PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 11072185

Optimizing target coverage by dosimetric feedback during prostate brachytherapy.

R A Cormack·C M Tempany·A V D'Amico
View original source ↗Export metadata ↓

Abstract

PURPOSE: Postimplant dosimetry of permanent prostate implants shows a loss of coverage compared to the preplan. One contributing factor is needle misplacement. The significance of needle misplacement and the clinical utility of dosimetric feedback were analyzed in the setting of interventional magnetic resonance (IMR) guided prostate brachytherapy. METHODS AND MATERIALS: Information provided by an intraoperative planning system was analyzed for 10 patients. Needle misplacement was measured and the dosimetric consequences calculated. Additional catheters and sources were placed following the insertion of all planned catheters to compensate for nonideal needle placement. RESULTS: Source misplacement ranged from 0.0 to 1.0 cm (median, 0.3 cm). The resulting loss of coverage ranged from 1% to 13%, and the intraoperative dosimetric feedback allowed a recovery of from 0% to 12% coverage. Between 0 and 3 (median, 2) additional needles and from 0 to 10 (median, 8) additional sources were required to restore coverage of the target. Final planned coverage exceeded 94% for all patients. CONCLUSION: The discrepancy between planned and achieved needle placement leads to a loss of dosimetric coverage of the target volume. Dosimetric feedback allows compensation for needle divergence. The technique of real-time dosimetric feedback does not require an IMR system, and could be generalized to ultrasound-guided implants.

Explore related subjects

BrachytherapyHumansIodine RadioisotopesMagnetic Resonance ImagingMaleProstatic NeoplasmsRadiotherapy DosageJournal ArticleResearch Support, Non-U.S. Gov't

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

R A Cormack, C M Tempany, A V D'Amico. 2000-11-01. Optimizing target coverage by dosimetric feedback during prostate brachytherapy.. https://doi.org/10.1016/s0360-3016(00)00742-2

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2003

Incorporating clinical measurements of hypoxia into tumor local control modeling of prostate cancer: implications for the alpha/beta ratio.

BACKGROUND AND PURPOSE: The recently obtained low value of approximately 1.5 for the alpha/beta of prostate cancer has led us to reexamine the optimal prostate tumor biology parameters, while taking into account everything known about the radiation response of prostate clonogens for use in a predictive dose-response model. METHODS AND MATERIALS: Averages of the literature values of the alpha- and beta-inactivation coefficients for human prostate cancer cell lines were calculated. A robust tumor local control probability (TLCP) model was used that required average alpha and beta, as well as sigma(alpha), for the interpatient variation in single-hit killing (alpha). Median PO(2) values <or=1 mm Hg in the prostates of Fox Chase Cancer Center brachytherapy patients had been found in 21% of 115 cases. The oxygen enhancement ratios of 1.75 and 3.25 for alpha- and beta-inactivation, respectively, measured for tumor cells in vitro, were incorporated into the TLCP model, together with a clonogen density of approximately 10(5) cells/cm(3). Severe hypoxia and radioresistance were estimated for a proportion of tumors that was increased with PSA level. RESULTS: For asynchronous human prostate cell lines irradiated in air, alpha(mean) was 0.26 +/- 0.07 (standard error) Gy(-1), sigma(alpha) = 0.06 Gy(-1), and beta(mean) was 0.0312 Gy(-2) +/- 0.0064 (standard error) Gy(-2). The TLCP data indicated that most tumors that contained aerobic cells would be cured, whereas most tumors that contained hypoxic cells would not be cured by total doses of 76 to 80 Gy. Clinical response data from the literature for external beam dose escalation, stratified by PSA value, and for low-dose-rate brachytherapy, were well predicted by the model, where the alpha/beta ratio was 8.5 and 15.5 for well-oxygenated and hypoxic clonogens, respectively. CONCLUSIONS: Neither alpha/beta ratio nor clonogen number need be extremely low to explain the response of prostate cancer to brachytherapy and external beam therapy, contradicting other recent analyses. It is strongly suggested that severe hypoxia in the prostates of certain patients limits the overall cancer cure rate by conventional radiation therapy.

Brachytherapy↗
PubMed2003

Dosimetric consequences of using a surrogate urethra to estimate urethral dose after brachytherapy for prostate cancer.

PURPOSE: To assess the accuracy and dosimetric consequences of defining a surrogate urethra at the geometric center of the prostate in postimplant CT scans. METHODS AND MATERIALS: Eighty postimplant CT scans were obtained with a Foley catheter in place at Day 0 and at 1 month for 40 patients who had undergone (125)I prostate brachytherapy. The percentage of urethral volume receiving at least 275% of the prescribed dose (uV(275)), uV(250), uV(200), uV(150), maximal dose received by 90% of urethral volume (uD(90)), uD(70), uD(30), and uD(1) were measured for the Foley catheter and surrogate urethra. The distance between the Foley catheter and surrogate urethra was measured at the base, middle, and apex of the prostate. RESULTS: A statistically significant difference was found in all the above-listed dosimetric parameters between the Foley catheter and surrogate urethra at Day 0 (p <or= 0.001). At 1 month, the uD(90), uD(70), and uD(1) remained significantly different between the Foley catheter and surrogate urethra (p <or= 0.05). The difference in the uV(275) (p = 0.055) and uV(150) (p = 0.059) between the Foley catheter and surrogate urethra showed a trend toward statistical significance at 1 month. The uV(250), uV(200), and uD(30) were greater for the surrogate urethra than for the Foley catheter at 1 month, but were not significantly different statistically. The mean distance between the Foley catheter and the surrogate urethra was greatest at the base (1.2 cm) in the vertical axis at Day 0 and decreased substantially to 0.87 cm at 1 month (p = 0.0004). CONCLUSION: Using a surrogate urethra at the geometric center of the prostate may significantly overestimate the urethral dose at Day 0 and certain dosimetric parameters at 1 month. An alternative position for a surrogate urethra accounting for the difference in the location of the Foley catheter near the base of the prostate at Day 0 and 1 month could be considered in future studies.

Brachytherapy↗
PubMed2003

Intraoperative dural irradiation by customized 192iridium and 90yttrium brachytherapy plaques.

PURPOSE: After vertebral or paravertebral tumor resection, tumor cells may remain on the dura. Because a tumoricidal dose is difficult to achieve using external beam radiotherapy without exceeding the spinal cord tolerance, we developed intraoperative applicators to deliver additional dose to the dura. METHODS AND MATERIALS: Eight patients with vertebral or paravertebral tumor underwent conformal external beam radiotherapy, tumor resection, and intraoperative radiotherapy to the dura involved by tumor. At surgery, vertebra, soft tissue, and epidural tumor were resected. A radioactive applicator plaque was placed on the dura to deliver 7.5-15 Gy, and then removed. Vertebral reconstruction and stabilization was completed. Chemotherapy was administered for large, high-grade sarcomas. RESULTS: We progressed through three plaque designs, initially (192)Ir, subsequently liquid (90)Y, and finally (90)Y foil in a semicylindrical polycarbonate plaque, in the treatment of 8 patients. The low-energy (90)Y beta-emissions provided a more attractive depth dose profile than that achievable with iridium and gave negligible staff radiation exposure. The (90)Y depth dose measured 29% at 2 mm and 9% at 4 mm from the surface of the foil plaque, with acceptable surface dose homogeneity. The average surface dose rate ranged from 18.7 to 47.6 cGy/min for the iridium plaques and 45.2 to 187.5 cGy/min for the (90)Y plaques. The treatments have been without acute or late neurologic complications. The disease of 6 of 8 patients was locally controlled at median potential follow-up of 24 months. CONCLUSIONS: The (90)Y foil applicator is technically elegant, easy to use, and superior to the earlier models. It has been incorporated into a protocol for spinal tumor treatment.

Brachytherapy↗