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International audience; PURPOSE:To evaluate the dose distribution of additional radioactive seeds implanted during salvage permanent prostate implant (sPPI) after a primary permanent prostate implant (pPPI).METHODS AND MATERIALS:Patients with localized prostate cancer were primarily implanted with iodine-125 seeds and had a dosimetric assessment based on day 30 postimplant CT (CT1). After an average of 6 years, these patients underwent sPPI followed by the same CT-based evaluation of dosimetry (CT2). Radioactive seeds on each CT were detected. The detected primary seeds on CT1 and CT2 were registered and then removed from CT2 referred as a modified CT2 (mCT2). Dosimetry evaluations (D90 and V100) of sPPI were performed with dedicated planning software on CT2 and mCT2. Indeed, prostate volume, D90, and V100 differences between CT2 and either CT1 or mCT2 were calculated, and values were expressed as mean (standard deviation).RESULTS:The mean prostate volume difference between sPPI and pPPI over the 6 patients was 9.85 (7.32) cm3. The average D90 and V100 assessed on CT2 were 486.5 Gy (58.9) and 100.0% (0.0), respectively, whereas it was 161.3 Gy (47.5) and 77.3% (25.2) on mCT2 (p = 0.031 each time). The average D90 the day of sPPI [145.4 Gy (11.2)] was not significantly different from that observed on mCT2 (p = 0.56).CONCLUSION:Postimplant D90 and V100 of sPPI after pPPI can be estimated on CT images after removing the primary seeds.Copyright © 2018 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

The construction of a conventional prostate needle (seeds) implant template restricts needles tilting or incline insertion when it is necessary to approach a seminal vesicle or to avoid the obstruction of symphysis pubis. To overcome the disadvantages of conventional templates, we developed a special template for guiding needles incline insertion and fixation for prostate needle implant. Phantom needles implantation was performed. Two acrylic boards, each 7.5 cm in width by 7.5 cm in length and 0.5 cm thickness, were drilled with a set of domed holes and cones with embedded template ball inside this combination to provide firm grip and fixation in prostate needle implantation. The specially designed domed‐cones combination acrylic board provides a needle of up to 60° rotation flexibility application. Some areas that could not be covered in a conventional parallel needle holes template could now be covered by using this new template. The covering index of prostate radiation dosage is up to 84.5%. The specially designed domed‐cones acrylic board combination provides not only a reliable means of needle fixation and rotational function, but also a superior dose distribution in the anterior portion of the prostate and good coverage of a seminal vesicle. This special template is a feasible design for prostate needles or seeds implant brachytherapy. PACS number(s): 87.57.uq

Purpose To report results of an initial pilot study assessing iodine-125 prostate implant treatment plans created automatically by a new seed-placement method. Methods and Materials A novel mixed-integer linear programming method incorporating spatial constraints on seed locations in addition to standard dose–volume constraints was used to place seeds. The approach, described in detail elsewhere, was used to create treatment plans fully automatically on a retrospective basis for 20 patients having a wide range of prostate sizes and shapes. Corresponding manual plans used for patient treatment at a single institution were combined with the automated plans, and all 40 plans were anonymized, randomized, and independently evaluated by five clinicians using a common scoring tool. Numerical and clinical features of the plans were extracted for comparison purposes. Results A full 51% of the automated plans were deemed clinically acceptable without any modification by the five practitioners collectively versus 90% of the manual plans. Automated plan seed distributions were for the most part not substantially different from those for the manual plans. Two observed shortcomings of the automated plans were seed strands not intersecting the prostate and strands extending into the bladder. Both are amenable to remediation by adjusting existing spatial constraints. Conclusions After spatial and dose–volume constraints are set, the mixed-integer linear programming method is capable of creating prostate implant treatment plans fully automatically, with clinical acceptability sufficient to warrant further investigation. These plans, intended to be reviewed and refined as necessary by an expert planner, have the potential to both save planner time and enhance treatment plan consistency.

375 Background: A recent large single institutional study reported excellent long-term biochemical control and survival for Cs-131 prostate implant. This isotope has short half-life (9.7 days) with clinical advantages including shorter duration of symptoms. We previously showed Cs-131 dosimetry to be quantitatively similar to I-125 with improved homogeneity (mean percent V150 36% for I-125 versus 27% for Cs-131 (p < 0.0001). Our objective was to evaluate PSA failure rates and dosimetric outcomes in a multi-institutional community based setting. Methods: Within an IRB approved retrospective study, we compared outcomes for three groups of permanent prostate implant patients treated at Ascension Macomb Oakland, Ascension Saint John, and Ascension Providence Rochester Hospitals over a 10 year time interval. The comparison groups included isotopes Cs-131 (n = 66; t1/2 9.7 days), I-125 (n = 60; t1/2 60 days), and Pd-103 (n = 60; t1/2 17 days). Kaplan Meier estimates of PSA failure used the nadir plus 2 (Phoenix) definition. Results: Standard permanent implant doses employed were 145 Gy for I-125 monotherapy or 109 Gy for combination therapy. The dose for Cs-131 was 115 Gy for monotherapy and 85 Gy for combination therapy. For Pd-103, the doses employed were 125 Gy and 90 Gy for mono- and combination therapy, respectively. Median age at diagnosis was Cs-131; 69 (range 49-80), I-125; 71 (49-78), and Pd-103; 70 (60-82). Mean pretreatment PSA values were Cs-131 5.73 ng/ml, I-125 6.62 ng/ml, and for Pd-103 8.87 ng/ml. Median PSA follow up was 30 months and the median PSA value at 60 months was 0.11 ng/ml. There was excellent PSA control for all three groups of cases (p = NS), however with fewer failures using Cs-131. Conclusions: Permanent interstitial brachytherapy continues to be an attractive option for treatment early stage prostate cancer. Only a few large single institutional studies have examined PSA failure rates or dosimetric aspects of shorter half-life Cs-131 seed implants. This series confirms wide applicability of Cs-131 permanent prostate seed implant in the community hospital setting.

Purpose: To find permanent prostate implant (PPI) pre-plan dosimetric parameters that predict post-implant D 90 ≥ 140 Gy. Material and methods: Pre-plans were evaluated for 504 patients undergoing PPI with 125 I seeds for low or intermediate risk prostate cancer. Baseline patient and disease factors, numbers of seeds, ratios of number of seeds to available positions (occupancy proportion), and distances between the 100% isodose line and edge of the prostate (margin) planned for the whole prostate (WP), superior (S), inferior (I), anterior (A), and posterior (P) halves, SA, SP, IA, and IP quarters, and superior (S T ), inferior (I T ), and middle (M T ) thirds, and anterior (A T ) and posterior (P T ) middle one-sixth segments were analyzed by post-implant D 90 subset (≥ 140 Gy vs. < 140 Gy). Results: 20% had post-implant D 90 < 140 Gy (mean: 128.0 Gy, range: 97.5-139.2) vs. ≥ 140 Gy (mean: 154.4 Gy, range: 140.0-193.5). The D 90 ≥ 140 Gy subset had larger A T and IA segment mean numbers of seeds (p = 0.01, 0.046), larger WP, S, A, SA, S T , A T , and M T segment mean margins (p = 0.01, 0.01, 0.001, 0.0001, 0.03, 0.005, 0.02), and lower P T segment occupancy proportion (p = 0.004). On multivariate analysis, independent predictors of post-implant D 90 ≥ 140 Gy were increased SA mean margin, no pre-implant 5-α-reductase inhibitor, higher pre-plan D 90 , decreased P occupancy proportion, no pre-implant hormone therapy, and decreased SP mean margin. Conclusions: Higher occupancy proportion and larger margins anteriorly and reduced occupancy proportion, and smaller margins posteriorly on PPI pre-plans predict post-implant D 90 ≥ 140 Gy. J Contemp Brachytherapy 2014; 6, 2: 143–153 DOI: 10.5114/jcb.2014.43248

Permanent prostate brachytherapy has been practiced for more than a century. This review examines the influence of earlier procedures on the modern transperineal ultrasound-directed technique. A literature review was conducted to examine the origin of current clinical practice. The dimensions of the modern brachytherapy seed, the prescription dose, and implant/teletherapy sequencing are vestigial features, which may be suboptimal in the current era of low-energy photon-emitting radionuclides and computerized dose calculations. Although the modern transperineal permanent prostate implant procedure has proven to be safe and effective, it should undergo continuous re-evaluation and evolution to ensure that its potential is maximized.

Purpose RayStretch is a simple algorithm proposed for heterogeneity corrections in low-dose–rate brachytherapy. It is built on top of TG-43 consensus data, and it has been validated with Monte Carlo (MC) simulations. In this study, we take a real clinical prostate implant with 71 125I seeds as reference and we apply RayStretch to analyze its performance in worst-case scenarios. Methods and Materials To do so, we design two cases where large calcifications are located in the prostate lobules. RayStretch resilience under various calcification density values is also explored. Comparisons against MC calculations are performed. Results Dose–volume histogram–related parameters like prostate D90, rectum D2cc, or urethra D10 obtained with RayStretch agree within a few percent with the detailed MC results for all cases considered. Conclusions The robustness and compatibility of RayStretch with commercial treatment planning systems indicate its applicability in clinical practice for dosimetric corrections in prostate calcifications. Its use during intraoperative ultrasound planning is foreseen.

Purpose: Accurate localization of prostate implants from several C-arm images is necessary for ultrasound-fluoroscopy fusion and intraoperative dosimetry. The authors propose a computational motion compensation method for tomosynthesis-based reconstruction that enables 3D localization of prostate implants from C-arm images despite C-arm oscillation and sagging. Methods: Five C-arm images are captured by rotating the C-arm around its primary axis, while measuring its rotation angle using a protractor or the C-arm joint encoder. The C-arm images are processed to obtain binary seed-only images from which a volume of interest is reconstructed. The motion compensation algorithm, iteratively, compensates for 2D translational motion of the C-arm by maximizing the number of voxels that project on a seed projection in all of the images. This obviates the need for C-arm full pose tracking traditionally implemented using radio-opaque fiducials or external trackers. The proposed reconstruction method is tested in simulations, in a phantom study and on ten patient data sets. Results: In a phantom implanted with 136 dummy seeds, the seed detection rate was 100% with a localization error of 0.86 {+-} 0.44 mm (Mean {+-} STD) compared to CT. For patient data sets, a detection rate of 99.5% was achieved in approximately 1 min permore » patient. The reconstruction results for patient data sets were compared against an available matching-based reconstruction method and showed relative localization difference of 0.5 {+-} 0.4 mm. Conclusions: The motion compensation method can successfully compensate for large C-arm motion without using radio-opaque fiducial or external trackers. Considering the efficacy of the algorithm, its successful reconstruction rate and low computational burden, the algorithm is feasible for clinical use.« less

Purpose To provide practical dosimetric advice on mending suboptimal permanent implants using low-dose-rate (LDR) or high-dose-rate (HDR) brachytherapy. The problem is to make the combination of the two radiation treatments (the initial, flawed one and the compensatory boost) clinically isoeffective with the planned dose. Methods and Materials The device of isoeffective dose is the appropriate tool for this purpose as it accounts for the physical (temporal distribution of dose) and biologic (radiosensitivity, repair kinetics, proliferation rate) treatment settings. Results I give, as a function of separation time from the initial, flawed treatment, and stratified by risk group representative values for the additional dose (low-dose-rate or high-dose-rate) needed to make the combined treatment isoeffective with a prescription of 144 Gy of permanently implanted 125 I seeds. Conclusions Although the isoeffective dose concept, within the constraints stated in the text, is rigorously valid, its practical implementation depends importantly on the relevant radiobiologic parameters, and in this respect the reader is urged to use his own critical judgment.

The goals of interstitial implant brachytherapy include delivery of the target dose in a uniform manner while sparing sensitive structures, and minimizing the number of needles and sources. We investigated the use of a multi-species source arrangement ({sup 192}Ir with {sup 125}I) for treatment in interstitial prostate brachytherapy. The algorithm utilizes an 'adjoint ratio', which provides a means of ranking source positions and is the criterion for the Greedy Heuristic optimization. Three cases were compared, each using 0.4 mCi {sup 125}I seeds: case I is the base case using {sup 125}I alone, case II uses 0.12 mCi {sup 192}Ir seeds mixed with {sup 125}I, and case III uses 0.25 mCi {sup 192}Ir mixed with {sup 125}I. Both multi-species cases result in lower exposure of the urethra and central prostate region. Compared with the base case, the exposure to the rectum and normal tissue increases by a significant amount for case III as compared with the increase in case II, signifying the effect of slower dose falloff rate of higher energy gammas of {sup 192}Ir in the tissue. The number of seeds and needles decreases in both multi-species cases, with case III requiring fewer seeds and needles than case II. Further,more » the effect of {sup 192}Ir on uniformity was investigated using the 0.12 mCi {sup 192}Ir seeds in multi-species implants. An increase in uniformity was observed with an increase in the number of 0.12 mCi {sup 192}Ir seeds implanted. The effects of prostate size on the evaluation parameters for multi-species implants were investigated using 0.12 mCi {sup 192}Ir and 0.4 mCi {sup 125}I, and an acceptable treatment plan with increased uniformity was obtained.« less

The geometry of a permanent prostate implant varies over time. Seeds can migrate and edema of the prostate affects the position of seeds. Seed movements directly influence dosimetry which relates to treatment quality. We present a method that tracks all individual seeds over time allowing quantification of seed movements. This linking procedure was tested on transrectal ultrasound (TRUS) and cone-beam CT (CBCT) datasets of 699 patients. These datasets were acquired intraoperatively during a dynamic implantation procedure, that combines both imaging modalities. The procedure was subdivided in four automatic linking steps. (I) The Hungarian Algorithm was applied to initially link seeds in CBCT and the corresponding TRUS datasets. (II) Strands were identified and optimized based on curvature and linefits: non optimal links were removed. (III) The positions of unlinked seeds were reviewed and were linked to incomplete strands if within curvature- and distance-thresholds. (IV) Finally, seeds close to strands were linked, also if the curvature-threshold was violated. After linking the seeds an affine transformation was applied. The procedure was repeated until the results were stable or the 6th iteration ended. All results were visually reviewed for mismatches and uncertainties. Eleven implants showed a mismatch and in 12 cases an uncertainty was identified. On average the linking procedure took 42 ms per case. This accurate and fast method has the potential to be used for other time spans, like Day 30, and other imaging modalities. It can potentially be used during a dynamic implantation procedure to faster and better evaluate the quality of the permanent prostate implant.

The aim of this study was to evaluate the potential of bGPUMCD, a Monte Carlo algorithm executed on Graphics Processing Units (GPUs), for fast dose calculations in permanent prostate implant dosimetry. It also aimed to validate a low dose rate brachytherapy source in terms of TG-43 metrics and to use this source to compute dose distributions for permanent prostate implant in very short times. The physics of bGPUMCD was reviewed and extended to include Rayleigh scattering and fluorescence from photoelectric interactions for all materials involved. The radial and anisotropy functions were obtained for the Nucletron SelectSeed in TG-43 conditions. These functions were compared to those found in the MD Anderson Imaging and Radiation Oncology Core brachytherapy source registry which are considered the TG-43 reference values. After appropriate calibration of the source, permanent prostate implant dose distributions were calculated for four patients and compared to an already validated Geant4 algorithm. The radial function calculated from bGPUMCD showed excellent agreement (differences within 1.3%) with TG-43 accepted values. The anisotropy functions at r = 1 cm and r = 4 cm were within 2% of TG-43 values for angles over 17.5°. For permanent prostate implants, Monte Carlo-based dose distributions with a statistical uncertainty of 1% or less for the target volume were obtained in 30 s or less for 1 × 1 × 1 mm(3) calculation grids. Dosimetric indices were very similar (within 2.7%) to those obtained with a validated, independent Monte Carlo code (Geant4) performing the calculations for the same cases in a much longer time (tens of minutes to more than a hour). bGPUMCD is a promising code that lets envision the use of Monte Carlo techniques in a clinical environment, with sub-minute execution times on a standard workstation. Future work will explore the use of this code with an inverse planning method to provide a complete Monte Carlo-based planning solution.

We investigated the difference between measured and manufacturer's nominal source strength in a large sample of a single model of (125)I seeds. Physical characteristics of single seed measurement by the well-type ionization chamber were also investigated to provide dosimetric data.A well-type ionization chamber with a single seed holder was used to measure source strength of all 1935 (125)I seeds implanted in the initial 28 patients in our hospital. Physical characteristics including linearity of readings for different integral time intervals, reproducibility, isotropy, and axial positional sensitivity were assessed. To calculate the source strength, the integral charge during 30 s was measured and converted to air kerma strength. The nominal activity stated by the manufacturer was compared with the measured value.Linearity, reproducibility, and isotropy of the well-type ionization chamber were within 0.2%. Measured source strength was on average 2.1% (range -7.6% to +7.2%), lower than the nominal value. Standard deviation of all measured seeds was 2.0%. The maximum difference between the measured and the manufacturer's nominal source strength in each patient was -3.7%. The standard deviation averaged 1.6%.The nominal source strength of the (125)I seeds agreed well with the measured value. Our study can be helpful as guidance for individual (125)I seed source strength measurement.

In this paper, we examine the effect of treatment parameters in a model used to evaluate permanent prostate implants. The model considers the prostate to be composed of 12 sub-sections, each sub-section is assigned a cell density based on the probability of finding cancer foci in that sub-section. Wasted dose as a result of the dose rate from the implant falling below a level adequate to counteract repopulation was found to vary by 2-16% over the range of radiosensitivity and repopulation rates considered. Within the model, applied to five dose distributions, the uncertainty in the tumour control probability (TCP) values calculated for each sub-section as a result of differences in the model parameters, was found to be less than 12% in most cases for the good quality implants. The difference in TCP values was much larger for the poor quality implant. Substituting a heterogeneous distribution of alpha for a single mean value resulted in generally lower TCP values though introducing a cutoff value with a Gaussian distribution had a profound effect on the calculated values. Despite uncertainties in the parameters, the model was able to identify sub-sections at risk of local recurrence but as a result of these uncertainties, the TCP values can only be considered in the relative rather than absolute sense.

Purpose: Prostate brachytherapy is an effective treatment for early prostate cancer. The current prostate implant is limited to using 2D transrectal ultrassound (TRUS) or machenical motor driven 2D array either in the end or on the side. Real-time 3D images can improve the accuracy of the guidance of prostate implant. The concept of our system is to allow realtime full visualization of the entire prostate with the multiple transverse scan. Methods: The prototype of 3D Multiple-Transverse-Plane Transrectal Ultrasound probe (MTP-TRUS) has been designed by us and manufactured by Blatek inc. It has 7 convex linear arrays and each array has 96 elements. It is connected to cQuest Fire bird research system (Cephasonics inc.) which is a flexible and configurable ultrasound-development platform. The size of cQuest Firebird system is compact and supports the real-time wireless image transferring. A relay based mux board is designed for the cQuest Firebird system to be able to connect 672 elements. Results: The center frequency of probe is 6MHz±10%. The diameter of probe is 3cm and the length is 20cm. The element pitch is 0.205 mm. Array focus is 30mm and spacing 1.6cm. The beam data for each array was measured and met our expectation. The interface board of MTP-TURS is made and able to connect to cQuest Firebird system. The image display interface is still under the development. Our real-time needle tracking algorithm will be implemented too. Conclusion: Our MTP-TRUS system for prostate implant will be able to acquire real-time 3D images of prostate and do the real-time needle segmentation and tracking. The system is compact and have wireless function.

Palladium-103-(103Pd) seed has been increasingly used in prostate implantation as either definitive or boost therapy because of its shorter half-life and higher initial dose rate. Because a growing number of radiation oncologists prefer real-time implantation in the operating room, it will be helpful if the total activity of the seeds can be determined based on the gland size before the patient is taken to the operating room. Based on our clinic data, nomograms have therefore been developed for one of the widely used 103Pd seeds, the MED3633 seed, which is produced by North American Scientific, Inc. (NASI). The total activities for implant volume ranging from 15 cc to 55 cc are provided for both seed “monotherapy” and seed boost.

To compare the prostate gland volumes and subsequent quantifiers of implant adequacy determined by five separate brachytherapists on postimplant CT images performed 1 day after prostate brachytherapy.Ten consecutive patients underwent a CT scan 1 day after prostate brachytherapy, using 125I. Four experienced prostate brachytherapists were recruited to participate in this study in addition to the lead author. Each reviewer was asked to independently contour the prostate on sequential axial CT images for all 10 patients using a commercially available treatment planning system. Prostate volumes were calculated along with commonly reported quantifiers of implant adequacy (minimal dose received by 90% of the prostate gland [D(90)] and percentage of prostate volume receiving 100% of prescribed minimal peripheral dose [V(100)]).The mean prostate volume (SD) was significantly different according to the individual reviewers: Rev 1, 50.89 cm(3) (10.6); Rev 2, 55.42 cm(3) (15.79); Rev 3, 40.02 cm(3) (9.95); Rev 4, 56.70 cm(3) (12.16); and Rev 5, 44.52 cm(3) (10.95); p0.0001. Significant differences were also observed for the mean V(100): Rev 1, 83.4% (5.5); Rev 2, 85.4% (7.6); Rev 3, 89.9% (5.4); Rev 4, 77.7% (6.3); and Rev 5, 81.5 (4.3); p0.0001; and for the mean D(90), reported as the percentage of the prescription dose: Rev 1, 87.9 (8.9); Rev 2, 92.5 (15.4); Rev 3, 102.6 (16.7); Rev 4, 75.1 (11.3); and Rev 5, 81.4 (8.1); p0.0001. Reproducibility was measured using the intraclass correlation coefficient (ICC). The reproducibility of the prostate volume was fair (ICC = 0.639) but was poor for the dosimetric quantifiers (V(100) ICC = 0.344 and D(90) ICC = 0.275).Significant interobserver differences in prostate volume defined on postimplant CT scans were observed. These differences led to significant differences in commonly used dosimetric quantifiers according to the individual reviewer. Until a greater degree of agreement among reviewers can be established, inferences concerning postimplant CT-based dosimetric analysis will be problematic at best. Additional efforts to increase interobserver agreement are required.

Purpose: In conventional treatment planning for permanent I-125 prostate implants, it has been suggested that lower seed activities result in more homogeneous dose distributions and also less overdose of the critical structures. We sought to determine if this hypothesis holds by analyzing treatment plans constructed using an automated optimized approach. Methods and Materials: We studied treatment plans for 10 patients using mixed-integer programming and the branch-and-bound method. Two mixed-integer models (that yielded somewhat different treatment plans) were developed: a "basic" model and a "dose homogeneity" model. For each resulting treatment plan, we examined dose homogeneity (by evaluating the dose non-uniformity ratio [DNR] and the full-width half-maximum [FWHM] of the differential dose-volume histogram [DVH]) as a function of three different source activities (0.35 mCi, 0.44 mCi, and 0.66 mCi). In addition, target coverage and critical structure dose distributions were evaluated. Plans using multiple source activities were also evaluated for resulting dose inhomogeneities. Results: The homogeneity model results in a more homogeneous dose distribution than the basic model. DNR is lowered by an average of 42% (standard deviation [SD] = 19%), 39% (SD = 21%), and 33% (SD = 21%) for the 0.35 mCi, 0.44 mCi, and 0.66 mCi seeds, respectively, when the homogeneity model is employed over the basic model. Corresponding average decreases in the FWHM of the DVH for 0.35 mCi, 0.44 mCi, and 0.66 mCi, respectively, are 29 Gy (SD = 28 Gy), 24 Gy (SD = 22 Gy), and 27 Gy (SD = 13 Gy). Seeds of 0.35 mCi and 0.44 mCi result in the lowest DNR and narrower FWHM of the DVH relative to 0.66 mCi seeds. In general, the 0.44 mCi seeds produce greater target coverage and require fewer seeds and needles than the 0.35 mCi seeds. Although 0.66 mCi seeds result in the greatest target coverage, they yield highest critical structure doses. They also yield solutions requiring the least number of seeds and needles. However, the dose distributions from 0.66 mCi seeds are highly inhomogeneous. Multiple source activities in the same treatment plan produce dose distributions that are comparable in homogeneity to 0.44 mCi seed implants. Conclusions: Even when an optimization model that seeks to minimize dose inhomogeneity is employed, all factors involved in seed implants make 0.44 mCi the best activity choice in comparison with 0.35 mCi and 0.66 mCi.

Radiation exposure to the public is estimated if the body of an I-125 prostate implant patient is cremated. Precautions regarding the handling of cremated remains are suggested. Cremation can be performed safely at any time. 2001 American College of Medical Physics.

A dosimetric study of a new 125I seed for permanent prostate implant, the Symmetra 1251 Seed model I25.S06, has been undertaken utilizing Monte Carlo photon transport calculations. All dosimetric quantities recommended by the AAPM Task Group 43 (TG-43) report have been calculated. Quantities determined are dose rate constant, radial dose function, anisotropy function, anisotropy factor, and anisotropy constant. The recently (January 1999) revised NIST (National Institute of Standards and Technology) 1251 standard for air kerma strength calibration was taken into account as well as updated interaction cross-section data. Calculations were done for the competing model 6702 source for the purpose of comparison. The calculated dose-rate constants for the two seeds are 1.010 and 1.016 cGyh(-1)U(-1) for the Symmetra and model 6702 seeds, respectively. The latter value deviates from the value, 1.039 cGyh(-1)U(-1), recommended in the TG-43 report. The calculated radial dose function for the Symmetra new seed is more penetrating than that of the model 6711 seed (by 20% at 5 cm distance) but agrees closely (within statistical errors) with that of the model 6702 seed up to distances of 10 cm. The anisotropy function for the seed is also close to that for the 6702 seed with a tendency of somewhat more pronounced anisotropy (lower values at small angles from the longitudinal axis). Compared to the model 6711 seed, the Symmetra new seed is more isotropic. The anisotropy constants (the anisotropy function averaged with respect to angle and distance) for the three seed models are within 2%.

Although there is renewed interest in prostate brachytherapy, little information is available on the effect of the procedure on prostate-specific antigen (PSA) changes over time. This study describes PSA kinetics after iodine-125 (I-125) transrectal ultrasound-guided transperineal implantation of the prostate. From February 1991-September 1997, 207 patients were treated with an I-125 prostate implant alone for T1-T2 prostate cancer. PSA values were obtained prior to treatment and at 1-73 months (median, 24 months). The change in PSA after implantation of the prostate was measured as a fraction of the pretreatment PSA (PSA at follow-up/pretreatment PSA). PSA failure was defined as two elevations in PSA or PSA > 1 ng/ml. One hundred fifty-five patients had PSA values recorded at the 1-month time period. A PSA value greater than the pretreatment PSA at 1 month was found in 27% (42/155). This had no significant effect on future PSA failure. The median percentage change in PSA after implantation for all patients were as follows: 1 month, 0.73; 3 months, 0.30; 6 months, 0.18; 12 months, 0.12; 18 months, 0.12; 24 months, 0.08; 30 months, 0.07; 36 months, 0.08; 42 months, 0.08; and 48 months, 0.05. The most significant decline occurred in the first 12 months. This was followed by a more gradual decline between 12-24 months. There was little change in PSA values after 24 months. The 1-year PSA value had a significant effect on PSA failure. Patients with a 1-year PSA 1 ng/ml (69) (P = 0.002). Twenty-seven patients developed PSA failure. The time to PSA failure ranged from 12-48 months (median, 24 months), but most (20/27) failures occurred after 18 months. We conclude that the greatest decline in PSA after I-125 implantation of the prostate occurs during the first year, and little change occurs after 2 years. A 1-year PSA value > 1 ng/ml is highly predictive of eventual PSA failure, which occurs in most patients after 18 months posttreatment.

Real time optimized treatment planning at the time of the implant is desirable for ultrasound-guided transperineal 125 I permanent prostate implants. Currently available optimization algorithms are too slow to be used in the operating room. The goal of this work is to develop a robust optimization algorithm, which is suitable for such application. Three different genetic algorithms (sGA, sureGA and securGA) were developed and compared in terms of the number of function evaluations and the corresponding fitness. The optimized dose distribution was achieved by searching the best seed distribution through the minimization of a cost function. The cost function included constraints on the periphery dose of the planned target volume, the dose uniformity within the target volume, and the dose to the critical structure. Adjustment between the peripheral dose, the dose uniformity and critical structure dose can be achieved by varying the weighting factors in the cost function. All plans were evaluated in terms of the dose nonuniformity ratio, the conformation number and the dose volume histograms. Among these three GA algorithms, the securGA provided the best performance. Within 2500 function evaluations, the near optimum results were obtained. For a large target volume (5 cm×4 cm×4.5 cm) including urethra with 20 needles, the computer time needed for the optimization was less than 5 min on a HP735 workstation. The results showed that once the best set of parameters was found, they were applicable for all sizes of prostate volume. For a fixed needle geometry, the optimized plan showed much better dose distribution than that of nonoptimized plan. If the critical structure was considered in the optimization, the dose to the critical structure could be minimized. In the cases of irregular and skewed needle geometry, the optimized treatment plans were almost as good as ideal needle geometry. It is concluded that this new genetic algorithm (securGA) allows for an efficient and rapid optimization of dose distribution, which is suitable for real time treatment planningoptimization for ultrasound-guided prostate implant.

Transperineal interstitial permanent prostate brachytherapy is being selected as the treatment of choice for early-stage prostatic carcinoma with increasing frequency by both patients and medical practitioners. This trend is surprising to many who are aware of the disappointing results following the retropubic technique of a few decades ago. Others advocate that the newer techniques, which use technologically advanced imaging of the prostate and sophisticated treatment planning systems, allow highly conformal source placement within the gland, resulting in a dose distribution that is superior to that previously achieved. Does improved dose distribution correlate with a higher local control rates in prostate implant patients? This review compares the historical technique of open laparotomy and retropubic implantation as practiced at Memorial Sloan-Kettering Cancer Center in the 1970s to the contemporary technique of transperineal ultrasound-guided permanent seed placement of the 1990s. The results to date show that the present techniques are producing substantially better outcomes, probably resulting from better patient selection as well as improved dose delivery. This is a US government work. There are no restrictions on its use.

Objective: To determine the α/β ratio of prostate cancer using the linear quadratic model taking into account different radiation prescription doses and RBE for low energy gamma rays. Methods and material: The linear quadratic model was used to evaluate the α/β ratio for prostate cancer taking into account the dosimetric errors resulting from seed displacements in prostate permanent implant brachytherapy with 125I and 103Pd. The study assessed the variability of the α/β ratio with different prescribed external beam radiation therapy doses and published values of the relative biological effectiveness (RBE) for both 125I and 103Pd. The biological effective dose (BED) for prostate implant brachytherapy was equated to the external beam radiation therapy dose to derive an equation for α/β ratio. Results: The results showed that the α/β ratio for prostate cancer varied between 1 and 4.5 for an RBE of 1.0 when an external beam dose of 78.0 Gy was prescribed. When published values of RBEs were incorporated into the analysis, the α/β ratio varied between 0.37 and 4.4. The α/β ratio changed by 30% when the external beam radiation dose was increased from 72 Gy to 80 Gy. Conclusions: Assuming an average reduction in implanted seeds brachytherapy dose between 10–20% using 125I or 103Pd, the realistic value of the α/β ratio for prostate tumors likely lies between 0.7 and 2.0.

A new method of treatment planning for the I-125 and Pd-103 permanent interstitial prostate implant is developed, which does not use the traditional nomograms but automatically generates optimized source configurations. An iterative algorithm is used that places one seed at a step. The volume dose of target is calculated at each step to determine the coldest spot where the next source is to be placed, so that the dose uniformity of target is best improved as source placement proceeds. At each step, the total activity required for the seed configuration as so established is calculated by normalizing the minimal dose to the prescribed dose. An optimized configuration is the one that takes the minimized total activity. Around its minimum the total activity has a very small variation with the number of seeds. Consequently multiple clinically acceptable seed configurations with similar total activity but different individual activities are generated simultaneously. In our computer generated treatment plans most of the seeds are distributed in the periphery of the target, similar to the Paterson-Parker pattern of a volume implant.

A fast knowledge-based radioactive seed localization method for brachytherapy was developed to automatically localize radioactive seeds in an intraoperative volumetric cone beam CT (CBCT) so that corrections, if needed, can be made during prostate implant surgery. A transrectal ultrasound (TRUS) scan is acquired for intraoperative treatment planning. Planned seed positions are transferred to intraoperative CBCT following TRUS-to-CBCT registration using a reference CBCT scan of the TRUS probe as a template, in which the probe and its external fiducial markers are pre-segmented and their positions in TRUS are known. The transferred planned seeds and probe serve as an atlas to reduce the search space in CBCT. Candidate seed voxels are identified based on image intensity. Regions are grown from candidate voxels and overlay regions are merged. Region volume and intensity variance is checked against known seed volume and intensity profile. Regions meeting the above criteria are flagged as detected seeds; otherwise they are flagged as likely seeds and sorted by a score that is based on volume, intensity profile and distance to the closest planned seed. A graphical interface allows users to review and accept or reject likely seeds. Likely seeds with approximately twice the seed volume are automatically split. Five clinical cases are tested. Without any manual correction in seed detection, the method performed the localization in 5 seconds (excluding registration time) for a CBCT scan with 512×512×192 voxels. The average precision rate per case is 99% and the recall rate is 96% for a total of 416 seeds. All false negative seeds are found with 15 in likely seeds and 1 included in a detected seed. With the new method, updating of calculations of dose distribution during the procedure is possible and thus facilitating evaluation and improvement of treatment quality.

Purpose : The objective of this work is to investigate whether the minimum peripheral dose is a practical parameter for dose specification in permanent 125I implants of the prostate. Methods and Materials : The investigation was carried out by use of a computer model of ellipsoidal 125I implants in which the average dimension and elongation factor were varied to provide a wide range of geometries. Both ideal and nonideal implants were investigated. The 125I seeds were confined to the target volume except for a portion of the study in which the effect of placing seeds outside the target volume was investigated. Results : The minimum peripheral dose was found to be very sensitive to the seed placement. The irregularities in the seed spacing that inevitably occur in actual implants tend to lower the minimum peripheral dose. As a result, the minimum peripheral dose is generally significantly less than planned by an amount that is unpredictable, and often exceeds 25%. However, the percentage of the target volume that receives a dose less than the prescribed minimum peripheral dose is generally less than 10%. Implanting seeds outside the target volume improves the dose uniformity, but does not appear to offer any advantage in dose coverage, and increases the volume of normal tissue irradiated. Conclusion : If a minimum peripheral dose is prescribed for a permanent 125I prostate implant, and the implant is planned using an idealized implant having precisely spaced seeds, the prescribed dose will rarely, if ever, be achieved. Reasonable agreement with the prescribed dose can be achieved only if the requirement for coverage is relaxed from 100 to 90%, or if the total source strength is increased by 20% to compensate for the anticipated imperfections in seed placement.

Purpose: To study the feasibility using MR imaging to improve target definition on ultrasound during permanent prostate implants and aid in source strength determination for treatment planning in the OR. Methods: Patients who receive permanent prostate implants undergo MR and CT imaging prior to the implant procedure to determine the volume of the prostate, bony restriction to the procedure, bladder extension, external sphincter length and neurovascular bundle. The volume of the prostate is generally used to order seeds for the procedure. In 10 patients, the MR was used as the preplanning study with the PTV defined as a 2 mm expansion of the MR prostate in all directions except the posterior. Various dose volume parameters for the MR prostate and the PTV were compared to the actual preplan developed and executed in the OR. In addition, there parameters were compared to the post implant dosimetry performed 3 weeks after the implant procedure. Results: The results show that the number of seeds used using MR and US (ultrasound) planning was generally with 2 seeds and the maximum difference was 7 seeds. There is no significant difference between any of the dose index parameters of V100, V150, V200, D99 and D90 parameters between MR planning, US planning and postimplant evaluation There was a significant difference between planned D99 (avg of 105%) and achieved D99 (avg 91%). Conclusion: MR imaging is an invaluable tool to improve target definition for permanent prostate implants. Use of MR images for preplanning improves the confidence with which source can be ordered for the procedure that is OR planned. Ordering a maximum of 10 seeds more than planned would be sufficient to deliver a plan in the OR using US. Moving ahead to non-rigid registration between MR ad US images could further increase the confidence level of MR planning.

Purpose: To present a new accelerated Monte Carlo code (MCPI: Monte Carlo for Prostate Implant) intended for use as a dose calculation engine for planning clinical prostate implants. MCPI simulates physically a set of radioactive seeds with arbitrary positions and orientations, merged in a 3D CT-based heterogeneous phantom representing the prostate and surrounding tissue.

The purpose of this paper is to report the clinical benefits of our in house inverse planning routine (IPSA) for the treatment planning of permanent prostate implant (PPI). IPSA has been designed for 3D image guided brachytherapy treatment planning. The optimization process is guided by dose objectives define for each organ extracted from medical imaging. IPSA takes into account multiple targets (prostate, boost) and multiple organs at risk (urethra, rectum, bladder, etc.). IPSA is setup to maximize the prostate dose coverage while taking into account other clinical objectives like the dose homogeneity and the organs at risk protection. A simulated annealing algorithm optimizes the source and needle positions to fulfill the dose objectives and few source placement rules in less than 1 minute. For ten patients IPSA is compared to conventional manual planning. IPSA is also tested to optimize with different maximum number of needles and different source activity. IPSA needs about 15 seconds for each optimization. In comparison an experienced physicist needs about 20 minutes to perform a manual planning. The prostate volumes range from 17 to 51cc. IPSA consistently and rapidly produces equivalent dosimetric indices as manual planning while respecting severe restrictions on source placement rules. IPSA produces implant without seeds outside of the prostate, without needles with only one seed and without needles with 3 consecutive seeds. This reduces the risk of complication due to seed misplacement and edema. IPSA also uses a smaller number of needles reducing the cause of trauma. IPSA is appropriate for pre-planning, intra-operative pre-planning and intra-operative real-time planning taking into account the implanted sources and needles. This technology is not intended to replace the physicist but to accelerate the planning process making intra-operative treatment planning more effective.

108 Background: Patients with intermediate risk prostate cancer choosing radiotherapy may be treated with a number of regimens. The current study compares the direct treatment cost for five therapeutic options based on Fiscal Year 2014 Medicare allowable reimbursements. Methods: Hypothetical charge sheets were generated along with the expected Medicare allowable reimbursements (based on global billing where applicable) for the following regimens: 1.) Image Guided Intensity Modulated Radiotherapy (IGIMRT) to a dose of 78Gy in 39 fractions with one field reduction (IGIMRT); 2.) Dose escalated IGIMRT to 84.60Gy in 47 fractions with one field reduction (MSKCC-IGIMRT); 3.)IGIMRT to a dose of 45Gy in 25 fractions followed by a 90 seed I125 prostate implant (IGIMRT-BTX); 4.) Image Guided Proton Therapy to a dose of 78Gy(RBE) in 39 fractions with one field reduction (SFPT); 5.) Image Guided Hypofractionated Proton Therapy to a dose of 72.50Gy(RBE) in 29 fractions with one field reduction (HFPT). Results: Based on Fiscal Year 2014 Medicare allowable reimbursements, the direct cost for each of these interventions including professional fees, technical fees, isotope costs and facility fees is shown in the Table. Conclusions: This data presents a framework for evaluating the cost effectiveness of proton therapy as compared to competing therapeutic options. Under current Medicare allowable reimbursements, the cost of proton therapy relative to the cost of other therapeutic options is highly dependent on the number of radiotherapy fractions delivered. The feasibility of delivering hypofractionated proton therapy for patients with localized prostate cancer is being investigated at a number of institutions as well as within the framework of a multicenter protocol. Ultimately the cost of proton therapy will need to be weighed against tumor control probabilities as well as the economic and quality of life benefits associated with reduced normal tissue exposure. [Table: see text]

Purpose: To report outcomes and toxicity of the first Canadian permanent prostate implant program. Methods and Materials: 396 consecutive patients (Gleason ≤6, initial prostate specific antigen (PSA) ≤10 and stage T1-T2a disease) were implanted between June 1994 and December 2001. The median follow-up is of 60 months (maximum, 136 months). All patients were planned with fast-simulated annealing inverse planning algorithm with high activity seeds ([gt] 0.76 U). Acute and late toxicity is reported for the first 213 patients using a modified RTOG toxicity scale. The Kaplan-Meier biochemical failure-free survival (bFFS) is reported according to the ASTRO and Houston definitions. Results: The bFFS at 60 months was of 88.5% (90.5%) according to the ASTRO (Houston) definition and, of 91.4% (94.6%) in the low risk group (initial PSA ≤10 and Gleason ≤6 and Stage ≤T2a). Risk factors statistically associated with bFFS were: initial PSA >10, a Gleason score of 7–8, and stage T2b-T3. The mean D90 was of 151 ± 36.1 Gy. The mean V100 was of 85.4 ± 8.5% with a mean V150 of 60.1 ± 12.3%. Overall, the implants were well tolerated. In the first 6 months, 31.5% of the patients were free of genitourinary symptoms (GUs), 12.7% had Grade 3 GUs; 91.6% were free of gastrointestinal symptoms (GIs). After 6 months, 54.0% were GUs free, 1.4% had Grade 3 GUs; 95.8% were GIs free. Conclusion: The inverse planning with fast simulated annealing and high activity seeds gives a 5-year bFFS, which is comparable with the best published series with a low toxicity profile.

Background To date, there are few descriptive analyses of postimplant dosimetry from multi-institutional clinical trials. The purpose of this report is to describe the postimplant dosimetry achieved in Radiation Therapy Oncology Group (RTOG) 0019. Methods and materials Patients were treated with external beam radiation therapy (45 Gy/25 fractions) followed by a prostate implant (I-125, prescription dose 108 Gy). Postimplant dosimetric assessment was accomplished by obtaining a CT scan of the prostate 1 month after the date of the implant procedure. Prostate volume was outlined by the first author. Dose–volume histograms were calculated by the Radiologic Physics Center. Four dosimetric quantifiers (DQs) were examined: D 90 is the dose (reported as percentage of the prescription dose) received by 90% of the prostate; V 100 , V 150 , V 200 is the percentage of the prostate volume receiving 100%, 150%, and 200% of the prescription dose, respectively. For the purposes of analysis, institutions were divided into three groups according to accrual ( Results One hundred thirty-eight patients from 27 institutions were registered in the study. Nineteen patients were excluded from this analysis; 14 who had no data and 5 who were ineligible, leaving 119 for analysis. The mean, median, and range of the four DQs are as follows: D 90 105.6%, 106.0%, 57.6–174.8%; V 100 89.8%, 92.6%, 11.2–100%; V 150 58.4%, 59.6%, 0.9–93.7%; and V 200 27.9%, 25.1%, 0.3–85.2%. Statistically significant differences according to institutional accrual were observed for D 90 ( p = 0.0283) and V 200 ( p = 0.0075), but not for V 100 ( p = 0.1534) and V 150 ( p = 0.0509). Conclusions The DQ observed in this multi-institutional prospective study are roughly comparable to series from single institutions with considerable brachytherapy experience. Differences in DQs were observed according to institutional accrual. These data could be used to determine a community standard with respect to postimplant dosimetry.