Prostate volume change after radioactive seed implantation: possible benefit of improved dose volume histogram with perioperative steroid

Patient-specific dose correction for prostate postimplant evaluation with flexible timing of postimplant imaging

PURPOSE

The dosimetric effect of edema on prostate implants have long been realized, but large uncertainties still exist in the estimation of dose actually received by the prostate. This study attempted to develop a new method to accurately estimate dose delivered to the prostate accounting for the variation of prostate volume and seed distribution, edema half-lives, and times for postimplant evaluation.

METHODS AND MATERIALS

A series of prostate seed implants for Cs-131, Pd-103, and I-125 with various prostate volumes were simulated in a water phantom using the TG-43 algorithm on the Varian Eclipse treatment planning system. Dose analysis was performed to derive a quantitative relationship between the prostate peripheral dose and the prostate radius with the variation of prostate volume and seed distribution. Using this relationship to calculate dynamically, the total dose accumulated in the prostate (D_T ) accounting for the variation of prostate volume and seed distribution and edema half-lives. Moreover, the total dose can be estimated statically based on the prostate volume that can be determined in a computerized tomography (CT) image taken at a time after implantation. The statically estimated total dose (D_CT ) was compared with D_T to determine optimal imaging times as well as dose correction factors for other imaging times.

RESULTS

An inverse power law was established between the prostate peripheral dose and prostate radius. The value of the power was 1.3 for Cs-131 and I-125, and 1.5 for Pd-103, respectively. D_T was derived dynamically using the inverse power law. Given the edema half-lives, T_E , of 4, 9.3, and 25 days and the volume expansion of 1.1 and 2.0 times of the prostate without edema, the optimal times for postimplant imaging were: 7, 9, and 16 days for T_E  = 4 days; 10, 14, and 28 days for T_E  = 9.3 days; and 12, 19, 45 days T_E  = 25 days, for Cs-131, Pd-103, and I-125, respectively. D_CT calculated using the prostate volume determined on the optimal days agreed with D_T to 0.0%-1.8% and within 0.3% for most cases. For various prostate volumes, edema half-lives, and nonoptimal times, D_CT was able to achieve a 1% accuracy.

CONCLUSION

The postimplant dose calculation based on the proposed inverse power law for prostate seed implants with edema has improved the accuracy of postimplant dosimetry with accurate and patient-specific dose corrections accounting for prostate size, edema half-life, and postimplant imaging times. Optimal times for postimplant imaging have been accurately determined, and the high accuracy of postimplant dose calculation can be achieved for both optimal imaging times and nonoptimal imaging times.

Predictors of prostate volume reduction following neoadjuvant cytoreductive androgen suppression

Purpose

Limited duration cytoreductive neoadjuvant hormonal therapy (NHT) is used prior to definitive radiotherapeutic management of prostate cancer to decrease prostate volume. The purpose of this study is to examine the effect of NHT on prostate volume before permanent prostate brachytherapy (PPB), and determine associated predictive factors.

Material and methods

Between June 1998 and April 2012, a total of 1,110 patients underwent PPB and 207 patients underwent NHT. Of these, 189 (91.3%) underwent detailed planimetric transrectal ultrasound before and after NHT prior to PPB. Regression analysis was used to assess predictors of absolute and percentage change in prostate volume after NHT.

Results

The median duration of NHT was 4.9 months with inter quartile range (IQR), 4.2-6.6 months. Prostate-specific antigen (PSA) reduced by a median of 97% following NHT. The mean prostate volume before NHT was 62.5 ± 22.1 cm³ (IQR: 46-76 cm³), and after NHT, it was 37.0 ± 14.5 cm³ (IQR: 29-47 cm³). The mean prostate volume reduction was 23.4 cm³ (35.9%). Absolute prostate volume reduction was positively correlated with initial volume and inversely correlated with T-stage, Gleason score, and NCCN risk group. In multivariate regression analyses, initial prostate volume (p < 0.001) remained as a significant predictor of absolute and percent prostate volume reduction. Total androgen suppression was associated with greater percent prostate volume reduction than luteinizing hormone releasing hormone agonist (LHRHa) alone (p = 0.001).

Conclusions

Prostate volume decreased by approximately one third after 4.9 months of NHT, with total androgen suppression found to be more efficacious in maximizing cytoreduction than LHRHa alone. Initial prostate volume is the greatest predictor for prostate volume reduction.

Shape analysis of the prostate: establishing imaging specifications for the design of a transurethral imaging device for prostate brachytherapy guidance

PURPOSE

To examine specific prostate and urethra dimensions and prostate shape to facilitate the design of a transurethral ultrasonographic imaging device.

METHODS AND MATERIALS

Computed tomographic (CT) data sets were retrospectively evaluated from 191 patients who underwent permanent prostate brachytherapy at our institution. The prostate, rectum, urethra, and bladder were each segmented with imaging software. Collected data and calculations included prostate volume at specific distances from the urethra and rectum, distances from seeds to urethra (SU), distances from seeds to rectum (SR), prostate length, and curvilinear prostatic urethra length.

RESULTS

The CT-based, postimplant mean prostate volume was 49cm(3) (range, 22-106cm(3)). Mean prostate length was 4.5cm (range, 3.1-6.0cm). The mean curvilinear length of the prostatic urethra was 4.5cm. The mean (standard deviation) prostatic urethra bend was 29.0° (12.2°). The mean surface distance from the prostate to the urethra was 2.9cm and from the prostate to the rectum w as 4.6cm (p<0.001, paired t test). The mean SU distance was 1.6cm, and the mean SR distance was 2.3cm (p<0.001). In the largest prostate, the mean SU distance was 3.9cm and the mean SR distance was 6.0cm.

CONCLUSIONS

A urethral imaging device for prostate brachytherapy and other minimally invasive prostate therapies should ideally have a 6-cm imaging field of view to image all the prostates in this series in a single image. The mean distance from the SU in permanent prostate brachytherapy is less than 70% of the mean SR distance.

Prostate volume changes during permanent seed brachytherapy: an analysis of intra-operative variations, predictive factors and clinical implication

Background

To determine prostate volume (Pvol) changes at 3 different time points during the course of I¹²⁵ permanent seed brachytherapy (PB). To assess the impact of these changes on acute urinary retention (AUR) and dosimetric outcome.

Methods

We analyzed 149 hormone-naïve patients. Measurements of the prostate volume were done using three-dimensional transrectal ultrasound (3D-TRUS) in the operating room before insertion of any needle (V1), after the insertion of 2 fixation needles with a harpoon (V2) and upon completion of the implant (V3). The quality of the implant was analyzed with the D90 (minimum dose in Grays received by 90% of the prostate volume) at day 30.

Results

Mean baseline prostate volume (V1) was 37.4 ± 9.6 cc. A volume increase of >5% was seen in 51% between V1-V2 (mean = 2.5 cc, p < 0.01), in 42% between V2-V3 (mean = 1.9 cc, p < 0.01) and in 71% between V1-V3 (mean = 4.5 cc, p < 0.01). Pvol changes caused by insertion of the fixation needles were not statistically different than those caused by the implant itself (p = 0.23).

In multivariate linear regression analysis, baseline Pvol is predictive of Pvol changes between V2 and V1 and V3 and V1 but not between V3 and V2. The extent of prostate swelling had an influence on D90. An increase of 10% in prostate volume between V1 and V2 results in an increase of D90 at Day 30 by 11.7%. Baseline Pvol (V1) was the only predictor of the duration of urinary retention in both univariate and multivariate (p = 0.04) regression analysis.

Conclusions

A large part of intraoperative swelling occurs already after the insertion of the fixation needles. This early prostate swelling predicts for D90 but not for AUR.

The impact of prostate edema on cell survival and tumor control after permanent interstitial brachytherapy for early stage prostate cancers

Previous studies have shown that procedure-induced prostate edema during permanent interstitial brachytherapy (PIB) can cause significant variations in the dose delivered to the prostate gland. Because the clinical impact of edema-induced dose variations strongly depends on the magnitude of the edema, the temporal pattern of its resolution and its interplay with the decay of radioactivity and the underlying biological processes of tumor cells (such as tumor potential doubling time), we investigated the impact of edema-induced dose variations on the tumor cell survival and tumor control probability after PIB with the (131)Cs, (125)I and (103)Pd sources used in current clinical practice. The exponential edema resolution model reported by Waterman et al (1998 Int. J. Radiat. Oncol. Biol. Phys. 41 1069-77) was used to characterize the edema evolutions previously observed during clinical PIB for prostate cancer. The concept of biologically effective dose, taking into account tumor cell proliferation and sublethal damage repair during dose delivery, was used to characterize the effects of prostate edema on cell survival and tumor control probability. Our calculation indicated that prostate edema, if not appropriately taken into account, can increase the cell survival and decrease the probability of local control of PIB. The magnitude of an edema-induced increase in cell survival increased with increasing edema severity, decreasing half-life of radioactive decay and decreasing photon energy emitted by the source. At the doses currently prescribed for PIB and for prostate cancer cells characterized by nominal radiobiology parameters recommended by AAPM TG-137, PIB using (125)I sources was less affected by edema than PIB using (131)Cs or (103)Pd sources due to the long radioactive decay half-life of (125)I. The effect of edema on PIB using (131)Cs or (103)Pd was similar. The effect of edema on (103)Pd PIB was slightly greater, even though the decay half-life of (103)Pd (17 days) is longer than that of (131)Cs (9.7 days), because the advantage of the longer (103)Pd decay half-life was negated by the lower effective energy of the photons it emits (∼21 keV compared to ∼30.4 keV for (131)Cs). In addition, the impact of edema could be reduced or enhanced by differences in the tumor characteristics (e.g. potential tumor doubling time or the α/β ratio), and the effect of these factors varied for the different radioactive sources. There is a clear need to consider the effects of prostate edema during the planning and evaluation of permanent interstitial brachytherapy treatments for prostate cancer.

Image fusion techniques in permanent seed implantation

Over the last twenty years major software and hardware developments in brachytherapy treatment planning, intraoperative navigation and dose delivery have been made. Image-guided brachytherapy has emerged as the ultimate conformal radiation therapy, allowing precise dose deposition on small volumes under direct image visualization. In this process imaging plays a central role and novel imaging techniques are being developed (PET, MRI-MRS and power Doppler US imaging are among them), creating a new paradigm (dose-guided brachytherapy), where imaging is used to map the exact coordinates of the tumour cells, and to guide applicator insertion to the correct position. Each of these modalities has limitations providing all of the physical and geometric information required for the brachytherapy workflow. Therefore, image fusion can be used as a solution in order to take full advantage of the information from each modality in treatment planning, intraoperative navigation, dose delivery, verification and follow-up of interstitial irradiation. Image fusion, understood as the visualization of any morphological volume (i.e. US, CT, MRI) together with an additional second morphological volume (i.e. CT, MRI) or functional dataset (functional MRI, SPECT, PET), is a well known method for treatment planning, verification and follow-up of interstitial irradiation. The term image fusion is used when multiple patient image datasets are registered and overlaid or merged to provide additional information. Fused images may be created from multiple images from the same imaging modality taken at different moments (multi-temporal approach), or by combining information from multiple modalities. Quality means that the fused images should provide additional information to the brachytherapy process (diagnosis and staging, treatment planning, intraoperative imaging, treatment delivery and follow-up) that cannot be obtained in other ways. In this review I will focus on the role of image fusion for permanent seed implantation.

Comparison of intraoperative ultrasound with postimplant computed tomography--dosimetric values at Day 1 and Day 30 after prostate brachytherapy

PURPOSE

To compare the results of intraoperative dosimetry with those of postimplant computed tomography (CT)-based dosimetry after (125)I prostate brachytherapy.

METHODS AND MATERIALS

We treated 412 prostate cancer patients with (125)I prostate brachytherapy, with or without external beam radiotherapy at our institution. Neoadjuvant hormone therapy was administered to 331 patients (80.3%). Implantation was performed using an intraoperative interactive technique. Postimplant dosimetry was performed on Day 1 and Day 30 using CT imaging. The dosimetric results for the prostate, urethra, and rectum were compared among intraoperative ultrasound, and CT scans of Day 1 and Day 30.

RESULTS

The mean intraoperative minimal dose received by 90% of the prostate volume (D(90)) was 118.8% of the prescribed dose vs. 106.4% for Day 1 (p < 0.01) and 119.2% for Day 30 (p = 0.25). There were no significant correlations between the intraoperative D(90) and the postimplant D(90) values (intraclass correlation coefficients=0.42 and 0.33 for Day 1 and Day 30, respectively). Prostatic edema at Day 1 had the largest effect on the Day 1 D(90) (p < 0.01). The factor significantly affecting the Day 30 D(90) was neoadjuvant hormone therapy (p < 0.01). The mean Day 30 D(90) for the hormone-treated patients was 117.9%, compared with 124.6% for those who remained hormone naïve. The intraoperative and postimplant dosimetric values differed significantly for the urethra and rectum.

CONCLUSIONS

Our results demonstrate that there are no significant differences between the D(90) assessments obtained intraoperatively and at Day 30 postoperatively. Furthermore, there are no definite correlations between intra- and postimplantation dosimetric values. Other D(90) values differed significantly between the intraoperative and postimplant dosimetry. This study suggests that dosimetry has negligible clinical utility for informing patients, at discharge, of whether or not their implants are adequate.

Effect of Edema on Postimplant Dosimetry in Prostate Brachytherapy Using CT/MRI Fusion

PURPOSE

To investigate the time course of prostatic edema and the effect on the dose-volume histograms of the prostate for patients treated with brachytherapy.

METHODS AND MATERIALS

A total of 74 patients with prostate cancer were enrolled in this prospective study. A transrectal ultrasound-based preplan was performed 4 weeks before implantation and computed tomography/magnetic resonance imaging fusion-based postimplant dosimetry was performed on the day after implantation (Day 1) and 30 days after implantation (Day 30). The prostate volume, prostate volume covered by 100% of the prescription dose (V100), and dose covering 90% of the prostate (D90) were evaluated with prostatic edema over time.

RESULTS

Prostatic edema was greatest on Day 1, with the mean prostate volume 36% greater than the preplan transrectal ultrasound-based volume; it thereafter decreased over time. It was 9% greater than preplan volume on Day 30. The V(100) increased 5.7% from Day 1 to Day 30, and the D90 increased 13.1% from Day 1 to Day 30. The edema ratio (postplan/preplan) on Day 1 of low-quality implants with a V(100) of <80% was significantly greater than that of intermediate- to high-quality implants (>80% V100; p = 0.0272). The lower V100 on Day 1 showed a greater increase from Day 1 to Day 30. A V100 on Day 1 of >92% is unlikely to increase >0% during the interval studied.

CONCLUSION

Low-quality implants on Day 1 were highly associated with edema; however, such a low-quality implant on Day 1, with significant edema, tended to improve by Day 30. If a high-quality implant (V100 >92%) can be obtained on Day 1, a re-examination is no longer necessary.

Comparison of MRI-based and CT/MRI fusion–based postimplant dosimetric analysis of prostate brachytherapy

PURPOSE

The aim of this study was to compare the outcomes between magnetic resonance imaging (MRI)-based and computed tomography (CT)/MRI fusion-based postimplant dosimetry methods in permanent prostate brachytherapy.

METHODS AND MATERIALS

Between October 2004 and March 2006, a total of 52 consecutive patients with prostate cancer were treated by brachytherapy, and postimplant dosimetry was performed using CT/MRI fusion. The accuracy and reproducibility were prospectively compared between MRI-based dosimetry and CT/MRI fusion-based dosimetry based on the dose-volume histogram (DVH) related parameters as recommended by the American Brachytherapy Society.

RESULTS

The prostate volume was 15.97+/-6.17 cc (mean+/-SD) in MRI-based dosimetry, and 15.97+/-6.02 cc in CT/MRI fusion-based dosimetry without statistical difference. The prostate V100 was 94.5% and 93.0% in MRI-based and CT/MRI fusion-based dosimetry, respectively, and the difference was statistically significant (p=0.002). The prostate D90 was 119.4% and 114.4% in MRI-based and CT/MRI fusion-based dosimetry, respectively, and the difference was statistically significant (p=0.004).

CONCLUSION

Our current results suggested that, as with fusion images, MR images allowed accurate contouring of the organs, but they tended to overestimate the analysis of postimplant dosimetry in comparison to CT/MRI fusion images. Although this MRI-based dosimetric discrepancy was negligible, MRI-based dosimetry was acceptable and reproducible in comparison to CT-based dosimetry, because the difference between MRI-based and CT/MRI fusion-based results was smaller than that between CT-based and CT/MRI fusion-based results as previously reported.

Class solution for inversely planned permanent prostate implants to mimic an experienced dosimetrist

The purpose of this paper is to present a method for the selection of inverse planning parameters and to establish a set of inverse planning parameters (class solution) for the inverse planning included in a commercial permanent prostate implant treatment planning system. The manual planning of more than 750 patients since 1996 led to the establishment of general treatment planning rules. A class solution is tuned to fulfill the treatment planning rules and generate equivalent implants. For ten patients, the inverse planning is compared with manual planning performed by our experienced physicist. The prostate volumes ranged from 17 to 51 cc and are implanted with low activity 1-125 seeds. Dosimetric indices are calculated for comparison. The inverse planning needed about 15 s for each optimization (400 000 iterations on a 2.5 GHz PC). In comparison, the physicist needed about 20 min to perform each manual plan. A class solution is found that consistently produces dosimetric indices equivalent or better than the manual planning. Moreover, even with strict seed placement rules, the inverse planning can produce adequate prostate dose coverage and organ at risk protection. The inverse planning avoids implant with seeds outside of the prostate and too close to the urethra. It also avoids needles with only one seed and needles with three consecutive seeds. This reduces the risk of complication due to seed misplacement and edema. The inverse planning also uses a smaller number of needles, reducing the cause of trauma. The quality of the treatment plans is independent of the gland size and shape. A class solution is established that consistently and rapidly produces equivalent dosimetric indices as manual planning while respecting severe seed placement rules. The class solution can be used as a starting point for every patient, dramatically reducing the time needed to plan individual patient treatments. The class solution works with inverse preplanning, intraoperative inverse preplanning, and intraoperative real-time planning. This technology is not intended to replace the physicist but to accelerate the planning process, making intraoperative treatment planning more effective.

Prostatic edema in I125 permanent prostate implants: Dynamical dosimetry taking volume changes into account

The purpose of this study is to determine the impact of edema on the dose delivered to the target volume. An evaluation of the edema characteristics was first made, and then a dynamical dosimetry algorithm was developed and used to compare its results to a standard clinical (static) dosimetry. Source positions and prostate contours extracted from 66 clinical cases on images taken at different points in time (planning, implant day, post-implant evaluation) were used, via the mean interseed distance, to characterize edema [initial increase (deltar0), half-life (tau)]. An algorithm was developed to take into account the edema by summing a time series of dose-volume histograms (DVHs) with a weight based on the fraction of the dose delivered during the time interval considered. The algorithm was then used to evaluate the impact of edema on the dosimetry of permanent implants by comparing its results to those of a standard clinical dosimetry. The volumetric study yielded results as follows: the initial prostate volume increase was found to be 1.58 (ranging from 1.15 to 2.48) and the edema half-life, approximately 30 days (range: 3 to 170 days). The dosimetric differences in D90 observed between the dynamic dosimetry and the clinical one for a single case were up to 15 Gy and depended on the edema half-life and the initial volume increase. The average edema half-life, 30 days, is about 3 times longer than the previously reported 9 days. Dosimetric differences up to 10% of the prescription dose are observed, which can lead to differences in the quality assertion of an implant. The study of individual patient edema resorption with time might be necessary to extract meaningful clinical correlation or biological parameters in permanent implants.

Effect of post-implant edema on prostate brachytherapy treatment margins

PURPOSE

To determine if postimplant prostate brachytherapy treatment margins calculated on Day 0 differ substantially from those calculated on Day 30.

METHODS

Thirty patients with 1997 American Joint Commission on Cancer clinical stage T1-T2 prostatic carcinoma underwent prostate brachytherapy with I-125 prescribed to 144 Gy. Treatment planning methods included using loose seeds in a modified peripheral loading pattern and treatment margins (TMs) of 5-8 mm. Postimplant plain radiographs, computed tomography scans, and magnetic resonance scans were obtained 1-4 hours after implantation (Day 0). A second set of imaging studies was obtained at 30 days after implantation (Day 30) and similarly analyzed. Treatment margins were measured as the radial distance in millimeters from the prostate edge to the 100% isodose line. The TMs were measured and tabulated at 90 degrees intervals around the prostate periphery at 0.6-cm intervals. Each direction was averaged to obtain the mean anterior, posterior, left, and right margins.

RESULTS

The mean overall TM increased from 2.6 mm (+/-2.3) on Day 0 to 3.5 mm (+/-2.4) on Day 30. The mean anterior margin increased from 1.2 mm on Day 0 to 1.8 mm on Day 30. The posterior margin increased from 1.2 mm on Day 0 to 2.8 mm on Day 30. The lateral treatment margins increased most over time, with mean right treatment margin increasing from 3.9 mm on Day 0 to 4.7 mm on Day 30.

CONCLUSION

Treatment margins appear to be durable in the postimplant period, with a clinically insignificant increase from Day 0 to Day 30.

Sequential evaluation of prostate edema after permanent seed prostate brachytherapy using CT-MRI fusion

PURPOSE

To analyze the extent and time course of prostate edema and its effect on dosimetry after permanent seed prostate brachytherapy.

METHODS AND MATERIALS

Twenty patients scheduled for permanent seed (125)I prostate brachytherapy agreed to a prospective study on postimplant edema. Implants were preplanned using transrectal ultrasonography. Postimplant dosimetry was calculated using computed tomography-magnetic resonance imaging (CT-MRI) fusion on the day of the implant (Day 1) and Days 8 and 30. The prostate was contoured on MRI, and the seeds were located on CT. Factors investigated for an influence on edema were the number of seeds and needles, preimplant prostate volume, transitional zone index (transition zone volume divided by prostate volume), age, and prostate-specific antigen level. Prostate dosimetry was evaluated by the percentage of the prostate volume receiving 100% of the prescribed dose (V(100)) and percentage of prescribed dose received by 90% of the prostate volume (D(90)).

RESULTS

Prostate edema was maximal on Day 1, with the median prostate volume 31% greater than preimplant transrectal ultrasound volume (range, 0.93-1.72; p < 0.001) and decreased with time. It was 21% greater than baseline at Day 8 (p = 0.013) and 5% greater on Day 30 (p < 0.001). Three patients still had a prostate volume greater than baseline by Day 30. The extent of edema depended on the transition zone volume (p = 0.016) and the preplan prostate volume (p = 0.003). The median V(100) on Day 1 was 93.6% (range, 86.0-98.2%) and was 96.3% (range, 85.7-99.5%) on Day 30 (p = 0.079). Patients with a Day 1 V(100) >93% were less affected by edema resolution, showing a median increase in V(100) of 0.67% on Day 30 compared with 2.77% for patients with a V(100) <93 % on Day 1.

CONCLUSION

Despite the extreme range of postimplant edema, the effect on dosimetry was less than expected. Dose coverage of the prostate was good for all patients during Days 1-30. Our data indicate that postimplant dosimetry on the day of implant is sufficient for patients with good dose coverage (Day 1 V(100) >93%).

Prostate volume before and after permanent prostate brachytherapy in patients receiving neoadjuvant androgen suppression

PURPOSE

Limited duration neoadjuvant cytoreductive hormonal therapy (NHT) is used before the definitive radiotherapeutic management of prostate cancer to decrease target volume size and/or to decrease urinary obstructive symptoms. The purpose of this study is to examine the effect of NHT on prostate volume before permanent prostate brachytherapy (PPB) and on prostatic edema after PPB.

METHODS AND MATERIALS

Between May 1998 and February 2004, 408 patients underwent PPB at our institution and provided research authorization for the use of their records. Of these, 122 (30%) underwent NHT. Of the 122, 78 (64%) underwent transrectal ultrasound before the start of NHT. Patients undergoing PPB who received NHT were compared with a similar non-NHT group (N = 286). Detailed measurements of prostate volume were performed by transrectal ultrasound before and after NHT, if applicable. In addition, intraoperative preimplantation transrectal ultrasound and post-implantation transrectal ultrasound were also performed. Post-implantation computed tomography was per formed within 1 day of PPB.

RESULTS

The mean duration of NHT was 4.0 +/- 1.1 months (range, 1-8 months). The mean prostate volume before NHT was 63.3 +/- 22.8 cc (range, 19-138 cc), and after NHT (before PPB), it was 41.6 +/- 16.4 cc (18-98 cc). The median prostate volume decrease after NHT was 22.7 cc or 34.9%. There was no significant difference in the degree of postimplantation prostate edema, as measured by the postimplantation to preimplantation ratio (1.18 +/- 0.05 [range, 0.8-1.9]) for the NHT group and 1.21 +/- 0.03 (range, 0.8-1.9) for the non-NHT group (P = 0.5).

CONCLUSIONS

Prostate volume decreased by approximately one third after 4 months of NHT. NHT did not affect the degree of post-PPB prostatic edema.

Does anesthesia method affect implant-induced prostate swelling?

OBJECTIVES

To investigate the impact of anesthesia selection on prostate gland swelling, acute toxicity, and implant quality. The outcome of prostate brachytherapy is dependent on the dose intensity and distribution. Preoperative and intraoperative planning are intended to optimize radiation delivery, but do not account for the impact of postoperative swelling on interseed spacing. Factors that increase swelling can be expected to increase the disparity between the intended and actual dose delivery. General anesthesia has been implicated in increased intraoperative bleeding during prostate surgery.

METHODS

All iodine prostate implants planned and performed by the same radiation oncologist during a defined period were retrospectively reviewed. Excluded from the study were patients who had undergone preimplantation external beam radiotherapy or androgen deprivation. The remaining cases were analyzed to determine any association between the anesthesia type (general or spinal) and an increase in gland volume (from mapping transrectal ultrasonography to immediate postoperative computed tomography), implant quality (dosimetrically determined by minimal dose received by 90% of the volume [D90] and volume receiving 100% of prescribed dose [V100]), and acute toxicity (urinary retention, perineal/scrotal bruising).

RESULTS

A total of 83 implants met the inclusion criteria. The outcomes did not significantly differ in regard to the median volume increase (23% versus 23.5%), D90 (115% versus 113%), V100 (97% versus 96.5%), acute urinary retention (3% versus 4%), or incidence or severity of perineal or scrotal bruising. No correlation was found between anesthesia type and any of the studied outcomes.

CONCLUSIONS

Although only a prospective, randomized trial can definitively answer the question, our results suggest that the anesthesia selection for prostate brachytherapy does not influence prostate swelling, acute toxicity, or implant dosimetric quality.

Image guided I125 prostate brachytherapy with Hybrid Interactive Mick technique in the community setting: How does it compare?

The aim of this study is to evaluate the target coverage, procedural techniques, and merits of Hybrid Interactive Mick (HIM) I125 transperineal permanent implantation (TPPI) of the prostate performed with 10 urologists in a community hospital. Detailed day 0 post-implant dosimetric evaluations of TPPI procedures were performed on 333 consecutive monotherapy patients treated between September 2000 and November 2003 at a single institution. All patients underwent TPPI with HIM. Pelvic and CXR films were obtained for a manual seed count at day 0 and again > day 90 on 175 patients. The HIM-prostate brachytherapy performed in a community hospital provided median D(90), V100, and V150 values of 157Gy, 94%, and 42.3%, respectively. 18% of patients had seed migration to the lungs while 2% had seed migration to the bladder. Only 7 patients (4%) had 2 or more seeds migrate to the lungs. Procedure times average 38 minutes and number of needles used averaged 18. The post-implant urinary retention rate was 2.1% Use of HIM-prostate brachytherapy in the community setting with multiple urologists reproducibly maintained excellent and consistent dosimetric coverage. Procedure times and number of needles used were minimized, and with careful attention to image-guided technique, seed migration to bladder and lung was also minimized.

Prostate volume measurement by transrectal ultrasound and computed tomography before and after permanent prostate brachytherapy

PURPOSE

To quantify prostate volume (pvol) changes with transrectal ultrasound (TRUS) immediately after permanent prostate brachytherapy (PPB) and to correlate these changes with postimplant computed tomography (CT) volumetrics. To provide data relevant to evaluating the potential of TRUS-based image fusion for intraoperative dosimetry.

METHODS AND MATERIALS

Between July 2000 and January 2003, 177 patients underwent (125)I PPB monotherapy at our institution, and 165 patients provided research authorization. A total of 136 patients (82%) completed 4 imaging studies: planning TRUS, intraoperative pre- and postimplant TRUS, and CT.

RESULTS

Mean planning TRUS pvol was 38.7 +/- 11.7 cc standard deviation (SD), 95% confidence interval (CI) (36.7, 40.7). Mean intraoperative TRUS pvol preimplant was 37.1 +/- 11.7 cc SD, 95% CI (35.1, 39.0), and postimplant was 44.5 +/- 15.1 cc SD, 95% CI (42.0, 47.1). The mean ratio of postimplant:preimplant intraoperative TRUS pvols was 1.2 +/- 0.2 SD, 95% CI (1.18, 1.24), and the difference in mean values was 7.5 cc (p < 0.0001). CT performed within 1 day revealed a mean pvol of 47.9 +/- 15.7 cc SD, 95% CI (45.2, 50.5). The mean volumetric ratio of CT to postimplant TRUS pvol was 1.13 +/- 0.36, 95% CI (1.07-1.19).

CONCLUSIONS

Whereas mean preimplant step-section TRUS pvol measurements are similar, postimplant TRUS and CT measurements have greater variability that depend on initial pvol. CT-based pvol measurements determined a mean of 10.6 hours after implant were more likely to be identical to those of immediate postimplant TRUS in prostates >33 cc. These data are relevant for establishing accuracy in image-fusion based approaches being investigated for real-time intraoperative PPB dosimetry.

The effect of the radial function on I-125 seeds used for permanent prostate implantation

The purpose of this study was to evaluate the integrity of eight commercially-available low-activity Iodine-125 (125I) seeds for their radial function g(r) and its effect on the dose delivered to the adjacent critical structures when used in permanent prostate implants (PPI). Ten previously treated patients were retrospectively used in this comparison. The Amersham Health Oncura seed was used to peripherally design an isodose distribution with urethral and anterior rectal wall sparing. Plan criteria included minimum coverage of 144 Gy to the planning target volume (PTV), < or = 70% dose to 150% of the PTV volume (V150-PTV), and the quantity of needles < or = 70% of the size of the PTV, in cc. Upon completion of the Oncura plan, the seed type was changed and the activity was adjusted until the V100-PTV for each of the other 7 seed types matched the V100-PTV defined by the Oncura seed. Computed tomography (CT)-based postimplant dosimetry was used to determine the dose to 40% (D40) of the bulb of the penis (in Gy). Dose-volume histograms (DVH) were used to evaluate the differences to V100 (in %) and D40 (in Gy) of the anterior rectal wall and bulb of the penis, and V100 (in %) of the urethra. The data was tabulated. Radioactive 125I sources included in this study were 125I Source 2301 (Best); I-Plant (MedTech), IoGold (Mentor), Oncura (Amersham Health), ProstaSeed (UroCor), SelectSeed (Nucletron), SourceTech (Bard), and Symmetra (UroMed). The sizes of the PTV for the 10 patients ranged from 18.82 cc to 48.99 cc. The Oncura seed was used as the reference seed and all other seed types were normalized to it for data comparison. It was determined that the dose rate constant (Delta) and anisotropy factor (phi) contribute to the activity needed to achieve comparable V100-PTV doses, but a strong dependence on the radial function g(r) was found to effect the doses to the critical structures studied. Values of g(r) at 4 cm were calculated and the IoGold and SourceTech seeds were determined to have the highest g(r) values, with ProstaSeed and SelectSeed having the lowest values. 125I Source 2301 and IoGold required less activity per seed to achieve the same dose to the V100-PTV due to the higher dose rate and anisotrophy constants (Delta.phi). The seed types with silver were less penetrating and resulted in the production of characteristic x-rays that modified the energy spectrum and influenced the radial function. The seeds requiring the lowest activity showed the highest dose to the anterior rectal wall, a posterior adjacent structure; the urethra, an interior structure; and the bulb, an inferior structure. This study was designed to investigate the integrity of eight different commercially-available seed types, and their dependence on the g(r) in seed choice. It was determined that the dose rate constant and anisotropy factor determine the activity needed for implantation but a strong dependence on the radial function was found to effect the doses to the adjacent structures.

MRI-CT fusion to assess postbrachytherapy prostate volume and the effects of prolonged edema on dosimetry following transperineal interstitial permanent prostate brachytherapy

PURPOSE

Quality assurance through postplan assessment is an integral part of permanent seed prostate implants. The use of MRI-CT fusion for 1-month postimplant dosimetry permits accurate assessment of prostate volume without seed induced artifact and uncertainties of prostate contour inherent to CT assessments. Routine use of MRI-CT fusion reveals significant prostate edema may persist several weeks. This study evaluates the effect of edema, and its subsequent resolution, on dosimetry.

METHODS AND MATERIALS

From May 2001 to June 2003, 241 men were treated with (125)I seed implants based on a transrectal ultrasound (TRUS) preplan. Quality assessment was performed at 1 month by CT-MRI fusion using VariSeed software. Over this 24-month period, 29 patients (12%) with residual edema at 1 month (12-60% >TRUS plan volume), had repeat CT-MRI fusion at 2-4 months to reassess volume and dosimetry. Eleven of the 29 had received prior androgen ablation to shrink the prostate preimplant.

RESULTS

For the entire group (n = 241), mean preimplant prostate volume was 33.7 cc and median postplan dosimetric parameters were: V100, 92.2%; D90, 153 Gy; and V150, 53%. For the 29 patients with prolonged edema, mean preimplant volume was 34.8 cc and 1-month volume was 46.1 cc (p <0.001). Mean volume reduction between 1 and 2 months was 13%. The decrease in prostate volume had a significant effect on dosimetry with median increase between 1 month and 2 months in calculated V100 of 9.5%, V150 22.6%, V200 30.1%, and D90 11.5%.

CONCLUSIONS

Significant residual edema is seen 1-month postimplant in 12% of prostates and may have a profound effect on dosimetry. Further study is underway to characterize the time course of resolution of the edema, and to perform integral dosimetry based on the changing volume.

Dosimetric consequences of using a surrogate urethra to estimate urethral dose after brachytherapy for prostate cancer

PURPOSE

To assess the accuracy and dosimetric consequences of defining a surrogate urethra at the geometric center of the prostate in postimplant CT scans.

METHODS AND MATERIALS

Eighty postimplant CT scans were obtained with a Foley catheter in place at Day 0 and at 1 month for 40 patients who had undergone (125)I prostate brachytherapy. The percentage of urethral volume receiving at least 275% of the prescribed dose (uV(275)), uV(250), uV(200), uV(150), maximal dose received by 90% of urethral volume (uD(90)), uD(70), uD(30), and uD(1) were measured for the Foley catheter and surrogate urethra. The distance between the Foley catheter and surrogate urethra was measured at the base, middle, and apex of the prostate.

RESULTS

A statistically significant difference was found in all the above-listed dosimetric parameters between the Foley catheter and surrogate urethra at Day 0 (p <or= 0.001). At 1 month, the uD(90), uD(70), and uD(1) remained significantly different between the Foley catheter and surrogate urethra (p <or= 0.05). The difference in the uV(275) (p = 0.055) and uV(150) (p = 0.059) between the Foley catheter and surrogate urethra showed a trend toward statistical significance at 1 month. The uV(250), uV(200), and uD(30) were greater for the surrogate urethra than for the Foley catheter at 1 month, but were not significantly different statistically. The mean distance between the Foley catheter and the surrogate urethra was greatest at the base (1.2 cm) in the vertical axis at Day 0 and decreased substantially to 0.87 cm at 1 month (p = 0.0004).

CONCLUSION

Using a surrogate urethra at the geometric center of the prostate may significantly overestimate the urethral dose at Day 0 and certain dosimetric parameters at 1 month. An alternative position for a surrogate urethra accounting for the difference in the location of the Foley catheter near the base of the prostate at Day 0 and 1 month could be considered in future studies.

Isodose patterns in patients with inadequate prostate brachytherapy coverage

PURPOSE

The development of a practical, real-time dosimetry system should result in improved implant dose distributions and higher prostate cancer control rates. Our purpose here is to demonstrate that intraoperative isodose reconstruction in relation to the seed distribution, even without accurate registration with the prostatic volume, can likely identify an inadequate implant intraoperatively and guide corrective seed placement.

METHODS AND MATERIALS

A total of 102 Pd-103 implants performed by standard techniques, using a modified peripheral loading pattern, were studied. A postimplant computed tomography (CT) scan was obtained 2-4 h after the implant. The contoured images and sources were entered into a Varian Variseed 7.0 treatment planning system. Dosimetric parameters analyzed included the percent of the postimplant prostate or rectal volume covered by the prescription dose (V100), and the dose that covers 90% of the postimplant prostate volume (D90). Isodose patterns were analyzed at midprostate, and for the entire prostate. Adverse isodose patterns were defined as gaps, holes, islands. Isodose gaps are subprescription intervals between the prostatic margin and the prescription isodose. Isodose holes are regions of subprescription dose within the prostate. Isodose islands are isolated regions > or =prescription dose inside the prostatic margins.

RESULTS

Characteristic isodose patterns were predictive for V100 values. Midprostatic isodose holes were seen in 55% of patients with a V100 < 80%, 5% of patients with a V100 of 80-90%, and only 1% of patients with a V100 > 90%. When analyzing the entire prostate, isodose holes were seen in 55% of patients with a V100 < 80%, 18% of patients with a V100 of 80-90%, and 9% of patients with a V100 > 90%. Midprostatic isodose islands were seen in 55% of patients with a V100 < 80%, 5% of patients with a V100 of 80-90%, and no patient with a V100 > 90%. When analyzing the entire prostate, isodose islands were seen in all patients with V100 < 80%, 36% of patients with a V100 of 80-90%, and only 1% of patients with a V100 > 90%. The likelihood of a V100 less than 80% was best predicted by the presence of isodose holes or islands at midprostate. Patients with either finding had an 86% chance of having a V100 < 80%.

CONCLUSIONS

These semiquantitative findings can provide practical guidelines for intraoperative dosimetry, to provide a more rational guide to intraoperative postimplant assessment and modification. If isodose holes or islands are seen within the implanted volume, additional seeds are added to the affected region to obtain a V100 > 80%.

Corticosteroid use after prostate brachytherapy reduces the risk of acute urinary retention

OBJECTIVES

To evaluate the role of short-term steroids after prostate brachytherapy to reduce oedema and thus the risk of urinary retention associated with brachytherapy, as this can require surgical intervention and may even result in incontinence.

PATIENTS AND METHODS

A retrospective review was conducted on 400 consecutive patients with early-stage prostate cancer who underwent ultrasonography-guided transperineal brachytherapy. Androgen deprivation was given to 146 patients for 3 months before the implant and 280 received a 2-week course of dexamethasone (4 mg twice daily for 1 week then 2 mg twice daily). Forty-five patients developed acute urinary retention at a median of 12 days after implantation. Univariate and multivariate analyses were used to evaluate the potential risk factors for urinary retention.

RESULTS

Acute urinary retention developed in 11.1% of the patients and the risk was predicted by increasing prostate volume at the time of diagnosis. This risk was higher (18.8%) for men receiving no dexamethasone and lower (8.2%) for those who did. In the multivariate analysis the volume at diagnosis and the use of dexamethasone remained significant. The use of steroids counterbalanced the effect of increasing prostate volume on the incidence of retention. The risk of retention was higher in those men receiving androgen deprivation to shrink their prostates than in those whose prostates were of suitable size for implantation at the time of diagnosis.

CONCLUSION

Reducing prostate volume by androgen deprivation before brachytherapy may be less important in preventing brachytherapy-related urinary retention than the use of corticosteroids to reduce oedema afterward.

Celecoxib to decrease urinary retention associated with prostate brachytherapy

PURPOSE

To retrospectively evaluate the effect of celecoxib in preventing urinary retention following prostate brachytherapy.

MATERIALS AND METHODS

Between December 1997 and November 2001, 149 patients underwent a prostate implant. Medical records were reviewed to identify those who had acute urinary retention after the procedure. Urinary retention was scored based on replacement of the urinary catheter and the number of calls to the clinic and/or unscheduled clinic visits within 1 month after the implant.

RESULTS

The use of celecoxib was associated with a decreased need for replacement of the catheter (p=.04) and decreased number of calls to the clinic and/or unscheduled clinic visits (p=.002). No patient who was given celecoxib for 1 week before brachytherapy required a urinary catheter compared to 14 (of 120) who did not receive celecoxib.

CONCLUSIONS

The use of celecoxib appears to result in decreased urinary retention following prostate brachytherapy.

Predictive factors of urinary retention following prostate brachytherapy

PURPOSE

To evaluate the incidence and duration of urinary retention requiring catheterization and the factors predictive for these end points.

METHODS AND MATERIALS

Two hundred eighty-two patients treated with prostate brachytherapy alone were evaluated. Clinical and treatment-related factors examined included: age, baseline International Prostate Symptom Score (IPSS), presence of comorbidity, planning ultrasound target volume (PUTV), postimplant prostate CT scan volume, the CT:PUTV ratio, number of seeds inserted, number of needles used, use of neoadjuvant hormones, procedural physician, clinical stage, Gleason score, and pretreatment PSA. Dosimetric quality indicators were also examined.

RESULTS

Urinary obstruction after prostate brachytherapy developed in 43 (15%) patients. The median duration of catheter insertion was 21 days (mean 49, range 1-365). Univariate analysis demonstrated that presence of diabetes, preimplant volume, postimplant volume, CT:PUTV ratio, number of needles, and dosimetric parameters were predictive for catheterization. However, in multivariate analysis, only the baseline IPSS, CT:PUTV ratio, and presence of diabetes were significant independent predictive factors for catheterization.

CONCLUSION

Baseline IPSS was the most important predictive factor for postimplantation catheterization. The extent of postimplant edema, as reflected by the CT:PUTV ratio, predicted for need and duration of catheterization. The presence of diabetes was predictive for catheterization, but may relate to the absence of prophylactic steroids, and therefore requires further evaluation.

Risk factors for acute urinary retention requiring temporary intermittent catheterization after prostate brachytherapy: a prospective study

PURPOSE

We prospectively investigated prognostic factors for men undergoing transperineal radioactive seed implantation for prostate cancer at the University of Washington.

METHODS AND MATERIALS

Between February and April, 1998, 62 consecutive unselected patients were prospectively followed after brachytherapy for early-stage prostate adenocarcinoma. Pretreatment variables included age, American Urological Association (AUA) score, uroflowimetry, and prostate volume by ultrasound. Nonrandomized variables included hormonal therapy, seed type, and use of pelvic radiotherapy. Patients were contacted by phone at one week postoperatively and at one-month intervals thereafter. Follow-up continued until all patients provided the date of last catheterization.

RESULTS

Urinary retention rate at one week was 34% (21 of 63 patients). At one month, 29%; at three months, 18%; and at six months, 10%. Preoperative flow rate and post-void residual did not predict for retention (p =.48 and p =.58). Use of alpha blockers, hormonal therapy, type of seed (103Pd or 1251), or external beam radiotherapy had no impact on risk of retention at any followup point. Preimplant volume and AUA score predicted for retention on univariate analysis, but on multivariate analysis only postimplant volume remained significant (p =.02) for predicting retention risk and duration.

CONCLUSION

Patients with large prostate size (>36 g) and higher AUA score (>10) appear to be at greater risk of risk of retention as well as duration of retention as defined in our study. Further investigation will be needed to clarify the risk of urinary retention for men undergoing brachytherapy.