RESUMO
PURPOSE: We evaluated the post-operative pattern of prostate volume (PV) changes following prostate brachytherapy (PB) and analyzed variables which affect swelling. MATERIAL AND METHODS: Twenty-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% (D(90)) of the prostate on day 30 (D(90)Day30) was obtained by dividing day 1 (D(90)Day1) by the CF. RESULTS: The mean PV recorded on post-operative day 1 was 67.7 cm(3), 18.8 cm(3) greater than average pre-op value (SD 15.6 cm(3)). 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 D(90)Day30 was not significant. CONCLUSIONS: We 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 D(90)Day1 by a correction factor of 0.76.
RESUMO
OBJECTIVES: To evaluate the use of real-time kilovoltage cone-beam computed tomography (CBCT) during prostate brachytherapy for intraoperative dosimetric assessment and correcting deficient dose regions. METHODS: A total of 20 patients were evaluated intraoperatively with a mobile CBCT unit immediately after implantation while still anesthetized. The source detector system was enclosed in a circular CT-like geometry with a bore that accommodates patients in the lithotomy position. After seed deposition, the CBCT scans were obtained. The dosimetry was evaluated and compared with the standard postimplantation CT-based assessment. In 8 patients, the deposited seeds were localized in the intraoperative CBCT frame of reference and registered to the intraoperative transrectal ultrasound images. With this information, a second intraoperative plan was generated to ascertain whether additional seeds were needed to achieve the planned prescription dose. The final dosimetry was compared with the postimplantation scan assessment. RESULTS: The mean differences between the dosimetric parameters from the intraoperative CBCT and postimplant CT scans were < .5% for percentage of volume receiving 100% of the prescription dose, minimal dose received by 90% of the prostate, and percentage of volume receiving 150% of the prescription dose. The minimal dose received by 5% (maximal dose) of the urethra differed by 8% on average and for the rectum an average difference of approximately 18% was observed. After fusion of the implanted seed coordinates from the intraoperative CBCT scans to the intraoperative transrectal ultrasound images, the dosimetric outcomes were not significantly different from the postimplantation CT dosimetric results. CONCLUSIONS: Intraoperative CT-based dosimetric evaluation of prostate permanent seed implantation before anesthesia reversal is feasible and might avert misadministration of dose delivery. The dosimetric measurements using the intraoperative CBCT scans were dependable and correlated well with the postimplant diagnostic CT findings.
