Clinical Investigations Case series analysis of post-brachytherapy prostate edema and its relevance to post-implant dosimetry. Post-implant prostate edema and dosimetry (original) (raw)
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Importance of Post-Implant Dosimetry in Permanent Prostate Brachytherapy
European Urology, 2002
Objective: Post-implant dosimetry has become the gold standard for implant evaluation and it is recommended that it be performed on all patients undergoing prostate brachytherapy. The technique, results and correlation with clinical outcomes will be presented. Methods: The method and outcomes of post-implant dosimetry are explored by outlining the experience at the Mount Sinai Medical Center, New York, as well as reviewing the literature. The most accurate time to perform postimplant dosimetry is 1 month after implant. Computed tomography (CT)-based dosimetry is currently the best available technique for performing this analysis. The technique involves taking 3-mm abutting CT slices throughout the implanted area. The prostate and normal structures are outline on the CT slices. These structures are recreated in three dimensions. Dose volume histograms (DVH) are created and allow the dose to these organs to be quanti®ed. Results: The relationship between dosimetric ®ndings and clinical outcomes has been established. The dose delivered to 90% of the prostate on DVH (D90) has been correlated to prostate-speci®c antigen (PCA) control and post-treatment biopsy results. D90 values of 140 Gy have been associated with improved biochemical control and lower positive post-treatment biopsy results. Doses derived from the dosimetric analysis to prostate, urethra and rectum have been correlated with the development of acute and chronic urinary morbidity, sexual potency and rectal morbidity. Future initiatives involve performing dosimetric calculations intraoperatively at the time of the implant. Conclusions: Post-implant CT-based dosimetry is an essential component of prostate brachytherapy. It is the only method of assessing the actual dose delivered to the prostate and normal surrounding structures. Future development in post-implant and intraoperative dosimetry will continue to improve permanent prostate brachytherapy as a safe an effective treatment for prostate cancer. # 2002 Published by Elsevier Science B.V.
International Journal of Radiation Oncology*Biology*Physics, 1998
Purpose: To characterize the magnitude and duration of post-implant edema following the implantation of I-125 or Pd-103 seeds into the prostate and to investigate its effect on the CT-based calculation of the total dose delivered by the implant. Materials and Methods: A pre-implant CT scan and 3 to 5 serial post-implant CT scans were obtained on 10 patients who received either I-125 or Pd-103 seed implants. None of the patients received hormone therapy. The magnitude and duration of edema were determined from the change in the spatial distribution of the implanted seeds as the edema resolves. Dose volume histograms were compiled to determine the percentage of the prostate volume that received a dose equal to, or greater than, the prescribed dose. Results: The magnitude of the edema, expressed as the ratio of the post-to pre-implant volume on the day of the procedure, ranged from 1.33 to 1.96 (mean 1.52). The edema decreased exponentially with time; however, the edema half-life (time for the edema to decrease by 1/2) varied from 4 to 25 days (mean 9.3 days). As the edema resolved, the percentage of the prostate that received a dose equal to or greater than the prescribed dose increased by at least 7% in 7 of the 10 patients and increased by more than 15% in 2. In those patients in whom dose coverage was unaffected by the resolution of edema, more than 90% of the prostate was covered by the prescribed dose in the initial CT scan. Conclusion: Post-implant edema increased the prostate volume by factors which ranged from 1.33 to 1.96 (mean: 1.52). The edema resolved exponentially with an edema half-life which varied from 4 to 25 days (mean: 9.3 days). Edema had a significant effect on the post-implant dosimetry in 7 of 10 cases. Factors that affect the impact of edema on the dosimetry are the magnitude of the edema and the planned margin between the prescribed isodose line and the periphery of the prostate. © 1998 Elsevier Science Inc. Brachytherapy, Prostate implants, Post-implant dosimetry, I-125, Pd-103.
Effect of post-implant edema on the rectal dose in prostate brachytherapy
International Journal of Radiation Oncology*Biology*Physics, 1999
Purpose: To characterize the effect of prostate edema on the determination of the dose delivered to the rectum following the implantation of 125 I or 103 Pd seeds into the prostate. Methods and Materials: From 3 to 5 post-implant computed tomography (CT) scans were obtained on 9 patients who received either 125 I or 103 Pd seed implants. None of the patients received hormone therapy. The outer surface of the rectum was outlined on each axial CT image from the base to the apex of the prostate. The D 10 rectal surface dose, defined as the dose which encompasses only 10% of the surface area of the rectum, was determined from each CT scan by compiling a dose-surface histogram (DSH) of the rectal surface. The magnitude and half-life of the post-implant edema in each of these implants is known from the results of a previously published study based on the analysis of the serial CT scans. Results: As the prostate edema resolved, the distance between the most posterior implanted seeds and the anterior surface of the rectum decreased. As a result, the D 10 rectal surface dose increased with each successive post-implant CT scan until the edema resolved. The dose increased exponentially at approximately the same rate the prostate volume decreased. The D 10 rectal surface dose at 30 days post-implant ranged from 16% to 190% (mean 68 ؎ 50%) greater than on day 0. The dose on day 30 was at least 50% greater in 6 of 9 cases. Conclusion: The rectal surface dose determined by analysis of a post-implant CT scan of an 125 I or 103 Pd prostate seed implant depends upon the timing of the CT scan. The dose indicated by the CT scan on day 30 is typically at least 50% greater than that indicated by the CT scan on day 0. Because of this difference, it is important to keep the timing of the post-implant CT in mind when specifying dose thresholds for rectal morbidity. © 1999 Elsevier Science Inc. Brachytherapy, Permanent prostate implant, Rectal dose, 125 I, 103 Pd, Transperineal, Interstitial.
The impact of postimplant edema on the urethral dose in prostate brachytherapy
International Journal of Radiation Oncology*Biology*Physics, 2000
Purpose: The objective of this work is to determine the effect of timing of the postimplant CT scan on the assessment of the urethral dose. Methods and Materials: A preimplant CT scan and two postimplant CT scans were obtained on 50 patients who received I-125 prostate seed implants. The first postimplant CT scan was obtained on the day of the implant; the second usually 4 to 9 weeks later (mean: 46 ؎ 23 days; range: 27-135 days). The urethra was localized in each postimplant CT scan and a dose-volume histogram (DVH) of the urethral dose was compiled from each CT study. The relative decrease in the prostate volume between the first and second postimplant CT scans was determined by contouring the prostate in each CT scan. Results: The prostate volume decreased by 27 ؎ 9% (mean ؎ SD) between the first and second postimplant CT scans. As a result, the averaged urethral dose derived from the second CT scan was about 30% higher. In terms of dose, the D 10 , D 25 , D 50 , D 75 , and D 90 urethral doses derived from the second CT scan were 90 ؎ 56 Gy, 81 ؎ 49 Gy, 67 ؎ 42 Gy, 49 ؎ 44 Gy, and 40 ؎ 46 Gy higher, respectively. The increase in the urethral dose is correlated with the decrease in the prostate volume (R ؍ 0.57, < 0.01). Conclusion: The assessment of the urethral dose depends upon the timing of the postimplant CT scan. The mean D 10 dose derived from the CT scans obtained at 46 ؎ 23 days postimplant was 90 ؎ 56 Gy higher than that derived from the CT scans obtained on the day of the implant. Because of this large difference, the timing of the postimplant CT scan needs to be specified when specifying dose thresholds for urethral morbidity. © 2000 Elsevier Science Inc. Prostate brachytherapy, Postimplant dosimetry, Urethral dose.
International Journal of Radiation Oncology*Biology*Physics, 2002
Purpose: To study the influence of radiobiologic and physical parameters and parameters related to edema on the biologically effective dose (BED) for permanent prostate implants and to determine the optimal timing of seed reconstruction for BED calculation. Methods and Materials: On the basis of the linear-quadratic model, an expression for the BED was derived, including the edema parameters. A set of parameter values was defined, and these parameter values were varied one at a time to examine the effect on the BED and the theoretically effective treatment time (t eff ). A ratio ⑀ was defined to investigate the optimal timing of seed reconstruction. Results: The maximal BED decreases when the extent of lethal damage is smaller, the potential tumor doubling time is smaller, the half-life time of the seeds is shorter, and the magnitude of prostate volume increase is larger. For 125 I, the optimal timing of seed reconstruction is 25 days after implantation. Seed reconstruction 1 day after the implantation results in an underestimation of the BED of at most 43%, depending on the magnitude and half-life of edema. An overestimation of the BED of at most 22% is calculated when seed reconstruction took place at the effective treatment time. Conclusion: The maximal BED depends strongly on the value of ␣, the potential tumor doubling time, and the choice of isotope. If prostate volume increase due to edema is not taken into account, the BED will be underestimated shortly after the implantation and overestimated if the calculations are based on images taken several months after implantation. The optimal timing of BED evaluation for 125 I seed implants and typical prostate edema values is 25 days after implantation. © 2002 Elsevier Science Inc. BED, Prostate, Brachytherapy, Edema.
Effect of prostatic edema on CT-based postimplant dosimetry
International Journal of Radiation Oncology*Biology*Physics, 2002
Purpose: To investigate the magnitude of edema after prostate brachytherapy and its effect on the CT-based postimplant dosimetry based on the sequential CT scans using dose-volume histograms, dose conformity, and homogeneity indices in patients with prostate cancer. Methods and Materials: CT scans were obtained for 25 patients who underwent prostate brachytherapy with 125 I or 103 Pd before implant and postimplant Day 1, Day 7, and Day 28. The prostate, rectum, and bladder volumes on each scan were contoured by the same physician. Posttreatment dose distributions were generated using FOCUS (CMS Inc., St. Louis, MO) brachytherapy planning software. Dose calculations were based on TG43 formalism. Dose-volume histograms for target, rectum, and bladder were created for all patients, and the quality of the implants was analyzed using the dose conformity indices: CT-based target volumes ratios, TVR 1 and TVR 2 ; dose homogeneity indices, DHI 1 , DHI 2 , and DNR; dose coverage index, CI; the percentage of the prostate volume enclosed by 100%, 90%, and 80% of the prescription dose: V 100 , V 90 , and V 80 ; the volume of the rectum covered by 100%, 80%, and 70% of the prescription dose; and the dose covering 90% of the prostate volume (D 90). Results: The prostate volume increased between the prescan and the implant Day 1 scans and then decreased between Day 1 and Day 28 scans. The average increase in prostate volume was 30% between the prescan and implant Day 1 scans for the 25 cases evaluated. The prostate volume decreased 20% between the Day 1 and Day 28 scans. The preplan dose coverage to the periphery of the prostate was 100% for all cases evaluated. V 100 increased from an average of 77% to 85% between the Day 1 and Day 28 scans, respectively. On average, D 90 increased from 84% for Day 1 to 93% for Day 28. The average TVR 1 , TVR 2 , and CI were 1.99, 2.28, and 0.87, respectively, based on the Day 28 scans. The average DHI 1 , DHI 2 , and DNR were 0.52, 0.46, and 0.48, respectively, based on the Day 28 scans. Conclusions: The decrease in prostate volume from Day 1 to Day 28 after the implant markedly improved the prescription dose covering the prostate from 77% to 85%. Day 28 prostate volumes were still about 10% larger than the preimplant CT volumes for the 25 cases evaluated. Postimplant dosimetry using dose conformity and homogeneity indices is dependent on the timing of CT studies, as a result of changing prostate volumes from edema.
Radiation Oncology, 2014
Background: In pulsed-dose rate prostate brachytherapy the dose is delivered during 48 hours after implantation, making the treatment sensitive to oedematic effects possibly affecting dose delivery. The aim was to study changes in prostate volume during treatment by analysing catheter configurations on three subsequent scans. Methods: Prostate expansion was determined for 19 patients from the change in spatial distribution of the implanted catheters, using three CT-scans: a planning CT (CT1) and two CTs after 24 and 48 hours (CT2, CT3). An additional 4 patients only received one repeat CT (after 24 hours). The mean radial distance (MRD) of all dwell positions to the geometric centre of all dwell positions used was calculated to evaluate volume changes. From three implanted markers changes in inter-marker distances were assessed. The relative shifts of all dwell positions were determined using catheter-and marker-based registrations. Wilcoxon signed-rank tests were performed to compare the results from the different time points.
The Effect of Pro-Qura Case Volume on Post-Implant Prostate Dosimetry
International Journal of Radiation Oncology*Biology*Physics, 2011
and z Lakewood Ranch Oncology, Bradenton, FL Purpose: To evaluate the effect of prostate brachytherapy case volume on postimplant dosimetric quality in Pro-Qura proctored programs. Methods and Materials: From August 1999 to December 2008, the computed tomography datasets for 6,600 prostate implants performed by 129 brachytherapists were submitted to Pro-Qura for dosimetric analysis. Brachytherapists were divided into three roughly equal-sized terciles based on total case volume. Postimplant computed tomography scans were obtained at a median of 30 days. Excellent target coverage was defined by a V100 9090% and D90 90100% minimum prescribed peripheral dose. To determine if the number of excellent implants improved with increasing case numbers, each brachytherapist's series of implants was bisected into early and late experience by a moveable critical point. Results: For the entire cohort, the mean V100 and D90 were 89.2% and 102.8%, respectively, with 47.7% of the implants scored as excellent. Brachytherapists in the highest-case tercile had a significantly greater fraction of excellent target coverage (57.9%) than did those in the two lower terciles (39.5% and 45.7%, p = 0.015). Twenty-one (25.6%) of the 82 brachytherapists with sufficient case volume for dosimetric improvement analyses demonstrated quality improvement over time. Although there was no significant difference between prostate volume and seed strength, the number of seeds used was significantly greater in adequate implants. Conclusions: The highest-volume brachytherapists were most likely to obtain excellent target coverage. We are encouraged that in general practice, nearly 48% of all implants were scored excellent. It is conceivable that with greater expert third-party involvement, an even greater percentage of cases with excellent target coverage will become reality. Ó 2011 Elsevier Inc.
Brachytherapy, 2014
PURPOSE: To characterize prostate swelling and dosimetry in patients with small prostate volumes (PVs) undergoing brachytherapy. METHODS AND MATERIALS: We studied 25 patients with PV !25 cc (range, 15.1e24.8) and 65 patients with PV $25 cc (range, 25.0e66.2) based on three-dimensional ultrasound contours who underwent brachytherapy monotherapy with intraoperative planning. Postoperative Days 1 and 30 dosimetry was done by CTeMRI fusion. RESULTS: Small PVs had greater Day 1 swelling than large PVs (32.5% increase in volume vs. 23.7%, p 5 0.04), but by Day 30, swelling was minimal and not significantly different ( p 5 0.44). Small PVs had greater seed and needle densities at implant ( p ! 0.001). Rectal and urethral doses were nearly identical by Day 30 (small PV rectum receiving 100% of the prescription dose [145 Gy] [V 100 ] 5 0.32 cc; large PV rectum V 100 5 0.33 cc, p 5 0.99; small PV urethra receiving 150% of the prescription dose [145 Gy] [V 150