David Lockman

William Beaumont Army Medical Center, El Paso, Texas, United States

Are you David Lockman?

Claim your profile

Publications (36)112.23 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Previous work has found a highly significant relationship between the irradiated small-bowel volume and development of Grade 3 small-bowel toxicity in patients with rectal cancer. This study tested the previously defined parameters in a much larger group of patients. A total of 96 consecutive patients receiving pelvic radiation therapy for rectal cancer had treatment planning computed tomographic scans with small-bowel contrast that allowed the small bowel to be outlined with calculation of a small-bowel dose-volume histogram for the initial intended pelvic treatment to 45 Gy. Patients with at least one parameter above the previously determined dose-volume parameters were considered high risk, whereas those with all parameters below these levels were low risk. The grade of diarrhea and presence of liquid stool was determined prospectively. There was a highly significant association with small-bowel dose-volume and Grade 3 diarrhea (p < or = 0.008). The high-risk and low-risk parameters were predictive with Grade 3 diarrhea in 16 of 51 high-risk patients and in 4 of 45 low-risk patients (p = 0.01). Patients who had undergone irradiation preoperatively had a lower incidence of Grade 3 diarrhea than those treated postoperatively (18% vs. 28%; p = 0.31); however, the predictive ability of the high-risk/low-risk parameters was better for preoperatively (p = 0.03) than for postoperatively treated patients (p = 0.15). Revised risk parameters were derived that improved the overall predictive ability (p = 0.004). The highly significant dose-volume relationship and validity of the high-risk and low-risk parameters were confirmed in a large group of patients. The risk parameters provided better modeling for the preoperative patients than for the postoperative patients.
    International Journal of Radiation OncologyBiologyPhysics 03/2008; 70(2):413-8. · 4.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To identify factors predictive for chronic urinary toxicity secondary to high-dose adaptive three-dimensional conformal radiation. From 1999 to 2002, 331 consecutive patients with clinical Stage II-III prostate cancer were prospectively treated (median dose, 75.6 Gy). The bladder was contoured, and the bladder wall was defined as the outer 3 mm of the bladder solid volume. Toxicity was quantified according to the National Cancer Institute Common Toxicity Criteria 2.0. Median follow-up was 1.6 years. The 3-year rates of Grade > or =2 and Grade 3 chronic urinary toxicity were 17.0% and 3.6%, respectively. Prostate volume, confidence-limited patient-specific planning target volume, bladder wall volume, and acute urinary toxicity were all found to be accurate predictors for chronic urinary toxicity. The volume of bladder wall receiving > or =30 Gy (V30) and > or =82 Gy (V82), along with prostate volume, were all clinically useful predictors of Grade > or =2 and Grade 3 chronic urinary toxicity and chronic urinary retention. Both Grade > or =2 (p = 0.001) and Grade 3 (p = 0.03) acute urinary toxicity were predictive for the development of Grade > or =2 (p = 0.001, p = 0.03) and Grade 3 (p = 0.05, p < 0.001) chronic urinary toxicity. On Cox multivariate analysis the development of acute toxicity was independently predictive for the development of both Grade > or =2 and Grade 3 chronic urinary toxicity. Acute urinary toxicity and bladder wall dose-volume endpoints are strong predictors for the development of subsequent chronic urinary toxicity. Our recommendation is to attempt to limit the bladder wall V30 to <30 cm(3) and the V82 to <7 cm(3) when possible. If bladder wall information is not available, bladder solid V30 and V82 may be used.
    International Journal of Radiation OncologyBiologyPhysics 12/2007; 69(4):1100-9. · 4.52 Impact Factor
  • Qiuwen Wu, David Lockman, John Wong, Di Yan
    [Show abstract] [Hide abstract]
    ABSTRACT: Treatment simulation is usually performed with a conventional simulator using kV X-rays or with a computed tomography (CT) simulator before the treatment course begins. The purpose is to verify patient setup under the same conditions as for treatment planning. Systematic (preparation) setup errors can be introduced by this process. The purpose of this study is to characterize the setup errors using electronic portal image (EPI) analyses and to propose a method to reduce the systematic component by performing simulation and patient preparation on the treatment machine. In this study, the first four or five days EPIs were analyzed from a total of 533 prostate cancer patients who were simulated on conventional simulators. We characterized setup errors using four parameters: {M(microi), Sigma (microi), RMS(microi), sigma (sigmai)}, where microi and sigmai are individual patient mean and standard deviation, M, Sigma, and RMS are the mean, standard deviation, and root-mean-square of underlying variables (microi and sigmai). We have performed a simulation of removing systematic components by correcting the first day setup error. As a comparison, we also carried out a similar analyses for patients simulated on a CT simulator and patients treated on a linac with an on-board kV CT imaging system, although a limited number of patients were available in these two samples. We found that Sigma (/ui)=(2.6,3.4,2.4) mm, and RMS(sigmai)=(1.5,1.9,1.0) mm in lateral, anterior/posterior, and cranial/caudal directions, indicating that systematic errors are much larger than random errors. Strong correlations were found between measurement on the first day and microi, implying the first day's measurement is a good predictor for microi. The same parameters were also computed for days 2-4, with and without the first day correction. Without correction, M(microi)2-4=(0.7,1.6,-1.0) mm, and Sigma(microi)2-4=(2.6,3.5,2.4) mm. With correction, M(microi)2-4=(0.0,0.4,0.4) mm, much closer to zero, and Sigma(microi)2-4=(1.8,2.2, 1.2) mm, also much smaller. While the use of a CT simulator can reduce the systematic errors, the benefits of first day correction can still be observed, although at a smaller magnitude. Therefore, the systematic setup error can be significantly reduced if the patient is marked and fields are verified on the treatment machine on the first fraction, preferably with an on-board kV imaging system.
    Medical Physics 06/2007; 34(5):1789-96. · 2.91 Impact Factor
  • Di Yan, David Lockman, J V Lebesque
    International Journal of Radiation OncologyBiologyPhysics 05/2006; 64(5):1613-4; author reply 1614-5. · 4.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate an online image-guidance strategy for conformal treatment of prostate cancer and to estimate margin-reduction benefits. Twenty-eight patients with at least 16 helical computed tomography scans were each used in this study. Two prostate soft-tissue registration methods, including sagittal rotation, were evaluated. Setup errors and rigid organ motion were corrected online; non-rigid and intrafraction motion were included in offline analysis. Various clinical target volume-planning target volume (CTV-PTV) margins were applied. Geometrical evaluations included analyses of isocenter shifts and rotations and overlap index. Dosimetric evaluations included minimum dose and equivalent uniform dose (EUD) for prostate and gEUD for rectum. Average isocenter shift and rotation were (dX,dY,dZ,theta) = (0.0 +/- 0.7,-1.1 +/- 4.0,-0.1 +/- 2.5,0.7 degrees +/- 2.0 degrees ) mm. Prostate motion in anterior-posterior (AP) direction was significantly higher than superior-inferior and left-right (LR) directions. This observation was confirmed by isocenter shift in perspectives AP (1.8 +/- 1.8 mm) and RL (3.7 +/- 3.0 mm). Organ motion degrades target coverage and reduces doses to rectum. If 2% dose reduction on prostate D(99) is allowed for 90% patients, then minimum 3 mm margins are necessary with ideal image registration. Significant margin reduction can be achieved through online image guidance. Certain margins are still required for nonrigid and intrafraction motion. To further reduce margin, a strategy that combines online geometric intervention and offline dose replanning is necessary.
    International Journal of Radiation OncologyBiologyPhysics 05/2006; 64(5):1596-609. · 4.52 Impact Factor
  • International Journal of Radiation OncologyBiologyPhysics 10/2005; 63. · 4.52 Impact Factor
  • International Journal of Radiation OncologyBiologyPhysics 10/2005; 63. · 4.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In our Phase II prostate cancer Adaptive Radiation Therapy (ART) study, the highest possible dose was selected on the basis of normal tissue tolerance constraints. We analyzed rectal toxicity rates in different dose levels and treatment groups to determine whether equivalent toxicity rates were achieved as hypothesized when the protocol was started. From 1999 to 2002, 331 patients with clinical stage T1 to T3, node-negative prostate cancer were prospectively treated with three-dimensional conformal adaptive RT. A patient-specific confidence-limited planning target volume was constructed on the basis of 5 CT scans and 4 sets of electronic portal images after the first 4 days of treatment. For each case, the rectum (rectal solid) was contoured in its entirety. The rectal wall was defined by use of a 3-mm wall thickness (median volume: 29.8 cc). The prescribed dose level was chosen using the following rectal wall dose constraints: (1) Less than 30% of the rectal wall volume can receive more than 75.6 Gy. (2) Less than 5% of the rectal wall can receive more than 82 Gy. Low-risk patients (PSA < 10, Stage < or = T2a, Gleason score < 7) were treated to the prostate alone (Group 1). All other patients, intermediate and high risk, where treated to the prostate and seminal vesicles (Group 2). The risk of chronic toxicity (NCI Common Toxicity Criteria 2.0) was assessed for the different dose levels prescribed. HIC approval was acquired for all patients. Median follow-up was 1.6 years. Grade 2 chronic rectal toxicity was experienced by 34 patients (10%) (9% experienced rectal bleeding, 6% experienced proctitis, 3% experienced diarrhea, and 1% experienced rectal pain) at a median interval of 1.1 year. Nine patients (3%) experienced grade 3 or higher chronic rectal toxicity (1 Grade 4) at a median interval of 1.2 years. The 2-year rates of Grade 2 or higher and Grade 3 or higher chronic rectal toxicity were 17% and 3%, respectively. No significant difference by dose level was seen in the 2-year rate of Grade 2 or higher chronic rectal toxicity. These rates were 27%, 15%, 14%, 17%, and 24% for dose levels equal to or less than 72, 73.8, 75.6, 77.4, and 79.2 Gy, respectively (p = 0.3). Grade 2 or higher chronic rectal bleeding was significantly greater for Group 2 than for Group 1, 17% vs. 8% (p = 0.035). High doses (79.2 Gy) were safely delivered in selected patients by our adaptive radiotherapy process. Under the rectal dose-volume histogram constraints for the dose level selection, the risk of chronic rectal toxicity is similar among patients treated to different dose levels. Therefore, rectal chronic toxicity rates reflect the dose-volume cutoff used and are independent of the actual dose levels. On the other hand, a larger PTV will increase the rectal wall dose and chronic rectal toxicity rates. PTV volume and dose constraints should be defined, considering their potential benefit.
    International Journal of Radiation OncologyBiologyPhysics 09/2005; 63(1):141-9. · 4.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Interfractional patient variation occurs regularly and considerably during the radiotherapy course. Consequently, a generic but large planning target margin has to be applied when patient treatment plan design based on a single pre-treatment computed tomography scan is used to guide multifraction radiation treatment, which creates a major limiting factor for radiotherapy improvement. Planning target margins can be significantly reduced using multiple (or 4-dimensional) image feedback management in the routine treatment process. The most effective method in multiple-image feedback management of radiotherapy is the adaptive control methodology. The adaptive radiotherapy technique aims to customize each patient's treatment plan to patient-specific variation by evaluating and characterizing the systematic and random variations through image feedback and including them in adaptive planning. Adaptive radiotherapy will become a new treatment standard, in which a predesigned adaptive treatment strategy, including the schedules of imaging and replanning, will eventually replace the predesigned treatment plan in the routine clinical practice.
    Seminars in Radiation Onchology 08/2005; 15(3):168-79. · 3.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We analyzed our experience treating localized prostate cancer with image-guided off-line correction with adaptive high-dose radiotherapy (ART) in our Phase II dose escalation study to identify factors predictive of chronic rectal toxicity. From 1999-2002, 331 patients with clinical stage T1-T3N0M0 prostate cancer were prospectively treated in our Phase II 3D conformal dose escalation ART study to a median dose of 75.6 Gy (range, 63.0-79.2 Gy), minimum dose to confidence limited-planning target volume (cl-PTV) in 1.8 Gy fractions (median isocenter dose = 79.7 Gy). Seventy-four patients (22%) also received neoadjuvant/adjuvant androgen deprivation therapy. A patient-specific cl-PTV was constructed using 5 computed tomography scans and 4 sets of electronic portal images by applying an adaptive process to assure target accuracy and minimize PTV margin. For each case, the rectum (rectal solid) was contoured from the sacroiliac joints or rectosigmoid junction (whichever was higher) to the anal verge or ischial tuberosities (whichever was lower), with a median volume of 81.2 cc. The rectal wall was defined using the rectal solid with an individualized 3-mm wall thickness (median volume = 29.8 cc). Rectal wall dose-volume histogram was used to determine the prescribed dose. Toxicity was quantified using the National Cancer Institute Common Toxicity Criteria 2.0. Multiple dose-volume endpoints were evaluated for their association with chronic rectal toxicity. Median follow-up was 1.6 years. Thirty-four patients (crude rate = 10.3%) experienced Grade 2 chronic rectal toxicity at a median interval of 1.1 years. Nine patients (crude rate = 2.7%) experienced Grade > or =3 chronic rectal toxicity (1 was Grade 4) at a median interval of 1.2 years. The 3-year rates of Grade > or =2 and Grade > or =3 chronic rectal toxicity were 20% and 4%, respectively. Acute toxicity predicted for chronic: Acute Grade 2-3 rectal toxicity (p < 0.001) including any acute rectal Grade 2-3 tenesmus (p = 0.02) and pain (p = 0.008) were significant predictors of chronic Grade > or =2 rectal toxicity. Any acute rectal toxicity (p = 0.001), any acute tenesmus (p = 0.03), and any acute diarrhea (p < 0.001) were also found to be predictive for chronic toxicity, as continuous variables. Dose-volume histogram predicted for chronic toxicity: Rectal wall absolute and relative V50, V60, V66.6, V70, and V72 and rectal solid relative V60-V72 were significantly associated with chronic Grade > or =2 rectal toxicity both as categorical and continuous variables (t test, linear regression) and when divided into subgroups (chi-square table). The chronic rectal toxicity Grade > or =2 risk was 9%, 18%, and 25% for the rectal wall relative V70 <15%, 25%-40%, and >40% respectively. The volume of rectum or rectal wall radiated to > or =50 Gy was a strong predictor for chronic rectal toxicity. Nonpredictive factors: Rectal solid/wall absolute or relative volumes irradiated to < or =40 Gy, dose level, and use of androgen deprivation were not found predictive. In our ART dose escalation study, rectal wall or rectum relative > or =V50 are closely predictive for chronic rectal toxicity. If rectal dose-volume histogram constraints are used to select the dose level, the risk of chronic rectal toxicity will reflect the risk of toxicity of the selected constraint rather than the dose selected as found in our study using an adaptive process. To select the prescribed dose, different dose-volume histogram constraints may be used including the rectal wall V70. Patients experiencing acute rectal toxicity are more likely to experience chronic toxicity.
    International Journal of Radiation OncologyBiologyPhysics 08/2005; 62(5):1297-308. · 4.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image-guidance applications in our clinic. The objective of this work was to assess the magnitude and stability of the residual setup error associated with CBCT online-guided prostate cancer patient setup. Residual error pertains to the uncertainty in image registration, the limited mechanical accuracy, and the intrafraction motion during imaging and treatment. The residual error for CBCT online-guided correction was first determined in a phantom study. After online correction, the phantom residual error was determined by comparing megavoltage portal images acquired every 90 degrees to the corresponding digitally reconstructed radiographs. In the clinical study, 8 prostate cancer patients were implanted with three radiopaque markers made of high-winding coils. After positioning the patient using the skin marks, a CBCT scan was acquired and the setup error determined by fusing the coils on the CBCT and planning CT scans. The patient setup was then corrected by moving the couch accordingly. A second CBCT scan was acquired immediately after the correction to evaluate the residual target setup error. Intrafraction motion was evaluated by tracking the coils and the bony landmarks on kilovoltage radiographs acquired every 30 s between the two CBCT scans. Corrections based on soft-tissue registration were evaluated offline by aligning the prostate contours defined on both planning CT and CBCT images. For ideal rigid phantoms, CBCT image-guided treatment can usually achieve setup accuracy of 1 mm or better. For the patients, after CBCT correction, the target setup error was reduced in almost all cases and was generally within +/-1.5 mm. The image guidance process took 23-35 min, dictated by the computer speed and network configuration. The contribution of the intrafraction motion to the residual setup error was small, with a standard deviation of +/-0.9 mm. The average difference between the setup corrections obtained with coil and soft-tissue registration was greatest in the superoinferior direction and was equal to -1.1 +/- 2.9 mm. On the basis of the residual setup error measurements, the margin required after online CBCT correction for the patients enrolled in this study would be approximatively 3 mm and is considered to be a lower limit owing to the small intrafraction motion observed. The discrepancy between setup corrections derived from registration using coils or soft tissue can be due in part to the lack of complete three-dimensional information with the coils or to the difficulty in prostate delineation and requires further study.
    International Journal of Radiation OncologyBiologyPhysics 08/2005; 62(4):1239-46. · 4.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents efficient and generalized processes for the clinical application of on-line X-ray volumetric cone-beam CT imaging (XVI) to improve the accuracy of patient set-up in radiation therapy. XVI image-guided therapy is illustrated by application to two contrasting sites, intra-cranial radiosurgery and prostate radiation therapy, with very different characteristics regarding organ motion, treatment precision, and imaging conditions. On-line set-up errors are determined in a two-step process. First the XVI data is registered to the planning data by matching the machine-isocenter with the planning-isocenter, respectively. The machine isocenter is defined in the XVI data during the reconstruction. The planning-isocenter is defined during the planning process in the planning CT data. Set-up errors are then determined from a second registration to remove residual displacements. The accuracy of the entire procedure for on-line set-up error correction was investigated in precision radiosurgery phantom studies. The phantom studies showed that sub-pixel size set-up errors (down to 0.5mm) can be correctly determined and implemented in the radiosurgery environment. XVI is demonstrated to provide quality skull detail enabling precise skull based on-line alignment in radiosurgery. A 'local XVI' technique was found to give encouraging soft-tissue detail in the high-scatter pelvic environment, enabling on-line soft-tissue based set-up for prostate treatment. The two-step process for determination of set-up errors was found to be efficient and effective when implemented with a dedicated six panel interface enabling simultaneous visualization on the XVI and planning CT data sets. XVI has potential to significantly improve the accuracy of radiation treatments. Present image quality is highly encouraging and can enable bony and soft-tissue patient set-up error determination and correction. As with all image guided treatment techniques the development of efficient procedures to utilize on-line data are of paramount importance.
    Radiotherapy and Oncology 07/2005; 75(3):271-8. · 4.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate the validity of the chosen adaptive radiotherapy (ART) dose-volume constraints while testing the hypothesis that toxicity would not be greater at higher tumor dose levels. In the ART dose escalation/selection trial, treatment was initiated with a generic planning target volume (PTV) formed as a 1-cm expansion of the clinical target volume (CTV). After the first week of therapy, the patient was replanned with a patient-specific PTV, constructed with CT and electronic portal images obtained in the first 4 days of treatment. A new multileaf collimator beam aperture was used. A minimum dose prescribed to the patient-specific PTV, ranging 70.2-79.2 Gy, was determined on the basis of the following rectal and bladder constraints: <5% of the rectal wall has a dose >82 Gy, <30% of the rectal wall has a dose >75.6 Gy, <50% of the bladder volume has a dose >75.6 Gy, and the maximum bladder dose is 85 Gy. A conformal four-field and/or intensity-modulated radiotherapy (IMRT) technique was used. Independent reviewers scored toxicities. The worst toxicity score seen was used as per the Common Toxicity Criteria grade scale (version 2). We divided the patients into three separate groups: 70.2-72 Gy, >72-75.6 Gy, and >75.6-79.2 Gy. Toxicities in each group were quantified and compared by the Pearson chi-squared test to validate our dose escalation/selection model. Grades 0, 1, 2, and 3 were censored as none vs. each category and none vs. any. We analyzed patients with follow-up greater than 1 year. The mean duration of follow-up was 29 months (range, 12-46 months). We report on 280 patients, mean age 72 years (range, 51-87 years). Only 60 patients received adjuvant hormones. Mean pretreatment prostate-specific antigen level was 9.3 ng/mL (range, 0.6-120 ng/mL). Mean Gleason score was 6 (range, 3-9). The lowest dose level was given to 49 patients, the intermediate dose to 131 patients, and 100 patients received the highest dose escalation. One hundred eighty-one patients (65%) were treated to a prostate field only and 99 patients (35%) to prostate and seminal vesicles. Chronic genitourinary and/or gastrointestinal categories were incontinence, persistent urinary retention, increased urinary frequency/urgency, urethral stricture, hematuria, diarrhea, rectal pain, bleeding, ulcer, fistula, incontinence, and proctitis. Toxicity at the high dose level was not different from toxicity at the intermediate or lower dose levels. No significant difference was observed in any of the individual toxicity categories. By applying the ART process--namely, developing a patient-specific PTV--to prostate cancer patients, significant dose escalation can be achieved without increases in genitourinary or gastrointestinal toxicity. Our data validate the rectal and bladder dose-volume constraints chosen for our three-dimensional conformal and IMRT prostrate radiotherapy planning.
    International Journal of Radiation OncologyBiologyPhysics 03/2005; 61(2):400-8. · 4.52 Impact Factor
  • International Journal of Radiation Oncology Biology Physics - INT J RADIAT ONCOL BIOL PHYS. 01/2005; 63.
  • International Journal of Radiation Oncology Biology Physics - INT J RADIAT ONCOL BIOL PHYS. 01/2005; 63.
  • International Journal of Radiation OncologyBiologyPhysics 09/2004; 60(1). · 4.52 Impact Factor
  • International Journal of Radiation OncologyBiologyPhysics 09/2004; 60. · 4.52 Impact Factor
  • International Journal of Radiation OncologyBiologyPhysics 09/2004; 60(1). · 4.52 Impact Factor
  • D LOCKMAN, D YAN, J WONG, A MARTINEZ
    International Journal of Radiation OncologyBiologyPhysics 09/2004; 60. · 4.52 Impact Factor
  • International Journal of Radiation OncologyBiologyPhysics 09/2004; 60. · 4.52 Impact Factor