PurposeWe evaluated the post-operative pattern of prostate volume (PV) changes following prostate brachytherapy (PB) and analyzed variables which affect swelling.Material and methodsTwenty-nine patients treated with brachytherapy (14) or combined brachytherapy and external beam radiotherapy modality (15) underwent pre- and post-implant computed tomography (CT). Prostate volume measurements were done on post-operative days 1, 9, 30, and 60. An observer performed 139 prostate volume (PV) measurements. We analyzed the influence of pre-implant PV, number of needles and insertion attempts, number and activity of seeds, Gleason score, use of hormonal therapy and external beam radiation therapy on the extent of edema. We computed a volume correction factor (CF) to account for dosimetric changes between day 1 and day 30. Using the calculated CF, the dose received by 90% (D90) of the prostate on day 30 (D90Day30) was obtained by dividing day 1 (D90Day1) by the CF.ResultsThe mean PV recorded on post-operative day 1 was 67.7 cm3, 18.8 cm3 greater than average pre-op value (SD 15.6 cm3). Swelling returned to pre-implant volume by day 30. Seed activity, treatment modality, and Gleason score were significant variables. The calculated CF was 0.76. After assessment using the CF, the mean difference between estimated and actual D90Day30 was not significant.ConclusionsWe observed maximum prostate size on post-operative day 1, returning to pre-implant volume by day 30. This suggests that post-implant dosimetry should be obtained on or after post-operative day 30. If necessary, day 30 dosimetry can be estimated by dividing D90Day1 by a correction factor of 0.76.
Objectives
Evaluate real-time kilovoltage cone-beam computed tomography (CBCT) during prostate brachytherapy for intraoperative dosimetric assessment and correcting deficient dose regions.
Methods
Twenty patients were evaluated intraoperatively with a mobile CBCT unit immediately after implantation while still anesthetized. The source-detector system is enclosed into a circular CT-like geometry with a bore that accommodates patients in the lithotomy position. After seed deposition, CBCT scans were obtained, Dosimetry was evaluated and compared to standard postimplantation CT-based assessment. In eight patients deposited seeds were localized in the intraoperative CBCT frame of reference and registered to the intraoperative transrectal ultrasound (TRUS) images. With this information, a second intraoperative plan was generated to ascertain if additional seeds were needed to achieve the planned prescription dose. Final dosimetry was compared with postimplantation scan assessment.
Results
Mean differences between dosimetric parameters from the intraoperative CBCT and post-implant CT scans were <0.5% for V100, D90, and V150 target values. Mean percentage differences for average urethral doses were not significantly different. Differences for D5 (maximum dose) of the urethra were <4%. The dose to 2 cc of the rectum differed by 10% on average. After fusion of implanted seed coordinates from the intraoperative CBCT scans onto the intraoperative TRUS images, dosimetric outcomes were similar to postimplantation CT dosimetric results.
Conclusions
Intraoperative CT-based dosimetric evaluation of prostate permanent seed implantation prior to anesthesia reversal is feasible and may avert misadministration of dose delivery. Dosimetric measurements based on the intraoperative CBCT scans are dependable and correlate well with postimplant diagnostic CT evaluation.
15563 Purpose: Prostate brachytherapy (PB) has been linked with increase in prostate volume (PV). This study evaluates post- operative PV changes and the variables that might affect prostate swelling. Methods: Twenty four patients (pts) were analyzed. Twelve were treated with PB only, 8 with external beam radiation (EBRT) prior to implant, and 4 with EBRT after PB. Pre-treatment PSA and Gleason score ranges were 1.9–10.8 and 5–8 respectively. Pre- implant and post-implant day 1, 9, 30, and 60 (PV0, PV1, PV9, PV30, and PV60) measurements were done using computed tomography. Univariate analysis of PV change and the following was done: PV0, number of needles, seeds, and needle insertion attempts, seed activity (0.3 vs 0.5mCi), hormonal ablation therapy, and prior EBRT. Urinary symptoms were assessed using International Prostate Scoring System (IPSS). Results: Ninety six PV measurements were done by a single observer. PV0 ranged from 27.1 to 89.4 cc (mean 48.2). Largest PV was observed on day 1 (40.1–118.7, mean 67.1). Successive PV measurements afterwards continued to decrease. Mean PV values on day 9, 30, and 60 were 58.6, 51.5, and 42.3cc respectively. The differences between PV0 and all successive PV’s were statistically significant. Mean increase in PV1 from PV0 was 18.9±16.8cc (p<0.001), PV0 and PV9 9.7cc, PV0 and PV30 2.6cc. PV60 was smaller than PV0 by an average of 6.6cc. Statistically significant positive correlation was found between PV increase and seed activity (p=0.02) while treatment with EBRT prior to PB was associated with less prostate swelling (p=0.043). Other variables were not significantly correlated with PV changes. Although the mean IPSS score increased from pre-implant value of 9.2 to 13.7 on day 60, the differences between IPSS values were not statistically significant. Conclusions: Maximum prostate size is observed on the first day after implant. Prostate begins to decrease in size between day 1 and day 9 and reaches pre-procedure volume after day 30. Higher seed activity results in greater prostate swelling, while less brachytherapy- induced swelling is observed in patients treated with external radiation prior to implant. Resolution of prostate swelling does not appear to parallel with improvement in urinary symptoms in the first 2 months after implant. No significant financial relationships to disclose.
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