ABSTRACT
The Delta4 biplanar diode array dosimeter was validated for helical tomotherapy delivery QA. The basic detector characteristics were found to be satisfactory in terms of short-term reproducibility (0.1%), linearity (<0.1%), dose rate dependence (0.4%), and absolute calibration accuracy (0.4% in the center of the phantom compared with the independently calibrated diode). Relative calibration of the arrays was verified by comparison with film and by rotating the detector 180°. The dosimeter response to rotational irradiation changed by no more than 0.2% when one of the detector boards was replaced by the homogeneous phantom material. The daily output correction factor can be derived from a Delta4 measurement in a uniform cylindrical field. The γ(3%, 3 mm) passing rate (absolute dose) was above 90% for all 9 evaluated clinical plans, and above 96% for all but one. The mean passing rate was 97 ± 2.7%. The plans varied in modulation factor, pitch, and calculation grid size. For best results, the phantom needs to be aligned carefully, preferably by megavoltage computed tomography imaging.
Subject(s)
Radiometry/instrumentation , Radiotherapy, Conformal/instrumentation , Semiconductors , Equipment Design , Equipment Failure Analysis , Radiotherapy Dosage , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
The effects of edema on urethral dose after interstitial prostate brachytherapy with palladium-103 (103Pd) were studied. Fifty patients underwent a 90-Gy 103Pd implant followed by dosimetric computed tomography (CT). Twenty-one days later, a Foley catheter was reinserted and a dosimetric CT was repeated. The mean reduction in prostate volume between day 0 and day 21 was 16%. Median prostate D90 on day 0 was 89.7 Gy (range 59.5 to 127) and 99.5 Gy (range 62.5 to 130) on day 21. Median prostate V100 was 90% (range 63 to 98%) on day 0 and 96% (range 66 to 99%) on day 21. Median V150 was 61% (range 31 to 85%) on day 0 and 75% (range 39 to 93%) on day 21. Median urethral D50 was 107 Gy (range 57 to 201) on day 0 and 126 Gy (range 64 to 193) on day 21. Regression analysis demonstrated a significant correlation between the decrease in the prostate volume and the increased urethral D50 (r 0.58, p < 0.05). Acute urinary toxicity was 32% grade 0, 38% grade 1, and 30% grade 2. The median urethral D50 increased by a mean of 18% with a correlation coefficient of 0.58 (p < 0.05). Catheterization of the urethra was well tolerated and was of value in better characterizing urethral dose after 103Pd brachytherapy.
