Biomedical subjects

Hanne Kooy

Publications and source records attributed to Hanne Kooy.

4 recordsLinked to original sources

PubMed2006

Optimization of current modulation function for proton spread-out Bragg peak fields.

Proton treatments with spread-out Bragg peak (SOBP) fields often use a rotating modulation wheel of varying thickness to modulate the pristine Bragg peak in depth and intensity. The technique of modulating also the beam current independently over the wheel rotation provides an additional control over the intensities of the pulled-back Bragg peaks. As a result, a single wheel can be used over a large range of energies and SOBP parameters and field-specific wheels are no longer necessary. An essential task in commissioning a particular treatment depth is the determination of this current modulation function. We have developed a method for the optimization of the current modulation function. The basic idea is to treat the entire beam nozzle, housing the various beam scattering and modulating components, as a whole and to characterize its effect as a transformation from a modulating beam current to a depth-dose distribution. While this transformation is difficult to calculate theoretically due to the complex scattering paths in the nozzle and the phantom, it can, however, be determined by time-resolved dose measurements. Using this transformation, we can calculate SOBP depth-dose distributions for any current modulation function and optimize it by a simple numerical optimization. We have applied the new method to a number of proton beams with satisfactory results.

Computer Simulation↗

PubMed2005

Stereotactic radiotherapy for localized low-grade gliomas in children: final results of a prospective trial.

PURPOSE: To evaluate the efficacy of stereotactic radiotherapy (SRT) for small, localized, pediatric brain tumors and to determine the patterns of failure. METHODS AND MATERIALS: A total of 81 patients were enrolled in an institutional review board-approved prospective Dana-Farber Cancer Institute protocol between 1992 and 1998. Of the 81 patients, 50 had low-grade astrocytoma, 23 had residual or recurrent craniopharyngioma, 4 had posterior fossa ependymoma, and 4 had other histologic types. All patients underwent biopsy for diagnosis, with the exception of patients with neurofibromatosis and radiographic evidence of an optic system tumor. The neurocognitive outcome for all patients was also an endpoint of the study and will be reported separately. This report focused on the patients with low-grade gliomas only. Of the 50 patients, 26 were males and 24 females; the median age was 9 years (range, 2-26 years). The indications for treatment of patients with low-grade gliomas were progression during or after chemotherapy or progression after surgery alone. SRT was delivered using a dedicated 6-MV linear accelerator. Immobilization was accomplished with a removable head-frame. CT and MRI fusion was used for treatment planning. The target volume generally included the preoperative tumor plus a 2-mm margin for the planning target volume. The median collimator size was 47.25 mm (range, 30-60 mm). Three to nine arcs were used to deliver a mean total dose of 52.2 Gy in 1.8-Gy daily fractions. RESULTS: With a median follow-up of 6.9 years (range, 0.9-10.2 years), the progression-free survival rate was 82.5% at 5 years and 65% at 8 years. The overall survival was 97.8% at 5 years and 82% at 8 years. Six patients had local progression. Two of the patients with local progression had pathologic progression to anaplastic astrocytoma 3 and 7 years after initial SRT. Five patients, all with optic system/hypothalamic primary tumors, developed central nervous system dissemination 1.0-7.4 years after SRT. One patient developed a presumed radiation-induced primitive neuroectodermal tumor 6 years after initial treatment. Six patients died, three of dissemination, two of progression to higher grade tumors, and one of a secondary radiation-induced tumor. All 6 cases of local progression were within the primary tumor bed at the time of progression and had received the full prescription dose. No marginal failures occurred. CONCLUSION: Stereotactic radiotherapy provides excellent local control for children with small, localized low-grade glial tumors. Marginal failures have not been observed, supporting the use of limited margins to minimize late sequelae using stereotactic immobilization and planning techniques.

Adolescent↗

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↗