### Prostate Edema and Seed Implants - Related Abstracts

**Potential impact of prostate edema on the dosimetry of permanent seed implants using the new 131Cs (model CS-1) seeds.**

**Chen Z**

**,**

**Deng J**

**,**

**Roberts K**

**,**

**Nath R**

**.**

**Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut 06504, USA.**

**Our aim in this work was to study the potential dosimetric effect of prostate edema on the accuracy of conventional pre- and post-implant dosimetry for prostate seed implants using the newly introduced 131Cs seed, whose radioactive decay half-life (approximately 9.7 days) is directly comparable to the average edema resolution half-life (approximately 10 days) observed previously by Waterman et al. for 125I implants [Int. J. Radiat. Oncol. Biol. Phys. 41, 1069-1077 (1998)]. A systematic calculation of the relative dosimetry effect of prostate edema on the 131Cs implant was performed by using an analytic solution obtained previously [Int. J. Radiat. Oncol. Biol. Phys. 47, 1405-1419 (2000)]. It was found that conventional preimplant dosimetry always overestimates the true delivered dose as it ignores the temporary increase of the interseed distance caused by edema. The overestimation for 131Cs implants ranged from 1.2% (for a small edema with a magnitude of 10% and a half-life of 2 days) to approximately 45% (for larger degree edema with a magnitude of 100% and a half-life of 25 days). The magnitude of pre- and post-implant dosimetry error for 131Cs implants was found to be similar to that of 103Pd implants for typical edema characteristics (magnitude <>**

**PMID: 16696473 [PubMed - indexed for MEDLINE]**

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**Effect of edema, relative biological effectiveness, and dose heterogeneity on prostate brachytherapy.**

**April 2006**

**Wang JZ**

**,**

**Mayr NA**

**,**

**Nag S**

**,**

**Montebello J**

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**Gupta N**

**,**

**Samsami N**

**,**

**Kanellitsas C**

**.**

**Department of Radiation Medicine, The Ohio State University, Columbus, Ohio 43210, USA.**

**wang.993@osu.edu**

**Many factors influence response in low-dose-rate (LDR) brachytherapy of prostate cancer. Among them, edema, relative biological effectiveness (RBE), and dose heterogeneity have not been fully modeled previously. In this work, the generalized linear-quadratic (LQ) model, extended to account for the effects of edema, RBE, and dose heterogeneity, was used to assess these factors and their combination effect. Published clinical data have shown that prostate edema after seed implant has a magnitude (ratio of post- to preimplant volume) of 1.3-2.0 and resolves exponentially with a half-life of 4-25 days over the duration of the implant dose delivery. Based on these parameters and a representative dose-volume histogram (DVH), we investigated the influence of edema on the implant dose distribution. The LQ parameters (alpha=0.15 Gy(-1) and alpha/beta=3.1 Gy) determined in earlier studies were used to calculate the equivalent uniform dose in 2 Gy fractions (EUD2) with respect to three effects: edema, RBE, and dose heterogeneity for 125I and 103Pd implants. The EUD2 analysis shows a negative effect of edema and dose heterogeneity on tumor cell killing because the prostate edema degrades the dose coverage to tumor target. For the representative DVH, the V100 (volume covered by 100% of prescription dose) decreases from 93% to 91% and 86%, and the D90 (dose covering 90% of target volume) decrease from 107% to 102% and 94% of prescription dose for 125I and 103Pd implants, respectively. Conversely, the RBE effect of LDR brachytherapy [versus external-beam radiotherapy (EBRT) and high-dose-rate (HDR) brachytherapy] enhances dose effect on tumor cell kill. In order to balance the negative effects of edema and dose heterogeneity, the RBE of prostate brachytherapy was determined to be approximately 1.2-1.4 for 125I and 1.3-1.6 for 103Pd implants. These RBE values are consistent with the RBE data published in the literature. These results may explain why in earlier modeling studies, when the effects of edema, dose heterogeneity, and RBE were all ignored simultaneously, prostate LDR brachytherapy was reported to show an overall similar dose effect as EBRT and HDR brachytherapy, which are independent of edema and RBE effects and have a better dose coverage.**

**PMID: 16696479 [**

**PubMed - indexed for MEDLINE**

**]**

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**Dosimetric effects of edema in permanent prostate seed implants: a rigorous solution.**

**Chen Z**

**,**

**Yue N**

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**Wang X**

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**Roberts KB**

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**Peschel R**

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**Nath R**

**.**

**Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06504, USA.**

**zhe.chen@yale.edu**

**PURPOSE: To derive a rigorous analytic solution to the dosimetric effects of prostate edema so that its impact on the conventional pre-implant and post-implant dosimetry can be studied for any given radioactive isotope and edema characteristics.**

**METHODS AND MATERIALS: The edema characteristics observed by Waterman et al (Int. J. Rad. Onc. Biol. Phys, 41:1069-1077; 1998) was used to model the time evolution of the prostate and the seed locations. The total dose to any part of prostate tissue from a seed implant was calculated analytically by parameterizing the dose fall-off from a radioactive seed as a single inverse power function of distance, with proper account of the edema-induced time evolution. The dosimetric impact of prostate edema was determined by comparing the dose calculated with full consideration of prostate edema to that calculated with the conventional dosimetry approach where the seed locations and the target volume are assumed to be stationary.**

**RESULTS: A rigorous analytic solution on the relative dosimetric effects of prostate edema was obtained. This solution proved explicitly that the relative dosimetric effects of edema, as found in the previous numerical studies by Yue et. al. (Int. J. Radiat. Oncol. Biol. Phys. 43, 447-454, 1999), are independent of the size and the shape of the implant target volume and are independent of the number and the locations of the seeds implanted. It also showed that the magnitude of relative dosimetric effects is independent of the location of dose evaluation point within the edematous target volume. It implies that the relative dosimetric effects of prostate edema are universal with respect to a given isotope and edema characteristic. A set of master tables for the relative dosimetric effects of edema were obtained for a wide range of edema characteristics for both (125)I and (103)Pd prostate seed implants.**

**CONCLUSIONS: A rigorous analytic solution of the relative dosimetric effects of prostate edema has been derived for a class of edema characterized by Waterman et al. The solution proved that the dosimetric effects caused by the edema are universal functions of edema characteristics for a given isotope. It provides an efficient tool to examine the relative dosimetric effects of edema for any given edema characteristics and for any isotopes that may be considered for prostate implants.**

**PMID: 10889396 [**

**PubMed - indexed for MEDLINE**

**]**

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**Edema-induced increase in tumour cell survival for 125I and 103Pd prostate permanent seed implants--a bio-mathematical model.**

**April 2002**

**Yue N**

**,**

**Chen Z**

**,**

**Nath R**

**.**

**Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520-8040, USA.**

**Edema caused by the surgical procedure of prostate seed implantation expands the source-to-point distances within the prostate and hence decreases the dose coverage. The decrease of dose coverage results in an increase in tumour cell survival. To investigate the effects of edema on tumour cell survival, a bio-mathematical model of edema and the corresponding cell killing by continuous low dose rate irradiation (CLDRI) was developed so that tumour cell surviving fractions can be estimated in an edematous prostate for both 125I and 103Pd seed implants. The dynamic nature of edema and its resolution were modelled with an exponential function V(T) = V(p)(1 + M exp(-0.693T/ T(e))) where V(p) is the prostate volume before implantation, M is the edema magnitude and T(e) is edema half-life (EHL). The dose rate of a radioactive seed was calculated according to AAPM TG43, i.e. D = SkAg(r)phi(an)/r2, where r is the distance between a seed and a given point. The distance r is now a function of time because of edema. The g(r) was approximated as 1/r(0,4) and 1/r(0.8) for 125I and 103Pd, respectively. By expanding the mathematical expression of the resultant dose rate in a Taylor series of exponential functions of time, the dose rate was made equivalent to that produced from multiple fictitious radionuclides of different decay constants and strengths. The biologically effective dose (BED) for an edematous prostate implant was then calculated using a generalized Dale equation. The cell surviving fraction was computed as exp(-alphaBED), where alpha is the linear coefficient of the survival curve. The tumour cell survival was calculated for both 125I and 103Pd seed implants and for different tumour potential doubling time (TPDT) (from 5 days to 30 days) and for edemas of different magnitudes (from 0% to 95%) and edema half-lives (from 4 days to 30 days). Tumour cell survival increased with the increase of edema magnitude and EHL. For a typical edema of a half-life of 10 days and a magnitude of 50%. the edema increased tumour cell survival by about 1 and 2 orders of magnitude for 125I and 103Pd seed implants respectively. At the extreme (95% edema magnitude and an edema half-life of 30 days), the increase was more than 3 and 5 orders of magnitude for 125I and I03Pd seed implants respectively. The absolute increases were almost independent of TPDT and the prostate edema did not significantly change the effective treatment time. Tumour cell survival for prostate undergoing CLDRI using 125I or 103Pd seeds may be increased substantially due to the presence of edema caused by surgical trauma. This effect appears to be more pronounced for 103Pd than 125I because of the shorter half-life of 103Pd. If significant edema is observed post implantation, then a boost to the prostate using external beam radiotherapy may be considered as a part of the treatment strategy.**

**PMID: 11996063 [PubMed - indexed for MEDLINE]**

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**Edema-induced increase in tumour cell survival for 125I and 103Pd prostate permanent seed implants--a bio-mathematical model.**

**April 2002**

**Yue N**

**,**

**Chen Z**

**,**

**Nath R**

**.**

**Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520-8040, USA.**

**Edema caused by the surgical procedure of prostate seed implantation expands the source-to-point distances within the prostate and hence decreases the dose coverage. The decrease of dose coverage results in an increase in tumour cell survival. To investigate the effects of edema on tumour cell survival, a bio-mathematical model of edema and the corresponding cell killing by continuous low dose rate irradiation (CLDRI) was developed so that tumour cell surviving fractions can be estimated in an edematous prostate for both 125I and 103Pd seed implants. The dynamic nature of edema and its resolution were modelled with an exponential function V(T) = V(p)(1 + M exp(-0.693T/ T(e))) where V(p) is the prostate volume before implantation, M is the edema magnitude and T(e) is edema half-life (EHL). The dose rate of a radioactive seed was calculated according to AAPM TG43, i.e. D = SkAg(r)phi(an)/r2, where r is the distance between a seed and a given point. The distance r is now a function of time because of edema. The g(r) was approximated as 1/r(0,4) and 1/r(0.8) for 125I and 103Pd, respectively. By expanding the mathematical expression of the resultant dose rate in a Taylor series of exponential functions of time, the dose rate was made equivalent to that produced from multiple fictitious radionuclides of different decay constants and strengths. The biologically effective dose (BED) for an edematous prostate implant was then calculated using a generalized Dale equation. The cell surviving fraction was computed as exp(-alphaBED), where alpha is the linear coefficient of the survival curve. The tumour cell survival was calculated for both 125I and 103Pd seed implants and for different tumour potential doubling time (TPDT) (from 5 days to 30 days) and for edemas of different magnitudes (from 0% to 95%) and edema half-lives (from 4 days to 30 days). Tumour cell survival increased with the increase of edema magnitude and EHL. For a typical edema of a half-life of 10 days and a magnitude of 50%. the edema increased tumour cell survival by about 1 and 2 orders of magnitude for 125I and 103Pd seed implants respectively. At the extreme (95% edema magnitude and an edema half-life of 30 days), the increase was more than 3 and 5 orders of magnitude for 125I and I03Pd seed implants respectively. The absolute increases were almost independent of TPDT and the prostate edema did not significantly change the effective treatment time. Tumour cell survival for prostate undergoing CLDRI using 125I or 103Pd seeds may be increased substantially due to the presence of edema caused by surgical trauma. This effect appears to be more pronounced for 103Pd than 125I because of the shorter half-life of 103Pd. If significant edema is observed post implantation, then a boost to the prostate using external beam radiotherapy may be considered as a part of the treatment strategy.**

**PMID: 11996063 [**

**PubMed - indexed for MEDLINE**

**]**

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**The impact of edema on planning 125I and 103Pd prostate implants.**

**Yue N**

**,**

**Dicker AP**

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**Nath R**

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**Waterman FM**

**.**

**Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.**

**Permanent transperineal interstitial 125I and 103**

**Pd prostate implants are generally planned to deliver a specific dose to a clinically defined target volume; however, the post-implant evaluation usually reveals that the implant delivered a lower or higher dose than planned. This difference is generally attributed to such factors as source placement errors, overestimation of the prostate volume on CT, and post-implant edema. In the present work we investigate the impact of edema alone. In routine prostate implant planning, it is customary to assume that both the prostate and seeds are static throughout the entire treatment time, and post-implant edema is not taken into consideration in the dosimetry calculation. However, prostate becomes edematous after seed implantation, typically by 50% in volume [Int. J. Radiat. Oncol., Biol., Phys. 41, 1069-1077 (1998)]. The edema resolves itself exponentially with a typical half-life of 10 days. In this work, the impact of the edema-induced dynamic change in prostate volume and seed location on the dose coverage of the prostate is investigated. The total dose delivered to the prostate was calculated by use of a dynamic model, which takes edema into account. In the model, the edema resolves exponentially with time, as reported in a separate study based on serial CT scans [Int. J. Radiat. Oncol., Biol., Phys. 41, 1069-1077 (1998)]. The model assumes that the seeds were implanted exactly as planned, thus eliminating the effect of source placement errors. Implants based on the same transrectal ultrasound (TRUS) images were planned using both 125I and 103Pd sources separately. The preimplant volume and planned seed locations were expanded to different degrees of edema to simulate the postimplant edematous prostate on day 0. The model calculated the dose in increments of 24 h, appropriately adjusting the prostate volume, seed locations, and source strength prior to each time interval and compiled dose-volume histograms (DVH) of the total dose delivered. A total of 30 such DVHs were generated for each implant using different combinations of edema half-life and magnitude. In addition, a DVH of the plan was compiled in the conventional manner, assuming that the prostate volume and seeds were static during treatment. A comparison of the DVH of the static model to the 30 edema corrected DVHs revealed that the plan overestimated the total dose by an amount that increased with the magnitude of the edema and the edema half-life. The maximum overestimation was 15% for 125I and 32% for 103Pd. For more typical edema parameters (a 50% increase in volume and a 10 day half-life) the static plan for 125I overestimated the total dose by about 5%, whereas that for 103Pd overestimated it by about 12%.**

**PMID: 10360539 [**

**PubMed - indexed for MEDLINE**

**]**

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