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Shidong Li

Bio: Shidong Li is an academic researcher from University of Chicago. The author has contributed to research in topics: Imaging phantom & Position (vector). The author has an hindex of 6, co-authored 7 publications receiving 203 citations.

Papers
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Journal ArticleDOI
TL;DR: Application of the method to a larger patient data set has the potential to facilitate the construction of a full dose-surface-complication relationship, which would be most useful in guiding clinical practice.
Abstract: Purpose: To develop a method of analyzing rectal surface area irradiated and rectal complications in prostate conformal radiotherapy. Methods and Materials: Dose-surface histograms of the rectum, which state the rectal surface area irradiated to any given dose, were calculated for a group of 27 patients treated with a four-field box technique to a total (tumor minimum) dose ranging from 68 to 70 Gy. Occurrences of rectal toxicities as defined by the Radiation Therapy Oncology Group (RTOG) were recorded and examined in terms of dose and rectal surface area irradiated. For a specified end point of rectal complication, the complication probability was analyzed as a function of dose irradiated to a fixed rectal area, and as a function of area receiving a fixed dose. Lyman’s model of normal tissue complication probability (NTCP) was used to fit the data. Results: The observed occurrences of rectal complications appear to depend on the rectal surface area irradiated to a given dose level. The patient distribution of each toxicity grade exhibits a maximum as a function of percentage surface area irradiated, and the maximum moves to higher values of percentage surface area as the toxicity grade increases. The dependence of the NTCP for the specified end point on dose and percentage surface area irradiated was fitted to Lyman’s NTCP model with a set of parameters. The curvature of the NTCP as a function of the surface area suggests that the rectum is a parallel structured organ. Conclusions: The described method of analyzing rectal surface area irradiated yields interesting insight into understanding rectal complications in prostate conformal radiotherapy. Application of the method to a larger patient data set has the potential to facilitate the construction of a full dose-surface-complication relationship, which would be most useful in guiding clinical practice. Normal tissue complication probability (NTCP), Dose-surface histogram, Conformal radiotherapy, Prostate cancer.

58 citations

Journal ArticleDOI
TL;DR: The DSHs and DWHs for the rectum and bladder in patients undergoing four-field-prostate treatment and gynecological intracavitary brachytherapy were computed with a refined numerical algorithm to demonstrate the difference between the DWH and DSH was small for a fully filled bladder or rectum but large for an empty rectum or a contracted bladder.
Abstract: Dose distribution throughout a hollow organ is represented by either a dose-surface histogram (DSH) or a dose-wall histogram (DWH). A spherical shell model for the bladder and a cylindrical shell model for the rectum were introduced for quantifying the difference between the DWH and DSH. The difference was given by subtraction of the percent volume of the wall from the percent area of the surface for any specific dose level. Taking the dose-grid size and contour-delineation uncertainties into account, the DSH and DWH calculation errors were estimated by simplified formulas. The DSHs and DWHs for the rectum and bladder in patients undergoing four-field-prostate treatment and gynecological intracavitary brachytherapy were computed with a refined numerical algorithm. Results of the analytic models and the numerical calculations demonstrated that the difference between the DWH and DSH was small (about 5%) for a fully filled bladder or rectum but large (about 10%) for an empty rectum or a contracted bladder. The error of DSH was about 3%, which is smaller than that of DWH.

57 citations

Journal ArticleDOI
TL;DR: Dose-surface histograms are studied and compared with dose-volume histograms, as an evaluation tool for prostate treatment planning, and the use of the dose- surface histograms in analysis of organ motion and/or patient setup uncertainty, and analysis of rectal complications, is discussed.
Abstract: Dose-surface histograms are studied and compared with dose-volume histograms, as an evaluation tool for prostate treatment planning. For thin walled hollow organs, such as the rectum and bladder, the surface area irradiated is a more appropriate measure of the biological effect than the full volume. It is also more accurate and efficient to define the surface for a hollow structure and compute the surface area histograms. Application of the dose-surface histograms provide new insights into prostate treatment planning. A simple idealized geometry model demonstrates that the percentage surface area intersected by the geometric beam edge differs from the percentage volume intersected. For a group of prostate patients, it is shown that the dose-surface histograms yield substantially different results from the dose-volume histograms in ranking four-, six-, and, eight-field treatment plans and in calculating the fraction of the rectum irradiated to high dose. The difference in terms of surface area between these plans in the high-dose region is usually less than that in terms of the volume, and a reverse of plan ranking order can consequently occur. The percentage of organ surface irradiated to high dose is typically greater than the percentage volume by 5% to 10%. The use of the dose-surface histograms in analysis of organ motion and/or patient setup uncertainty, and analysis of rectal complications, is also discussed.

48 citations

Journal ArticleDOI
TL;DR: In comparing with some other reconstruction algorithms, the point pair method can significantly improve source localization or point reconstruction in the presence of patient motion.
Abstract: A method of unfolding patient movement between biplane radiographs is presented This method requires biplane projections of two points with a known separation to determine a translation motion or biplane projections of two or three point pairs to determine a general patient motion Such a point pair can be provided by two ends of a line source or two radiopaque marks, with a fixed distance between them The point pairs can be taped on skin, implanted in the target volume, or embedded in the bony structures After obtaining the point locations on each film, the three‐dimensional coordinates of points of interest at the instant of each view can be reconstructed, with an error of less than 05 mm The motion parameters, characterized by a pseudotranslation vector and three axial rotational angles for the region of interest relative to the machine coordinate system, are also provided In comparing with some other reconstruction algorithms, the point pair method can significantly improve source localization or point reconstruction in the presence of patient motion Computer simulations and phantom experiments demonstrates the feasibility and accuracy of the method

20 citations

Proceedings ArticleDOI
11 Apr 1996
TL;DR: A new, simple technique for accurate determination of the imaging geometry for calibration of projection imaging systems by translating and rotating the phantom model until it aligned optimally with the set of lines connecting the focal spot with the corresponding image points.
Abstract: We have developed a new, simple technique for accurate determination of the imaging geometry for calibration of projection imaging systems. Images of a phantom containing lead beads were obtained after it was placed at arbitrary, unknown locations which were near the isocenter of a radiation therapy simulator. The location of the lead beads were identified in the images. A computer model of the phantom was generated and positioned at an arbitrary location. Projection images of the model were generated and compared with the actual image locations. A modified projection-Procrustes algorithm was then used to translate and rotate the phantom model until it aligned optimally with the set of lines connecting the focal spot with the corresponding image points. The rotation matrix and translation vector relating the multiple projection geometries were then determined using a Procrustes algorithm and the calculated positions of the phantom for each projection. For a wide range of starting points, the technique converged to 3D locations with an approximate precision of 0.1 cm in position and approximately 0.2 degrees in orientation. The calculated angles and distances agreed with the readouts on the imaging systems to within approximately 0.25 degrees.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

14 citations


Cited by
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Journal ArticleDOI
TL;DR: A survey of recent publications concerning medical image registration techniques is presented, according to a model based on nine salient criteria, the main dichotomy of which is extrinsic versus intrinsic methods.

3,426 citations

Journal ArticleDOI
TL;DR: These data show that dose escalation up to 78 Gy, using a conformal technique, is feasible, however, these data have also demonstrated that the incidence of severe late rectal bleeding is increased above certain dose-volume thresholds.
Abstract: Purpose: To investigate whether Dose–Volume Histogram (DVH) parameters can be used to identify risk groups for developing late gastrointestinal (GI) and genitourinary (GU) complications after conformal radiotherapy for prostate cancer. Methods and Materials: DVH parameters were analyzed for 130 patients with localized prostate cancer, treated with conformal radiotherapy in a dose-escalating protocol (70–78 Gy, 2 Gy per fraction). The incidence of late (>6 months) GI and GU complications was classified using the RTOG/EORTC and the SOMA/LENT scoring system. In addition, GI complications were divided in nonsevere and severe (requiring one or more laser treatments or blood transfusions) rectal bleeding. The median follow-up time was 24 months. We investigated whether rectal and bladder wall volumes, irradiated to various dose levels, correlated with the observed actuarial incidences of GI and GU complications, using volume as a continuous variable. Subsequently, for each dose level in the DVH, the rectal wall volumes were dichotomized using different volumes as cutoff levels. The impact of the total radiation dose, and the maximum radiation dose in the rectal and bladder wall was analyzed as well. Results: The actuarial incidence at 2 years for GI complications ≥Grade II was 14% (RTOG/EORTC) or 20% (SOMA/LENT); for GU complications ≥Grade III 8% (RTOG/EORTC) or 21% (SOMA/LENT). Neither for GI complications ≥Grade II (RTOG/EORTC or SOMA/LENT), nor for GU complications ≥Grade III (RTOG/EORTC or SOMA/LENT), was a significant correlation found between any of the DVH parameters and the actuarial incidence of complications. For severe rectal bleeding (actuarial incidence at 2 years 3%), four consecutive volume cutoff levels were found, which significantly discriminated between high and low risk. A trend was observed that a total radiation dose ≥ 74 Gy (or a maximum radiation dose in the rectal wall >75 Gy) resulted in a higher incidence of severe rectal bleeding ( p = 0.07). Conclusions: These data show that dose escalation up to 78 Gy, using a conformal technique, is feasible. However, these data have also demonstrated that the incidence of severe late rectal bleeding is increased above certain dose–volume thresholds.

405 citations

Journal ArticleDOI
TL;DR: It is essential that postimplant dosimetry should be performed on all patients undergoing permanent prostate brachytherapy and guidelines were established for the performance and analysis of such Dosimetry.
Abstract: Purpose: The purpose of this report is to establish guidelines for postimplant dosimetric analysis of permanent prostate brachytherapy. Methods: Members of the American Brachytherapy Society (ABS) with expertise in prostate dosimetry evaluation performed a literature review and supplemented with their clinical experience formulated guidelines for performing and analyzing postimplant dosimetry of permanent prostate brachytherapy. Results: The ABS recommends that postimplant dosimetry should be performed on all patients undergoing permanent prostate brachytherapy for optimal patient care. At present, computed tomography (CT) - based dosimetry is recommended, based on availability cost and the ability to image the prostate as well as the seeds. Additional plane radiographs should be obtained to verify the seed count. Until the ideal postoperative interval for CT scanning has been determined, each center should perform dosimetric evaluation of prostate implants at a consistent postoperative interval. This interval should be reported. Isodose displays should be obtained at 50%, 80%, 90%, 100%, 150%, and 200% of the prescription dose and displayed on multiple cross - sectional images of the prostate. A dose - volume histogram (DVH) of the prostate should be performed and the D 90 (dose to 90% of the prostate gland) reported by all centers. Additionally, the D 80, D 100, the fractional V 80, V 90, V 100, V 150, and V 200, (i.e., the percentage of prostate volume receiving 80%, 90%, 100%, 150%, and 200% of the prescribed dose, respectively), the rectal, and urethral doses should be reported and ultimately correlated with clinical outcome in the research environment. On - line real - time dosimetry, the effects of dose heterogeneity, and the effects of tissue heterogeneity need further investigation. Conclusion: It is essential that postimplant dosimetry should be performed on all patients undergoing permanent prostate brachytherapy. Guidelines were established for the performance and analysis of such dosimetry.

382 citations

Journal ArticleDOI
TL;DR: The rectum is the most investigated organ: the largest studies on dose-volume modelling of rectal toxicity show quite consistent results, suggesting that sufficiently reliable dose- volume/EUD-based constraints can be safely applied in most clinical situations.

259 citations

Journal ArticleDOI
TL;DR: D dose escalation from 64 to 74 Gy using conformal radiotherapy may improve long-term PSA control, but a treatment margin of 1.5 cm is unnecessary and is associated with increased acute bowel and bladder reactions.
Abstract: Radical radiotherapy is a standard form of management of localised prostate cancer. Conformal treatment planning spares adjacent normal tissues reducing treatment-related side effects and may permit safe dose escalation. We have tested the effects on tumour control and side effects of escalating radiotherapy dose and investigated the appropriate target volume margin. After an initial 3–6 month period of androgen suppression, 126 men were randomised and treated with radiotherapy using a 2 by 2 factorial trial design. The initial radiotherapy tumour target volume included the prostate and base of seminal vesicles (SV) or complete SV depending on SV involvement risk. Treatments were randomised to deliver a dose of 64 Gy with either a 1.0 or 1.5 cm margin around the tumour volume (1.0 and 1.5 cm margin groups) and also to treat either with or without a 10 Gy boost to the prostate alone with no additional margin (64 and 74 Gy groups). Tumour control was monitored by prostate-specific antigen (PSA) testing and clinical examination with additional tests as appropriate. Acute and late side effects of treatment were measured using the Radiation Treatment and Oncology Groups (RTOG) and LENT SOM systems. The results showed that freedom from PSA failure was higher in the 74 Gy group compared to the 64 Gy group, but this did not reach conventional levels of statistical significance with 5-year actuarial control rates of 71% (95% CI 58–81%) in the 74 Gy group vs 59% (95% CI 45–70%) in the 64 Gy group. There were 23 failures in the 74Gy group and 33 in the 64 Gy group (Hazard ratio 0.64, 95% CI 0.38–1.10, P=0.10). No difference in disease control was seen between the 1.0 and 1.5 cm margin groups (5-year actuarial control rates 67%, 95% CI 53–77% vs 63%, 95% CI 50–74%) with 28 events in each group (Hazard ratio 0.97, 95% CI 0.50–1.86, P=0.94). Acute side effects were generally mild and 18 weeks after treatment, only four and five of the 126 men had persistent ⩾Grade 1 bowel or bladder side effects, respectively. Statistically significant increases in acute bladder side effects were seen after treatment in the men receiving 74 Gy (P=0.006), and increases in both acute bowel side effects during treatment (P=0.05) and acute bladder sequelae (P=0.002) were recorded for men in the 1.5 cm margin group. While statistically significant, these differences were of short duration and of doubtful clinical importance. Late bowel side effects (RTOG⩾2) were seen more commonly in the 74 Gy and 1.5 cm margin groups (P=0.02 and P=0.05, respectively) in the first 2 years after randomisation. Similar results were found using the LENT SOM assessments. No significant differences in late bladder side effects were seen between the randomised groups using the RTOG scoring system. Using the LENT SOM instrument, a higher proportion of men treated in the 74 Gy group had Grade ⩾3 urinary frequency at 6 and 12 months. Compared to baseline scores, bladder symptoms improved after 6 months or more follow-up in all groups. Sexual function deteriorated after treatment with the number of men reporting some sexual dysfunction (Grade⩾1) increasing from 38% at baseline to 66% at 6 months and 1 year and 81% by year 5. However, no consistent differences were seen between the randomised groups. In conclusion, dose escalation from 64 to 74 Gy using conformal radiotherapy may improve long-term PSA control, but a treatment margin of 1.5 cm is unnecessary and is associated with increased acute bowel and bladder reactions and more late rectal side effects. Data from this randomised pilot study informed the Data Monitoring Committee of the Medical Research Council RT 01 Trial and the two studies will be combined in subsequent meta-analysis.

233 citations