated radiation therapy, image-guided radiation therapy, and stereotactic body radiation therapy-have the potential to improve radiation treatments by conforming the delivered radiation dose distribution tightly to the tumor or target volume outline while sparing normal liver tissue from high-dose radiation. Image guidance allows for a reduction of added (normal tissue) safety margins designed to account for interfraction patient and target setup variability, and stereotactic targeting will further reduce residual target setup uncertainty. Combining improvements in tumor targeting with normal tissue sparing, radiation dose delivery will enable clinically effective and safe radiation delivery for liver tumors such as hepatocellular carcinoma. This article reviews the role of radiotherapy for hepatocellular carcinoma; presents modern radiation therapy modalities and concepts such as intensity-modulated, image-guided, and stereotactic body radiation therapy; and hypothesizes about their future effect on primary treatment alternatives.

Carcinoma, Hepatocellular↗

PubMed2004

Repositioning accuracy of a commercially available double-vacuum whole body immobilization system for stereotactic body radiation therapy.

We evaluated the repositioning accuracy of a commercially available stereotactic whole body immobilization system (BodyFIX, Medical Intelligence, Schwabmuenchen, Germany) in 36 patients treated by hypofractionated stereotactic body radiation therapy. CT data were acquired for positional control of patient and tumor before each fraction of the treatment course. Those control CT datasets were compared with the original treatment planning CT simulation and analyzed with respect to positional misalignment of bony patient anatomy, and the respective position of the treated small lung or liver lesions. We assessed the stereotactic coordinates of distinct bony anatomical landmarks in the original CT and each control dataset. In addition, the target isocenter was recorded in the planning CT simulation dataset. An iterative optimization algorithm was implemented, utilizing a root mean square scoring function to determine the best-fit orientation of subsequent sets of anatomical landmark measurements relative to the original treatment planning CT data set. This allowed for the calculation of the x, y and z-components of translation of the patient's body and the target's center-of-mass for each control CT study, as well as rotation about the principal room axes in the respective CT data sets. In addition to absolute patient/target translation, the total magnitude vector of patient and target misalignment was calculated. A clinical assessment determined whether or not the assigned planning target volume safety margins would have provided the desired target coverage. To this end, each control CT study was co-registered with the original treatment planning study using immobilization system related fiducial markers, and the computed isodose calculation was superimposed. In 109 control setup CT scans available for comparison with their respective treatment planning CT simulation study (2-5 per patient, median 3), anatomical landmark analysis revealed a mean bony landmark translation of -0.4 +/- 3.9 (mean +/- SD), -0.1 +/- 1.6 and 0.3 +/- 3.6 mm in x, y and z-directions, respectively. Bony landmark setup deviations along one or more principal axis larger than 5 mm were observed in 32 control CT studies (29.4%). Body rotations about the x-, y- and z-axis were 0.9 +/- 0.7, 0.8 +/- 0.7 and 1.8 +/- 1.6 degrees, respectively. Assuming a rigid body relationship of target and bony anatomy, the mean computed absolute target translation was 2.9 +/- 3.3, 2.3 +/- 2.5 and 3.2 +/- 2.7 mm in x, y and z-directions, respectively. The median and mean magnitude vector of target isocenter displacement was computed to be 4.9 mm, and 5.7 +/- 3.7 mm. Clinical assessment of PTV/target volume coverage revealed 72 (66.1%), 23 (21.1%), and 14 (12.8%), of excellent (100% isodose coverage), good (>90% isodose coverage), and poor GTV/isodose alignment quality (less than 90% isodose coverage to some aspect of the GTV), respectively. Loss of target volume dose coverage was correlated with translations >5 mm along one or more axes (p<0.0001), rotations >3 degrees about the z-axis (p=0.0007) and body mass index >30 (p<0.0001). The analyzed BodyFIX whole body immobilization system performed favorably compared with other stereotactic body immobilization systems for which peer-reviewed repositioning data exist. While the measured variability in patient and target setup provided clinically acceptable setup accuracy in the vast majority of cases, larger setup deviations were occasional observed. Such deviations constitute a potential for partial target underdosing warranting, in our opinion, a pre-delivery positional assessment procedure (e.g., pre-treatment control CT scan).

Body Weights and Measures↗

PubMed2003

Quality assurance for computed-tomography simulators and the computed-tomography-simulation process: report of the AAPM Radiation Therapy Committee Task Group No. 66.

This document presents recommendations of the American Association of Physicists in Medicine (AAPM) for quality assurance of computed-tomography- (CT) simulators and CT-simulation process. This report was prepared by Task Group No. 66 of the AAPM Radiation Therapy Committee. It was approved by the Radiation Therapy Committee and by the AAPM Science Council.

Computer Simulation↗

PubMed2003

Daily stereotactic ultrasound prostate targeting: inter-user variability.

We analyzed the inter-user variability of patient setup for prostate radiotherapy using a stereotactic ultrasound-targeting device. Setup variations in 20 prostate cancer patients were analyzed. Users were a radiation oncologist, a medical physicist, four radiation technologists (RTT) and a radiologist. The radiation oncologist, radiologist, physicist and two RTTs were experienced users of the system (>18 months of experience); two RTTs were users new to the system. Gold standard for this analysis was a control CT acquired immediately following ultrasound targeting. For inter-user variability assessments, the radiation oncologist provided a set of axial and sagittal freeze-frames (standard freeze-frames) for virtual targeting by all users. Additionally each user acquired individual freeze-frames for target alignments. We analyzed the range of virtual setups in each patient along the principal room axes based on standard and individual freeze-frames. The magnitude of residual setup error and percentage of setup change for each user was assessed by control CT/planning CT comparison with individual virtual shifts. A total of 184 alignments were analyzed. The range of virtual shifts between users was 2.7+/-1.4, 3.6+/-1.1, and 4.4+/-1.4 mm (mean+/-SD) in x, y and z-direction for setups based on standard freeze-frames and 3.9+/-2.6, 6.0+/-4.7, and 5.4+/-2.7 mm for setups based on individual freeze-frames. When only virtual shifts of experienced users were analyzed, the mean ranges were reduced by up to 2.4 mm. Average magnitude of initial setup error before ultrasound targeting was 14.3 mm. Average improvement of prostate setup was 63.1+/-23.4% in experienced and 35.14+/-37.7% in inexperienced users, respectively (p<0.0001). Only 5 of 184 (2.7%) virtual alignments would have introduced new larger setup errors (mean 3.2 mm, range 0.2 to 9.5 mm) than the magnitude of the initial setup error. We conclude that ultrasound guided treatment setup for patients treated for prostate cancer can be performed with high inter-user consistency and does lead to improved treatment setup in more than 97% of attempted setups. Experienced use is correlated with a reduced range of setups between users and higher degree of setup improvement when compared with users new to the system

Humans↗

PubMed2002

Fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT) for small acoustic neuromas.

Eight patients with acoustic neuromas were treated using a novel method developed at our institution for delivering fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT). We present treatment parameters, dosimetry analysis, and preliminary clinical outcome. The method incorporates high-precision invasive fixation, obliquely-oriented tomotherapy arcs, and reduced dimension pencil beams. The delivered dose distributions for the 8 patients treated from April 1999 to May 2001 were assessed for dose conformality, homogeneity, and doses to organs at risk. Total doses prescribed were 54 Gy in daily doses of 1.8 Gy. Results show that the median planning target volume (gross tumor volume plus a safety margin of 2 mm) was 2.48 cm3 (1.64 to 16.86 cm3) and that the median conformality and homogeneity indices were 1.69 (1.56 to 2.16) and 1.12 (1.09 to 1.19), respectively. The respective average mean and maximum doses to the brain stem were 12.67 Gy and 53.86 Gy. The treatment parameters for the novel FS-IMRT method developed here document excellent dose conformality and normal tissue sparing. Preliminary short-term follow-up (mean 17, median 18.5 months) revealed a 100% local control and hearing preservation rate. No new persistent impairment of facial and trigeminal nerve was observed. Our current follow-up experience indicates a reasonable potential for achieving outcomes comparable to established stereotactic radiotherapy techniques.

Brain Stem↗