Biomedical subjects

Gerald E Hanks

Publications and source records attributed to Gerald E Hanks.

27 records · Page 2Linked to original sources

PubMed2002

MRI simulation: effect of gradient distortions on three-dimensional prostate cancer plans.

PURPOSE: To quantify the dosimetric consequences of external patient contour distortions produced on low-field and high-field MRIs for external beam radiation of prostate cancer. METHODS AND MATERIALS: A linearity phantom consisting of a grid filled with contrast material was scanned on a spiral CT, a 0.23 T open MRI, and a 1.5 T closed bore system. Subsequently, 12 patients with prostate cancer were scanned on CT and the open MRI. A gradient distortion correction (GDC) program was used to postprocess the MRI images. Eight of the patients were also scanned on the 1.5 T MRI with integrated GDC correction. All data sets were fused according to their bony landmarks using a chamfer-matching algorithm. The prostate volume was contoured on an MRI image, irrespective of the apparent prostate location in those sets. Thus, the same target volume was planned and used for calculating the anterior-posterior (AP) and lateral separations. The number of monitor units required for treatment using a four-field conformal technique was compared. Because there are also setup variations in patient outer contours, two different CT scans from 20 different patients were fused, and the differences in AP and lateral separations were measured to obtain an estimate of the mean interfractional separation variation. RESULTS: All AP separations measured on MRI were statistically indistinguishable from those on CT within the interfractional separation variations. The mean differences between CT and low-field MRI and CT and high-field MRI lateral separations were 1.6 cm and 0.7 cm, respectively, and were statistically significantly different from zero. However, after the GDC was applied to the low-field images, the difference became 0.4 +/- 0.4 mm (mean +/- standard deviation), which was statistically insignificant from the CT-to-CT variations. The mean variations in the lateral separations from the low-field images with GDC would result in a dosimetric difference of <1%, assuming an equally weighted four-field 18-MV technique for patient separations up to approximately 40 cm. CONCLUSIONS: For patients with lateral separations <40 cm, a homogeneous calculation simulated using a 1.5 T MRI or a 0.23 T MRI with a gradient distortion correction will yield a monitor unit calculation indistinguishable from that generated using CT simulation.

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PubMed2002

Posttreatment prostate-specific antigen nadir highly predictive of distant failure and death from prostate cancer.

PURPOSE: To link posttreatment biochemical profiles to distant failure and cause-specific survival by assessing the relationship between posttreatment prostate-specific antigen (PSA) nadir and PSA doubling time (PSADT) with these outcome measures. METHODS AND MATERIALS: A total of 615 men were treated at the Fox Chase Cancer Center between April 1989 and December 1995 with three-dimensional conformal radiotherapy alone (median dose 73 Gy). The median follow-up was 64 months (range 2-135). Kaplan-Meier methods were used to estimate the rates of biochemical control, freedom from distant metastasis (FDM), and cause-specific survival. Multivariate predictors of outcome were assessed using stepwise Cox regression analysis. RESULTS: Multivariate analyses demonstrated that the predictors of improved biochemical control were a lower PSA nadir (p <0.0001), lower pretreatment PSA level (p <0.0001), Gleason score of 2-6 (p = 0.001), Stage T1-T2a tumors (p = 0.03), and higher RT dose (p = 0.02). The predictors of improved FDM were a lower PSA nadir (p <0.0001), longer interval to nadir from start of treatment (p = 0.0002), Gleason score of 2-6 (p = 0.005), androgen deprivation for biochemical failure (p = 0.001), and Stage T1-T2a tumors (p = 0.01). The predictors of improved cause-specific survival were a lower PSA nadir (p = 0.006) and longer interval to nadir from the start of treatment (p = 0.03). The 8-year FDM rate was 96%, 89%, and 61% for PSA nadir values of 2.0 ng/mL (p <0.0001), respectively. The 8-year cause-specific survival rate was 97%, 96%, and 78% for posttreatment PSA nadir values of 2.0 ng/mL (p <0.0001), respectively. For patients with sufficient PSA follow-up for PSADT calculations (n = 136), multivariate analysis of FDM from the time of biochemical failure demonstrated that androgen deprivation (p = 0.001), longer PSADT (p = 0.003), lower PSA nadir (p = 0.02), and longer interval to nadir from start of treatment (p = 0.04) were independent predictors of improved FDM. CONCLUSION: This is the first study, to our knowledge, to demonstrate the overwhelming predictive power of posttreatment PSA nadir for distant failure and death from prostate cancer. It is also the first study, to our knowledge, to demonstrate a strong association between posttreatment PSADT and distant failure. The results provide new information regarding disease progression as a function of posttreatment PSA profiles (time to achieve nadir from start of treatment, nadir, and PSADT) and the timing of androgen deprivation for biochemical relapse. This study may be used for the early identification of patients at high risk of distant metastasis and who may be directed to applicable systemic treatment clinical trials.

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PubMed2002

Advantages of using noncoplanar vs. axial beam arrangements when treating prostate cancer with intensity-modulated radiation therapy and the step-and-shoot delivery method.

PURPOSE: The focus of this work was to compare noncoplanar beam arrangements used for intensity-modulated radiation therapy (IMRT) step-and-shoot delivery to several axial beam arrangements used in the treatment of clinically localized prostate cancer. METHODS AND MATERIALS: A 5-field coronal crossfire beam arrangement was developed for IMRT with the objective of improving upon the rectal and bladder dose-volume histograms obtained using 5-, 7-, and 9-field axial beam arrangements. Additionally, a modified 7-field crossfire technique was developed yielding improved dose distributions. The average values of dose-volume histograms and the time for treatment delivery were evaluated for all plans for 10 randomly chosen patients. RESULTS: Both crossfire IMRT techniques exhibited a 15-25% decrease in dose to the hottest 10% and 20% of the rectum relative to all three axial IMRT techniques. The 5-field crossfire orientation yields slightly higher bladder doses when compared to the other techniques. In selected cases, the 7-field crossfire beam arrangement demonstrates decreased dose to the bladder when compared to all three axial techniques. A mean delivery time of 14 to 17.5 min is noted for the noncoplanar arrangements after positioning and localization. CONCLUSIONS: A technique is described that allows additional normal tissue sparing during dose escalation to the prostate during IMRT delivery. This technique takes advantage of the spatial orientation between the prostate, rectum, and bladder. With patient setup and target localization time aside, a mean treatment time of 14 to 17.5 min allows the delivery of the crossfire plans to conform to standard treatment times.

Humans↗

PubMed2002

Relationship between prostate volume, prostate-specific antigen nadir, and biochemical control.

PURPOSE: In patients treated with definitive three-dimensional conformal radiotherapy (3D-CRT) for localized prostatic adenocarcinoma, we sought to evaluate the relationship between pretreatment prostate gland volume and posttreatment prostate-specific antigen (PSA) nadir, as well as the relationship of prostate volume and PSA nadir with biochemical control (bNED). Two subgroups were studied: favorable (PSA <10 ng/mL, Gleason score 2-6, and T1-T2A) and unfavorable (one or more: PSA >/=10 ng/mL, Gleason score 7-10, T2B-T3). MATERIALS AND METHODS: A total of 655 men (n = 271 favorable and 384 unfavorable) were treated with 3D-CRT alone between May 1989 and November 1997. All patients had information on prostate volume and a minimum follow-up of 24 months (median 56, range 24-126). Of the 655 men, 481 (n = 230 favorable and 251 unfavorable) remained bNED at time of analysis, with biochemical failure defined in accordance with the American Society for Therapeutic Radiology and Oncology consensus definition. Factors analyzed for predictors of bNED included pretreatment prostate volume, posttreatment PSA nadir, pretreatment PSA, palpation T stage, Gleason score, center of the prostate dose, and perineural invasion (PNI). We also analyzed pretreatment prostate volume and its correlation to prognostic factors. For bNED patients, the relationship between PSA nadir and prostate volume was evaluated. RESULTS: On multivariate analysis, prostate volume (p = 0.04) and palpation T stage (p = 0.02) were the only predictors of biochemical failure in the favorable group. On multivariate analysis of the unfavorable group, pretreatment PSA (p <0.0001), Gleason score (p = 0.02), palpation T stage (p = 0.009), and radiation dose (p <0.0001) correlated with biochemical failure, and prostate volume and PNI did not. For all 481 bNED patients, a positive correlation between pretreatment volume and PSA nadir was demonstrated (p <0.0001). Subgroup analysis of the favorable and unfavorable patients also demonstrated a positive correlation between prostate volume and PSA nadir (p = 0.003 and p = 0.0002, respectively). Using multiple regression analysis, the following were found to be predictive of PSA nadir in all bNED patients: prostate volume (p <0.0001), pretreatment PSA (p <0.0001), palpation T stage (p = 0.0002), and radiation dose (p = 0.0034). Gleason score and PNI were not predictive. For the favorable group, palpation T stage (p = 0.0006), pretreatment PSA (p = 0.0083), prostate volume (p = 0.0186), and Gleason score (p = 0.0592) were predictive of PSA nadir, and PNI and radiation dose were not predictive. In the unfavorable group, prostate volume (p = 0.0024), radiation dose (p = 0.0039), pretreatment PSA (p = 0.0182), and palpation T stage (p = 0.0296) were predictive of PSA nadir, and Gleason score and PNI were not predictive. CONCLUSION: This report is the first demonstration that prostate volume is predictive of PSA nadir for patients who are bNED in both favorable and unfavorable subgroups. PSA nadir did not correlate with bNED status in the favorable patients, but it was strongly predictive in the unfavorable patients. Prostate gland volume was also predictive of bNED failure in the favorable but not the unfavorable group.

Aged↗

PubMed2002

Hypoxic prostate/muscle pO2 ratio predicts for biochemical failure in patients with prostate cancer: preliminary findings.

OBJECTIVES: To investigate whether low partial pressure of oxygen (PO2) in prostate cancer (CaP) predicts for biochemical outcome after radiotherapy. We previously reported that hypoxic regions exist in human CaP. METHODS: Custom-made Eppendorf PO2 microelectrodes were used to obtain approximately 100 PO2 readings from both pathologically involved regions of the prostate (as determined by sextant biopsies) and normal muscle (as an internal control). Fifty-seven patients with localized disease were prospectively studied; all received brachytherapy implants (48 low dose rate and 9 high dose rate) under spinal anesthesia. Nine patients had received prior hormonal therapy. Biochemical failure was defined as two consecutive rises in prostate-specific antigen level, without a return to baseline. Cox proportional hazards regression analysis was used to evaluate the influence of hypoxia on biochemical control, while adjusting for prostate-specific antigen, Gleason score, stage, implant type (low dose rate versus high dose rate), perineural invasion, hemoglobin level, use of hormonal therapy, average (mean) of the median prostate PO2, average median muscle PO2, and prostate/muscle PO2 (P/M) ratio. RESULTS: With a median follow-up of 19 months (range 4 to 31), 9 patients developed biochemical failure. A threshold analysis of the P/M ratio demonstrated that biochemical control at 2 years differed significantly at a ratio of less than 0.05 versus 0.05 or greater (31% versus 92%, P <0.0001). However, the classic prognosticators were similar in these two groups. On multivariate analysis, the P/M ratio was the only predictor of biochemical control (P = 0.0002). CONCLUSIONS: To our knowledge, this is the first study to correlate the degree of hypoxia in CaP with treatment outcome after radiotherapy. The P/M PO2 ratio was the strongest predictor for biochemical control on stepwise multivariate analysis. Longer follow up with more patients is planned to confirm this result.

Aged↗

PubMed2002

Decision-making strategies for patients with localized prostate cancer.

Patients diagnosed with early-stage prostate cancer not only have to cope with the impact of the cancer diagnosis, but also need to interpret complicated medical information to make an informed treatment decision. We report initial results from an ongoing longitudinal investigation examining treatment decision making among men diagnosed with early stage prostate cancer. Men (N = 654) were recruited into the assessment study after an initial treatment consultation with a urologic surgeon or radiation oncologist. Patients were, on average, 66 years old, married (85%), had at least a high school education (45%), were retired (58%), and were Caucasian (91%) or African American (7%). Guided by a cognitive-affective theoretical framework, we assessed treatment and disease-relevant beliefs and affects in addition to clinical variables. The majority of patients decided on external beam radiation therapy (52%), followed by brachytherapy (25%), prostatectomy (17%), and watchful waiting (6%). Patients who decided on prostatectomy were significantly younger (mean age, 58 yr) than patients who received radiation therapy (mean age, 67 yr) and brachytherapy (mean age, 66 yr). When asked for the most important reason influencing their treatment decision, patients indicated physician recommendation (51%), advice from friends and family (19%), information obtained from books and journals (18%), or the Internet (7%). Among cognitive variables, patients who decided on surgery perceived prostate cancer as being significantly more serious (P <.001), and had greater difficulties in making a treatment decision (P <.005) compared with patients receiving radiation therapy or brachytherapy. Surgical patients were also more distressed about their treatment decision (P <.001) and concerned that the cancer might spread (P <.005). To date, patients followed-up after treatment have not indicated significant regrets about their therapeutic choice. These data suggest that unique treatment-related beliefs and affects need to be taken into account during the treatment counseling process. Implications for the development of decision aids are discussed.

Aged↗

PubMed2002

Characteristics and quality assurance of a dedicated open 0.23 T MRI for radiation therapy simulation.

A commercially available open MRI unit is under routine use for radiation therapy simulation. The effects of a gradient distortion correction (GDC) program used to post process the images were assessed by comparison with the known geometry of a phantom. The GDC reduced the magnitude of the distortions at the periphery of the axial images from 12 mm to 2 mm horizontally along the central axis and distortions exceeding 20 mm were reduced to as little as 2 mm at the image periphery. Coronal and sagittal scans produced similar results. Coalescing these data into distortion as a function of radial distance, we found that for radial distances of <10 cm, the distortion after GDC was <2 mm and for radial distances up to 20 cm, the distortion was <5 mm. The dosimetric errors resulting from homogeneous dose calculations with this level of distortion of the external contour is <2%. A set of triangulation lasers has been added to establish a virtual isocenter for convenient setup and marking of patients and phantoms. Repeated measurements of geometric phantoms over several months showed variations in position between the virtual isocenter and the magnetic isocenter were constrained to <2 mm. Additionally, the interscan variations of 12 randomly selected points in space defined by a rectangular grid phantom was found to be within the intraobserver error of approximately 1 mm in the coronal, sagittal, and transverse planes. Thus, the open MRI has sufficient geometric accuracy for most radiation therapy planning and is temporally stable.

Computer Simulation↗

PubMed2002

Prostate-specific antigen as a marker of disease activity in prostate cancer.

Despite the impact of prostate-specific antigen (PSA) testing on the detection and management of prostate cancer, controversy about its usefulness as a marker of disease activity continues. This review, based on a recent roundtable discussion, examines whether PSA measurements can be used rationally in several clinical settings. Following radical prostatectomy and radiation therapy, prediction of survival by PSA level is most reliable in high-risk patients. PSA doubling time after radiation therapy is the strongest predictor of biochemical failure. PSA measurements have been associated with inconsistent results following hormonal treatment; reduced PSA levels may result from antiandrogen treatment, which decreases expression of the PSA gene, and therefore, the level of PSA production. In the setting of primary and secondary cancer prevention, PSA is important in risk stratification when selecting patients for studies. Part 1 of this two-part article, which concludes in the September issue, focuses on the physiology of PSA, its measurement and use in clinical practice, and its predictive value following radical prostatectomy and radiation therapy.

Biomarkers, Tumor↗

PubMed2002

Prostate-specific antigen as a marker of disease activity in prostate cancer.

Despite the impact of prostate-specific antigen (PSA) testing on the detection and management of prostate cancer, controversy about its usefulness as a marker of disease activity continues. This review, based on a recent roundtable discussion, examines whether PSA measurements can be used rationally in several clinical settings. Following radical prostatectomy and radiation therapy, prediction of survival by PSA level is most reliable in high-risk patients. PSA doubling time after radiation therapy is the strongest predictor of biochemical failure. PSA measurements have been associated with inconsistent results following hormonal treatment; reduced PSA levels may result from antiandrogen treatment, which decreases expression of the PSA gene, and therefore, the level of PSA production. In the setting of primary and secondary cancer prevention, PSA is important in risk stratification when selecting patients for studies. Part 2 of this two-part article, which began in the August issue, discusses the role of PSA in hormonal and drug therapies and in primary and secondary chemoprevention.

Biomarkers, Tumor↗