Prostate deformation from inflatable rectal probe cover and dosimetric effects in prostate seed implant brachytherapy (original) (raw)
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Strahlentherapie und Onkologie, 2008
Purpose: To evaluate seed displacements after permanent prostate brachytherapy considering different prostate levels. Patients and Methods: In 61 patients, postimplant CT scans were performed 1 day and 1 month after an implant with stranded seeds. Seed and prostate surface displacements were determined relative to pelvic bones. Four groups of seed locations were selected: seeds at the base (n = 305; B), at the apex (n = 305; A), close to the urethra (n = 306; U), and close to the rectal wall (n = 204; R). The length of two strands (always containing four seeds) per patient was measured in all CT scans and compared. Results: The largest inferior seed displacements were found at the base: mean 5.3 mm (B), 2.2 mm (A), 2.7 mm (U), 3.3 mm (R; p < 0.001). Posterior displacements predominated both at the base and the central region: mean 2.2 mm (B), 2.0 mm (U), 0.8 mm (A), -0.6 mm (R; p < 0.001). With a decreasing edema between day 1 and 30 (mean prostate volume of 51 cm 3 vs. 41 cm 3 ; p < 0.001), a mean caudal prostate base displacement of 3.9 mm was found, whereas the mean inward displacement ranged from 1.2 to 1.6 mm at the remaining borders (lateral, anterior, posterior, apical). The analysis of the strand lengths revealed an implant compression between day 1 and 30 (mean 1.7 mm; p < 0.001). Conclusion: The largest prostate tissue and seed displacements were observed at the prostate base, associated with an implant compression. Predominantly inferior and posterior displacements implicate consequential smaller preplanning margins at the apex and the posterior prostate.
Effect of post-implant edema on the rectal dose in prostate brachytherapy
International Journal of Radiation Oncology*Biology*Physics, 1999
Purpose: To characterize the effect of prostate edema on the determination of the dose delivered to the rectum following the implantation of 125 I or 103 Pd seeds into the prostate. Methods and Materials: From 3 to 5 post-implant computed tomography (CT) scans were obtained on 9 patients who received either 125 I or 103 Pd seed implants. None of the patients received hormone therapy. The outer surface of the rectum was outlined on each axial CT image from the base to the apex of the prostate. The D 10 rectal surface dose, defined as the dose which encompasses only 10% of the surface area of the rectum, was determined from each CT scan by compiling a dose-surface histogram (DSH) of the rectal surface. The magnitude and half-life of the post-implant edema in each of these implants is known from the results of a previously published study based on the analysis of the serial CT scans. Results: As the prostate edema resolved, the distance between the most posterior implanted seeds and the anterior surface of the rectum decreased. As a result, the D 10 rectal surface dose increased with each successive post-implant CT scan until the edema resolved. The dose increased exponentially at approximately the same rate the prostate volume decreased. The D 10 rectal surface dose at 30 days post-implant ranged from 16% to 190% (mean 68 ؎ 50%) greater than on day 0. The dose on day 30 was at least 50% greater in 6 of 9 cases. Conclusion: The rectal surface dose determined by analysis of a post-implant CT scan of an 125 I or 103 Pd prostate seed implant depends upon the timing of the CT scan. The dose indicated by the CT scan on day 30 is typically at least 50% greater than that indicated by the CT scan on day 0. Because of this difference, it is important to keep the timing of the post-implant CT in mind when specifying dose thresholds for rectal morbidity. © 1999 Elsevier Science Inc. Brachytherapy, Permanent prostate implant, Rectal dose, 125 I, 103 Pd, Transperineal, Interstitial.
Medical Dosimetry, 2000
As computer-aided margin tools become more sophisticated, physicists will be increasingly called upon to convert ultrasound prostate volumes to expanded planning target volumes (PTVs) to treat adequately extracapsular disease. The American Association of Physicists in Medicine Task Group 43 formalism and the new National Institute of Standards and Technology calibration system suitable for single low-energy seeds have been crucial in smoothly implementing changes in established seeds and in incorporating data from new manufacturers. However, the lack of consensus on treatment design and evaluation has led to an uncomfortably wide spectrum of clinical practice, only part of which can be attributed to variations inherent to any surgical procedure due to the practitioner's skill. The relative merits of implanting the prostate and margin with a modified uniform seed-loading approach to create plans with a relatively homogeneous dose distribution and a corresponding low risk of overdosing critical structures are addressed. Likewise, the advantages of performing postoperative dosimetry at the physically optimum time of greater than 2 weeks post implant are contrasted with the clinical advantages of obtaining the dosimetry as soon as possible. Proposed lower limits for quality parameters such D 90 and V 100 are reviewed. Measures of doses to the urethra, rectum, and neurovascular bundles are presented, along with correlations between various dosimetric parameters and other patient specific data with quality of life metrics involving urinary incontinence, rectal damage, and sexual dysfunction.
Radiation Oncology, 2014
Background: In pulsed-dose rate prostate brachytherapy the dose is delivered during 48 hours after implantation, making the treatment sensitive to oedematic effects possibly affecting dose delivery. The aim was to study changes in prostate volume during treatment by analysing catheter configurations on three subsequent scans. Methods: Prostate expansion was determined for 19 patients from the change in spatial distribution of the implanted catheters, using three CT-scans: a planning CT (CT1) and two CTs after 24 and 48 hours (CT2, CT3). An additional 4 patients only received one repeat CT (after 24 hours). The mean radial distance (MRD) of all dwell positions to the geometric centre of all dwell positions used was calculated to evaluate volume changes. From three implanted markers changes in inter-marker distances were assessed. The relative shifts of all dwell positions were determined using catheter-and marker-based registrations. Wilcoxon signed-rank tests were performed to compare the results from the different time points.
Edema and Seed Displacements Affect Intraoperative Permanent Prostate Brachytherapy Dosimetry
International journal of radiation oncology, biology, physics, 2016
We sought to identify the intraoperative displacement patterns of seeds and to evaluate the correlation of intraoperative dosimetry with day 30 for permanent prostate brachytherapy. We analyzed the data from 699 patients. Intraoperative dosimetry was acquired using transrectal ultrasonography (TRUS) and C-arm cone beam computed tomography (CBCT). Intraoperative dosimetry (minimal dose to 40%-95% of the volume [D40-D95]) was compared with the day 30 dosimetry for both modalities. An additional edema-compensating comparison was performed for D90. Stranded seeds were linked between TRUS and CBCT using an automatic and fast linking procedure. Displacement patterns were analyzed for each seed implantation location. On average, an intraoperative (TRUS to CBCT) D90 decline of 10.6% ± 7.4% was observed. Intraoperative CBCT D90 showed a greater correlation (R(2) = 0.33) with respect to Day 30 than did TRUS (R(2) = 0.17). Compensating for edema, the correlation increased to 0.41 for CBCT and ...
International Journal of Radiation Oncology*Biology*Physics, 2000
Objectives: Permanent implantation with 125 I in patients with localized prostate cancer who have prostate volumes > 50 cm 3 is often technically difficult owing to pubic arch interference. The objective of this study was to describe dosimetry outcomes in a group of patients who were implanted using the real-time ultrasound-guided technique who had prostate volumes > 50 cm 3. Materials and Methods: A total of 331 patients received an 125 I prostate seed implant from January 1, 1995, to June 1, 1999, of whom 66 (20%) had prostate volumes > 50 cm 3 at the time of the procedure. The real-time seed implant method was used in all patients and consisted of intraoperative planning and real-time seed placement using a combination of axial and sagittal ultrasound imaging. Pubic arch interference was managed using an extended lithotomy position or by angling the tip of the ultrasound probe in an anterior direction. No preimplant pubic arch CT scan study was performed and no patients were excluded from treatment because of prostate size. Implant quality was assessed using CT-based dosimetry performed 1 month postimplant. Dose-volume histograms for the prostate, bladder, rectum, and urethra volumes were generated. The target dose for these implants was 160 Gy and an adequate implant was defined as the dose delivered to 90% of the prostate (D90) > 140 Gy. The dose delivered to 95% of the prostate (D95) and doses to 30% of the rectal (DRECT30) and urethral (DURE30) volumes were also calculated. Results: Prostate volumes in the 66 patients ranged from 50 to 93 cm 3 (median 57, mean 61 cm 3). Total activity implanted was 27.8-89.1 mCi (median 57 mCi), with a range in activity per seed of 0.36-0.56 mCi (median 0.4 mCi). The prostate D90s and D95s ranged from 13,245 to 22,637 cGy (median 18,750) and 11,856 to 20,853 cGy (median 16,725), respectively. Only one patient (1.5%) had a D90 < 140 Gy. The DURE30 values ranged from 15,014 to 27,800 cGy (median 20,410) and the DRECT30 values were 3137-9910 cGy (median 5515). Conclusion: Implantation of the large prostate can be accomplished using the real-time method. A total of 98.5% of the patients receive a high-quality implant. In addition, these implants should not put patients at increased risk for significant urinary and bowel complications because urethral and rectal doses can be kept at acceptable levels.
Brachytherapy, 2011
Purpose: To investigate the adequacy of the model based nomogram in predicting the total seed activity necessary for optimal dosimetry in intraoperative real-time prostate seed implant (PSI). Materials and Methods: From 2007 to 2010, twenty-nine patients with early stage (T1-T2) prostatic carcinoma underwent ultrasound-guided transperineal real-time implant with I-125 radioactive sources in our institution. The pre-treatment prostate volumes ranged from 20.69 cc to 51.65 cc. Intraoperative plans were generated for patient treatments in the operation room using Variseed planning software from Varian. A modified peripheral loading technique was used during the treatment planning process to cover the prostate gland with prescription dose of 144 Gy, while maintaining all normal tissue dose constraints. In addition, manual dose optimization and real time dosimetric adjustments were used to fine tune the needle and source positions as well as numbers. Two types of radioactive I-125 sources (6711, General Electric; and I125-SL, Mills Biopharmaceuticals) were utilized in this study. The intraoperative plan was executed using Mick applicator. Postimplant CT analysis was performed 1 month after treatment to determine appropriate dosimetric outcome such as V100 (prostate), D90 (prostate), V150 (urethra), and V110 (rectum) recommended by American Brachytherapy Society (ABS). In each case, the total actual administrated seed activity was compared to that activity determined from a standard look-up nomogram. Additionally, prostate width (W), length (L), height (H) and other dosimetric parameters were determined. Results: Postimplant CT analysis meets ABS requirements. Improved dose homogeneity, and lower normal tissue doses were observed. Regardless of source types, an average 15% reduction of total seed activity in the realtime approach was found compared to nomogram prediction which accounts also the source misalignments during the seed delivery process. From our experience, we suggest a new power law formula (activity (mCi) 5 1.84 d 2 , where d in cm 5 1/3 (WþLþH) of the prostate). Conclusions: The amount of activity required to effectively treat a prostate of a given volume was found lower with real-time intraoperative technique compared to that with the pre/post plan technique. Our experience indicates that the power law formula is still an appropriate method to predict the total seed activity in the real-time prostate seed implant procedure.
Prostate gland motion and deformation caused by needle placement during brachytherapy
Brachytherapy, 2002
Purpose: To determine the extent of edge and gland position changes caused by needle insertion in patients undergoing prostate brachytherapy. Methods and Materials: Nineteen patients with T1-T3 prostate cancer were implanted with the realtime method by using a two-phase peripheral loading technique. Serial contours of the prostate at 5-mm intervals were acquired by the dose-planning system. All of the peripheral needles were then placed and spaced 5-10 mm apart by using the largest transverse ultrasound image as the reference plane. The position of the probe was relocated at the zero plane, and the difference between the preneedle and postneedle zero plane was recorded as the difference in the z axis. Axial ultrasound images were again acquired. The second set of captured images, which matched in number the first set, was contoured over the previously contoured preneedle images. Prostate gland deformation and displacement were determined by comparing the preneedle contoured image with the images captured after needle placement. Deformation was determined by calculating the differences between the edges of the gland as measured at the major axis of the gland (x and y planes). Displacement was determined by measuring the differences between the center positions of the two contoured structures. Deformation and displacement were determined on each acquired 5-mm image. Differences were compared by student's t test. Results: The mean preneedle prostate volume was 47 ml (range, 21.5-68.7 ml), compared with 48.1 ml (range, 19.4-80.3 ml; p ϭ 0.228) after peripheral needle placement. A median of 16 (range, 12-19) peripheral needles were placed. The median change in the base position of the prostate was 1.5 cm (range of 0 to 3.0 cm; p ϭ 0.0034). The mean x and y deformation was 6.8 mm (median, 7.9 mm; range, 4.3-8.1 mm) and 3.6 mm (median, 3.3 mm; range, 1.0-5.5 mm), respectively. The greatest deformation for any individual slice for x was 21.6 mm and for y was 15.3 mm. The mean number of slices that were found with a Ͼ 2-, 5-, and 10-mm deformation in the x axis was 7 (range, 3-10), 4 (range, 1-3), and 1 (range, 0-4), respectively. Similar deformation in the y axis was found in 6 (range, 3-10), 2.5 (range, 0-6), and 0.3 (range, 0-2) slices. The mean x and y displacement was 1.9 mm (median, 1.8 mm; range, 0.3-6.6 mm) and 2.8 mm (median, 1.9 mm; range, 2-5.8 mm). The greatest displacement for any individual slice for x was 7 mm and for y was 10 mm. The mean number of slices with a displacement Ͼ 2, 5, and 10 mm in the x axis was 5 (range, 1-10), 0.8 (range, 0-5), and 0, respectively. Similar displacement in the y axis was found in 5 (range, 0-9), 1.7 (range, 0-7), and 0 slices, respectively. Conclusions: Placing most needles in the periphery results in a minimal prostate volume increase, suggesting little need to overplan the implant when this method is used. However, significant edge and gland position changes caused by the needle insertion did occur. These changes may explain some of the difficulty in reproducing the preplan and should be taken into consideration for all types of prostate brachytherapy planning.
Medical Physics, 1999
There is now considerable evidence to suggest that technical innovations, 3D image-based planning, template guidance, computerized dosimetry analysis and improved quality assurance practice have converged in synergy in modern prostate brachytherapy, which promise to lead to increased tumor control and decreased toxicity. A substantial part of the medical physicist's contribution to this multi-disciplinary modality has a direct impact on the factors that may singly or jointly determine the treatment outcome. It is therefore of paramount importance for the medical physics community to establish a uniform standard of practice for prostate brachytherapy physics, so that the therapeutic potential of the modality can be maximally and consistently realized in the wider healthcare community. A recent survey in the U.S. for prostate brachytherapy revealed alarming variance in the pattern of practice in physics and dosimetry, particularly in regard to dose calculation, seed assay and time/method of postimplant imaging. Because of the large number of start-up programs at this time, it is essential that the roles and responsibilities of the medical physicist be clearly defined, consistent with the pivotal nature of the clinical physics component in assuring the ultimate success of prostate brachytherapy. It was against this background that the Radiation Therapy Committee of the American Association of Physicists in Medicine formed Task Group No. 64, which was charged ͑1͒ to review the current techniques in prostate seed implant brachytherapy, ͑2͒ to summarize the present knowledge in treatment planning, dose specification and reporting, ͑3͒ to recommend practical guidelines for the clinical medical physicist, and ͑4͒ to identify issues for future investigation.