Gary Luxton - Academia.edu (original) (raw)

Papers by Gary Luxton

Stereotactic and Functional Neurosurgery, 1996

During the course of a patient treatment with a North American U-type gamma unit, the remote hydr... more During the course of a patient treatment with a North American U-type gamma unit, the remote hydraulic valve controlling the direction of couch motion failed to change state. The couch, helmet and patient remained in treatment position after the expiration of treatment time for one of the target shots. No unusual equipment warning indications had been observed prior to the malfunction. The gamma unit was new, having been used to treat approximately 20 patients since it had begun to be used clinically 11 weeks previously. This specific situation was not addressed in our posted Emergency Procedures, which dealt explicitly with loss of electrical power, and loss of hydraulic pressure. In the present case, the hydraulic gauges indicated full pressure. After attempts to disengage the patient remotely proved unsuccessful, personnel entered the room. The table clutch at the foot of the couch was operated to disengage the couch/helmet assembly from its docked position. While this was not mentioned in our emergency procedures, the act had the effect of causing the cobalt-60 sources to be misaligned with the collimator apertures, thereby immediately terminating the patient treatment. This also had the unanticipated effect of substantially reducing radiation leakage exposure rate next to the couch near the tunnel opening. The patient was released from the helmet trunnions using a manufacturer-supplied long-handled special Allen key. The key was used conventionally, to release the trunnion locking mechanism, and also unconventionally to force a separation of a trunnion from the docking slot on the patient head frame. The patient was then removed from the tunnel by sliding out the pad on which she was lying. Anesthesiology personnel accompanied the patient out of the room. The unit functioned properly upon the replacement of the valve by manufacturer service personnel the next day. The patient returned for completion of treatment 1 week later. There were only minor changes to the overall patient dosimetry as a result of the malfunction. Personnel exposures were very low. The malfunction was reported to State authorities, who conducted an investigation, that was in turn followed up by an investigation by the Nuclear Regulatory Commission.

Radiotherapy and Oncology, 1996

Radiotherapy and Oncology, 1990

Medical Physics, 2011

Purpose: Medical linacs with dose rates as high as 2400 cGy/min at 10MV and 1400 cGy/min at 6MV h... more Purpose: Medical linacs with dose rates as high as 2400 cGy/min at 10MV and 1400 cGy/min at 6MV have been clinically installed in many institutions. In reality, little is known about the accuracy of delivery at these high dose rates, particularly for complex treatment plans with simultaneous motion of gantry and multileaf‐collimator (MLC) aperture. We present measurements that examine the dosimetric accuracy of dynamically‐shaped RapidArc™ and IMRT beams at the highest available dose rates. Methods: An Eclipse™ ver. 8.9 planning system commissioned with the analytic anisotropy algorithm (AAA™) for the flattening‐filter‐free X‐ray beams of the Varian TrueBeam™ linear accelerator with a high‐definition 120‐leaf MLC (HDMLC) accessory was used to create RapidArc™ and IMRT lung‐ and abdominal‐target patient treatment plans deliverable in the FFF mode of TrueBeam™. Verification plans applied to a 22‐cm diameter cylindrical polymethylmethacrylate phantom configured as water‐ equivalent material with an electron density of 1.147 were delivered at the highest available dose rates. Dose was measured with TG‐51 cross‐ calibrated ScandiDos® Delta4™dual orthogonal‐plane 1069‐diode system for conventional 2 Gy fractions and for 15Gy–16.5 Gy fractions characteristic of stereotactic body radiotherapy(SBRT). Delivery was repeated with conventional dose rate (400 cGy/min). Measured results for the two dose rates were compared with each other, and with Eclipse treatment plans. Results: Excellent agreement was found between 2400 and 400 MU/min delivery. A sample 2‐arc RapidArc™ plan gave absolute relative dose difference ratio of 0.42%±0.21% for the 439 points measuring above 10% of prescription dose, with maximum dose difference over all 1069 measurement points being 0.76% of prescription. For a small‐field 1‐ arc plan, quantities were 0.96%±0.14% for 103 points, and maximum difference over all 1069 points was 1.61%. Gated versus ungated delivery for 200 cGy/fx showed negligible differences at both 400 and 2400 dose rates. Eclipse calculations demonstrated reasonable agreement with absolute dose measurement.

International Journal of Radiation Oncology*Biology*Physics, 2009

International Journal of Radiation Oncology*Biology*Physics, 1990

International Journal of Radiation Oncology*Biology*Physics, 1991

International Journal of Radiation Oncology*Biology*Physics, 1995

Conventional radiosurgery refers to single isocenter focused beam irradiation of small intracrani... more Conventional radiosurgery refers to single isocenter focused beam irradiation of small intracranial targets with a single collimator. Conventional radiosurgery is characterized by spherical-shaped isodose surfaces. Nonspherical targets require a different approach to avoid exposing a large volume of nontarget brain tissue to high dose, particularly for lesions larger than 25 mm. Multiple isocenters are frequently used to treat nonspherical large targets, but multiple isocenter treatments are associated with a relative dose inhomogeneity of approximately 100% within the target volume, and may be correlated with an increased rate of complications. The feasibility of conformally treating elongated targets to an approximately homogeneous dose using a single isocenter methodology will be demonstrated. A prolate ellipsoid of revolution, 25 mm in diameter, 35 mm in length, positioned at five representative locations in a head phantom, was used as a target model. The alignment of the target was taken to be parallel in turn to each of the three principal axes of the head model (A/P, R/L, and C/C). Dose conformation is achieved by nonuniform arc weighting, selective limitation of the extent of individual arcs, and the use of different collimator apertures for the different arcs in accordance with the aperture size required to encompass the target for that arc. Treatment plans were selected based on considerations of dose-volume histograms and conformation of the 80% dose surface with the surface of the target. The goal was that the minimum target dose would not be less than 80% of the maximum dose. Practical treatment plans for which the minimum target dose exceeded 80% were obtained for the three orthogonal orientations of the target for the five target locations. Plan parameters were essentially independent of the target position, dependent only on target orientation. The 80% isodose contour surface enclosed on average 2.8 cm3 larger volume (range: 2.1-3.9 cm3) than the prescribed 11.45 cm3 target. The minimum dose to the target ranged from 80.1 to 84.5%, and the average dose to the target was 94.26%. The 80-to-50% dose volume enclosed an average of 14.8 cm3 of nontarget volume (range: 12.7-15.9 cm3). Average deviation in the principal planes of the 80% isodose lines from the surface of the target volume was 0.95 mm for the 25 mm dimension (range 0.0 to +1.9 mm) and 0.86 mm (range 0.0 to + 2.4 mm) for the 35 mm dimension. Standardized single isocenter treatment plans with the isocenter at the center of the target can achieve good conformation of the dose distribution to targets elongated along any of the principal axes, and located anywhere in the brain.

International Journal of Radiation Oncology*Biology*Physics, 2011

Medical Physics, 1999

A comprehensive set of dose distributions from monoenergetic photon-emitting isotropic point sour... more A comprehensive set of dose distributions from monoenergetic photon-emitting isotropic point sources in a medium can be used as a reference database for the dosimetry of photon emitter sources in that medium. Data of this type for water over the photon energy range from 15 keV to 2 MeV have been published based on calculations using a one-dimensional photon transport model. The present work, based on a previously published EGS4 Monte Carlo code, updates the classic data set of Berger and provides more extensive calculations than previously available. Air kerma strength per unit photon emission rate from an isotropic point emitter is obtained as a function of energy using published data for mass energy absorption coefficients. The TG-43 dose rate constant for water as a function of energy is calculated for monoenergetic photon emitters as the ratio of dose rate to water at 1 cm to air kerma strength for unit photon emission rate. Results for the radial dose distribution agree well with the data of Berger between 40 and 400 keV. For energies > or =500 keV, a previously undescribed buildup region for the radial dose function is identified. Thickness of the buildup region ranges from 1 mm at 500 keV to 8 mm at 2 MeV. Between 15 and 30 keV, the radial dose function within a few millimeters of the emitter is calculated to be 4%-5% higher than values derived from Berger's data. The maximum dose rate constant for monoenergetic photon emitters occurs at an energy of 60 keV, and has the value 1.355 cGy h(-1)U(-1), where U is the unit of air kerma strength, 1 microGy m2 h(-1). This would correspond to the maximum hypothetical dose rate constant for a brachytherapy photon source emitting photons of energy < or =2 MeV.

The Use of Computers in Radiation Therapy, 2000

Stereotactic and functional neurosurgery, 1996

The physical creation of a gamma unit facility requires the development of a broad-perspective mu... more The physical creation of a gamma unit facility requires the development of a broad-perspective multidisciplinary plan. The primary goal is radiosurgical treatment of intracranial lesions in a functional environment. The practical realization of a facility optimally designed for patient treatment is dependent on factors which include the facility setting, architectural goals, radiation safety requirements, and patient and medical team needs. This necessitates combined intellectual resources from neurosurgery, radiation oncology and physics, anesthesia, radiology, nursing, administration, and architectural and engineering teams. We undertook the development of a gamma unit facility which optimized the ergonomics and efficiency of patient evaluation, care and treatment, given the instrument requirements. This general plan based on our experience can be used for the development of other gamma unit facilities.

Clinical neurosurgery, 1983

The Journal of thoracic and cardiovascular surgery, 1988

During a 10-year period, 46 patients with unresectable or inoperable carcinoma of the esophagus w... more During a 10-year period, 46 patients with unresectable or inoperable carcinoma of the esophagus were treated with teletherapy-brachytherapy combination at the University of Southern California School of Medicine. Stage distribution was as follows: stage I, 5 (11%) patients; stage II, 23 (50%) patients; stage III, six (13%) patients; and stage IV, 12 (26%) patients. Thirteen patients were treated for recurrent disease, including 11 patients initially treated with teletherapy and two who had had surgical resection. Radiotherapy was given by teletherapy in 33 and brachytherapy in all 46 patients. An average tumor dose was 50 Gy with teletherapy and 20 Gy per application with brachytherapy. There were 25 patients who had more than one brachytherapy application. The 5-year actuarial survival rate for 28 patients with stage I or II disease was 12%, with a median of 13 months. This compared with no 5-year survivals and a median survival of 10 months for the 18 patients with stage III or IV...

American Journal of Clinical Oncology, Mar 1, 1991

This is an analysis of treatment results over a 23-year period in 241 patients with carcinoma of ... more This is an analysis of treatment results over a 23-year period in 241 patients with carcinoma of the esophagus. The treatment for unresectable patients was external beam radiotherapy (EBRT) alone (mean dose 55 Gy) in 137 (57%) combined with brachytherapy (mean dose 50 + 40 Gy) in 46 (19%), and chemotherapy alone in 3 (1%) patients. In the 55 resectable patients, treatment was resection alone in 9 (4%), and combined with radiotherapy (mean dose 43 Gy) in 46 (19%) patients. The 1-, 2-, and 5-year survival for the 241 patients was 36, 15, and 5%, respectively (median 38 weeks). The 5-year survival was 18% for radiotherapy (RT)-surgery (S) patients, 11% for EBRT with brachytherapy, 2% for EBRT alone, and 0% for patients who had S alone, p less than 0.001. Survival correlated well with initial performance status, treatment, stage of disease, tumor size, radiation dose, and degree of response, p less than 0.001, but not with tumor location in the esophagus and patients' race and sex, p = 0.44. Serious complications occurred in 5 (2%) patients treated with RT alone and in 4 (7%) patients treated with S alone or combined with RT. The leading cause of death was persistent or recurrent tumor in the chest found in 39% patients.