Biologically effective dose for permanent prostate brachytherapy taking into account postimplant edema (original) (raw)

Optimum timing for image-based dose evaluation of 125I and 103Pd prostate seed implants

International Journal of Radiation Oncology*Biology*Physics, 1999

Purpose/Objective: Image-based dose evaluation of permanent brachytherapy implants for prostate cancer is important for optimal patient management after implantation. Because of edema caused by the surgical procedure in the implantation, if the dose evaluation is based on the images obtained too early after implantation, dose coverage will usually be underestimated. Conversely, if the images are obtained too late, the dose coverage will be overestimated. This study uses a biomathematical model to simulate edema and its resolution on 29 patients, so that the optimum time to obtain image scans and perform dose evaluation can be investigated and estimated. Methods and Materials: Edema of a prostate and its resolution has been shown to follow an exponential function V(t) ‫؍‬ V(0)(1 ؉ ⌬V[e ؊0.693t/Te ؊ 1]) where ⌬V is the initial relative increase in the prostate volume due to edema (and is related to edema magnitude), and T e (edema half-life) is the time for the edema to decrease by half in volume. In this study, edema was simulated by increasing the volume of preimplant prostate (obtained from ultrasound volume study) to a given magnitude of edema. Similarly, the locations of planned seeds were changed to their corresponding locations in the edematous prostate proportionally. The edema was then allowed to resolve according to the exponential function. The correct dose distribution was calculated by taking into account the dynamic variations of the prostate volume, seed locations, and source strengths with respect to time. Dose volume histograms (DVHs) were then generated from this dose distribution. The conventional postimplant DVHs, which assume the prostate volume and seed locations are as in the image scans and constant in time, were also calculated based on the simulated image scans for various days postimplantation. The conventional DVHs of prostate on various days after implantation were compared to the DVH calculated assuming dynamic conditions. The optimum timing for conventional postimplant dose evaluation was identified as the time at which a minimum difference between the conventional DVH and the dynamic model DVH was achieved. The analysis was done on 29 prostate seed implant patients for both 125 I and 103 Pd. The edema magnitude was assumed to be 30%, 40%, 50%, 75%, and 100% of original prostate volume, and the half-life of edema was assumed to be 4, 7, 10, 15, 20, and 25 days. In this study, the original volume of prostate varied from 17 cm 3 to 91 cm 3 , and number of seeds in the implants varied from 57 to 119. Results: The optimum timing was mainly dependent on the half-lives of edema and radionuclides, and varied slightly with edema magnitude, prostate volume, and number of seeds. It can be expressed as a function of edema half-life in the form of C 0 ؉ C 1 exp(؊C 2 T e ). However, if the dose evaluation was performed based on the image scans taken too early or too late, the error became larger, as the edema magnitude was larger. By averaging all 29 patients and various edemas, it was found that for 125 I seed implants, if the postimplant dose evaluation is performed based on image scans taken between 5 and 9 weeks, the average error will be less than 5%, with a maximum possible error less than 10% in 80% coverage dose; for 103 Pd seed implants, if the postimplant dose evaluation is performed based on image scans taken between 2 and 4 weeks, the average error will be less than 5%, with a maximum error less than 15% in 80% coverage dose. Because of edema, a conventional preimplant plan also overestimates dose coverage of prostate. On the average, a standard preimplant planning overestimates dose coverage by about 6% for 125 I implants and 14% for 103 Pd implants in our study. Conclusion: Based on the dynamic model, the optimum timing of image scans for postimplant dose evaluation of prostate seed implantation is 7 weeks postimplantation for 125 I implants and about 3 weeks for 103 Pd implants. The time-window for reasonable accuracy (؎ 5%) is ؎ 2 weeks for 125 I and ؎ 1 week for 103 Pd around the optimum timing. During preimplant procedure, the minimum prescribed coverage dose should be increased by an amount of about 6% for 125 I implants and about 14% for 103 Pd implants to compensate for the effect of edema. © 1999 Elsevier Science Inc.

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.

Clinical Investigations Case series analysis of post-brachytherapy prostate edema and its relevance to post-implant dosimetry. Post-implant prostate edema and dosimetry

Journal of Contemporary Brachytherapy, 2012

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.

Edema associated with I-125 or Pd-103 prostate brachytherapy and its impact on post-implant dosimetry: an analysis based on serial CT acquisition

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.

Clinical Investigations Radiobiologically based treatment plan evaluation for prostate seed implants

Journal of Contemporary Brachytherapy, 2011

Purpose: Accurate prostate low dose-rate brachytherapy treatment plan evaluation is important for future care decisions. Presently, an evaluation is based on dosimetric quantifiers for the tumor and organs at risk. However, these do not account for effects of varying dose-rate, tumor repopulation and other biological effects. In this work, incorporation of the biological response is used to obtain more clinically relevant treatment plan evaluation. Material and methods: Eleven patients were evaluated. Each patient received a 145 Gy implant. Iodine-125 seeds were used and the treatment plans were created on the Prowess system. Based on CT images the post-implant plan was created. In the post-plan, the tumor, urethra, bladder and rectum were contoured. The biologically effective dose was used to determine the tumor control probability and the normal tissue complication probabilities for the urethra, bladder, rectum and surrounding tissue. Results: The average tumor control probability and complication probabilities for the urethra, bladder, rectum and surrounding tissue were 99%, 29%, 0%, 12% and 6%, respectively. These measures provide a simpler means for evaluation and since they include radiobiological factors, they provide more reliable estimation of the treatment outcome. Conclusions: The goal of this work was to create more clinically relevant prostate seed-implant evaluation by incorporating radiobiological measures. This resulted in a simpler descriptor of treatment plan quality and was consistent with patient outcomes.

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.

Impact of postimplant edema on V100 and D90 in prostate brachytherapy: can implant quality be predicted on day 0?

International Journal of Radiation Oncology*Biology*Physics, 2002

Purpose: To determine the effect of edema on the dosimetric parameters V 100 (percentage of prostate volume that received a dose equal to or greater than the prescribed dose) and D 90 (minimal dose delivered to 90% of prostate volume) in 125 I prostate brachytherapy and to determine whether the edema can be used to predict implant quality on the day of the implant (Day 0). Methods and Materials: Fifty consecutive patients treated with 125 I implants who had two postimplant CT scans were selected for this study. The mean interval between the studies was 46 ؎ 23 days. The implants were preplanned to deliver 150 Gy to the prostate plus a 3-5-mm symmetric dose margin using peripherally loaded 0.4 -0.6-mCi (NIST-99) 125 I seeds. A dose-volume histogram was compiled for each postimplant CT scan. The V 100 and D 90 from the first and second CT scans were compared to determine the effect of edema on these parameters. A multivariate regression analysis was performed to define the linear relationships for predicting the V 100 or D 90 at 30 -60 days after implant from the magnitude of the edema and the values of V 100 and D 90 on Day 0. Results: V 100 and D 90 increased by 5% ؎ 6% and 15% ؎ 17%, respectively, during the interval between the first and second postimplant CT scans. The mean edema was 1.53 ؎ 0.20. The increases in V 100 and D 90 were found to be proportional to the edema and the values of V 100 and D 90 on Day 0. The increase in V 100 was also found to depend on the width of the preplan dose margin. Linear relationships were derived that predict the V 100 and D 90 at 30 -60 days after implant with a standard error of ؎4% and ؎24 Gy, respectively. Conclusion: V 100 and D 90 increased by 5% ؎ 6% and 15% ؎ 17%, respectively, during the first 30 -60 days after implant. The results of a multivariate linear regression analysis showed that the increases in V 100 and D 90 were proportional to both the magnitude of the edema and the values of these parameters on Day 0. The relationships derived by linear regression analysis predict V 100 and D 90 at 30 -60 days after implant to within ؎4% and ؎24 Gy, respectively. However, predicting the 30 -60-day V 100 and D 90 on Day 0 is a poor substitute for obtaining a 30 -60-day CT scan, because the uncertainty in the predicted values is greater by a factor of >2. Nevertheless, on average, the predicted values should provide a more reliable estimate of the actual V 100 and D 90 than the Day 0 values that ignore the effect of edema altogether. The increase in V 100 was also found to depend on the width of the preplan dose margin; therefore, our results for V 100 are only valid for implants planned with a 3-5-mm margin.

Edema and Seed Displacements Affect Intraoperative Permanent Prostate Brachytherapy Dosimetry

International journal of radiation oncology, biology, physics, 2016

We sought to identify the intraoperative displacement patterns of seeds and to evaluate the correlation of intraoperative dosimetry with day 30 for permanent prostate brachytherapy. We analyzed the data from 699 patients. Intraoperative dosimetry was acquired using transrectal ultrasonography (TRUS) and C-arm cone beam computed tomography (CBCT). Intraoperative dosimetry (minimal dose to 40%-95% of the volume [D40-D95]) was compared with the day 30 dosimetry for both modalities. An additional edema-compensating comparison was performed for D90. Stranded seeds were linked between TRUS and CBCT using an automatic and fast linking procedure. Displacement patterns were analyzed for each seed implantation location. On average, an intraoperative (TRUS to CBCT) D90 decline of 10.6% ± 7.4% was observed. Intraoperative CBCT D90 showed a greater correlation (R(2) = 0.33) with respect to Day 30 than did TRUS (R(2) = 0.17). Compensating for edema, the correlation increased to 0.41 for CBCT and ...

Dosimetric quality and evolution of edema after low-dose-rate brachytherapy for small prostates: Implications for the use of newer isotopes

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

Significant Underdosage of the Prostate Base after 125-I Brachytherapy on Day 1 Post-implant Dosimetry

International Journal of Radiation Oncology*Biology*Physics, 2009

migration, or OR procedure time were seen. No seed drift greater than 10 mm outside the "packet" of other seeds was seen in the Anchorseed cohort. Conclusions: This report is the first to show the unique "fixity" of AnchorSeedÔ to remain in position after deployment from the Mick applicator. Minimizing seed drag can reduce dose to the penile bulb, and maximize radiation coverage to the apex of the gland.