The impact of prescription depth, dose rate, plaque size, and source loading on the central axis using 103Pd, 125I, and 131Cs.

PURPOSE: Modern dosimetry data are not available for Collaborative Ocular Melanoma Study-based eye plaques. This report aims to provide these data for eye plaques ranging from 10 to 22 mm, and for three different low-energy, photon-emitting radionuclides. METHODS AND MATERIALS: Recent publications on brachytherapy dosimetry parameters for 103Pd, 125I, and 131Cs were evaluated for use as eye plaque reference data. These data were entered into the Pinnacle treatment planning system for 3D calculations of brachytherapy dose distributions along the central axis for depths ranging from -1 to 10 mm based on the origin positioned at the inner sclera. In accordance with the original Collaborative Ocular Melanoma Study protocol and in the absence of radionuclide-specific heterogeneity factors, inhomogeneity corrections were not applied. RESULTS: As expected due to the mean photon energies, 103Pd, 125I, and 131Cs provided increasingly penetrating dose distributions. Dose distribution tables were prepared for fully loaded plaques and for plaques with the central source(s) removed. Over the entire range of central axis depths, and for all plaque sizes and loadings, 131Cs produced minimal outer scleral doses. Similarly, 103Pd generally produced more favorable dose distributions than 125I for depths less than 4mm. CONCLUSIONS: A modern analysis of eye plaque dosimetry evaluated dose as a function of lesion height and applicator size, and showed dependence on radionuclide selection and implant duration. For a fixed dose at the prescription point, we observed higher scleral dose corresponded with lower photon energy for a variety of plaque sizes and lesion heights.

Limited resection for non-small cell lung cancer: observed local control with implantation of I-125 brachytherapy seeds.

BACKGROUND: Limited resection for lung cancer has been associated with a relatively high incidence of local recurrence. This retrospective study evaluates the impact of implanting radioactive iodine-125 (125I) seeds along the resection margin in these patients. METHODS: Thirty-three patients with lung cancer who were not candidates for lobectomy or pneumonectomy underwent a limited resection of 35 primary non-small cell lung cancers. 125I brachytherapy seeds were implanted along the resection margin to reduce the risk of local recurrence. Survival using the Kaplan-Meier method and sites of recurrence were documented. Follow-up ranged from 20 to 98 months (median, 51 months). RESULTS: The 5-year survival was 47% for all patients. For patients with T1N0 tumors, it was 67%, and for patients with T2N0 tumors, it was 39%. However, the cancer-specific survivals were 77% and 53% for patients with T1N0 and T2N0 tumors, respectfully. Ten patients experienced recurrence, with two local (at the resection margin) and six regional recurrences (five mediastinum, one chest wall). Both local recurrences and one regional recurrence occurred in the 19 patients with T1N0 tumors. CONCLUSIONS: 125I seed implantation along the resected margin for compromised patients undergoing limited resection of lung cancer results in a relatively low incidence of local recurrence and may prolong survival.

Implementation and utility of a daily ultrasound-based localization system with intensity-modulated radiotherapy for prostate cancer.

PURPOSE: To evaluate the clinical feasibility of daily computer-assisted transabdominal ultrasonography for target position verification in the setting of intensity-modulated radiotherapy (IMRT) for prostate cancer. METHODS AND MATERIALS: Twenty-three patients with clinically localized prostate cancer were treated using a sequential tomotherapy IMRT technique (Peacock) and daily computer-assisted transabdominal ultrasonography (BAT) for target localization. Patients were instructed to maintain a full bladder and were placed in the supine position using triangulation tattoos and a leg immobilizer to minimize pelvic rotation. The BAT ultrasound system is docked to the treatment collimator and electronically imports the CT simulation target contours and isocenter. The system is able to use the machine isocenter as a reference point to overlay the corresponding CT contours onto the ultrasound images captured in the transverse and sagittal planes. A touch screen menu is used to maneuver the CT contours in three dimensions such that they match the ultrasound images. The system then displays the three-dimensional couch shifts required to produce field alignment. Data were prospectively collected to measure the frequency by which useful ultrasound images were obtained, the amount of time required for localization/setup, and the direction/magnitude of the positional adjustments. RESULTS: Of the 23 patients, the BAT ultrasound system produced images of sufficient quality to perform the overlay of the CT contours in 19 patients such that positional verification could be reliably performed. Poor image quality was associated with patient inability to maintain a full bladder, large body habitus, or other anatomic constraints. Of the 19 assessable patients, a total of 185 treatment alignments were performed (mean 8.8/patient). For all cases, the average time required for the daily ultrasound imaging and positional adjustments was 11.9 min. After the initial 5 cases, the user experience skills improved such that the time required for image verification/positional adjustments decreased to a mean of 5.6 min. The average right-left, AP, and cranial-caudal adjustment was 2.6 +/- 2.1 mm, 4.7 +/- 2.7 mm, and 4.2 +/- 2.8 mm, respectively. Positional adjustments >10 mm were infrequent and related primarily to misidentification of the target structures on the ultrasound image, patient movement, or improper registration of the triangulation tattoos. CONCLUSION: Daily computer-assisted BAT ultrasound positional verification of the prostate can be successfully performed through the acquisition of high-quality images in most patients with only a modest increase in treatment setup time. Positional data obtained with this system resulted in clinically meaningful adjustments in daily setup for sequential IMRT that would not be otherwise apparent from other verification modalities.