Comparison between postoperative TRUS-CT fusion with MRI-CT fusion for postimplant quality assurance in prostate LDR permanent seed brachytherapy

PURPOSE/OBJECTIVE Permanent seed Low-Dose-Rate brachytherapy is planned and delivered using transrectal ultrasound (TRUS). Post-implant evaluation for quality assurance is usually performed using Computed Tomography (CT). Registration of the CT images with MRI reduces subjectivity in contouring by improving prostate edge detection. We hypothesized that a set of TRUS images post procedure may provide the same benefit.MATERIAL/METHODS Consecutive patients undergoing Low-Dose-Rate prostate brachytherapy were recruited. TRUS images were recorded under anesthesia at completion of their implant. In addition, all patients underwent standard post-implant quality assurance including prostate CT and MRI at day 30. These were co-registered, contoured and seeds were identified. Three independent observers contoured and registered the post implant TRUS images to the Day 30 CT using seed matching. Prostate volumes and dosimetric parameters were compared through Intraclass Correlation Coefficient (ICC) to evaluate the concordance between MRI and ultrasound (US).RESULTS 26 patients were recruited from 10/17 to 01/18. Mean prostate volume was 34.5 (SD 10.8) cm³ at baseline on planning TRUS images, 37.4 (SD 11.3) cm³ on Day 0 post implant TRUS and 36.7 (SD 11.7) cm³ on Day 30 MRI. D90 was 112.6% (SD 9.3) on CT-MRI and 112.9% (SD 11.1) on CT-US. V100 was 94.6% (SD 3.8) for CT-MRI, 95.1% (SD 4.3) for CT-US. Student t-tests were used to compare groups. No significant differences were noted.CONCLUSION Post implant TRUS may be useful for quality assurance for post-implant dosimetry particularly if access to an MRI is limited.     

The effect of interobserver variability on transrectal ultrasonography-based postimplant dosimetry

PURPOSE: To investigate interobserver variability in contouring the prostate on postimplant transrectal ultrasonography (TRUS) images and its effect on dosimetric parameters that quantify implant quality. METHODS AND MATERIALS: Twenty preplanned peripherally loaded prostate implants were performed using 125I seeds and spacers linked together in linear arrays that maintain precise seed spacing and prevent seeds from rotating about their longitudinal axis. A set of two-dimensional transverse images spaced at 0.50-cm intervals was obtained with a high-resolution TRUS probe at the conclusion of the procedure with the patient still under anesthesia. A high percentage of the seeds (> 85%) were localized based on their visible echoes. The remaining seeds were identified based on the known locations of the "missing" seeds in the arrays. Two experienced ultrasonographers and a prostate brachytherapist independently contoured the prostate on the postimplant TRUS images. The prostate volumes defined by each observer were used to calculate the minimal dose received by 90% of the prostate volume (D90) and the percentage of the prostate volume receiving 100% of the prescribed minimal peripheral dose (V100). The observers also contoured the prostate on six preimplant TRUS studies to compare the variability in defining the prostate on pre- and postimplant TRUS images. RESULTS: The mean postimplant prostate volumes ranged from 20.8 to 66.9 cm3 (median: 45.7 cm3). The standard deviations (SDs), which reflect the variation in the volumes of the three observers, ranged from 1.4% to 26.1% of the mean (median: 11%). Multiple pairwise comparisons showed that the prostate volumes delineated by observer 3 differed significantly from those of observers 1 and 2 (p < 0.003). The volumes of observers 1 and 2 were not significantly different (p > 0.5). The mean values of D90 ranged from 124.2 to 171.1 Gy (median: 154.7 Gy) having SDs that ranged from 0.6% to 24.4% of the mean D90 (median: 7.8%). The mean values of V100 ranged from 82.3% to 95.1% (median: 92.8%) having SDs that ranged from 0.4% to 11.2% of the mean V100 (median: 4.0%). The values of both D90 and V100 calculated from the volumes of observer 3 were significantly (p < 0.003) different from those of observers 1 and 2, which did not differ significantly (p > 0.5). There was less interobserver variability in contouring the preimplant TRUS volumes. The mean volumes ranged from 20.3 to 54.3 cm3 having SDs that ranged from 1.9% to 14.1% (median: 8.6%). CONCLUSIONS: Significant interobserver differences in delineating the prostate volume on postimplant TRUS images were observed; however, these differences were less than generally reported for postimplant CT images. The interobserver differences in contouring the prostate in both TRUS and CT images produced significant differences in the dosimetric parameters, D90 and V100.     

Comparative study of dosimetry between high-dose-rate and permanent prostate implant brachytherapies in patients with prostate adenocarcinoma

PURPOSE: To compare the dose coverage, conformity, and homogeneity between high-dose-rate (HDR) brachytherapy and permanent prostate implant (PPI) in the treatment of prostate adenocarcinoma. METHODS AND MATERIALS: From January 2003 to August 2004, 54 patients (108 implants) underwent HDR brachytherapy of prostate cancer with iridium-192 stepping source. Of patients who underwent PPI brachytherapy with iodine-125, 72 patients were randomly selected for the purpose of dosimetric comparison. PPI preplan was done based on transrectal ultrasound study, and postplan was done using CT 1 month after implant. Dosimetric parameters of HDR were compared to that of PPI preplan and postplan. RESULTS: HDR brachytherapy had lower D90 (111.5% vs. 120.2%), lower V100 (97.2% vs. 99.6%), lower natural dose ratio (1.03 vs. 1.13), higher conformal index (0.69 vs. 0.62), and higher homogeneity index (0.63 vs. 0.52) than PPI preplan (all p < 0.0001). All the dosimetric parameters of PPI postplan including D90 (86.7%), V100 (82.0%), natural dose ratio (0.92), conformal index (0.53), and homogeneity index (0.42) were inferior to HDR brachytherapy (all p < 0.0001). CONCLUSIONS: HDR brachytherapy of the prostate can provide better dose coverage, conformity, and homogeneity compared to PPI.     

Impact of selection of post-implant technique on dosimetry parameters for permanent prostate implants

PURPOSE: To investigate the variability of prostate implant quality indices between three different methods of calculating the post-implant dose distribution. METHODS AND MATERIALS: In a study of 9 permanent prostate implant patients, post-implant dosimetry was carried out using three methods of identifying seed positions within the prostate volume: (1) prostate volumes defined by transrectal ultrasound (TRUS) immediately following implant were registered with shift-film defined seed positions, (2) seeds were identified directly from the post-implant TRUS images, and (3) CT was used to define seed positions and prostate volumes from images acquired at 41-65 days post-implant. For each method, the volume of prostate receiving 90%, 100%, and 150% of the prescribed dose (V90, V100, V150) and the dose delivered to 90% of the prostate volume (D90) were calculated. RESULTS: Post-implant TRUS volumes were within 15% of the preimplant TRUS volumes in 8 of the 9 patients investigated. The post-implant CT volume was within 15% of the preimplant (TRUS) volume in only 3 of the 9 cases. The value of the dosimetry parameters was dependent on the method used and varied by 5-25% for V90, 5-30% for V100, 42-134% for V150, and 9-60% for D90. No simple relationship was found between change in volume and the resultant change in dosimetry parameter. Differences in dosimetry parameters due to source localization uncertainties was found to be small (< or = 10% for V100) when comparing methods (1) and (2). CONCLUSIONS: There are many uncertainties in the calculation of parameters that are commonly used to describe the quality of a permanent prostate implant. Differences in the parameters calculated were most likely a result of a combination of factors including uncertainties in delineating the prostate with different imaging modalities, differences in source identification techniques, and intraobserver variability.     

Prostate brachytherapy intraoperative dosimetry using a combination of radiographic seed localization with a C-arm and deformed ultrasound prostate contours

PurposeThe purpose of the study was to assess the feasibility of performing intraoperative dosimetry for permanent prostate brachytherapy by combining transrectal ultrasound (TRUS) and fluoroscopy/cone beam CT [CBCT] images and accounting for the effect of prostate deformation.Methods and Materials13 patients underwent TRUS and multiview two-dimensional fluoroscopic imaging partway through the implant, as well as repeat fluoroscopic imaging with the TRUS probe inserted and retracted, and finally three-dimensional CBCT imaging at the end of the implant. The locations of all the implanted seeds were obtained from the fluoroscopy/CBCT images and were registered to prostate contours delineated on the TRUS images based on a common subset of seeds identified on both image sets. Prostate contours were also deformed, using a finite-element model, to take into account the effect of the TRUS probe pressure. Prostate dosimetry parameters were obtained for fluoroscopic and CBCT-dosimetry approaches and compared with the standard-of-care Day-0 postimplant CT dosimetry.ResultsHigh linear correlation (R² > 0.8) was observed in the measured values of prostate D_90%, V_100%, and V_150%, between the two intraoperative dosimetry approaches. The prostate D_90% and V_100% obtained from intraoperative dosimetry methods were in agreement with the postimplant CT dosimetry. Only the prostate V_150% was on average 4.1% (p-value <0.05) higher in the CBCT-dosimetry approach and 6.7% (p-value <0.05) higher in postimplant CT dosimetry compared with the fluoroscopic dosimetry approach. Deformation of the prostate by the ultrasound probe appeared to have a minimal effect on prostate dosimetry.ConclusionsThe results of this study have shown that both of the proposed dosimetric evaluation approaches have potential for real-time intraoperative dosimetry.     

Sector analysis of dosimetry of prostate cancer patients treated with low-dose-rate brachytherapy

PurposeBrachytherapy is an effective single treatment modality for low- and intermediate-risk prostate cancer. Here, we compare the radiation doses in different prostate sectors between the preimplant planning images and the postimplant dosimetry.Methods and MaterialsTwo hundred fifteen consecutive patients treated for prostate cancer by ¹²⁵I seed brachytherapy were assessed. Pretreatment plans using transrectal ultrasound images of the prostate were compared with the dose calculated on posttreatment MRI and CT scans obtained 1 month after seed implantation. Twelve sectors were generated by dividing the prostate base, midgland, and apex into four quadrants each. Pretreatment and posttreatment dosimetry were compared between the 12 different sectors of the prostate.ResultsAverage V₁₀₀ (percentage of prostate volume that receives 100% of the prescribed dose) in the preimplant planning images of the prostate was 99.9 ± 0.25% compared with postimplant V₁₀₀ of 94.8 ± 3.77% (p < 0.0001). Prostate V₁₀₀ in the postimplant dosimetry was >91% in all sectors, except the anterior base sector, in which it was 64.87 ± 20.96%. Average 1-month D₉₀ (the dose to 90% of the prostate volume) was 114.5 ± 10.55%. D₉₀ at 1 month compared with preimplant planning was lower in the prostate base and higher in the prostate apex (p < 0.001).ConclusionsOur results show that in ¹²⁵I seed brachytherapy, prostate base receives a lower dose and apex receives a higher dose compared with preimplant planned dose coverage.     

Evaluation of Dose-Volume Histograms after Prostate Seed Implantation

BACKGROUND AND PURPOSE: Permanent interstitial brachytherapy by seed implantation is a treatment alternative for low-volume low-risk prostate cancer and a complex interdisciplinary treatment with a learning curve. Dose-volume histograms are used to assess postimplant quality. The authors evaluated their learning curve based on dose-volume histograms and analyzed factors influencing implantation quality. PATIENTS AND METHODS: Since 1999, 38 patients with a minimum follow-up of 6 months were treated at the authors' institution with seed implantation using palladium-103 or iodine-125, initially using the preplan method and later real-time planning. Postimplant CT was performed after 4 weeks. The dose-volume indices D90, V100, V150, the Dmax of pre- and postplans, and the size and position of the volume receiving the prescribed dose (high-dose volume) of the postplans were evaluated. In six patients, postplan imaging both by CT and MRI was used and prostate volumes were compared with preimplant transrectal ultrasound volumes. The first five patients were treated under external supervision. RESULTS: Patients were divided into three consecutive groups for analysis of the learning curve (group 1: n = 5 patients treated under external supervision; group 2: n = 13 patients; group 3: n = 20 patients). D90post for the three groups were 79.3%, 74.2%, and 99.9%, the V100post were 78.6%, 73.5%, and 88.2%, respectively. The relationship between high-dose volume and prostate volume showed a similar increase as the D90, while the relationship between high-dose volume lying outside the prostate and prostate volume remained constant. The ratio between prostate volumes from transrectal ultrasound and CT imaging decreased with increasing D90post, while the preplanning D90 and V100 remained constant. The different isotopes used, the method of planning, and the implanted activity per prostate volume did not influence results. CONCLUSION: A learning curve characterized by an increase in the D90post can be observed and results in a stable technique after 18 patients. An important factor influencing the learning curve in addition to the precision of seed positioning is organ volume definition on postimplant imaging.     

Prostate brachytherapy in obese patients

PURPOSE: To identify and illustrate the potential problems with brachytherapy in obese patients. METHODS AND MATERIALS: Three patients with body mass index greater than 30 were treated with prostate brachytherapy. Transrectal ultrasound (TRUS) was performed using a 6.0-MHz Siemens Sonoline Prima ultrasound machine and a Barzell-Whitmore stepper unit. The patients' weight required use of an accessory table support. RESULTS: Once set up, there was ample room to maneuver, providing that the patient's legs were abducted fully. TRUS imaging of the prostate was unaffected by patients' obesity. The amount of periprostate adipose tissue visualized on TRUS appeared to be no different than that noted in nonobese patients. Similarly, there was no increased distance between the prostate and rectal surface, either on preimplant CT or transverse TRUS. To date, our experience is that the perineal skin to prostate distance was not so great that standard 20-cm applicator needles could not be used. For the 2 sub-350-pound patients who could be imaged on our CT scanner, postimplant target coverage (V100) was 88% and 95%. CONCLUSIONS: Standard TRUS and brachytherapy needles are sufficient to implant even the largest patients.     

Interobserver variation in postimplant computed tomography contouring affects quality assessment of prostate brachytherapy

PURPOSE: Permanent seed implants are accepted treatment of early stage prostate cancer. Implant quality is assessed by post implant CT-based dosimetry but prostate contours on CT images are obscured by metallic seed artefact and edema. Outcome depends on implant quality, but perceived implant quality depends on accurate prostate contouring. This study documents inter observer variation in prostate contouring on post implant CT scans. METHODS AND MATERIALS: Ten patients had implant dosimetry calculated on 4 copies of the post implant CT scan. Prostate contours from MRI-CT fusion were the gold standard for prostate edge identification. CTs were contoured by an experienced prostate brachytherapist matching CT images to the pre implant TRUS, and by 2 GU radiation oncologists experienced in conformal radiotherapy planning. Dosimetry was compared to that obtained using MRI-CT fusion in terms of D90 and V100. RESULTS: Contours and dosimetry were not reproducible among the 3 observers. The V100's of the experienced brachytherapist differed from that of MRI-CT fusion by a mean of 2.4% compared to 9.1% and 4.4% for observers 1 and 2, and the D90 by a mean of 9.3 Gy compared to 30.3 and 14.4 Gy for observers 1 and 2. CONCLUSIONS: Quality assessment of prostate brachytherapy based on 1 month post implant CT is difficult. This may obscure the dose-response relationship in brachytherapy as well as create problems for quality assurance in multicentre trials evaluating brachytherapy against standard modalities. Whenever possible, MRI-CT fusion should be employed to verify prostate contours post implant.     

Salvage of suboptimal prostate seed implantation: Reimplantation of underdosed region of prostate base

PURPOSE: To demonstrate how a suboptimal (125)I prostate implant can be salvaged by reimplantation. METHODS AND MATERIALS: A (125)I implant was preplanned to deliver 150 Gy to the prostate of a patient with early stage prostate cancer. A CT scan at 35 days postimplant indicated that V(100) and D(90) were 46% and 49 Gy, respectively. The cause was a systematic source placement error that left the base significantly underdosed. A reimplantation of the underdosed region was planned by superimposing a template grid onto the 35-day postimplant CT scan images and digitizing them into the treatment planning computer as if they were TRUS images. The reimplantation was carried out under fluoroscopy guidance so that the initial implant was visible. RESULTS: The reimplantation increased V(100) and D(90) to 98% and 201 Gy, respectively. The misplaced seeds resulted in a high dose to the apical region and urethra, which was further increased by the reimplantation. The patient experienced increased urinary morbidity, which was relieved by medication. CONCLUSION: It is feasible to salvage a suboptimal prostate seed implant by reimplanting the underdosed regions under fluoroscopy guidance based on a plan generated from the postimplant CT scan.     

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.     

Live implant dosimetry may be an effective replacement for postimplant computed tomography in localized prostate cancer patients receiving low dose rate brachytherapy

PurposeTo determine if Live Implant Dosimetry (LIDO) utilizing intraoperative transrectal ultrasound (TRUS) is equivalent to postimplant CT dosimetry (either day 0 or day 30) in patients with localized prostate cancer (PC) treated with low dose rate (LDR) prostate seed brachytherapy.Methods and MaterialsThe treated population consisted of 628 men with localized (T1-T2) PC. All d'Amico risk categories (low, intermediate, and high) were included, and 437 patients were treated with monotherapy (160 Gy) [low and low tier intermediate], and the remainder (191) [high tier intermediate and high risk] with an implant boost (106 Gy) post external beam radiation, to a volume including the prostate and seminal vesicles (46 Gy). LIDO with intraoperative TRUS, postimplant CT (day 0 and day 30) were performed in all cases. Prostate volumes (V), V₁₀₀ (prostate) and dose (D) D₉₀ (prostate), D₃₀ (urethra), and Rectum D_2cc, were recorded. No urinary catheter was used on Day 30 CT.ResultsMore than 91.33% of monotherapy patients reached the target D₉₀ according to LIDO while only 82.99% of Day 0 CT and 92.82% of Day 30 CT achieved target D₉₀. When considering V₁₀₀, monotherapy patients recorded target dosimetry in 90.93%, 82.31%, and 92.02% of cases assessed by LIDO, Day 0 CT and Day 30 CT, respectively. Strong correlations are observed in D₉₀, Rectum D_2cc and Urethra D₃₀ across imaging modalities but V₁₀₀ and V₁₅₀ were poorly correlated due to the relative quantification of this parameter and high degree of error in measurement. Of all monotherapy patients with satisfactory dosimetry on LIDO, 94.82% reached target D₉₀ at day 30 CT and 94.19% reached target V₁₀₀.ConclusionsLIDO and CT are both effective tools for assessing postimplant dosimetry. Patients with satisfactory LIDO dosimetry are highly likely to have equivalent dosimetry on CT at follow-up, indicating that postimplant CT may be eliminated in PC a patients implanted with this technique.     

Toward a dynamic real-time intraoperative permanent prostate brachytherapy methodology

PURPOSE: To evaluate dosimetry and source location relative to CT-based dosimetry when performing real-time dynamic permanent prostate brachytherapy (PPB) with inverse treatment planning. METHODS AND MATERIALS: A treatment algorithm for dynamic PPB was developed using inverse treatment planning. The technique utilizes real-time transrectal ultrasound prostate imaging connected to the treatment planning software. The implementation of the plan with the Mick interstitial gun is monitored with up-to-date dosimetry assessments based on the registration of each seed when placed. Real-time dose assessment is monitored and adjustments can be made during the case, if necessary. A final OR dosimetric (OR-D) assessment based on the registered seed locations is performed. Postoperative CT scans obtained at 3 weeks are used for traditional dosimetry analysis (CT-D). A matrix algorithm was developed to match the seed locations from the ultrasound registration to that of the CT-scan parameters. RESULTS: Twenty-six consecutive patients with clinically localized prostate cancer underwent PPB using the algorithm designed for dynamic real-time planning. The OR-D identified a mean D90 of 109% (range 100-118%) whereas the mean CT-D D90 at 3 weeks was 105% (range 89-122%) (p=0.894). Analysis of the OR-D V100 and V150 relative to the 3-week CT-dose V100 and V150 were also insignificant (p=0.112 and 0.167, respectively). Assessment of seed locations relative to the intraoperative ultrasound and postimplant CT identified a mean root-mean-square error of 4.6 mm (0-21 mm). The mean error for the x, y, and z coordinates were 2.01 mm, 2.24 mm, and 2.85 mm, respectively. CONCLUSIONS: This study reports the preliminary results of a new treatment algorithm for PPB that incorporates intraoperative inverse planning with dynamic dosimetry assessment during the case. Correlation was seen between the completed intraoperative, postimplant plan and the CT based plan at 3 weeks. Seed to seed deviations between the OR-D matched well with the CT-D. Additional study is necessary to assess whether this approach can assist in improving implant dosimetry and whether it appropriately documents the OR-dose without the need for postimplant dosimetry.     

Appropriate timing for postimplant imaging in permanent breast seed implant: Results from a serial CT study

PurposePostimplant analysis in permanent breast seed implant (PBSI) is performed at inconsistent times subsequent to seed implantation across cancer centers, creating challenges in the interpretation of dosimetric data and ultimately the correlation with clinical outcomes. The purpose of this study is to determine the most appropriate time postimplant to perform this analysis.Methods and MaterialsNine patients treated at our institution with PBSI were included in this analysis. Each underwent 4 postimplant CT scans: 0, 15, 30, and 60 days postimplant. A model of the accumulated dose was created by deformably registering the Day 15, 30, and 60 postimplant CT scans and dose matrices to the Day 0 scan, scaling for seed decay. The results from this model were compared to each individual postplan by integral comparison of dose–volume histogram curves for a dose evaluation volume.ResultsThe Day 30 postplan showed the best agreement with the accumulated dose model and the smallest interpatient variability across the patient cohort. The mean (±SD) for the dose evaluation volume V₉₀, V₁₀₀, V₁₅₀, and V₂₀₀ for the accumulated dose model was 90 ± 7%, 86 ± 8%, 66 ± 14%, and 41 ± 16%, respectively.ConclusionsBased on the results of this patient cohort, we recommend that postimplant dosimetric analysis for PBSI be performed approximately 30 days following the implant.     

Applicability and Dosimetric Impact of Ultrasound-Based Preplanning in High-Dose-Rate Brachytherapy of Prostate Cancer

BACKGROUND AND PURPOSE: Analyses of permanent brachytherapy seed implants of the prostate have demonstrated that the use of a preplan may lead to a considerable decrease of dosimetric implant quality. The authors aimed to determine whether the same drawbacks of preplanning also apply to high-dose-rate (HDR) brachytherapy. PATIENTS AND METHODS: 15 patients who underwent two separate HDR brachytherapy implants in addition to external-beam radiation therapy for advanced prostate cancer were analyzed. A pretherapeutic transrectal ultrasound was performed in all patients to generate a preplan for the first brachytherapy implant. For the second brachytherapy, a subset of patients were treated by preplans based on the ultrasound from the first brachytherapy implant. Preplans were compared with the respective postplans assessing the following parameters: coverage index, minimum target dose, homogeneity index, and dose exposure of organs at risk. The prostate geometries (volume, width, height, length) were compared as well. RESULTS: At the first brachytherapy, the matching between the preplan and actual implant geometry was sufficient in 47% of the patients, and the preplan could be applied. The dosimetric implant quality decreased considerably: the mean coverage differed by -0.11, the mean minimum target dose by -0.15, the mean homogeneity index by -0.09. The exposure of organs at risk was not substantially altered. At the second brachytherapy, all patients could be treated by the preplan; the differences between the implant quality parameters were less pronounced. The changes of prostate geometry between preplans and postplans were considerable, the differences in volume ranging from -8.0 to 13.8 cm(3) and in dimensions (width, height, length) from -1.1 to 1.0 cm. CONCLUSION: Preplanning in HDR brachytherapy of the prostate is associated with a substantial decrease of dosimetric implant quality, when the preplan is based on a pretherapeutic ultrasound. The implant quality is less impaired in subsequent implants of fractionated brachytherapy.     

Critical organ dosimetry in permanent seed prostate brachytherapy: defining the organs at risk

PURPOSE: Although permanent seed prostate brachytherapy is associated with a low risk of serious morbidity, proctitis and prolonged irritative and obstructive urinary symptoms may occur. Data are accumulating to help establish thresholds or guidelines for minimizing toxicity, however, no uniform method of defining and calculating the dose to critical organs currently exists. We set out to examine the existing data and propose a uniform method of reporting such that results from different centers can more easily be compared. METHODS AND MATERIALS: In preparation for a panel discussion at the American Brachytherapy Society 2004 Annual Meeting, four members with expertise in prostate dosimetry and critical organ assessment performed a literature search and, supplemented with their clinical experience, formulated a proposal for defining and reporting dose in a standardized fashion to the critical organs for permanent seed prostate brachytherapy. RESULTS: As previously recommended by the American Brachytherapy Society, postimplant dosimetry should be performed on all patients undergoing permanent prostate brachytherapy. The standard imaging for postplan assessment is the CT scan. The interval between seed implantation and postplan assessment should be reported. For rectal and urinary morbidities, the critical organs are considered to be the anterior rectum and the prostatic urethra, respectively. For erectile dysfunction, both the neurovascular bundle and penile bulb have been implicated. The rectum should be contoured on all CT scan slices where radioactive seeds are visible. Both the inner and outer walls should be contoured. The dose should be reported as RV100 and RV150, the volumes in cubic centimeters of the rectal wall receiving 100% and 150% of the prescribed dose, respectively. The urethra should be contoured as a structure on each slice where seeds can be seen. The urethra should be identified by either catheterization or fusion with transrectal ultrasound. The dose should be reported as UrD5 and UrD30, which are, respectively, the dose to 5% and 30% of the urethra in Gray. As well, a UrV150 should be reported, which is the volume in cubic centimeters of the urethra receiving 150% of the prescribed dose. No recommendations can be made at this time for reporting neurovascular bundle or penile bulb doses. CONCLUSIONS: It is essential that toxicity data be collected and reported in a uniform fashion. Thus, the critical organs for toxicity must be defined and the corresponding dosimetry reported in a standard fashion such that guidelines can be established in the future based on data from a cross-section of centers.     

Identification of pubic arch interference in prostate brachytherapy: simplifying the transrectal ultrasound technique

PURPOSE: We report a simplified technique allowing identification of pubic arch interference (PAI) using transrectal ultrasound (TRUS). METHODS AND MATERIALS: Fifty consecutive brachytherapy patients implanted using a two-stage technique were studied. The pubic arch was outlined using a marker pen on the ultrasound monitor screen during the dose planning ultrasound. Where pubic arch interference (PAI) was identified attempted needle passage was used to confirm PAI (n = 3). RESULTS: Mean time to perform PAI assessment was 90 s. Three of 50 patients had PAI, which was confirmed by attempted needle passage. No patients required modification to the implant plan during the implant procedure. CONCLUSIONS: TRUS reliably identifies PAI. This simple technique may be used with any TRUS scanner and avoids the need for CT scanning or specific software to identify PAI. Our low incidence of PAI may be related to lower prostate volumes at implantation due to patient selection, neoadjuvant androgen deprivation, or improved patient positioning.