Urethra D10 Research Articles

Sci-Sat AM(2): Brachy-02: Image guided brachytherapy (IGBT) for HDR prostate treatment : Pre-treatment verification using cone beam imaging to determine catheter displacement.

Prostate HDR brachytherapy utilizes flexible catheters for treatment delivery. Catheters are inserted under US guidance and planning performed on CT images. This study investigates the efficacy of performing kV cone beam imaging prior to treatment to quantify catheter displacement and dose delivered. Twenty consecutive patients undergoing HDR prostate brachytherapy were planned using CT images. Under US guidance, catheters and four fiducial markers were placed into the prostate. Before treatment, visual check confirmed no movement of the template sutured to the perineum and no movement relative to the template. Cone beam imaging was performed using an isocentric mobile c-arm. Catheters were re-adjusted if required by the Radiation Oncologist. The cone beam images prior to adjustment were later fused with the planning CT. In 17 of the 20 patients, catheter displacements exceeding 0.5cm were observed. Compared to the CT based plan, an average catheter displacement of 1.0cm results in a decrease in the V100 of the prostate by approximately 27%, urethra V120 increased by about 7%, and urethra D10 increased by about 4%. Approximately 65% of patients had average catheter displacements of 1.0cm and larger. Three patients had catheter shifts larger than 2cm. Catheter movement within the patient can be significant and cone beam imaging prior to treatment delivery provides precise imaging to determine catheter displacement. Cone beam imaging time using an isocentric C-arm is sufficiently short enough (∼ 2 minutes) so as to make this a viable quality assurance tool in the OR.

SU‐GG‐T‐465: Sequential Optimization Script to Generate HDR‐Like Dose Distribution for Hypofractionated Prostate Treatment with CyberKnife System

Purpose: To develop a Sequential Optimization script that generates HDR‐like dose distribution for hypofractionated prostate treatment with CyberKnife® Robotic Radiosurgery System and evaluate its consistency over different patients. Method and Materials: Sequential Optimization is the latest optimization algorithm available for CyberKnife treatment planning. The optimization is performed sequentially, as a series of individual optimization steps. Each step corresponds to a specific clinical objective. First, dose constraints to organs at risk are defined that cannot be violated by during the optimization. Additional constraints are defined to the maximum Monitor Units for each beam, for each robot position, and for the entire treatment plan. Then the objectives of each optimization step are specified. The result of each step represents the optimal value for this objective that is achievable within the existing constraints. Each result is retained as an additional constraint for all subsequent steps. In this manner the treatment plan is built up one clinical objective at a time, with a gradual improvement observed at each step. A sequence of optimization steps (script) was created that generates HDR‐like dose distribution for prostate treatment delivering 38 Gy in 4 fractions. Treatment plans were generated with the same script and with the Iris Variable Aperture Collimator for 10 prostates. Results: Prostate volumes ranged from 25–70 cc. Prostate V100, V125 and V150 are ∼95%, 50% and 15%. Urethra Dmax and D10 are <4560 and 4180 cGy. Rectal wall Dmax and D10 are <3800 and 2560 cGy. Bladder Dmax and D10 are <4560 and 4180 cGy. The number of beams is less than 250. Conclusion: A script was created that consistently reproduces dose distribution similar to an HDR treatment. It was demonstrated that a script can be defined for particular clinical case and used as a starting point reducing planning time.Research sponsored by Accuray Incorporated.

SU‐FF‐T‐43: Objective Comparison of RAPID Strand and Free SelectSeeds Loading for Permanent Prostate Implants Using An Inverse Planning Approach

Purpose: To quantify differences in treatment plans of permanent implants between RAPID strand™ and free selectSeed™ loading patterns. Method and Materials: The 3‐D US scan and treatment plan from ten patients who have been treated for prostate cancer with the permanent seed implant technique were arbitrary selected. The plans were generated manually by an experienced dosimetrist backed up by a team. Essentially the RAPID strand™ seed‐loading pattern was used. Retrospectively the patients were re‐planned with a commercial 3‐D planning system (SPOT‐PRO™ 3.0) using the new inverse planning algorithm (IPSA). A plan with a RAPID strand loading pattern (IPSA‐R) was generated and a plan with a free seed‐loading pattern (IPSA‐F). Results: The calculation time of IPSA was < 15 s for 400,000 iterations (2.5 GHz PC), which is fast enough to be used intra‐operatively. The target coverage V100 was equal (98–99%) for all plans. The target and urethra DVHs of the manual and the IPSA‐R plan were similar. By contrast the urethra doses D40, D30, D20, D10, and Dmax of the free seed plan IPSA‐F were 27–41 Gy lower than in the RAPID strand plan IPSA‐R. Conclusion: When using free seeds instead of RAPID strands, the urethra dose is significantly reduced. Conflict of Interest: Part of this research was supported by Nucletron B.V., Veenendaal, The Netherlands.

CT–ultrasound fusion prostate brachytherapy: A dynamic dosimetry feedback and improvement method. A report of 54 consecutive cases

Purpose The authors describe a prostate brachytherapy technique with dynamic dosimetry feedback, using coregistered CT and ultrasound (US) images, to map initial dosimetry deficiencies and guide remedial source placement. Methods and materials Fifty-four consecutive patients treated with this method were analyzed for coregistration accuracy and dosimetry outcomes by evaluating the prostate V100, V150, D90, and urethral D50 and D10. Dosimetric improvements created by remedial source placement and preplan/postplan prostate D90 agreement were evaluated. Results Median CT–US coregistration discrepancy with this technique ranged from 0 to 4 mm, with the posterior midline prostate and base prostate providing the least consistent and the urethra providing the most consistent coregistration agreement. Final prostate V100 values ranged from 96.1% to 99.8% for all patients. The addition of remedial sources directed by CT–US fusion produced V100 and D90 improvements whose magnitude inversely correlated with the initial result and exceeded the effect of adding quantitatively identical randomly distributed increased millicuries. The final prostate D90 result agreed within (−) 5% to (+) 10% of the preplan result in 98% of all patients. Conclusions CT–US fusion prostate brachytherapy represents a dynamic dosimetry feedback and remediation method that consistently produced high prostate V100 and D90 values with acceptably low urethra D50 and D10 values in our study. The degree of prostate V100 and D90 dosimetry improvement created by remedial source placement effectively matched the degree of initial dosimetry deficiency. This method produced a high level of correlation between the preplan and final prostate D90 values.

Prostate brachytherapy seed migration and dosimetry: analysis of stranded sources and other potential predictive factors

Purpose The purpose of this study was to evaluate the influence of potential contributing factors to the incidence of seed migration and quality of prostate brachytherapy dosimetry. Methods and materials Sixty patients were evaluated with day one and 3–12 month plain films of the pelvis and chest, and day 1 CT-based dosimetry analysis. The incidence and types of seed migration were quantified. The seed migration outcome was evaluated with respect to source type (free vs. stranded), prostate volume, number of seeds, and needles. The day one prostate V100, V150, D90, and urethra D10 outcomes were evaluated with respect to source type, radiation type ( 125I vs. 103Pd), prostate volume, prostate swelling, and quantity of migrating seeds. Results An increased incidence of day one and cumulative seed migration was predicted by free vs. stranded source type, with a relative risk of 6.97 and 3.08, respectively. Pulmonary and distal (toward the perineum) migration patterns were significantly reduced in the stranded group. An increased day one prostate V100, V150, D90, and urethra D10 outcome was predicted by stranded source type. Conclusion Stranded source type was associated with decreased seed migration as well as higher prostate and urethra dosimetry values, resulting in an implant in which more radiation resided within the target volume, and less radiation metastasized to undesirable locations.

Prospective assessment of patient-reported long-term urinary morbidity and associated quality of life changes after 125I prostate brachytherapy

Purpose: Prostate brachytherapy has been reported to have less morbidity for patients than radical prostatectomy or external beam irradiation. However, to date there have been no long-term data to support these claims. With radiation doses in excess of 140 Gy required to control the tumor, disabling chronic urinary symptoms and associated quality of life (QOL) changes might be expected to occur. This study prospectively assessed the long-term effects of 125I prostate brachytherapy on urinary morbidity.Methods and Materials: A total of 248 patients with a median age of 67 years (range, 43–83 years) who presented with T1–T2 prostate cancer were treated with 125I seed implantation and followed up for a minimum of 18 months after treatment (range, 18 to 108 months; median, 31 months). There were 177 T1b–T2a cases and 41 patients with prostate-specific antigen >10 ng/ml; 20.2% were treated with hormonal therapy. All patients prospectively reported their urinary symptoms and QOL assessment on American Urological Association symptom score records before treatment and at each follow-up visit. Urinary symptoms at last follow-up were compared with pretreatment scores. Radiation doses to the prostate (dose delivered to 90% of the gland; D90) and urethra (D30) were determined by CT-based dosimetry.Results: The median prostate D90 was 165 Gy (range, 16.5–260 Gy), and the median urethra D30 was 192 Gy (range, 23.5–306 Gy). Mean individual scores and QOL ranged from 0.31 to 1.65 before implantation and 0.39 to 1.73 afterward. There were no significant differences between pretreatment and last mean scores for any of the categories except for a small but significant increase in urgency (p=0.01) and weak stream (p=0.03). The cohort of patients who initially presented with marked urinary symptoms (initial score ≥3) had improvement in individual scores by 31.4% to 58.2%, total score by 31.1% (p=0.0005), and QOL by 40.6% (p<0.0001).Conclusions: This study suggests that prostate brachytherapy is associated with minimal long-term urinary morbidity. The subgroup of patients who present with marked urinary symptoms before implantation has improvement in symptoms and QOL after implantation. These data substantiate the favorable long-term QOL outcomes associated with modern brachytherapy techniques.

Phase II prospective study of the use of conformal high-dose-rate brachytherapy as monotherapy for the treatment of favorable stage prostate cancer: A feasibility report

Purpose: To evaluate the technical feasibility and tolerance of image-guided transperineal conformal high-dose-rate (C-HDR) brachytherapy as the sole treatment modality for favorable, localized cancer of the prostate, and to analyze possible intrafraction and interfraction volume changes in the prostate gland which may affect dosimetric quality. Methods and Materials: Patients were eligible for this prospective Phase II trial if they had biopsy proven adenocarcinoma of the prostate with favorable prognostic factors (Gleason score ≤7, PSA ≤10 ng/ml and Stage ≤T2a). The technique consisted of a transperineal implant procedure using a template with transrectal ultrasound (TRUS) guidance. An interactive on-line real-time planning system was utilized with geometric optimization. This allowed dosimetry to be generated and modified as required intraoperatively. Prescription was to the minimum dose point in the implanted volume, assuring conformal coverage of the prostate at its widest dimension with no margin. Total dose was 3800 cGy in 4 fractions of 950 cGy each, delivered twice a day over 2 days. The dose to any segment of rectum and urethra was limited to ≤75% and ≤125% of the prescription dose, respectively. Before each fraction, needle positions were verified under fluoroscopy and adjusted as required. For the last 10 patients, the adjustments required were measured in a prospective fashion in representative extrema of the gland. TRUS images were recorded for all patients before any needle manipulation, again just before delivering the first fraction and immediately after the last fraction. This typically meant approximately 36 h to pass between the first and last measurements. Implant quality was assessed via dose–volume histograms (DVH). Results: Between 3/99 and 6/00, 41 patients received C-HDR interstitial brachytherapy as their only treatment for prostate cancer at our institution. Median age was 64 years (range 51–79). Stage distribution was 27 T1c patients and 14 T2a patients. Three patients had Gleason score (GS) of 5; 34 had GS of 6; 4 patients had GS of 7. Median pretreatment PSA was 4.7 ng/ml (range 0.8–13.3). All patients tolerated the treatment well with minimal discomfort. For 23 patients, data on volume changes in the gland during the implant were tabulated. They demonstrated a mean prostate volume of 30.7 cc before any manipulation with needles, 37.0 cc at the end of fraction 1, and 38.2 cc at the end of fraction 4. In addition, for those 10 patients prospectively evaluated for required adjustments, the overall mean adjustment between fraction 1 and fraction 2 was 2.0 cm, between fraction 2 and 3 was 0.4 cm, and between fractions 3 and 4 was 0.4 cm. For 10 consecutive patients, the average prescriptions dose -D90 for fractions 1 and 4 were 104% and 100%, respectively. The corresponding average urethral D10 for fractions 1 and 4 were 122% and 132%. Conclusions: Our protocol using C-HDR interstitial brachytherapy as monotherapy for early cancer of the prostate was feasible and well tolerated by 41 patients treated. Changes in interfraction prostate volume do not appear to be significant enough to warrant modification of dosimetry for each fraction. Both excellent dose coverage of the prostate gland and low urethral dose are achieved as measured by DVH. However, paramount attention should be given to needle displacement before each fraction. Needle movement is most significant between fractions 1 and 2. Acute toxicity (RTOG) has been modest. Late toxicity and tumor control rates will be reported as longer follow-up allows.

Determination of the urethral dose in prostate brachytherapy when the urethra cannot be visualized in the postimplant CT scan.

This study investigates the feasibility of locating the urethra at the geometric center of peripherally loaded 125I prostate implant when a urinary catheter is not utilized for the postimplant CT scan. Twenty postimplant CT scans utilizing a urinary catheter were randomly selected. The urethra was localized in each study and, in addition, a surrogate urethra was localized at the geometric center of the prostate. Dose-volume histograms of the urethra and surrogate urethra were compiled and compared. The values obtained for the urethra D10, D25, and D50 were in good agreement and demonstrate that the urethral dose can be determined reliably by locating a surrogate urethra at the geometric center of the prostate in a peripherally loaded implant when the urethra cannot be visualized.