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Ning J Yue

Publications and source records attributed to Ning J Yue.

13 recordsLinked to original sources
PubMed2006

Dosimetric effects of patient rotational setup errors on prostate IMRT treatments.

The purpose of this work is to determine dose delivery errors that could result from systematic rotational setup errors (DeltaPhi) for prostate cancer patients treated with three-phase sequential boost IMRT. In order to implement this, different rotational setup errors around three Cartesian axes were simulated for five prostate patients and dosimetric indices, such as dose-volume histogram (DVH), tumour control probability (TCP), normal tissue complication probability (NTCP) and equivalent uniform dose (EUD), were employed to evaluate the corresponding dosimetric influences. Rotational setup errors were simulated by adjusting the gantry, collimator and horizontal couch angles of treatment beams and the dosimetric effects were evaluated by recomputing the dose distributions in the treatment planning system. Our results indicated that, for prostate cancer treatment with the three-phase sequential boost IMRT technique, the rotational setup errors do not have significant dosimetric impacts on the cumulative plan. Even in the worst-case scenario with DeltaPhi=3 degrees, the prostate EUD varied within 1.5% and TCP decreased about 1%. For seminal vesicle, slightly larger influences were observed. However, EUD and TCP changes were still within 2%. The influence on sensitive structures, such as rectum and bladder, is also negligible. This study demonstrates that the rotational setup error degrades the dosimetric coverage of target volume in prostate cancer treatment to a certain degree. However, the degradation was not significant for the three-phase sequential boost prostate IMRT technique and for the margin sizes used in our institution.

Body Burden↗
PubMed2006

Limitations of silicon diodes for clinical electron dosimetry.

This work investigates the relevance of several factors affecting the response of silicon diode dosemeters in depth-dose scans of electron beams. These factors are electron energy, instantaneous dose rate, dose per pulse, photon/electron dose ratio and electron scattering angle (directional response). Data from the literature and our own experiments indicate that the impact of these factors may be up to +/-15%. Thus, the different factors would have to cancel out perfectly at all depths in order to produce true depth-dose curves. There are reports of good agreement between depth-doses measured with diodes and ionisation chambers. However, our measurements with a Scantronix electron field detector (EFD) diode and with a plane-parallel ionisation chamber show discrepancies both in the build-up and in the low-dose regions, with a ratio up to 1.4. Moreover, the absolute sensitivity of two diodes of the same EFD model was found to differ by a factor of 3, and this ratio was not constant but changed with depth between 5 and 15% in the low-dose regions of some clinical electron beams. Owing to these inhomogeneities among diodes even of the same model, corrections for each factor would have to be diode-specific and beam-specific. All these corrections would have to be determined using parallel plane chambers, as recommended by AAPM TG-25, which would be unrealistic in clinical practice. Our conclusion is that in general diodes are not reliable in the measurement of depth-dose curves of clinical electron beams.

Dose-Response Relationship, Radiation↗
PubMed2006

Modern radiation treatment planning and delivery--from Röntgen to real time.

The field of radiation oncology has advanced exponentially since the discovery of X-rays just over 100 years ago. With the advent of three-dimensional treatment planning, the therapeutic index was increased by dose escalation and more accurate shielding of normal tissues. Now, even greater advances are under way with IMRT, image-guided radiation therapy, delineation and control of organ motion, and real-time imaging. Similarly, the use of particle therapies such as protons has the potential to effect even more accurate dose distributions. Clinical studies investigating these modalities will likely further increase the efficacy of radiation in years to come.

Female↗
PubMed2006

Localizing moving targets and organs using motion-managed CTs.

Respiration-induced target and organ motion impacts the radiotherapy strategies of some cancers. Various methods and techniques have been used to investigate motion-related radiotherapy issues, including retrospective 4-dimensional (4D) computed tomography (CT), prospective gated CT, and breath-hold CT scans. This paper reviews these methods and, particularly, the method using retrospective 4D CT scans, which has been developed at our institution. Some motion studies based on retrospective 4D CT images of patients are also examined. These studies have led to reduced planning target volume (PTV) margins for a number of patients, because the respiratory motion was observed to be minimal or gated radiotherapy was used. Respiratory motion managed CTs and, particularly, retrospective 4D CTs are proving to be useful for measuring soft tissue motion, identifying patients who could benefit from gated radiotherapy, and evaluating the effects of respiratory motion during radiotherapy.

Humans↗
PubMed2006

A method to implement full six-degree target shift corrections for rigid body in image-guided radiotherapy.

Treatment position setup errors often introduce temporal variations in the position of target relative to the planned external radiation beams. The errors can be introduced by the movement of a target relative to external setup marks or to other relevant landmarks that are used to position a patient for radiotherapy. Those variations can cause dose deviations from the planned doses and result in suboptimal treatments where part of the target is not fully irradiated or a critical structure receives more than desired radiation doses. Clinically available technology for image-guided radiotherapy can detect variations of target position. In this study, a method has been developed to correct for target position variations and restore the original beam geometries relative to the target. The technique involves three matrix transformations: (1) transformation of beams from the machine coordinate system to the patient coordinate system as in the patient geometry in the approved dosimetric plan; (2) transformation of beams from the patient coordinate system in the approved plan to the patient coordinate system that is identified at the time of treatment; (3) transformation of beams from the patient coordinate system at the time of treatment in the treatment patient geometry back to the machine coordinate system. The transformation matrix used for the second transformation is determined through the use of image-guided radiotherapy technology and image registration. By using these matrix transformations, the isocenter shift, the gantry, couch and collimator angles of the beams for the treatment, adjusted for the target shift, can be derived. With the new beam parameters, the beams will possess the same positions and orientations relative to the target as in the plan for a rigid body. This method was applied to a head phantom study, and it was found that the target shift was fully corrected in treatment and excellent agreement was found in target dose coverage between the plan and the treatment.

Algorithms↗
PubMed2005

A dose verification method using a monitor unit matrix for dynamic IMRT on Varian linear accelerators.

Dosimetry verification is an important step during intensity modulated radiotherapy treatment (IMRT). The verification is usually conducted with measurements and independent dose calculations. However, currently available independent dose calculation methods were developed for step-and-shoot beam delivery methods, and their uses for dynamic multi-leaf collimator (MLC) delivery methods are not efficient. In this study, a dose calculation method was developed to perform independent dose verifications for a dynamic MLC-based IMRT technique for Varian linear accelerators. This method extracts the machine delivery parameters from the dynamic MLC (DMLC) files generated by the IMRT treatment planning system. Based on the parameters a monitor unit (MU) matrix was separately calculated as two terms: direct exposure from the open MLC field and leakage contributions, where the leaf-end leakage contribution becomes more important in higher dose gradient regions. The MU matrix was used to compute the primary dose and the scattered dose with a modified Clarkson technique. The doses computed using the method were compared with both measurement and treatment planning for 14 and 25 plans respectively. An average of less than 2% agreement was observed and the standard deviation was about 1.9%.

Algorithms↗
PubMed2004

Two-dimensional dosimetry in the near field of the model 200 103Pd source for interstitial brachytherapy implants using a thermoluminescent sheet.

A large area and highly sensitive thermoluminescent (TL) sheet film was used for two-dimensional dose distribution measurements at millimetre distances from a 103Pd interstitial brachytherapy source. The TL film is made of Teflon homogeneously mixed with small particles of thermoluminescent material (BaSO4: Eu doped). This TL sheet (5 cm x 5 cm) was used to determine the relative dosimetric characteristics (i.e., radial dose function, 2D and 1D anisotropy functions, as defined by the updated AAPM Task Group No 43 report) of the model 200 103Pd source that emits low energy photons (21 keV). The two-dimensional dosimetry data were obtained for distances from the source surface to 15 mm. The radial dose function measured with the TL sheet is in reasonable agreement within 11% with the values recommended in the updated AAPM TG-43 report. All the measured 2D dose distributions showed limited symmetry about the source axes. The differences between the 1D anisotropy function values measured with the TL sheet and the data recommended in the updated AAPM TG-43 report were 10% at 5 mm and 7.5% at 10 mm, respectively, for the model 200 103Pd seed. Our experiments have demonstrated that it is feasible to use the TL sheet as a dosimeter in the determination of the dosimetric characteristics in the immediate vicinity of interstitial brachytherapy sources emitting low energy photons.

Anisotropy↗
PubMed2004

A technique to re-establish dose distributions for previously treated brain cancer patients in external beam radiotherapy.

Tumor recurrences or new tumors may develop after irradiation of local lesion(s) in the brain, and additional radiotherapy treatments are often needed for previously treated patients. It is critical to re-establish the dose distributions delivered during the previous treatment in the current patient geometry, so that the previous dose distributions can be accurately taken into consideration in the design of the current treatment plan. The difficulty in re-establishing the previous treatment dose distributions in the current patient geometry arises from the fact that the patient position at the time of reirradiation is different from that at the previous treatment session. Simple re-entry of the previous isocenter coordinates, gantry, and couch and collimator angles into the new treatment plan would result in incorrect beam orientations relative to the new patient anatomy, and therefore incorrect display of the previous dose distributions on the current patient anatomy. To address this issue, a method has been developed so that the previous dose distributions can be accurately re-established in the framework of the current brain treatment. The method involves 3 matrix transformations: (1) transformation of beams from machine coordinate system to patient coordinate system in the previous treatment; (2) transformation of beams from patient coordinate system in the previous treatment to patient coordinate system in the current treatment; and (3) transformation of beams from patient coordinate system in the current treatment to machine coordinate system. The transformation matrices used in the second transformation are determined by registration using a mutual information-based algorithm with which the old and new computed tomography (CT) scan sets are registered automatically without human interpretation. A series of transformation matrices are derived to calculate the isocenter coordinates, the gantry, couch, and collimator angles of the beams for the previous treatment in the current patient geometry, and the previous dose distributions are re-established on the current CT images. The method has been proven to be successful and robust.

Algorithms↗
PubMed2004

Near-field dosimetry of 125I sources for interstitial brachytherapy implants measured using thermoluminescent sheets.

The dosimetric characteristics were measured for two types of 125I low-energy photon-emitting sources by using a wide and highly sensitive thermoluminescent (TL) sheet film, which was developed for two-dimensional dose distribution measurements. The TL film is made of Teflon homogeneously mixed with small powders of thermoluminescence (BaSO4:Eu doped). Various dosimetric parameters (i.e., radial dose function, 2D and 1D anisotropy functions) of model 6711 and 6702 125I sources were obtained at various distances from the source surfaces to 15 mm. These parameters obtained with TL sheet were compared with the data recommended in the updated AAPM TG-43 report. The radial dose functions measured with TL sheet are in agreement with those established data of model 6711 125I seed and model 6702 125I seed at most of the distances within 5% and 7%, respectively. All the measured anisotropy functions showed symmetry about the longitudinal source axis. The anisotropy of dose distributions was clearly present in the immediate vicinity of the source edges. The measured 2D anisotropy function values at 1 cm are in reasonably good agreement with the recommended values. The differences at two points in the 1D anisotropy functions measured with TL sheet and the established data at 1 cm from source center were 0.7% and 1.9% for model 6711 and 6702 125I sources, respectively; the differences at 0.5 cm were 1.5% and 1.7% for model 6711 and 6702 125I sources, respectively. The relative dosimetric characteristics in the vicinity of actual interstitial brachytherapy sources containing 125I have been experimentally determined by using the TL sheet as a 2D dosimeter.

Brachytherapy↗
PubMed2003

Comparison of an image registration technique based on normalized mutual information with a standard method utilizing implanted markers in the staged radiosurgical treatment of large arteriovenous malformations.

PURPOSE: To compare a noninvasive technique based on normalized mutual information for registering image sets associated with staged radiosurgical treatments of large arteriovenous malformations (AVMs), with a gold-standard method using radiographically evident markers implanted in the skull. METHODS: Nine patients receiving multistage treatment of large AVMs at the University of California at San Francisco (UCSF) gamma knife facility were included in this study. For each patient, the transformations of shot coordinates between a reference treatment stage and subsequent treatment stages were determined at UCSF, based on radiographically defined coordinates of implanted markers in each stereotactic space. A magnetic resonance (MR) image set was acquired for each treatment stage, and used for treatment planning. The two MR image sets for each treatment pair were sent to Yale for an unbiased, independent analysis of shot transformations. An image registration technique based on normalized mutual information was used to produce a single fused image study for each treatment pair. External copper sulfate fiducial markers for both image sets were evident on the fused images, allowing coordinates in both stereotactic systems to be defined. Coordinate transformation between the two systems was determined, based on digitized coordinates of seven common fiducial marker images. RESULTS: The average measured overall root-mean-square discrepancy between the Yale and UCSF transformed shot coordinates is 1.1 +/- 0.3 mm. The corresponding error in Yale transformed coordinates is 1.0 +/- 0.3 mm, assuming an inherent 0.5 mm error in the UCSF method. CONCLUSIONS: The normalized mutual information method can be used to obtain good image registration between successive sessions in staged treatments. Further improvements in the reported methodology are outlined. Because the mutual information method is less invasive than the implanted marker method, it may be preferable in many cases.

Algorithms↗