Biomedical subjects

Mira Keyes

Publications and source records attributed to Mira Keyes.

14 recordsLinked to original sources

PubMed2006

Decline in urinary retention incidence in 805 patients after prostate brachytherapy: the effect of learning curve?

PURPOSE: To evaluate the incidence and factors predictive of acute urinary retention (AUR) in 805 consecutive patients treated with prostate brachytherapy monotherapy and to examine the possible effect of a learning curve. METHODS AND MATERIALS: Between July 1998 and November 2002, 805 patients were treated with prostate brachytherapy. Low-risk patients (Gleason Score (GS) < or = 6; prostate specific antigen (PSA) < or = 10, and < or = T2b [UICC 1997]) received implant alone. Patients with prostate volume of 50 cc or more, GS = 7, or PSA = 10 to 15 received 6 months of androgen suppression (AS) with brachytherapy. Patient, treatment, and dosimetric factors examined include baseline prostate symptom score (IPSS), diabetes, vascular disease, PSA, Gleason score, clinical stage, AS, ultrasound planning target volume (PUTV), postimplant prostate volume (obtained with "Day 30" postimplant CT), CT:PUTV ratio (surrogate for postimplant edema), number of seeds, number of needles, number of seeds per needle, dosimetric parameters (V100, V150, and D90), date of implant (learning curve), and implanting oncologists. Univariate and multivariate analyses were carried out. RESULTS: Acute urinary retention in the first 200 patients was 17% vs. 6.3% in the most recently treated 200 patients (p = 0.002). Overall AUR was 12.7%, and prolonged urinary obstruction incidence (> 20 days) was 5%. On multivariate analysis, factors predictive of any AUR include baseline IPSS (p = < 0.004), CT:PUTV ratio (p = < 0.001), PUTV (p = < 0.001), and implant order (learning curve) (p = 0.001). Factors predictive for "prolonged" catheterization (> 20 days) on multivariate analysis include IPSS (p < 0.01), number of needles (p < 0.001), diabetes mellitus (p = 0.048), and CT:PUTV ratio (p < 0.001) CONCLUSION: Over the years, our AUR rate has fallen significantly (from 17% to 6.3%). On multivariate analysis, highly significant factors include IPSS, PUTV, CT:PUTV ratio (i.e., degree of prostate edema), and order of implant (learning curve). Over the course of the program, we have deliberately reduced the number of needles and OR time per patient, which have potentially minimized intraoperative trauma and may have contributed to less toxicity. A learning curve in prostate brachytherapy programs affect not only the outcome but also the toxicity from the treatment.

Acute Disease↗

PubMed2005

Predictive factors for erectile dysfunction in men with prostate cancer after brachytherapy: is dose to the penile bulb important?

PURPOSE: To determine predictive factors for postimplant erectile dysfunction (ED) in a cohort of patients, according to prospectively collected data; specifically, to assess the impact of penile bulb volume and D50 and D95 (dose covering 50% and 95% of the penile bulb volume, respectively) on ED. METHODS AND MATERIALS: Three hundred forty-two patients were identified who were potent before implant and who had at least 2 years' follow-up. Patient, tumor, treatment, and dosimetric data were collected on all patients. Postimplant ED was defined according to both physician-documented and patient-documented outcome data. Binary logistic regression analysis was used to create multivariable models of predictors for ED at 1, 2, and 3 years after implant. RESULTS: Physician-documented rates of ED were 57%, 48%, and 38% at 1, 2, and 3 years after implant, respectively. Patient-documented rates of ED were 70% and 66% at 1 and 2 years, respectively. Multivariable analyses revealed age and degree of pre-implant erectile function to be consistently significant predictors of ED. Use of hormones was significant at the 1-year physician-documented ED endpoint but not thereafter, in keeping with the time course of testosterone recovery. Penile bulb volume, D50, and D95 were not found to be predictive for ED at any time point, in contrast to previous studies. In addition, planning ultrasound target volume, number of needles, and institutional case sequence number were significant predictors of ED at various time points, consistent with a traumatic etiology of ED. CONCLUSIONS: We found no evidence to support penile bulb dosimetry as an independent predictive factor for ED after implant, using physician-documented or patient-documented outcomes.

Aged↗

PubMed2005

2003 survey of Canadian radiation oncology residents.

PURPOSE: Radiation oncology's popularity as a career in Canada has surged in the past 5 years. Consequently, resident numbers in Canadian radiation oncology residencies are at all-time highs. This study aimed to survey Canadian radiation oncology residents about their opinions of their specialty and training experiences. METHODS AND MATERIALS: Residents of Canadian radiation oncology residencies that enroll trainees through the Canadian Resident Matching Service were identified from a national database. Residents were mailed an anonymous survey. RESULTS: Eight of 101 (7.9%) potential respondents were foreign funded. Fifty-two of 101 (51.5%) residents responded. A strong record of graduating its residents was the most important factor residents considered when choosing programs. Satisfaction with their program was expressed by 92.3% of respondents, and 94.3% expressed satisfaction with their specialty. Respondents planning to practice in Canada totaled 80.8%, and 76.9% plan to have academic careers. Respondents identified job availability and receiving adequate teaching from preceptors during residency as their most important concerns. CONCLUSIONS: Though most respondents are satisfied with their programs and specialty, job availability and adequate teaching are concerns. In the future, limited time and resources and the continued popularity of radiation oncology as a career will magnify the challenge of training competent radiation oncologists in Canada.

Adult↗

PubMed2005

Computing intraoperative dosimetry for prostate brachytherapy using TRUS and fluoroscopy.

RATIONALE AND OBJECTIVES: There is a need to provide real-time dosimetric feedback during prostate brachytherapy based on the location of the implanted seeds. The objective of our approach is to develop a system to accurately locate seeds with minimal impact on the current protocol for prostate brachytherapy and without additional imaging equipment. MATERIALS AND METHODS: A new approach for intraoperatively computing dosimetry for prostate brachytherapy is presented. The approach uses transrectal ultrasound (TRUS) and fluoroscopic images. A fluoroscopic image of the TRUS probe is required to register the fluoroscopic and ultrasound images. The C-arm is not moved during the procedure and all images are acquired from the same C-arm angles. A needle path is interpolated for each needle based on the location of the needle tip in TRUS images and the known entry point of the needle. Throughout the procedure, fluoroscopic images are acquired to determine the coronal plane coordinates of the seeds and the remaining coordinate of each seed is computed from the needle path. For accurate results, intraoperative seed motion tracking is advised and a method to achieve such tracking is also presented. RESULTS: Experimentally, the TRUS and fluoroscopic images are registered with a mean and maximum error of 1.3 mm and 5.8 mm, respectively. In a phantom, 12 seeds are located using our approach and compared with the known locations, with a mean error in the x, y, and z direction of 0.96 mm, 0.33, and 0.68 mm, respectively, and a corresponding maximum error of 1.85 mm, 0.56 mm, and 1.63 mm. Experimental results show motion tracking in the y-direction with submillimeter accuracy. The feasibility of our approach is tested on five cases of clinical data using a semiautomated version of our system and the resulting dosimetry is compared with that found using postoperative computed tomography images. The D90 and V100 metrics computed using our approach and the computed tomography images differ by a maximum of 16.6% and 1.7%, respectively. CONCLUSIONS: TRUS can be combined with single pose fluoroscopic images to compute delivered dose intraoperatively for prostate brachytherapy. Phantom results demonstrate the accuracy of the method and preliminary clinical results show its potential.

Brachytherapy↗

PubMed2005

Urinary incontinence in prostate cancer patients treated with external beam radiotherapy.

BACKGROUND AND PURPOSE: To describe the incidence of urinary incontinence among prostate cancer patients treated with external beam radiotherapy (RT) and to investigate associated risk factors. PATIENTS AND METHODS: One thousand and hundred ninety-two patients with >or=24 months follow-up were the subjects of this series. All patients received between 50 and 72 Gy in 20-37 fractions (median 66 Gy/33#). Post-RT urinary incontinence was scored by direct patient interviewing according to the modified RTOG/SOMA scale: Grade 1--occasional use of incontinence pads, Grade 2--intermittent use of incontinence pads, Grade 3--persistent use of incontinence pads, and Grade 4--permanent catheter. Risk-factors investigated were: age, diabetes, TURP prior to RT, elapsed time from TURP to RT, clinical stage, RT dose and presence of Grade >or=2 acute GU and GI toxicity. Non-parametric, actuarial univariated (Kaplan-Meier) and multivariated tests (MVA, Cox regression) were performed. RESULTS: Median follow-up for the group is 52 months (24-109). Thirty-four patients (2.9%) had incontinence prior to RT, which was more common in TURP patients (7.8% vs 1.6% P<0.001). These are excluded from further analysis. Fifty-seven patients (4.9%) developed Grade 1 incontinence, 7 (0.6%) Grade 2, and 7 (0.6%) Grade 3. There was no Grade 4 incontinence. Actuarial rates for Grade >or=1 and >or=2 incontinence at 5 years are 7 and 1.7%, respectively. Risk factors on MVA associated with the development of Grade 1 or worse incontinence are pre-RT TURP (5-year rates 10% vs 6%, P=0.026), presence of Grade >or=2 acute GU toxicity (5-year rates 11% vs 5%, P=0.002). Age, diabetes, clinical stage, elapsed time from TURP to RT, RT dose or fraction size, acute GI toxicity were not significant. Patients who underwent post-RT TURP or dilatation for obstructive symptoms (4.3%), were more likely to develop Grade 2-3 incontinence (5-year rate 8 vs 1.5%, P=0.0015). CONCLUSIONS: Grade 2 or greater urinary incontinence is rare among patients who have been treated with external beam radiotherapy. Associated risk factors are pre-RT TURP and the presence of increased acute GU toxicity. Post-radiaton TURP increases the risk of incontinence five-fold.

Acute Disease↗

PubMed2004

PSA failure and the risk of death in prostate cancer patients treated with radiotherapy.

PURPOSE: To determine the relationship between prostate-specific antigen (PSA) failure and cause-specific and overall survival in prostate cancer patients treated with radical radiotherapy. METHODS AND MATERIALS: Patients with and without PSA failure were compared with respect to overall survival and cause-specific survival in a cohort of 1786 patients. The relationship between PSA failure and survival was further investigated among six subgroups defined by three tumor risk groups (high, intermediate, and low risk based on T stage, Gleason score, and presenting PSA) and two age groups (<75 years and >/=75 years). RESULTS: The 5-year overall survival among patients who had PSA failure was 79.5% vs. 87.5% among patients who had not failed (p = 0.0003). The corresponding 5-year cause-specific survival was 84.4% vs. 99.0% (p <0.0001). When the six subgroups are considered separately, PSA failure was associated with a worse cause-specific survival in the groups with intermediate- and high-risk disease. PSA failure was only associated with a worse overall survival in one subgroup: patients younger than 75 with high-risk disease. Deaths from nonprostate causes made the survival curves of patients with and without PSA failure in the other subgroups almost identical. CONCLUSION: PSA failure in prostate cancer patients treated with radiotherapy was associated with a poorer overall survival, which is seen mainly in younger patients with high-risk disease.

Aged↗

PubMed2004

125I reimplantation in patients with poor initial dosimetry after prostate brachytherapy.

PURPOSE: In this case report, we describe 7 patients with suboptimal dosimetry after (125)I prostate brachytherapy who underwent a second implant procedure to improve the dosimetric coverage of the prostate. METHODS AND MATERIALS: Seven patients underwent second (125)I implants for suboptimal dosimetry after their initial implant for prostate cancer. The pretreatment characteristics (clinical stage, Gleason score, initial prostate-specific antigen level, location of positive cores, International Prostate Symptom Score, potency, use of androgen suppression, initial implant planning characteristics) were noted. The "Day 30" CT-based dosimetry parameters after the first implant and "Day 0" CT-based dosimetry after the reimplant were recorded (volumes of prostate and rectum covered by 100% and 150% of the dose and dose covering 90% of the prostate volume). The toxicity of the second procedure, International Prostate Symptom Scores before and after reimplantation, the clinical course, and prostate-specific antigen outcomes after reimplant were examined. We described our reimplant planning and intraoperative procedure. RESULTS: In all 7 patients, we were able to achieve very favorable dosimetry after the second procedure. The acute toxicity of the reimplant procedure was reasonably low, and the short-term prostate-specific antigen outcome has been favorable. CONCLUSION: It is possible to add more seeds safely to the dosimetrically cool area after the initial brachytherapy procedure and achieve excellent postimplant dosimetry with acceptable acute toxicity. The ultimate benefits and long-term toxicity of reimplantation are unknown.

Aged↗

PubMed2004

Impact of neoadjuvant androgen ablation and other factors on late toxicity after external beam prostate radiotherapy.

PURPOSE: To evaluate the late toxicity profile of prostate cancer patients treated with external beam radiotherapy, to investigate the possible risk factors for late toxicity, and to determine whether neoadjuvant androgen ablation (NAA) is a factor. METHODS AND MATERIALS: The study population consisted of 1192 patients with > or =24 months' follow-up. Late GI and GU toxicities were scored with a modified Radiation Therapy Oncology Group/Subjective, Objective, Management, and Analytic scale. All patients were treated with external beam radiotherapy (52.5 Gy in 20 fractions to 72 Gy in 36 fractions), using either conventional or three-dimensional conformal techniques. Of the 1192 patients, 40% received NAA (median 5 months). Risk factors investigated on multivariate analysis were age, past medical history, use of pelvic fields, dose, fractionation, use and duration of neo- and adjuvant androgen ablation, and acute toxicity (Grade 2 or greater). RESULTS: The median follow-up for the group was 49 months (range 24-105). The incidence of late Grade 2-3 GI or GU toxicity was 30% at 5 years (GI 12% and GU 20%). The incidence of late Grade 3 GI or GU toxicity was 8% at 5 years (GI 2.7% and GU 5.5%). No Grade 4 toxicity occurred. The risk factors of significance in relation to the development of late Grade 3 GU toxicity were coexisting GU disease (p = 0.02), prior transurethral resection of the prostate or transurethral resection of bladder tumor (p <0.0001), and presence of acute GU toxicity (p = 0.012). For late Grade 3 GI toxicity, short-term (< or =2 months) NAA (p = 0.0002) and coexisting GI disease (p = 0.017) were risk factors. CONCLUSION: Short-term (< or =2 months) NAA, but not longer durations of NAA, increases the risk of developing Grade 3 GI late toxicity. The possible mechanism of this phenomenon is unclear.

Aged↗

PubMed2002

Urethral and periurethral dosimetry in prostate brachytherapy: is there a convenient surrogate?

PURPOSE: To assess and compare two models for a surrogate urethra to be used for postimplant dosimetry in prostate brachytherapy. METHODS AND MATERIALS: Twenty men with a urinary catheter present at the time of postimplant computed tomographic imaging were studied. Urethral and periurethral volumes were defined as 5-mm and 10-mm diameter volumes, respectively. Three contours of each were used: one contour of the true urethra (and periurethra), and two surrogate models. The true volumes were centered on the catheter center. One surrogate model used volumes centered on the geometrical center of each prostate contour (centered surrogate). The other surrogate model was based on the average deviation of the true urethra from a reference line through the geometrical center of the axial midplane of the prostate (deviated surrogate). Maximum point doses and the D(10), D(25), D(50), D(90), V(100), V(120), and V(150) of the true and surrogate volumes were measured and compared (D(n) is the minimum dose [Gy] received by n% of the structure, and V(m) is the volume [%] of the structure that received m% of the prescribed dose) as well as the distances between the surrogate urethras and the true urethra. RESULTS: Doses determined from both surrogate urethral and periurethral volumes were in good agreement with the true urethral and periurethral doses except in the superior third of the gland. The deviated surrogate provided a physically superior likeness to the true urethra. Certain dose-volume histogram (DVH)-based parameters could also be predicted reasonably well on the basis of the surrogates. Correlation coefficients > or =0.85 were seen for D(25), D(50), V(100), V(120), and V(150) for both models. All the other parameters had correlation coefficients in the range of 0.73 - 0.85. CONCLUSIONS: Both surrogate models predicted true urethral dosimetry reasonably well. It is recommended that the simpler deviated surrogate would be a more suitable surrogate for routine clinical practice.

Brachytherapy↗

PubMed2002

Comparison of methods for calculating rectal dose after (125)I prostate brachytherapy implants.

PURPOSE: To compare several different methods of calculating the rectal dose and examine how accurately they represent rectal dose surface area measurements and, also, their practicality for routine use. METHODS AND MATERIALS: This study comprised 55 patients, randomly selected from 295 prostate brachytherapy patients implanted at the Vancouver Cancer Center between 1998 and 2000. All implants used a nonuniform loading of 0.33 mCi (NIST-99) 125I seeds and a prescribed dose of 144 Gy. Pelvic CT scans were obtained for each patient approximately 30 days after implantation. For the purposes of calculating the rectal dose, several structures were contoured on the CT images: (1) a 1-mm-thick anterior rectal wall, (2) the anterior half rectum, and (3) the whole rectum. Point doses were also obtained along the anterior rectal surface. The thin wall contour provided a surrogate for a dose-surface histogram (DSH) and was our reference standard rectal dose measurement. Alternate rectal dose measurements (volume, surface area, and length of rectum receiving a dose of interest [DOI] of > or =144 Gy and 216 Gy, as well as point dose measures) were calculated using several methods (VariSeed software) and compared with the surrogate DSH measure (SA(DOI)). RESULTS: The best correlation with SA(144 Gy) was the dose volumes (whole or anterior half rectum) (R = 0.949). The length of rectum receiving > or =144 Gy also correlated well with SA(144 Gy) (R > or =0.898). Point dose measures, such as the average and maximal anterior dose, correlated poorly with SA(144 Gy) (R < or =0.649). The 216-Gy measurements supported these results. In addition, dose-volume measurements were the most practical (approximately 6 min/patient), with our surrogate DSH the least practical (approximately 20 min/patient). CONCLUSION: Dose-volume measurements for the whole or anterior half rectum, because they were the most practical measures and best represented the DSH measurements, should be considered a standard method of reporting the rectal dose when calculating the DSH is not practical. Average or maximal anterior rectal doses are not reliable indicators of surface area dosimetry.

Algorithms↗

PubMed2002

Predictive factors of urinary retention following prostate brachytherapy.

PURPOSE: To evaluate the incidence and duration of urinary retention requiring catheterization and the factors predictive for these end points. METHODS AND MATERIALS: Two hundred eighty-two patients treated with prostate brachytherapy alone were evaluated. Clinical and treatment-related factors examined included: age, baseline International Prostate Symptom Score (IPSS), presence of comorbidity, planning ultrasound target volume (PUTV), postimplant prostate CT scan volume, the CT:PUTV ratio, number of seeds inserted, number of needles used, use of neoadjuvant hormones, procedural physician, clinical stage, Gleason score, and pretreatment PSA. Dosimetric quality indicators were also examined. RESULTS: Urinary obstruction after prostate brachytherapy developed in 43 (15%) patients. The median duration of catheter insertion was 21 days (mean 49, range 1-365). Univariate analysis demonstrated that presence of diabetes, preimplant volume, postimplant volume, CT:PUTV ratio, number of needles, and dosimetric parameters were predictive for catheterization. However, in multivariate analysis, only the baseline IPSS, CT:PUTV ratio, and presence of diabetes were significant independent predictive factors for catheterization. CONCLUSION: Baseline IPSS was the most important predictive factor for postimplantation catheterization. The extent of postimplant edema, as reflected by the CT:PUTV ratio, predicted for need and duration of catheterization. The presence of diabetes was predictive for catheterization, but may relate to the absence of prophylactic steroids, and therefore requires further evaluation.

Adult↗

PubMed2002

Prostate brachytherapy postimplant dosimetry: a comparison of prostate quadrants.

PURPOSE: To investigate postimplant dosimetry for different regions of the prostate gland in patients treated with transperineal 125Iodine brachytherapy implants for low- and intermediate-risk prostate cancer. METHODS AND MATERIALS: Two hundred eighty-four patients treated with permanent interstitial prostate brachytherapy comprised the study population. A nonuniform, urethral-sparing algorithm was used to plan all patients. Prostate contours were outlined on postimplant CT images. Prostate volumes were then divided into four quadrants: anterior-superior quadrant (ASQ), posterior-superior quadrant (PSQ), anterior-inferior quadrant (AIQ), and posterior-inferior quadrant (PIQ). Dose-volume histograms (DVHs) were calculated for the whole prostate and each quadrant. RESULTS: The mean postimplant V(100) +/- 95% confidence (the percent prostate volume encompassed within the isodose surface comprising the prescription dose = 144 Gy) for the ASQ was 78.5 +/- 1.9, which was significantly lower than that of the PSQ, AIQ, and PIQ in which the V(100) plus minus 95% confidence values were 94.9 +/- 0.8, 92.6 +/- 1.2, and 98.7 +/- 0.3, respectively. The mean V(100) +/- 95% confidence for the whole prostate was 90.4 +/- 0.8. Mean values for V(150) and D(90) (the minimum dose in Gy received by 90% of the target volume) for the four quadrants and the whole prostate showed similar results. CONCLUSIONS: Underdosed areas of the planning target volume (PTV), if present, were largely confined to the ASQ, which received a significantly lower dose, on average, compared to the other three quadrants of the prostate.

Aged↗

PubMed2002

Testosterone recovery following prolonged adjuvant androgen ablation for prostate carcinoma.

BACKGROUND: This study was conducted to describe the rate and completeness of the recovery of testosterone production following prolonged temporary androgen ablative therapy in men with prostate carcinoma undergoing curative radiation therapy. METHODS: Two-hundred and sixty-seven men treated with between 3 months and 3 years of adjuvant androgen ablation (AA) were followed at 6-month intervals following cessation of their androgen deprivation therapy. A comparative group of 518 men not undergoing AA were also followed. RESULTS: Drugs used included low dose cyproterone/stilboestrol (CPA/DES) in combination (56%) and 1 month depot (18%) and 3 month depot (25%) leutinizing hormone releasing hormone agonist (LHRHa). Seventy-nine percent of men in the current study recovered normal testosterone levels (10nmol/L), and 93% recovered levels of at least 5nmol/L. In comparison, men who had never received androgen ablative therapy showed a fall of testosterone, with 17% having sub-normal levels after 3 years. Median time to testosterone recovery was 10 months. Factors associated on multivariate analysis with delayed testosterone recovery included advanced age (P = 0.008), low pre-therapy testosterone (P = 0.04), and the use of 3 month LHRHa preparations as compared with CPA/DES (P = 0.002) or 1 month LHRHa preparations (P = 0.015). The duration of drug use was not significantly associated with time to testosterone recovery. CONCLUSIONS: Long-acting LHRHa preparations appear to have a more prolonged action than previously supposed. Most men treated for up to 2 years recover normal testosterone levels after cessation of adjuvant androgen ablation, and the limited data available in the current study on patients treated for 3 years also suggests most will recover.

Adenocarcinoma↗

PubMedDate not supplied

Prostate brachytherapy postimplant dosimetry: a comparison of suture-embedded and loose seed implants.

PURPOSE: To compare postimplant dosimetry and seed embolization rates for prostate brachytherapy implants using suture-embedded and loose seeds. METHODS AND MATERIALS: Dosimetric analysis of the whole prostate, prostate quadrants, rectum, and surrogate urethra was performed on 54 loose seed and 81 RAPIDStrand (RS) patients. Seed embolization rates were determined from chest radiographs. RESULTS: Whole prostate V100 and D90 did not differ significantly for the loose seed (V100 = 90.5%, D90 =153.2 Gy) and RS groups (V100 = 91.5%, D90 = 151.6 Gy) (p = 0.43 and 0.65, respectively), but V150, V200, and contiguous V200 were higher (p < or = 0.003) for the RS group (59.9%, 28.3%, and 23.2%, respectively) than the loose seed group (52.5%, 22.8%, and 16.1%, respectively). Extraprostatic measures (conformity index and external index) were also different at the p < 0.05 level. The embolization rate was 40% in the loose seed group and 14% in the RS group. CONCLUSIONS: The most significant difference between the two study groups was a decrease in the embolization rate. Although some statistically significant changes in postimplant dosimetry were observed, they were nevertheless small.

Brachytherapy↗