Biomedical subjects

Jingeng Zhu

Publications and source records attributed to Jingeng Zhu.

5 recordsLinked to original sources

PubMed2005

Generation of wedge-shaped dose distributions through dynamic multileaf collimator dose delivery.

A new method of generating wedge-shaped dose distributions through dynamic multileaf collimator dose delivery rather than computer-controlled jaw motion is presented. The method starts with the calculation of a wedge-shaped beam profile for the desired wedge angle. The resultant wedge beam profile is then passed to the intensity-modulated radiation therapy (IMRT) leaf sequence generation algorithm to create multileaf collimator (MLC) segments for dose delivery. Wedge-shaped dose distributions are achieved through dynamic MLC dose delivery guided with the generated MLC segments. The method has been tested by generating wedgeshaped doses for a set of conventional wedge angles (i.e., 15 degrees, 30 degrees, 45 degrees, and 60 degrees). Film dosimetry is used for dose distribution verification. For each dose delivery guided with MLC segments created for the indicated wedge angle, the desired wedge-shaped dose distributions are observed. It is concluded that the dynamic MLC can be used to implement dynamic wedges in the clinic. This technique is different from the virtual wedge or the dynamic wedge developed for a particular type of LINAC. The same method can be applied to any machine equipped with a MLC. Other advantages are that it can generate a wedge field at an arbitrary orientation as the omni wedge does, and it creates wedged and shaped fields using a MLC only.

Dose Fractionation, Radiation↗

PubMed2003

Image-guided and intensity-modulated radiosurgery for patients with spinal metastasis.

BACKGROUND: Radiosurgery can deliver a single, large radiation dose to a localized tumor using a stereotactic approach and hence, requires accurate and precise delivery of radiation to the target. Of the extracranial organ targets, the spine is considered a suitable site for radiosurgery, because there is minimal or no breathing-related organ movement. The authors studied spinal radiosurgery in patients with spinal metastases to determine its accuracy and precision. METHODS: The spinal radiosurgery program was based on an image-guided and intensity-modulated, shaped-beam radiosurgical unit. It is equipped with micromultileaf collimators for beam shaping and radiation intensity modulation and with a noninvasive, frameless positioning device that uses infrared, passive marker technology together with corroborative image fusion of the digitally reconstructed image from computed tomography (CT) simulation and orthogonal X-ray imagery at the treatment position. These images were compared with the port films that were taken at the time of treatment to determine the accuracy of the isocenter position. Clinical feasibility was tested in 10 patients who had spinal metastasis with or without spinal cord compression. The patients were treated with fractionated external beam radiotherapy followed by single-dose radiosurgery as a boost (6-8 grays) to the most involved portion of the spine or to the site of spinal cord compression. RESULTS: The accuracy for the isocenter was within 1.36 mm +/- 0.11 mm, as measured by image fusion of the digitally reconstructed image from CT simulation and the port film. Clinically, the majority of patients had prompt pain relief within 2-4 weeks of treatment. Complete and partial recovery of motor function also was achieved in patients with spinal cord compression. The radiation dose to the spinal cord was minimal. The maximum dose of radiation to the anterior edge of the spinal cord within a transverse section, on average, was 50% of the prescribed dose. There was no acute radiation toxicity detected clinically during the mean follow-up of 6 months. CONCLUSIONS: Image-guided, shaped-beam spinal radiosurgery is accurate and precise. Rapid clinical improvement of pain and neurologic function also may be achieved. The results indicate the potential of spinal radiosurgery in the treatment of patients with spinal metastasis, especially those with solitary sites of spine involvement, to increase the prospects of long-term palliation.

Feasibility Studies↗

PubMed2003

Point dose verification for intensity modulated radiosurgery using Clarkson's method.

In clinical radiation physics chart checking, the dose calculation results generated by computer treatment planning software are usually verified by an independent computerized monitor unit calculation routine, or by "hand calculation" using percent depth dose (PDD), tissue phantom ratio (TPR), scatter factors, and the machine calibration factors. For intensity-modulated radiosurgery (IMRS) or intensity-modulated radiation therapy (IMRT), the "hand calculation" becomes not feasible due to the sophisticated multileaf collimator (MLC) segments created for intensity-modulated dose delivery. Therefore, an independent computerized dose calculation routine is needed for fast and reliable dose verification. In this work, a point dose calculation routine for IMRS/IMRT plan verification is developed by directly applying Clarkson's method. The method includes preparing data table by measuring TPRs for circular fields with diameters ranging 6 to 98 mm, extrapolating TPR for the zero field size (TPR0) from measured data and generating scatter phantom ratio (SPR) for each individual circular field. The segmented MLC sequences created by IMRS/IMRT inverse planning are converted into irregular fields for Clarkson's calculation. This method has been tested using 29 IMRS/IMRT cases. The results indicate that it is reliable, fast, and accurate. The average time to calculate one field is about 2 s with a 300 Mhz CPU.

Algorithms↗

PubMed2002

Dosimetric characteristics of Novalis shaped beam surgery unit.

The dosimetric characteristics of a new dedicated radiosurgical treatment unit are systematically measured in terms of its percent depth dose, beam profile, and relative scatter factor. High-resolution diode detector, mini-ion-chamber detector, and conventional Kodak XV films are used to measure dosimetric data for a range of field sizes from 6x6 mm to 100x100 mm. The effects of collimator size, micro-multileaf collimator shape, and detector type on the dosimetric data are investigated. Results indicate that, with careful design, accurate dosimetric data could be acquired using either a dedicated diode detector or a mini-ion-chamber detector, and film detector. Special attention is required when measuring dosimetric data for small field sizes such as 6x6 mm.

Equipment Failure Analysis↗

PubMed2002

A technique of intensity-modulated radiosurgery (IMRS) for spinal tumors.

This study is to demonstrate the feasibility of spinal radiosurgery using an image-guided intensity-modulated radiosurgical (IMRS) procedure. A dedicated Novalis shaped beam surgery unit equipped with a built-in micro-multileaf collimator (mMLC) with a single 6 MV photon beam was used. Each patient was simulated in the supine position using an AcQsim CT simulator with infrared sensitive markers for localization. A variety of different treatment plans were developed, but the most common plan was the use of seven coplanar intensity-modulated beams to minimize radiation to critical organs such as the spinal cord and kidneys. An automatic localization device based on infrared and video cameras was used to guide the initial patient setup. Two keV x-ray imaging systems were used to identify potential deviations from the planned isocenter. A total of 25 patients with spinal tumors have been treated using this procedure with a single prescription dose ranging from 6 to 12 Gy. The final verification images indicated that the average isocenter deviation from the planned isocenter was within 2 mm. The phantom verification of isocenter doses indicated that the average deviation of measured isocenter doses from the planned isocenter doses for all patients treated with intensity-modulated beams was less than 2%. Film dose measurement in a phantom study demonstrated good agreement of above 50% isodose lines between the planned and measured results. Preliminary experience shows that precision delivery of high dose radiation could be administered to the planned target volume while the dose to the critical organs is kept within tolerable limits.

Computer Simulation↗