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G S Merrick

Publications and source records attributed to G S Merrick.

At least 37 records · Page 2Linked to original sources
PubMed2000

Modified uniform seed loading for prostate brachytherapy: rationale, design, and evaluation.

PURPOSE: Despite a multitude of preplanning approaches and seed loading philosophies, multiple groups have reported comparable results in terms of biochemical disease-free survival and complication rates. None of the seed loading philosophies have been proven superior and no generally accepted loading philosophy has been adopted by the brachytherapy community. MATERIALS AND METHODS: Review of the preplanning philosophy, preplanning dosimetry, and preimplant evaluation is presented. RESULTS: A modified uniform seed loading approach is used because of its ability to deliver a relatively homogeneic dose to the prostate gland with a periprostatic margin, to routinely maintain the urethral dose at approximately 115% of the prescribed dose and to avoid significant rectal and urinary toxicity. CONCLUSION: Of the commonly utilized seed loading philosophies, a modified uniform approach delivers a relatively homogeneic dose to the prostate gland/periprostatic region and is the most forgiving of local and systematic errors in seed placement.

Brachytherapy↗
PubMed2000

Influence of prophylactic dexamethasone on edema following prostate brachytherapy.

PURPOSE: This work evaluates the prophylactic administration of dexamethasone as an adjunct to prostate brachytherapy to determine the effect of dexamethasone on postimplant edema, dosimetric quality, catheter dependency, and clinical outcome as assessed by serial American Urological Association (AUA) symptom score determinations. MATERIALS AND METHODS: In a controlled study, 22 unselected patients were placed alternately into either a dexamethasone or control arm. RESULTS: There was no statistically significant difference in volume between the experimental and control groups on either day 0 or day 28. Accordingly, the day 0 dosimetric parameters, short-term catheter dependency, and serial AUA symptom score determinations were equivalent in both patient groups. However, the patients receiving dexamethasone had a markedly smaller volume on day 3, but 9 of 11 experienced rebound edema with a volume on day 14 significantly greater than day 3. CONCLUSIONS: Because of the small number of patients evaluated, additional studies are essential to confirm these findings. At the present time, we do not recommend this dexamethasone schedule as a routine component of prostate brachytherapy.

Brachytherapy↗
PubMed1999

The dependence of prostate postimplant dosimetric quality on CT volume determination.

PURPOSE: The postoperative evaluation of permanent prostate brachytherapy requires a subjective determination of the implant volume. This work investigates the magnitude of the effect that various methods of treatment volume delineation have on dosimetric quality parameters for a treatment planning philosophy that defines a target volume as the prostate with a periprostatic margin. METHODS AND MATERIALS: Eight consecutive prostate brachytherapy patients with a prescribed dose of 145 Gy from 125I as monotherapy comprised the study population. The prostate ultrasound volume was enlarged to a planning volume by an average factor of 1.8 to encompass probable extracapsular extension in the periprostatic region. For this cohort, the mean pretreatment parameters were 30.3 cm3 ultrasound volume, 51.8 cm3 planning volume, 131 seeds per patient, and 42.9 mCi total activity. On CT study sets obtained less than 2 hours postoperatively, target volumes were drawn using three methods: prostate plus a periprostatic margin, prostate only which excluded the puborectalis muscles, the periprostatic fat and the periprostatic venous plexus, and the preplanning ultrasound magnified to conform to the magnification factor of the postimplant CT scan. Three sets of 5 dosimetric quality parameters corresponding to the different volumetric approaches were calculated: V100, V150, and V200 which are the fractions of the target volume covered by 100, 150, and 200% of the prescribed dose, and D90 and D100, which are the minimal doses covering 90 and 100% of the target volume. RESULTS: The postoperative CT volume utilizing the prostate plus margin technique was comparable to the initial planning volume (mean 55.5 cm3 vs. 51.8 cm3, respectively) whereas those determined via superimposing the preplan ultrasound resulted in volumes nearly identical to the initial ultrasound evaluation (mean 32.4 cm3 vs. 30.3 cm3). The prostate only approach resulted in volumes approximately 25% larger than the ultrasound volume approach. Despite the volume determinations being markedly different, no significant differences between the approaches were appreciated for V100, V150, V200, and D90. Large variations seen in D100 were uncorrelated to any of the other parameters and make D100 unsuitable as a quality indicator. CONCLUSIONS: In terms of a logarithmic measure, the variation between volumetric approach for V100, V150, V200, and D90 was less than one-fifth the variation of the CT volumes. These results which indicate relative independence of postimplant CT volume determination and dosimetric quality are only valid for a planning philosophy that includes the prostate with a periprostatic margin as the target volume.

Brachytherapy↗
PubMed1999

Potential role of various dosimetric quality indicators in prostate brachytherapy.

PURPOSE: Postoperative CT-based dosimetric analysis provides detailed information regarding the coverage and uniformity of an implant, but the assessment of implant quality remains an unanswered and controversial issue. There is no disagreement that a good implant should cover the target volume with an adequate dose, but there is no consensus as to what represents an adequate dose. MATERIALS AND METHODS: The American Brachytherapy Society has recently proposed that prostate brachytherapy quality be measured in terms of the following parameters: D90, V100, and V150 where D90 is defined as the minimal dose covering 90% of the prostate volume and V100 and V150 are defined as the percent volume of the prostate receiving at least 100% or 150% of the prescribed minimal peripheral dose (mPD), respectively. We report detailed day 0 dosimetric evaluation for 60 consecutive prostate brachytherapy patients implanted via a standard transperineal ultrasound guided approach in terms of D90, D100, V90, V100, and V150 and also the maximal and average rectal and urethral dose. RESULTS: Dosimetric evaluation resulted in a V100 greater than 80% of the prostate volume and a D90 greater than 90% of the mPD in the entire patient population. There was a statistically significant difference between the quality scores of 125I implants and 103Pd implants with the 125I mean V100 and D90 at 95.3% volume and 109.9% mPD, respectively, vs. 103Pd at 91.8% volume and 103.7% mPD. Likewise, the rectal and urethral doses as a fraction of mPD were significantly lower in 103Pd than in 125I implants. This occurred despite the fact that palladium implants were typically preplanned with significantly better coverage and hotter V150 than iodine implants. We consider V150 to be an important parameter for determining dose homogeneity although the clinical utility of dose homogeneity remains unknown. The mean V150 was 45.6 +/- 9.6% volume. There was no additional dosimetric utility from a determination of V90 while D100 was found to be overly sensitive to steep dose gradients at the periphery of the prostate. CONCLUSIONS: This report represents the first detailed postimplant day 0 dosimetric evaluation comparing ABS recommended quality parameters used to evaluate prostate brachytherapy. At the present time, no long-term clinical outcomes are available because of short follow-up. As PSA based follow-up data becomes available, however, this report may help define what represents an adequate implant.

Brachytherapy↗
PubMed1999

Rectal dosimetric analysis following prostate brachytherapy.

PURPOSE: To retrospectively assess the rectal tolerance dose in transperineal ultrasound-guided prostate brachytherapy using easily measured point doses. METHODS AND MATERIALS: Forty-five consecutive patients who underwent prostate seed implantation from January 1996 to October 1996, using either 125I or 103Pd as monotherapy or as a boost following 45 Gy of external beam radiotherapy (XRT), were evaluated. For monotherapy using 125I, the minimal peripheral dose (mPD) was 160 Gy, utilizing dosimetry parameters which are equivalent to 144 Gy under the American Association of Physicists in Medicine Task Group 43 (AAPM TG43) recommendations. Computed tomography (CT)-based dosimetry was performed within 9 days of the implant, with a urinary catheter in place for identification of the urethra, and a rectal obturator positioned prior to the CT scan for identification of the anterior rectal mucosa. Dosimetric parameters relevant to this study were the average, maximal and minimal anterior rectal mucosal dose, and the surface area and length of the anterior rectal mucosa irradiated to 50%, 75%, 90%, 100%, and 120% of the prescribed dose. Rectal complications were determined by patient reporting during office visits and telephone follow-up. Follow-up ranged from 19 to 28 months (median 23). RESULTS: Among the four cohorts, the average anterior rectal mucosal dose as a percent of the prescribed mPD was 82.5% +/- 14.1% (standard deviation, SD), and the average maximum was 120% +/- 35%. The length of the rectum receiving a given dose was found to be correlated with the rectal surface area receiving that dose (r2 = 0.82 - 0.93 over the dose range 0.5-1.2 mPD). Rectal complications occurred in only four patients, and consisted of mild, self-limited proctitis. Three of the four were in the top quartile of average and maximal rectal dose and length of rectum receiving > or = 100% of mPD, while the fourth was in the bottom quartile of these parameters. In terms of surface area, all four patients were in the upper half of the study group, with > or = 90 mm2 at dose levels > or = 100% of mPD. CONCLUSION: Our results indicate that in an implant program which maintains the anterior rectal mucosa point dose averages to about 85% of the prescribed dose (regardless of the choice of isotope or the treatment approach), the average maximum to 120% of mPD, and the length of the anterior rectal mucosa receiving 100% and 120% of the prescribed dose at approximately 10 mm and 5 mm, respectively, the incidence of mild self-limited proctitis will be in the range of approximately 9%, without incidence of rectal ulceration and/or fistula formation.

Brachytherapy↗
PubMed1999

Efficacy of sildenafil citrate in prostate brachytherapy patients with erectile dysfunction.

OBJECTIVES: To ascertain the efficacy of sildenafil citrate (Viagra) in patients with erectile dysfunction (ED) either before or after prostate brachytherapy by an open-label, nonrandomized study. METHODS: Sixty-two patients who underwent prostate brachytherapy between March 1995 and July 1998, had ED either before or after brachytherapy, and were interested in treatment with sildenafil comprised the patient population. Clinical and treatment parameters evaluated for medication efficacy included patient age at brachytherapy and at medication administration, hypertension, diabetes, smoking history, onset of ED, potency status before implant, frequency of intercourse before brachytherapy (if potent), use of neoadjuvant hormonal manipulation, use of moderate dose external beam radiation therapy before implantation, choice of isotope, V100 (the percentage of the prostate volume receiving at least 100% of the prescribed minimal peripheral dose), and sildenafil dose. RESULTS: Fifty (80.6%) of 62 patients responded favorably to sildenafil. None of the treatment parameters predicted medication failure, and among the clinical parameters, only diabetes predicted failure (3 of 5) and only with borderline statistical validity (P = 0.046). CONCLUSIONS: Our results suggest brachytherapy-induced impotence is as amenable to sildenafil treatment as ED from other causes. In addition, our 80.6% success rate is comparable to reported results for patients who underwent bilateral nerve-sparing radical prostatectomy and significantly better than patients who underwent unilateral nerve-sparing or non-nerve-sparing approaches.

Adenocarcinoma↗
PubMed1999

Nursing management of patients receiving brachytherapy for early stage prostate cancer.

New technologies used in the area of prostate brachytherapy have resulted in a resurgence of interest in this modality of therapy for early stage prostate cancer. Results of prostate brachytherapy have been reported to be as favorable as radical prostatectomy. Nursing care is multifaceted and necessitates a thorough understanding of brachytherapy techniques, sequelae, and radiation safety.

Brachytherapy↗
PubMed1998

Quality assurance calibration of 125I rapid strand in a sterile environment.

PURPOSE: 125I seeds encased in stiffened absorbable suture material, commercially available from Amersham Healthcare as 125I Rapid Strand, are not readily calibrated because of the necessity of maintaining the sterility and integrity of the Rapid Strand. A method is proposed to verify the activity of 125I seeds in Rapid Strand in a sterile environment and to provide quality assurance of the resultant loading by autoradiographing loaded needles. METHODS AND MATERIALS: A sterilizable insert for a Standard Imaging HDR 1000 Plus well chamber was designed to accommodate Amersham's plastic spacing jig that holds the strand. The insert has a cylindrical lead sleeve allowing five of the 10 seeds in the jig to be exposed within the well chamber. A grooved tray for holding a batch of 30 needles was designed for autoradiographing the implant set. RESULTS: Position-dependent calibration factors for each of the seed wells in the jig were determined; then these individual factors were combined into a single chamber factor of 21.6 pA/mCi. Starting from the most distal spacing jig slot, relative position factors were 0.99, 1.00, 0.99, 0.93, 0.73, and 0.13 for the six positions which produced a nonnegligible signal. Anisotropy in the chamber factor was determined by rotating the well in 30 degrees increments about the seeds in the jig. The chamber factor showed only a 0.2% variation with rotational angle. Attenuation due to the Vicryl suture cladding material was 0.2% and was measured by stripping the Vicryl from the strand and remeasuring the chamber factor with the seeds in their original orientation. In the operating room, charge was collected from sterile Rapid Strands for a fixed time between 30 and 50 s and the measured ion chamber current was compared with the value predicted from Amersham's nominal activity. The average deviation between nominal and measured activity of 73 Rapid Strands tested was +0.5% +/- 2.2%. For single measurements, the maximum and minimum deviations observed were +4.8% and -3.7%, respectively. Autoradiographs taken of the entire implant set on an aluminum tray milled to hold the needles confirmed the actual seed loadings. CONCLUSIONS: The Rapid Strand calibration procedure described maintains the sterility and integrity of 125I Rapid Strands and verifies that the manufacturer's stated activity is accurate to within 5%.

Algorithms↗
PubMed1998

Influence of timing on the dosimetric analysis of transperineal ultrasound-guided, prostatic conformal brachytherapy.

Postoperative computed tomography (CT)-based dosimetric analysis of transperineal ultrasound-guided conformal prostate brachytherapy provides detailed information regarding the coverage and uniformity of the implant. However, there is no generally accepted standard for the optimal timing of the postoperative dosimetry. This report details dosimetric analysis and the effect of timing based upon CT and orthogonal film evaluation for ten unselected patients implanted with either iodine-125 (125I) or palladium-103 (103Pd). Within 2 hours after implantation, patients underwent a CT scan and the first of four sequential sets of orthogonal films. Subsequent orthogonal films were obtained on days 3, 14, and 28 postimplant. CT-based dosimetry revealed coverage of the prostate to the prescribed minimal peripheral dose (mPD) at 93.1 +/- 3.6% of the volume, the prostate volume receiving 150% of mPD was 38.2 +/- 8.7%, and the urethral and rectal doses were 114 +/- 12% and 78 +/- 19% of mPD, respectively. The implanted seeds seen on orthogonal films acted as markers for temporal changes in prostate dimensions, and the standard deviation of each dimension was used as input in an ellipsoidal volume calculation. Seed coordinates were self normalized to the center of gravity of each two-dimensional view and were measured relative to the linear regression line in the superior-inferior direction. The reproducibility of the anteroposterior (AP) film setup in terms of temporal variation in the angle of the regression line was markedly better than that of the lateral films, 1.8 degrees +/- 1.2 degrees vs. 4.3 degrees +/- 2.6 degrees, respectively. Dimensional contraction from day 0 to day 28 averaged 11.3% in the superior-inferior direction, 8.5% in the AP/PA (posteroanterior) direction, and 2.5% in the right-left lateral direction. This translated into a volume change of 20.9% (ranged 11.6-31.6%), which was determined by using the ellipsoid method. The half-life for edema resolution was 10.6 +/- 1.8 days (range 8.6-14.3 days). However, because of variability in the degree and extent of edema and its rate of resolution, we believe that it may be futile to define a single point in time as the most accurate indicator of the postoperative dose distribution. Rather, it may be preferable to accept universal standardization of timing and methodology for CT-based postoperative dosimetry, which would facilitate comparison of results between centers and maximize the information content of that single measurement. We conclude that day 0 represents the optimal time, because dosimetric evaluation at that time minimizes patient discomfort and inconvenience (a catheter is already in place), provides information about edema when it is near its maximum extent, and provides prompt closure of the learning loop and, as such, hopefully will result in improved implantation techniques and results.

Aged↗
PubMed1997

Prostatic conformal brachytherapy: 125I/103Pd postoperative dosimetric analysis.

Widespread replication of the favorable long-term results of prostatic conformal brachytherapy achieved by the Seattle group requires evidence that the technical quality of their implants is achievable elsewhere. Preplanning with a modified uniform loading algorithm using low activity seeds produces virtually no regions within the planning volume at less than the prescribed dose and no interconnected volumes between seeds at double the dose. The operative procedure stabilizes the prostate and locates the prostate targets, needles, and seeds and their relationship to the bladder and rectum using transverse and longitudinal ultrasound as well as contrast enhanced fluoroscopy. A detailed postoperative dosimetric analysis of patients with clinical T1/T2 adenocarcinoma of the prostate gland who underwent transperineal ultrasound conformal prostatic brachytherapy from March through June 1996 was performed. The analysis involved 7 consecutive patients implanted with 125I seeds and 5 consecutive patients implanted with 103Pd seeds. Median coverage to the full minimal peripheral dose (mPD) was 96% (range 80-99%) of the prostate volume. At 80% of the mPD, median isodose coverage was 100% (range 91-100%) of the prostate volume. Regarding hot spots to critical structures, the median maximal urethral dose was 175% of the mPD (range 115-227%) and the median maximal dose to the anterior rectal mucosa was 105% of the mPD (range 83-133%). Analysis of postoperative dose-volume histograms has shown that our maximal dose surface to any volume greater than 5 cm3 is 203% (range 175-247%). These results indicate that good quality transperineal ultrasound prostatic conformal brachytherapy can be accurately reproduced in a community hospital setting and that biochemical no evidence of disease (NED) results and local control rates will be comparable to those of the Seattle group with no unexpected urethral or rectal complications or side effects.

Adenocarcinoma↗
PubMedDate not supplied

Radioactive seed embolization to the lung following prostate brachytherapy.

Over the past decade, prostate brachytherapy has been increasingly utilized as definitive management for early stage carcinoma of the prostate gland. One risk of the procedure is pulmonary seed embolization. In this article we report the incidence and timing of seed migration. Pulmonary embolization of radioactive seeds occurs in approximately 20% of patients undergoing prostate brachytherapy. To date, no acute or delayed detrimental effects have been reported which are attributable to the pulmonary embolization of the seeds; nevertheless, it is imperative that patients and health care providers be cognizant of this possible event.

Aged↗
PubMedDate not supplied

The role of urinary assessment scores in the nursing management of patients receiving prostate brachytherapy.

Nearly all patients experience some degree of urinary irritative or obstructive symptoms following brachytherapy for definitive treatment of early-stage prostate cancer. The American Urological Association (AUA) Symptom Index is a tool developed to measure urinary function and can be incorporated into postoperative nursing management. When this questionnaire is administered at regular intervals following surgery, the patient's urinary status can be assessed quickly and treatment changes made according to symptoms, with resultant improvement in comfort levels. The postoperative use of the AUA index is recommended for all nurses who care for patients undergoing prostate brachytherapy.

Brachytherapy↗