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Robert A Cormack

Publications and source records attributed to Robert A Cormack.

9 recordsLinked to original sources
PubMed2006

Deformable structure registration of bladder through surface mapping.

Cumulative dose distributions in fractionated radiation therapy depict the dose to normal tissues and therefore may permit an estimation of the risk of normal tissue complications. However, calculation of these distributions is highly challenging because of interfractional changes in the geometry of patient anatomy. This work presents an algorithm for deformable structure registration of the bladder and the verification of the accuracy of the algorithm using phantom and patient data. In this algorithm, the registration process involves conformal mapping of genus zero surfaces using finite element analysis, and guided by three control landmarks. The registration produces a correspondence between fractions of the triangular meshes used to describe the bladder surface. For validation of the algorithm, two types of balloons were inflated gradually to three times their original size, and several computerized tomography (CT) scans were taken during the process. The registration algorithm yielded a local accuracy of 4 mm along the balloon surface. The algorithm was then applied to CT data of patients receiving fractionated high-dose-rate brachytherapy to the vaginal cuff, with the vaginal cylinder in situ. The patients' bladder filling status was intentionally different for each fraction. The three required control landmark points were identified for the bladder based on anatomy. Out of an Institutional Review Board (IRB) approved study of 20 patients, 3 had radiographically identifiable points near the bladder surface that were used for verification of the accuracy of the registration. The verification point as seen in each fraction was compared with its predicted location based on affine as well as deformable registration. Despite the variation in bladder shape and volume, the deformable registration was accurate to 5 mm, consistently outperforming the affine registration. We conclude that the structure registration algorithm presented works with reasonable accuracy and provides a means of calculating cumulative dose distributions.

Algorithms↗
PubMed2005

CT computer-optimized high-dose-rate brachytherapy with surface applicator technique for scar boost radiation after breast reconstruction surgery.

PURPOSE: Immediate breast reconstruction has become increasingly prevalent after mastectomy for breast cancer. Postoperative scar boost radiation for the reconstructed breast presents many planning challenges due to the shape, size, and curvature of the scar. High-dose-rate (HDR) surface applicator brachytherapy is a novel and effective method of delivering scar boost radiation. Two cases, one with a saline implant and one with a transverse rectus abdominis musculocutaneous flap reconstruction, illustrate the method and advantages of HDR optimization of surface applicators. METHODS AND MATERIALS: For 2 patients a mold of the breast was made with Aquaplast sheets. A reproducible system was used for arm positioning. Skin fiducials, including tattoos from external beam planning, were matched to fiducials on the mold. HDR catheters were sited on the mold at 1cm intervals, with the central catheter situated along the scar. Topographically, both scars demonstrated extreme curvature in both craniocaudal and mediolateral directions. A CT computer-optimized HDR plan was developed, with the reference dose prescribed at the skin surface. The dosimetry was compared to single-field and matched-field electron plans. RESULTS: This surface applicator technique provided a uniform skin dose of 100% to the entire clinical target volume (CTV) without hot spots in both patients. The patient position and surface applicator setup were consistently reproducible. The patients tolerated the treatment well with minimal skin erythema. In the single-field electron plan, skin dose was decreased to 50% at the periphery of the scar. Matching fields addressed this depth dose decrement, but resulted in large localized hot spots of more than 200% centrally in each field. CONCLUSION: CT computer-optimized HDR surface applicator brachytherapy provided a reproducible homogeneous method of treating highly curved scars on the reconstructed breast. Electron beam treatment would result in longer and more complex treatments yet still provide a less homogeneous dose than this surface applicator technique.

Brachytherapy↗
PubMed2005

A comparative study of rectal dose histograms in prostate brachytherapy: some analytic and numerical results.

A cumulative dose histogram is the graph of an integral function integrated over a domain VCR3 and is dubbed the dose-volume histogram (DVH), the dose-surface histogram (DSH) or the dose-wall histogram (DWH), depending on the dimension and structure of the region V. This paper presents a comparative study of the three rectal dose histograms for sixty patients as well as for a cylindrical model of the rectum; in particular, the DSH and DVH for the cylindrical model with one point source are computed analytically in terms of elliptic integrals. The difference among the three relative dose histograms, averaged over the sixty patients, is less than 5%, whereas that between DVH and DWH for various wall-thickness can be as large as 3-12 cm3 in the range 60-100 Gy. The paper also contains an error analysis using two simple models of the rectum, for which the true DSH and DWH can be computed via numerical integration, to evaluate the effect of digitization. The digitized computation agrees quite well with the pre-digitization numerical integration, within 1% or 0.2 cm3, because of the low dose-gradient effect near the rectum in prostate brachytherapy.

Body Burden↗
PubMed2004

Dosimetric consequences of manual pullback procedure for coronary artery radiotherapy with 90Sr/90Y beta-source.

PURPOSE: This work presents a quantitative dosimetric analysis of the Novoste (90)Sr/(90)Y beta-source cardiovascular brachytherapy treatments using a manual pullback technique for patients with in-stent restenosis. METHODS AND MATERIALS: Based on our previous measurements, a model was developed to estimate the dose in the middle of the junction region for tandem irradiation expressed as fraction of prescription dose (FPD) and dosimetric overlap length (DOL) receiving more/less than a threshold dose. The overlap/gap size was measured using the digital cine images recorded during treatment and then FPD and DOL were quantified. RESULTS: Statistical analysis of 55 patients showed that the overlap size and the FPD at 2 mm radial distance were in range of 0 to 23 mm and 13-200% of prescription dose (Rx), respectively. Four gaps out of 76 pullback cases were found, but their size was at most 5 mm. CONCLUSION: Use of a 5 mm overlap avoided underdosed regions in the vast majority of the cases. These results are the first step towards an analysis of the clinical outcome of these patients.

Brachytherapy↗
PubMed2003

Late genitourinary and gastrointestinal toxicity after magnetic resonance image-guided prostate brachytherapy with or without neoadjuvant external beam radiation therapy.

BACKGROUND: This study was designed to estimate the rates of late genitourinary (GU) and rectal toxicity after magnetic resonance image (MRI)-guided prostate brachytherapy exclusively or in conjunction with external beam radiation therapy (EBRT). METHODS: Between November 1997 and April 2002, 201 patients with category T1C prostate carcinoma (according to the 2002 American Joint Committee on Cancer staging criteria), prostate specific antigen levels < 10 ng/mL, and biopsy Gleason score 3 + 4 disease were treated with MRI-guided brachytherapy exclusively or in conjunction with EBRT. The MRI-guided technique was designed to spare the urethra based on delivery of the prescription dose to the peripheral zone exclusively. The Kaplan-Meier method was used to estimate rates of freedom from late GU and rectal toxicity. Comparisons were made using a log-rank test. RESULTS: At a median follow-up of 2.8 years (range, 0.5-5.0 years), the 4-year estimates of rectal bleeding requiring coagulation for patients who underwent implantation therapy, compared with patients who received combined-modality therapy, were 8% versus 30%, respectively (log-rank P value = 0.0001). Although erectile dysfunction was common (range, 82-93%), with the use of sildenafil citrate (Viagra), it was estimated that at least two-thirds of patients had erectile function comparable to or superior to baseline function, independent of whether they received monotherapy or combined-modality therapy (P = 0.46). The 4-year estimate of freedom from radiation cystitis was 100% versus 95% (P = 0.01) for patients who received monotherapy and patients who received combined-modality therapy, respectively. No urethral strictures were observed, and no patients underwent postimplantation transurethral resection of the prostate. CONCLUSIONS: In the current study, rectal bleeding after MRI-guided prostate brachymonotherapy was infrequent, and urethral and bladder toxicity is reported to be rare and may be attributed to the urethral-sparing technique of the MRI-guided approach.

Aged↗
PubMed2003

Comparing PSA outcome after radical prostatectomy or magnetic resonance imaging-guided partial prostatic irradiation in select patients with clinically localized adenocarcinoma of the prostate.

OBJECTIVES: To determine whether high-dose radiation delivered to a subvolume of the prostate gland (peripheral zone) using intraoperative magnetic resonance imaging-guided brachytherapy provided comparable 5-year prostate-specific antigen (PSA) control rates to radical prostatectomy (RP) in select patients compared prospectively but in a nonrandomized setting. METHODS: Between 1997 and 2002, 322 and 196 patients with clinical Stage T1c, PSA less than 10 ng/mL, biopsy Gleason score 3 + 4 or less, and without perineural invasion underwent RP or intraoperative magnetic resonance imaging-guided brachytherapy, respectively, and had a 2-year minimal follow-up. Cox regression multivariable analysis was used to evaluate whether the initial therapy, pretreatment PSA level, biopsy Gleason score, percentage of positive biopsies, or prostate gland volume were predictors of the time to post-therapy PSA failure. PSA failure was estimated using the Kaplan-Meier method and defined using the American Society for Therapeutic Radiology Oncology consensus definition. RESULTS: Only the percentage of positive prostate biopsies (P(Cox) = 0.02) was a significant predictor of the time to post-treatment PSA failure. However, the distribution of this parameter between RP and brachytherapy-treated patients was not significantly different (P(chi-square) = 0.25). The initial therapy did not predict for the time to post-therapy PSA failure (P(Cox) = 0.18). The 5-year estimate of PSA control was 93% versus 95% (P(log-rank) = 0.16) for the RP and brachytherapy patients, respectively. CONCLUSIONS: Despite only partial prostatic irradiation using intraoperative magnetic resonance imaging-guided brachytherapy, similar 5-year estimates of PSA control were found for both brachytherapy and RP-managed patients.

Adenocarcinoma↗
PubMed2002

Using the magnitude of PSA bounce after MRI-guided prostate brachytherapy to distinguish recurrence, benign precipitating factors, and idiopathic bounce.

PURPOSE: To identify events that precipitated a prostate-specific antigen (PSA) bounce and characterize the magnitude, duration, and time to PSA bounce after MRI-guided prostate brachytherapy. METHODS AND MATERIALS: Between 1997 and 2001, 186 patients with low-risk prostate cancer underwent MRI-guided permanent 125I source implantation, with or without external beam radiotherapy. A PSA bounce was defined as a >or=15% elevation in PSA compared with the most recent value, followed by a decline to a level at or less than the prebounce value. At the time of PSA measurement, data were prospectively collected on whether the patient had recent ejaculation, ongoing radiation proctitis, or recent instrumentation. RESULTS: A total of 115 patients (61.8%) had a total of 156 PSA bounces. Of these, 36 patients had PSA bounces associated with ejaculation, proctitis, or instrumentation, and 79 experienced idiopathic PSA bounces (not associated with a precipitating event). The magnitude of the PSA bounce was significantly lower for the idiopathic PSA bounce (0.6 ng/mL) compared with that associated with ejaculation (p = 0.003), proctitis (p <0.0001), or instrumentation (p = 0.007). Patients with biopsy-proven local recurrence had a median PSA elevation of 1.2 ng/mL, significantly higher (p = 0.006) than the magnitude of the idiopathic PSA bounce, but not significantly different from the magnitude of the PSA bounce due to ejaculation, proctitis, or instrumentation. CONCLUSION: In patients treated with MRI-guided prostate brachytherapy, recent ejaculation, instrumentation, or ongoing radiation proctitis can cause a transient increase in PSA, the magnitude of which is significantly higher than that for idiopathic PSA bounce, but is similar to that in patients with recurrent disease.

Aged↗
PubMed2002

Quantitative MR imaging assessment of prostate gland deformation before and during MR imaging-guided brachytherapy.

RATIONALE AND OBJECTIVES: The authors performed this study to document the deformations that occur between pretreatment magnetic resonance (MR) imaging and intraoperative MR imaging during brachytherapy. MATERIALS AND METHODS: MR images obtained at 1.5 and 0.5 T in 10 patients with prostate cancer were analyzed for changes in the shape and substructure of the prostate. Three-dimensional models of the prostate were obtained. The authors measured anteroposterior dimension; total gland, peripheral zone, and central gland volumes; transverse dimension; and superoinferior height. RESULTS: Gland deformations were seen at visual inspection of the three-dimensional models. The anteroposterior dimension of the total gland, central gland, and peripheral zone increased from 1.5- to 0.5-T imaging (median dimension, 4.9, 1.5, and 1.8 mm, respectively), and the increase was greatest in the peripheral zone (P < .05, all comparisons). There was a decrease in the transverse dimension from 1.5- to 0.5-T imaging (median, 4.5 mm; P < .005). The total gland volume and the superoinferior height did not show a statistically significant change. CONCLUSION: There were significant deformations in the shape of the prostate, especially in the peripheral zone, between the two imaging studies. The likely causes of the shape change are differences in rectal filling (endorectal coil used in 1.5-T studies vs obturator in 0.5-T studies) and/or changes in patient position (supine vs lithotomy). These findings suggest that pretreatment images alone may not be reliable for accurate therapy planning. It may be useful to integrate pre-and intraoperative data.

Brachytherapy↗