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Purpose: Variations in dosimetric outcomes among patients treated with low-dose-rate brachytherapy for prostate cancer exist, even when implants are within dose constraints. Here, we used control charts to investigate reasons for intra-patient dosimetric variability., Material and Methods: Univariate and multivariate control charts for prostate V 100 (percentage of prostate volume that received 100% of prescribed radiation dose), D 90 (radiation dose to 90% of prostate volume), and RV 100 (rectal wall volume that received 100% of prescribed radiation dose) were generated for 212 consecutive prostate cancer patients implanted with iodine-125 ( 125 I) radioactive seeds at the Princess Margaret Cancer Centre. Control limits were calculated based on the first fifty implants. Data points that were out of control were identified, and their pre-treatment and post-treatment dosimetric and clinical parameters were compared to data points that were in-control, using Student's t -test., Results: All implants were clinically acceptable. Twelve data points exceeded multivariate control limits. Ten of those points fell below the lower control limit of V 100 control chart. Average prostate edema in the 10 out-of-control patients on both multivariate and V 100 charts was 8.3%, as compared to 0.4% for in-control patients ( p < 0.04). Two patients were observed to be out-of-control on multivariate control chart, but not on V 100 control chart, and were found to have a reduction in prostate volume of 19.1% and 20.1% at one month after seed implant, compared to prostate volumes of pre-implantation evaluations., Conclusions: Control charts helped in identifying cases with out-of-control variability in post-plan prostate dosimetry. Post-treatment prostatic edema and contraction are important factors predicting variability in patients treated with 125 I permanent seed brachytherapy., Competing Interests: The authors report no conflict of interest., (Copyright © 2022 Termedia.)

Purpose: To analyze the seed loss and displacement and their dosimetric impact in prostate low-dose-rate (LDR) brachytherapy while utilizing the combination of loose and stranded seeds., Material and Methods: Two hundred and seventeen prostate cancer patients have been treated with LDR brachytherapy. Loose seeds were implanted in the prostate center and stranded seeds in the periphery of the gland. Patients were imaged with transrectal ultrasound before implant and with computerized tomography/magnetic resonance imaging (CT/MR) one month after implant. The seed loss and displacement had been analyzed. Their impact on prostate dosimetry had been examined. The seed distribution beyond the prostate inferior boundary had been studied., Results: The mean number of seeds per patient that were lost to lung, pelvis/abdomen, urine, or unknown destinations was 0.21, 0.13, 0.03, and 0.29, respectively. Overall, 40.1% of patients had seed loss. Seed migration to lung and pelvis/abdomen occurred in 15.5% and 10.5% of the patients, respectively. Documented seed loss to urine was found in 3% of the patients while 20% of patients had seed loss to unknown destinations. Prostate length difference between pre-plan and post-implant images was within 6 mm in more than 98% of cases. The difference in number of seeds inferior to prostate between pre-plan and post-implant dosimetry was within 7 seeds for 93% of patients. At time of implant, 98% of seeds, inferior to prostate, were within 5 mm and 100% within 15 mm, and in one month post-implant 83% within 9 mm and 96.3% within 15 mm. Prostate post-implant V100, D90, and rectal wall RV100 for patients without seed loss were 94.6%, 113.9%, and 0.98 cm(3), respectively, as compared to 95.0%, 114.8%, and 0.95 cm(3) for the group with seed loss., Conclusions: Seed loss and displacement have been observed to be frequent. No correlation between seed loss and displacement and post-plan dosimetry has been reported.