Biomedical subjects

Alexandra J Stewart

Publications and source records attributed to Alexandra J Stewart.

5 recordsLinked to original sources

PubMed2006

Current controversies in high-dose-rate versus low-dose-rate brachytherapy for cervical cancer.

The use of brachytherapy in the treatment of cervical cancer has increased worldwide since its initial introduction over 100 years ago. However, certain aspects of the use of high-dose-rate (HDR) versus low-dose-rate (LDR) brachytherapy continue to be controversial, particularly the role of HDR in FIGO Stage III cervical cancer and the use of HDR with concurrent chemotherapy. This study represents a systematic literature review of prospective and retrospective series of patients with cervical carcinoma treated with external-beam radiation (EBRT) followed by either HDR or LDR radiation. The local control rates, survival rates, and treatment-related complications in patients with Stage III cervical cancer treated with HDR or LDR and those treated with concomitant chemotherapy are examined. Patients with Stage III cervical cancer treated with EBRT and brachytherapy have a local control rate of >50% in most series. Randomized prospective and retrospective studies show overall statistically equivalent local control, overall survival, and complication rates between HDR and LDR. However, LDR may be preferable for large, bulky tumors at the time of brachytherapy. Retrospective studies of HDR and concurrent chemotherapy are limited but have demonstrated toxicity rates similar to those with LDR. Selected patients with Stage III cervical carcinoma who have an adequate response to EBRT and concomitant chemotherapy may be treated with HDR brachytherapy. The existing literature shows no significant increase in complications in patients treated with HDR and concurrent chemotherapy; however, sufficient tumor shrinkage prior to HDR and careful monitoring of the dose to the normal tissues are imperative.

Brachytherapy↗

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

Prostate-specific antigen nadir and cancer-specific mortality following hormonal therapy for prostate-specific antigen failure.

PURPOSE: For men receiving androgen-suppression therapy (AST) for a rising postoperative or postradiation prostate-specific antigen (PSA), we evaluated whether a PSA nadir of more than 0.2 ng/mL was significantly associated with prostate cancer-specific mortality (PCSM). PATIENTS AND METHODS: The study cohort comprised 747 men with rising PSA and negative bone scan after surgery (n = 486) or radiation therapy (n = 261) who were treated with AST. Cox regression was used to evaluate whether a significant association existed between the PSA nadir level after 8 months of AST and the time to PCSM, controlling for treatment and known prognostic factors. RESULTS: The post-AST PSA nadir (pCox < .0001), the pre-AST PSA doubling time (DT) (pCox = .002), PSA level (P = .0001), and Gleason eight to 10 cancers (pCox = .01) were significantly associated with time to PCSM. The adjusted hazard ratio for PCSM was 20 (95% CI, 7 to 61; pCox < .0001), for men with a PSA nadir of more than 0.2 ng/mL as compared with all others. A PSA DT of less than 3 months was observed in 30% (224 of 747) of the study cohort. Of the 28 observed prostate cancer deaths, 21 (75%) occurred in men whose PSA nadir was more than 0.2 ng/mL and who had a PSA DT of less than 3 months. CONCLUSION: A PSA nadir of more than 0.2 ng/mL after 8 months of AST given for postoperative or postradiation PSA failure is significantly associated with PCSM and is clinically significant because it accounted for 75% of the cancer deaths observed in this study.

Aged↗

PubMed2005

The history of the smallpox vaccine.

Smallpox was a highly virulent, contagious disease. Initial attempts to control the disease by variolation were controversial and dangerous. Variolation was the subject of some of the earliest published clinical trials. Vaccination was discovered by Edward Jenner in 1796. From initial skepticism by the medical community the uptake became so widespread that smallpox vaccination was made compulsory in England and Wales in 1853. Eventually, this led to the eradication of smallpox in 1980. Parallels can be drawn with modern vaccination and the smallpox vaccine especially with the current intense media scrutiny of modern vaccinations.

History, 18th Century↗

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↗