A method for implementing the American Association of Physicists in Medicine Task Group-43 dosimetry recommendations for 125I transperineal prostate seed implants on commercial treatment planning systems.

PURPOSE: To present our experience implementing the American Association of Physicists in Medicine (AAPM) Task Group #43 (TG-43) recommendations for 125I dosimetry parameters utilizing two commercially available treatment planning systems. METHODS AND MATERIALS: Single seed point source calculations were performed on two treatment planning systems and intercomparisons were conducted between known points of interest for (a) previously published data on each system, (b) TG-43 data on each system, and (c) hand calculations. Additional calculations and intercomparisons were performed for a typical 35 cm3 prostate volume implant with a prescribed dose of 160 Gy. RESULTS: Intercomparisons of calculations for single seed point source approximations with previously published data and TG-43 data indicated good agreement between the two systems at a distance of 1 cm. Point source comparisons between previously published data and TG-43 recommendations show a difference in dose of 11% to the 1 cm point. Calculations for a 35 cm3 permanent interstitial prostate implant showed the 160 Gy isodose line pulled centrally toward the seeds 1-2 mm as a result of the 11% change. CONCLUSIONS: It is advisable for physicians, physicists, and dosimetrists to exercise caution when incorporating the TG-43 recommendations for 125I into treatment planning systems. The effects caused by differences in dosimetry parameters need to be understood and accounted for when matching prescribed doses in order to ensure continuity of treatment and clinical results as reported in the current literature.

In vivo diode dosimetry for total marrow irradiation.

PURPOSE: To describe a method and evaluate the efficacy of using a p-type silicon diode as an alternative to thermoluminescent dosimeters for verifying the accuracy of total marrow irradiation setups and calculations. METHODS AND MATERIALS: A calibration factor has been measured for a 6 MV photon beam incident horizontally onto a polystyrene phantom inside an in-house built total marrow irradiation stand. Signal responses due to positioning and orientation of the diode with respect to the source were compared to a 0.6 cc cylindrical ionization chamber inside a polystyrene phantom. Procedures for predicting the diode reading and taking entrance measurements have been developed and action levels established to determine causes for discrepancies when ratios between predicted and actual values fell outside a +/- 5% tolerance range. Measurements were taken at the skin surface over the umbilicus calculation point for alternating 1.5 Gy anterior and posterior fractions given bidaily over a 3-day period. RESULTS: A total of 137 measurements taken from January to September 1994 for 23 patients were analyzed using a frequency histogram. The histogram indicated a mean reading of 1.002 +/- 2.6, and that three of the measurements fell outside the 5% tolerance. Investigation into the cause of the discrepancies showed that the diode had been improperly placed one time and that further patient immobilization needs to be considered. CONCLUSION: It is possible to use a diode as an in vivo dosimeter for a total marrow irradiation technique. The ease of implementation and immediate readouts make a diode system preferable to a thermoluminescent system for identifying systematic errors and verifying treatment configurations and monitor unit calculations.

Should brachytherapy be considered a therapeutic option in localized prostate cancer?

Contemporary prostate brachytherapy incorporates advances in computer analysis, imaging technology, and delivery apparatus, allowing exacting and reproducible results compared with historical approaches. The advances permit brachytherapy to be performed on a cost-effective, outpatient basis with low morbidity in the appropriately selected patient. Although unsettled questions remain regarding dosimetric issues, long-term outcomes, and morbidity, the weight of evidence to date appears to support the use of brachytherapy in selected patients. Brachytherapy may be considered a therapeutic option: as monotherapy for early-stage disease and also a boost following moderate doses of external beam irradiation for locally advanced disease.