Biomedical subjects

Jun Duan

Publications and source records attributed to Jun Duan.

27 records · Page 2Linked to original sources

PubMed2004

[Asepsis sowing and tissue culture of Bletilla striata].

The asepsis sowing and tissue culture of Bletilla striata were studied. The results indicated that the embyro culture had highest sprouting percent and plantlets percent when their embryos were mature. The optimal medium for the embryo culture was 1/2 MS. Adding 10% coconut juice can promote embyros sprouting and plantlets formation, 1% active carbon can improve plantlets growing. The best medium for the top of plantlet on culture and multiplication was 1/2 MS + 6-BA 0.5 mg/L + NAA 0.2 mg/L. The best medium of rooting was 1/2 MS + NAA 0.5 mg/L, and 10% banana juice can improve rooting of plantlets.

Culture Media↗

PubMed2003

Comparison of methods for predicting myelotoxicity for non-marrow targeting I-131-antibody therapy.

Although marrow suppression is usually the dose-limiting toxicity in non-marrow ablative radionuclide therapy, calculated marrow dose has rarely been used for prescribing the radioactivity to be administered. This study assesses the correlation of myelotoxicity with mCi/m(2), patient-specific lean body dose, marrow dose from blood and body of reference man, or from blood and body using the patient-specific mass. Fourteen prostate cancer patients were treated with (131)I-CC49. Radioactivity in blood and body was determined and used to calculate their contributions to the marrow dose. Platelet nadir expressed as percentage (%) of the initial baseline was used as an indicator for myelotoxicity. Correlation between platelet nadir (%) and myelotoxicity predictors was evaluated. Platelet nadirs (%) varied substantially (5-33%) for a small range of injected radioactivity/m(2) (68-78 mCi/m(2), 2.5-2.9 GBq/m(2)). Patient-specific total body dose based on lean body mass exhibited a weak correlation (r = 0.48) with platelet nadir. Marrow dose from blood and body of reference man had a better correlation (r = 0.73). Patient-specific marrow dose from blood and body (or lean body) had a similar correlation (r = 0.74 or 0.73). Radioactivity in the remainder of the body contributed only 28% of the total dose, and thus changes to this dose component had small impact on total marrow dose. Marrow dose was a better predictor for myelotoxicity than mCi/m(2) or lean total body dose in this non-marrow targeting (131)I-antibody therapy with high blood contributions to total dose.

Antigens, Neoplasm↗

PubMed2003

Dosimetric effect of respiration-gated beam on IMRT delivery.

Intensity modulated radiation therapy (IMRT) with a dynamic multileaf collimator (DMLC) requires synchronization of DMLC leaf motion with dose delivery. A delay in DMLC communication is known to cause leaf lag and lead to dosimetric errors. The errors may be exacerbated by gated operation. The purpose of this study was to investigate the effect of leaf lag on the accuracy of doses delivered in gated IMRT. We first determined the effective leaf delay time by measuring the dose in a stationary phantom delivered by wedge-shaped fields. The wedge fields were generated by a DMLC at various dose rates. The so determined delay varied from 88.3 to 90.5 ms. The dosimetric effect of this delay on gated IMRT was studied by delivering wedge-shaped and clinical IMRT fields to moving and stationary phantoms at dose rates ranging from 100 to 600 MU/min, with and without gating. Respiratory motion was simulated by a linear sinusoidal motion of the phantom. An ionization chamber and films were employed for absolute dose and 2-D dose distribution measurements. Discrepancies between gated and nongated delivery to the stationary phantom were observed in both absolute dose and 2-D dose distribution measurements. These discrepancies increased monotonically with dose rate and frequency of beam interruptions, and could reach 3.7% of the total dose delivered to a 0.6 cm3 ion chamber. Isodose lines could be shifted by as much as 3 mm. The results are consistent with the explanation that beam hold-offs in gated delivery allowed the lagging leaves to catch up with the delivered monitor units each time that the beam was interrupted. Low dose rates, slow leaf speeds and low frequencies of beam interruptions reduce the effect of this delay-and-catch-up cycle. For gated IMRT it is therefore important to find a good balance between the conflicting requirements of rapid dose delivery and delivery accuracy.

Dose-Response Relationship, Radiation↗

PubMed2003

Custom step wedge blocking using dynamic multileaf collimation for parametrial pelvic boost irradiation following brachytherapy for carcinoma of the cervix.

Carcinoma of the cervix is typically treated with a combination of intracavitary brachytherapy and external beam radiation. The external beam dose is delivered with whole pelvis fields followed by split fields that protect midline organs at risk (bladder and rectum) while treating the parametria. Three approaches have been developed to shield midline structures: a simple rectangular block, a block customized to a single brachytherapy isodose line, and a step wedge filter constructed to conform to multiple brachytherapy isodose lines. A customized step wedge filter has the potential to produce a more homogeneous dose distribution but has not achieved widespread use due to labor intensive construction. We have developed a simple, novel method to produce a custom midline step wedge using dynamic multileaf collimation (dMLC). A comparison of film measurements in a phantom with the dose calculated by a commercial treatment planning system demonstrated agreement within 3% or 3 mm. The technique requires delivery times comparable to conventional techniques.

Algorithms↗

PubMed2003

Validation of target volume and position in respiratory gated CT planning and treatment.

The capability of a commercial respiratory gating system based on video tracking of reflective markers to reduce motion-induced CT planning and treatment errors was evaluated. Spherical plastic shells (2.8-82 cm3), simulating the gross target volume (GTV), were placed in a water-filled body phantom that was moved sinusoidally along the longitudinal axis of the CT scanner and the accelerator for +/- 1 cm at 15-30 cycle/min. During gated CT imaging, the x-ray exposure was initiated by the gating system shortly before the end of expiration (so that the imaging time would be centered at the end of expiration); it was terminated by the scanner after completion of each slice. In nongated CT images, the target appeared distorted and often broken up. GTVs volume errors ranged 16%-110% in axial scans, and 7%-36% in spiral scans. In gated CT images, the spheres appeared 3 and 5 mm longer than their actual diameters (volume errors 2%-16%), at the respective respiration rates of 15 and 20 cycles/min. At 30 cycles/min the target appeared 1 cm longer, and volume error ranged 25%-53%. During treatment, gating kept the beam on for a duration equal to the CT acquisition time of 1 s/slice. The difference in positional errors between gated CT and portal films was 1 mm, regardless the size of residual motion errors. Because of the potential of suboptimal placement of the gating window between CT imaging and treatment, an extra 1.5-2.5 mm safety margin can be added regardless of the size of residual motion error. For respiratory rates > or = 30 cycles/min, the effectiveness of gating is limited by large residual motion in the 1 s CT acquisition time.

Humans↗

PubMed2002

Model prediction of treatment planning for dose-fractionated radioimmunotherapy.

BACKGROUND: Clinical trials of radioimmunotherapy (RIT) often use dose fractionation to reduce marrow toxicity. The dosing scheme can be optimized if marrow and tumor cell kinetics following radiation exposure are known. METHODS: A mathematic model of tumor clonogenic cell kinetics was combined with a previously reported marrow cell kinetics model that included marrow stromal cells, progenitor cells, megakaryocytes, and platelets. Reported values for murine tumor and marrow cellular turnover rates and radiosensitivity were used in the model calculation. RESULTS: Given a tolerated level of thrombocytopenia, there is a fractionation scheme in which total radioactive dose administration can be maximized. Isoeffect doses that had different numbers of fractions and total radioactivity, but induced identical platelet nadirs of 20%, were determined. Assuming identical tumor uptake for all dose fractions, six tumor types were examined: early-responding tumors, late-responding tumors, and tumors that lacked a late-responding effect, with either constant or accelerated doubling time. For most tumor types, better tumor control (tumor growth delay and nadir of survival fraction) was predicted for a dosing scheme in which total radioactive dose was maximized. For late-responding tumors with accelerated doubling time, tumor growth delay increased, but the nadir of survival fraction became shallower as the number of fractions increased. CONCLUSIONS: A mathematic model has been developed that allows prediction of the nadir and duration of thrombocytopenia as well as tumor clonogenic cell response to various RIT doses and fractionation schemes. Given a maximum tolerated level of thrombocytopenia, the model can be used to determine a dosing scheme for optimal tumor response.

Abnormalities, Radiation-Induced↗

PubMed2002

Postoperative intravaginal brachytherapy for endometrial cancer; dosimetric analysis of vaginal colpostats and cylinder applicators.

PURPOSE: To investigate the dosimetric differences between colpostats and cylinder applicators for intravaginal brachytherapy. METHODS AND MATERIALS: Dose distributions near vaginal colpostats and dome cylinders were computed with a commercial high-dose-rate treatment-planning system and verified by spot measurements by using LiF thermoluminescent dosimeters. Taking source anisotropy into account, dwell times were optimized by the computer by using the polynomial optimization on dose points method to give uniform doses along the lateral surfaces of the applicators. In addition, the effects of vaginal packing and the separation distance between colpostats were studied by computing the dose to the vaginal mucosa, assuming 0.5 and 1.0 cm of vaginal packing and colpostat separation, respectively. RESULTS: The computed and measured doses agreed within +/- 7%. Surface doses were similar for both types of applicators when the effect of shielding in the colpostats was neglected. However, percent depth doses in the anterior/posterior and lateral directions were higher for the cylinder, whereas the dose fall-off along the longitudinal patient axis was less pronounced for the colpostats. When vaginal packing at the anterior and posterior surface of the colpostats was increased from 0 to 5, 10, and 15 mm, the corresponding vaginal dose decreased from 97% of the prescription dose to 60%, 39%, and 26%, respectively. Separating the colpostats from 0 to 5 and 10 mm reduced the surface dose near the bladder/rectum to 80% and 67%, respectively, whereas the respective apex dose decreased from 105% of prescription to 91% and 77%. CONCLUSIONS: Colpostats and cylinder applicators for intracavitary brachytherapy have their advantages and disadvantages in depth dose distribution and clinical use. If treatment is confined to the vaginal apex, either applicator can be used. However, the colpostat separation should be kept to a minimum, and vaginal packing should be applied with great care to avoid generating cold spots along the upper vaginal surface and vaginal cuff.

Brachytherapy↗

PubMed2002

Assaying 192Ir line sources using a standard length well chamber.

The strength of intravascular 192Ir sources is typically measured by the manufacturer before shipment, and treatment planning is based on that assay. However, in-house verification of source strength is required at some institutions by state law or internal policy, is recommended by the AAPM TG 60 report on intravascular brachytherapy, and is considered a necessity by many medical physicists. To accommodate the long sources used in intravascular therapy, special well chambers with extended regions of constant response have been designed. To allow assays using a widely available standard well chamber, we have measured its position dependent sensitivity and derived from it a table of correction factors that account for the extended length of intravascular sources. An experimental verification shows that application of these correction factors yields assays with sufficient accuracy for routine quality assurance tests.

Brachytherapy↗

PubMed2002

Improved prediction of myelotoxicity using a patient-specific imaging dose estimate for non-marrow-targeting (90)Y-antibody therapy.

UNLABELLED: For calculation of radiation dose to the marrow, standard dosimetry for radiopharmaceuticals that do not bind to the marrow includes dose contributions from radioactivity in blood and the remainder of the body. For a pure beta -emitter such as (90)Y, marrow dose is usually determined by the blood contribution. However, myelotoxicity from (90)Y-antibody therapy often correlates poorly with marrow dose estimated using the blood method. This study proposes a method to address 2 possible factors affecting marrow dose estimates. These include (a) recycled (90)Y in bone/marrow space after (90)Y-antibody has been processed in the liver and (b) use of the marrow mass of Reference Man for individual patients. METHODS: Thirty-three patients with advanced non-small cell lung cancer were treated with (90)Y-anti-TAG-72 murine antibody (CC49). TAG-72 is often expressed in epithelial-derived tumors but not in normal marrow. (111)In-CC49 was used as a tracer. The marrow doses from blood were calculated on the basis of radioactivity concentrations in blood. Marrow dose in the lumbar vertebrae was estimated from images for (111)In-CC49 uptake in L2-L4. In 20 patients who had CT images, trabecular bone volumes of L2-L4 were measured from CT images to estimate patient-specific marrow mass in L2-L4. The fraction of baseline platelet counts at nadir was used as an indicator of myelotoxicity. RESULTS: Marrow dose per unit injected radioactivity estimated from blood was lower than that from L2-L4 uptake values. Prediction of myelotoxicity using marrow dose estimated from blood was poorer than that using injected dose per body surface area (GBq/m(2)) (r = 0.31 vs. 0.51). Prediction was improved using marrow dose estimated from L2-L4 uptake, assuming the marrow mass of Reference Man (r = 0.67 for n = 33; r = 0.70 for n = 20). Prediction was worse if reference marrow mass was adjusted by body weight (r = 0.56 for n = 33; r = 0.63 for n = 20). Prediction was not improved if adjusted by body surface area or lean body mass but was improved if adjusted by height (r = 0.72 for n = 33; r = 0.78 for n = 20). The best prediction was obtained (r = 0.85 for n = 20) using patient-specific L2-L4 marrow mass estimated from CT. CONCLUSION: Marrow dose estimated from the blood radioactivity method was not a good predictor of myelotoxicity for non-marrow-targeting (90)Y-antibody therapy. Thrombocytopenia in this group of patients correlated much better with dose estimated from lumbar vertebrae imaging and patient-specific marrow mass than with that estimated from GBq/m(2) or standard marrow dose based on blood.

Adult↗