Impact of ultrasound and computed tomography prostate volume registration on evaluation of permanent prostate implants

Image fusion techniques in permanent seed implantation

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

Automated finite-element analysis for deformable registration of prostate images

Two major factors preventing the routine clinical use of finite-element analysis for image registration are: 1) the substantial labor required to construct a finite-element model for an individual patient's anatomy and 2) the difficulty of determining an appropriate set of finite-element boundary conditions. This paper addresses these issues by presenting algorithms that automatically generate a high quality hexahedral finite-element mesh and automatically calculate boundary conditions for an imaged patient. Medial shape models called m-reps are used to facilitate these tasks and reduce the effort required to apply finite-element analysis to image registration. Encouraging results are presented for the registration of CT image pairs which exhibit deformation caused by pressure from an endorectal imaging probe and deformation due to swelling.

Prostate volume contouring: a 3D analysis of segmentation using 3DTRUS, CT, and MR

PURPOSE

This study evaluated the reproducibility and modality differences of prostate contouring after brachytherapy implant using three-dimensional (3D) transrectal ultrasound (3DTRUS), T2-weighted magnetic resonance (MR), and computed tomography (CT) imaging.

METHODS AND MATERIALS

Seven blinded observers contoured 10 patients' prostates, 30 day postimplant, on 3DTRUS, MR, and CT images to assess interobserver variability. Randomized images were contoured twice by each observer. We analyzed length and volume measurements and performed a 3D analysis of intra- and intermodality variation.

RESULTS

Average volume ratios were 1.16 for CT/MR, 0.90 for 3DTRUS/MR, and 1.30 for CT/3DTRUS. Overall contouring variability was largest for CT and similar for MR and 3DTRUS. The greatest variability of CT contours occurred at the posterior and anterior portions of the midgland. On MR, overall variability was smaller, with a maximum in the anterior region. On 3DTRUS, high variability occurred in anterior regions of the apex and base, whereas the prostate-rectum interface had the smallest variability. The shape of the prostate on MR was rounder, with the base and apex of similar size, whereas CT contours had broad, flat bases narrowing toward the apex. The average percent of surface area that was significantly different (95% confidence interval) for CT/MR was 4.1%; 3DTRUS/MR, 10.7%; and CT/3DTRUS, 6.3%. The larger variability of CT measurements made significant differences more difficult to detect.

CONCLUSIONS

The contouring of prostates on CT, MR, and 3DTRUS results in systematic differences in the locations of and variability in prostate boundary definition between modalities. MR and 3DTRUS display the smallest variability and the closest correspondence.

Prostate volume determination: differential volume measurements comparing CT and TRUS

PURPOSE

To compare the differences in prostate volume assessed by computerized tomography (CT), step-section transrectal ultrasound (TRUS-step), and TRUS with ellipsoid-formula volume calculation (TRUS-ellipsoid).

METHODS AND MATERIALS

Thirty-one patients with localized prostate cancer treated with combined external conformal radiotherapy and high dose rate brachytherapy, who had prostate volumes evaluated using CT, TRUS-step and TRUS-ellipsoid according to our clinical routine for dose planning. The measurements were collected retrospectively based on actual dose-plans.

RESULTS

The prostate volume was on average 34 cc (range 18-60 cc) according to CT, 28 cc (range 12-57 cc) and 24 cc (range 13-44 cc) according to TRUS-step and TRUS-ellipsoid, respectively. The differences between the lengths measured were most pronounced with a mean length of 4.5 cm (range 3.0-6.0 cm) defined by CT as compared to 3.6 cm (range 3.0-5.0 cm) and 3.6 cm (range 2.8-5.0 cm) when defined by TRUS-step and TRUS-ellipsoid, respectively.

CONCLUSION

CT defined volumes are 30% larger than volumes defined with TRUS-step. This is probably due to uncertainty in defining the apex of the prostate and thereby the length of the prostate using CT. When defining target in radiotherapy, it is important to be aware of the differences in volumes depending on the technique used.

Influence of intrafraction motion on margins for prostate radiotherapy

PURPOSE

To assess the impact of intrafraction intervention on margins for prostate radiotherapy.

METHODS AND MATERIALS

Eleven supine prostate patients with three implanted transponders were studied. The relative transponder positions were monitored for 8 min and combined with previously measured data on prostate position relative to skin marks. Margins were determined for situations of (1) skin-based positioning, and (2) pretreatment transponder positioning. Intratreatment intervention was simulated assuming conditions of (1) continuous tracking, and (2) a 3-mm threshold for position correction.

RESULTS

For skin-based setup without and with inclusion of intrafraction motion, prostate treatments would have required average margins of 8.0, 7.3, and 10.0 mm and 8.2, 10.2, and 12.5 mm, about the left-right, anterior-posterior, and cranial-caudal directions, respectively. Positioning by prostate markers at the start of the treatment fraction reduced these values to 1.8, 5.8, and 7.1 mm, respectively. Interbeam adjustment further reduced margins to an average of 1.4, 2.3, and 1.8 mm. Intrabeam adjustment yielded margins of 1.3, 1.5, and 1.5 mm, respectively.

CONCLUSION

Significant reductions in margins might be achieved by repositioning the patient before each beam, either radiographically or electromagnetically. However, 2 of the 11 patients would have benefited from continuous target tracking and threshold-based intervention.

Semiautomatic nonrigid registration for the prostate and pelvic MR volumes

RATIONALE AND OBJECTIVES

Three-dimensional (3D) nonrigid image registration for potential applications in prostate cancer treatment and interventional magnetic resonance (iMRI) imaging-guided therapies were investigated.

MATERIALS AND METHODS

An almost fully automated 3D nonrigid registration algorithm using mutual information and a thin plate spline (TPS) transformation for MR images of the prostate and pelvis were created and evaluated. In the first step, an automatic rigid body registration with special features was used to capture the global transformation. In the second step, local feature points (FPs) were registered using mutual information. An operator entered only five FPs located at the prostate center, left and right hip joints, and left and right distal femurs. The program automatically determined and optimized other FPs at the external pelvic skin surface and along the femurs. More than 600 control points were used to establish a TPS transformation for deformation of the pelvic region and prostate. Ten volume pairs were acquired from three volunteers in the diagnostic (supine) and treatment positions (supine with legs raised).

RESULTS

Various visualization techniques showed that warping rectified the significant pelvic misalignment by the rigid-body method. Gray-value measures of registration quality, including mutual information, correlation coefficient, and intensity difference, all improved with warping. The distance between prostate 3D centroids was 0.7 +/- 0.2 mm after warping compared with 4.9 +/- 3.4 mm with rigid-body registration.

CONCLUSION

Semiautomatic nonrigid registration works better than rigid-body registration when patient position is changed greatly between acquisitions. It could be a useful tool for many applications in the management of prostate.

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 4mm, 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.

Quality of permanent prostate implants using automated delivery with seedSelectron™ versus manual insertion of RAPID Strands™

BACKGROUND AND PURPOSE

To compare the quality of manually inserted RAPID Strand implants with automatically inserted selectSeed implants using volumetric and dosimetric parameters.

PATIENTS AND METHODS

Patients with T1 to T2 prostate carcinoma were treated with brachytherapy. The (125)I seeds were implanted in the prostate in three different ways: manual insertion of RAPID Strands (R); insertion of selectSeeds using the seedSelectron (S); a combination of both techniques: manual insertion of RAPID Strands in the left half of the prostate and insertion of selectSeeds with the seedSelectron in the right half of the prostate (RS). The comparison is based on implant and target specific parameters. The implant specific parameters, V(100), homogeneity index (HI), and natural dose ratio (NDR), were determined at the time of implantation and four weeks later. MR images taken four weeks after the implantation were used for the calculation of the target specific parameters: D(90), HI, external index (EI), and conformation number (CN).

RESULTS

We found no significant difference between the groups of implants (R, S, RS) for the implant specific parameters V(100), HI, and NDR at t(0) and neither at t(4w). For each group, the V(100) values decreased significantly with time between t(0) and t(4w). The target specific parameters D(90), HI, EI and CN were not significantly different between the groups. For the group of patients with both RAPID Strands and selectSeeds, we found a significant difference in D(90) between both halves of the prostate.

CONCLUSIONS

The dosimetry parameters of a newly introduced implant technique using an automatic seed afterloader were not significantly different from the parameters of a manual insertion technique using RAPID Strands. Since either technique has its advantages and disadvantages regarding seed migration, physics quality assurance, efficiency, logistics, and ease of use, it was decided to use both techniques and to continue evaluations.

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.

Radioactive seed migration to the chest after transperineal interstitial prostate brachytherapy: extraprostatic seed placement correlates with migration

PURPOSE

To examine the incidence of seed migration detected on chest X-ray and to identify the predictors associated with its occurrence.

METHODS AND MATERIALS

Between May 1998 and April 2000, 102 patients underwent permanent prostate brachytherapy at our institution and 100 were eligible for the study. Chest X-rays obtained at follow-up were examined for the number and location of seeds. The patient and treatment variables potentially associated with the occurrence and number of seed migrations were analyzed.

RESULTS

One or more seeds were identified on the chest X-rays of 55 (55%) of 100 patients. The mean number of intrathoracic seeds in patients with migration was 2.2 (range, 1-10), and the proportion of seeds that migrated to the thorax was 0.98%. The rate of extraprostatic seeds planned was 43.9%, and postimplant CT identified 37.9% in such a location. The number of seeds planned for extraprostatic placement and below the apex were statistically significant (alpha = 0.05) predictors in univariate logistic analysis. Multivariate analysis revealed the planned number of extraprostatic seeds as the only statistically significant predictor (p = 0.04).

CONCLUSION

Extraprostatic placement of loose seeds is associated with an increased likelihood for, and frequency of, seed migration to the thorax. Nonetheless, the small proportion of implanted seeds that migrated (<or=1%) is highly unlikely to have significant dosimetric consequences.

A method to compare supra-pubic ultrasound and CT images of the prostate: Technique and early clinical results

We describe a unique method that allows the comparison of spatially registered ultrasound (SRUS) images and computed tomography-derived contours (CTDCs) that were acquired with a minimal time lapse. As such, we have a tool that will provide validation of the spatial accuracy of the US system and that will allow comparison of anatomical boundaries derived via the two different imaging modalities. We describe the method by which the commercial US system is mechanically registered to a CT simulator and a unique data processing procedure. This data processing procedure circumvents the standard data acquisition and manual contouring sequence, thus reducing the time lapse from CT to US image acquisition to 10 minutes on average. Verification using a phantom demonstrated the method to be spatially accurate to within +/- 1 mm in the anterior-posterior (AP) and lateral directions and +/- 3 mm in the inferior-superior (IS) direction. Early clinical results gathered on 8 patients demonstrated alignment between the US and the CTDCs to be 0 mm in the AP and lateral directions and 2 mm in the IS direction, on average. The technique was used to compare the appearance of the prostate using US and CT imaging. The lateral dimension of the prostate indicated by the CTDCs was larger than that indicated by US imaging in all cases and on average by 0.9 cm. The height of the prostate in the AP direction was larger on average by 0.3 cm using CTDCs than US, and was larger by 5 mm or more in 3 out of 7 cases. The role of uncertainties in the determination of the CTDCs is examined as a possible cause and implications for treatment planning are described.

The use of mutual information in registration of CT and MRI datasets post permanent implant

PURPOSE

To determine the feasibility of registration of MRI and CT datasets post permanent prostate implant by the use of mutual information.

METHODS AND MATERIALS

Five patients who underwent permanent (125)I implant for prostate carcinoma were studied. Two weeks postimplant an axial CT, T2-weighted-axial, sagittal and coronal MRI, and T1-fat-saturation MRI scans were obtained. Registrations of MRI to CT and MRI to MRI datasets were performed by mutual information, an automated process of data registration matching all information in specified dataset regions of interest. Registration quality was evaluated by visual inspection, agreement with seed- to-seed registration, and histogram analysis.

RESULTS

Rapid registration (<30 minutes) of CT and MRI datasets can be accomplished through the use of mutual information. All methods of registration evaluation confirmed excellent registration quality. Although D90 and V100 for the prostate were comparable between MRI- and CT-based dosimetry, dose to critical structures/microenvironments (anterior base, posterior base, bladder outlet, lower sphincter, bulbar urethra) defined on MRI varied widely.

CONCLUSIONS

Efficient and accurate registration of MRI and CT datasets following prostate implant is possible, and improves the accuracy of postimplant dosimetry by superior definition of the prostate. Definition of critical microenvironments and adjacent structures will improve dose and toxicity correlation and ultimately improve planning strategies.

Dosimetric quality endpoints for low-dose-rate prostate brachytherapy using biological effective dose (bed) vs. conventional dose

The purpose of this study was to compare conventional low-dose-rate prostate brachytherapy dosimetric quality parameters with their biological effective dose (BED) counterparts. To validate a model for transformation from conventional dose to BED, the postimplant plans of 31 prostate brachytherapy patients were evaluated using conventional dose-volume histogram (DVH) quality endpoints and analogous BED-DVH endpoints. Based on CT scans obtained 4 weeks after implantation, DVHs were computed and standard dosimetric endpoints V100 (volume receiving 100% of the prescribed dose), V150, V200, HI (1-[V150/V100]), and D90 (dose that 90% of the target volume received) were obtained for quality analysis. Using known and reported transformations, dose grids were transformed to BED-early (alpha/beta = 10 Gy) and BED-late (alpha/beta = 3 Gy) grids, and the same dosimetric endpoints were analyzed. For conventional, BED-early and BED-late DVHs, no differences in V100 were seen (0.896, 0.893, and 0.894, respectively). However, V150 and V200 were significantly higher for both BED-early (0.582 and 0.316) and BED-late (0.595 and 0.337), compared with the conventional (0.539 and 0.255) DVHs. D90 was significantly lower for the BED-early (103.1 Gy) and BED-late transformations (106.9 Gy) as compared with the conventional (119.5 Gy) DVHs. The conventional prescription parameter V100 is the same for the corresponding BED-early and BED-late transformed DVHs. The toxicity parameters V150 and V200 are slightly higher using the BED transformations, suggesting that the BED doses are somewhat higher than predicted using conventional DVHs. The prescription/quality parameter D90 is slightly lower, implying that target coverage is lower than predicted using conventional DVHs. This methodology can be applied to analyze BED dosimetric endpoints to improve clinical outcome and reduce complications of prostate brachytherapy.

Brachytherapy for prostate cancer

The use of prostate brachytherapy for the treatment of early-stage, low-grade, low-volume carcinoma of the prostate continues to rise. Given the prolonged natural history of these early lesions, treatment failures may take many years or even a decade or more before becoming clinically evident. It is therefore likely that as the brachytherapy data mature, clinicians will be asked to help manage a potentially large cohort of men who have failed this local therapy--a scenario that will provide a number of unique challenges for the treatment of the disease and the management of the lower urinary tract. This article offers a contemporary review and suggestions with regard to the follow-up of patients who have undergone prostate brachytherapy, including low-dose rate permanent implants and high-dose rate temporary implants for the management of localized prostate cancer. In addition, current controversies in defining biochemical failure following radioactive implantation--including important data regarding the "prostate-specific antigen bounce" phenomenon--are discussed. Finally, a comprehensive review of the management of local recurrence following brachytherapy is offered.

A comparative study of warping and rigid body registration for the prostate and pelvic MR volumes

A three-dimensional warping registration algorithm was created and compared to rigid body registration of magnetic resonance (MR) pelvic volumes including the prostate. The rigid body registration method combines the advantages of mutual information (MI) and correlation coefficient at different resolutions. Warping registration is based upon independent optimization of many interactively placed control points (CP's) using MI and a thin plate spline transformation. More than 100 registration experiments with 17 MR volume pairs determined the quality of registration under conditions simulating potential interventional MRI-guided treatments of prostate cancer. For image pairs that stress rigid body registration (e.g. supine, the diagnostic position, and legs raised, the treatment position), both visual and numerical evaluation methods showed that warping consistently worked better than rigid body. Experiments showed that approximately 180 strategically placed CP's were sufficiently expressive to capture important features of the deformation.

[Iodine-125 transperineal prostate brachytherapy with preplanning technique: pre and post-implant dosimetry results analysis]

PURPOSE

Post-implant CT-based dosimetry is the only method of assessing the quality of permanent prostate brachytherapy. As a consequence of our permanent feedback with the preplanned technique, geometric and dosimetric criteria for optimal seed implantation are proposed and pre and post-implantation dosimetric results are presented.

PATIENTS AND METHODS

In 2000 and 2001, one hundred and twenty patients with early stage prostate cancer were treated with transperineal I-125 preplanned brachytherapy (RAPID Strand, Amersham Health). The prescription dose was 145 Gy to the planning target volume. For the pre-planning and post-implant dosimetry the Variseed 6.7 version software was used (Varian Medical Systems). The D90, V100 and V150 values, the position of the dose peak [Dose] peak) and the full width at half maximum (FWHM) on differential dose volume histogram from both planned and post-implant dosimetry were compared for all patients.

RESULTS

For preplanned dosimetry, the mean values for D90, V100, V150, [Dose] peak, FWMH were respectively of 199Gy, 100%, 70%, 220Gy, 113Gy. For post-implantation, these values became respectively of 157Gy, 90%, 62%, 220Gy, 194Gy.

CONCLUSION

In our practice, differences are noted between preplanned and post-implant dosimetry parameters that should be anticipated to assure optimal definitive result. A working methodology both for performing the preplanned dosimetry and for evaluating the post-implantation dosimetric results is proposed.

Impact of prostate volume evaluation by different observers on CT-based post-implant dosimetry

PURPOSE

An analysis of computed tomography (CT)-based dosimetry was performed to evaluate the variability of different observers' judgements in marking the prostate gland on CT films, and its effect on the parameters that characterise the prostate implantation quality. Accuracy of data entry by the first author in the process of dosimetry procedure has also been evaluated.

MATERIALS AND METHODS

Four observers were asked to evaluate the prostate volume on CT films for six different patients. Each observer repeated the evaluation six times. The sample of patients has a prostate volume in the range of 21.4-42.0 cc derived from transrectal ultrasound volume study. After an average period of 6 weeks of the I-125 implantation, all patients had CT scans. CT-based post-implant dosimetry was performed and the dose volume histograms DVHs were calculated to report the re-constructed prostate volume, Vp100, Vp150, Vp90 and D90. Comparison between the four observers' output was performed.

RESULTS

Comparison between the four observers shows that each observer has a different way of estimating the prostate on CT films. Observers' precision also varies according to the prostate volume and the image quality. This can cause a variation in the resulting D90 value by up to 50%. Analysis of data entry shows a high degree of accuracy. The error of digitizing the prostate is +/-0.19 cc. This is correlated to an error of +/-0.78 Gy of the D90.

CONCLUSION

The evaluation of prostate gland volume on CT films varies between different observers. This has an effect on the dosimetric indices that characterise the implant quality in particular the D90.

Magnetic resonance spectroscopic imaging-guided brachytherapy for localized prostate cancer

PURPOSE

Prostate brachytherapy (PB) entails the placement of radioactive sources throughout the entire prostate gland to treat localized cancer. Typically, the target volume in PB encompasses the entire prostate gland because of the inability to localize the cancer and the multifocal nature of this malignancy. However, because of the unique biochemical nature of the prostate gland, recent advances in magnetic resonance spectroscopic imaging (MRSI) of the prostate have allowed precise delineation of the cancer location within the prostate gland. This report reveals our initial experience of MRSI-guided PB.

METHODS

A MRSI study was obtained in 15 localized prostate cancer patients before their scheduled PB. The results of this study were used to internally map 7 x 7 x 9-mm volumes of prostate tissue to assign cancerous areas a higher dose of radiation. Such tumor-bearing areas had a low citrate/(choline+creatine) ratio consistent with cancer. On the basis of the anatomic MRI and MRSI correlation, three-dimensional coordinates were assigned to the locations of MRSI-defined cancer. The entire target volume was treated to a standard prescription dose using I-125 or Pd-103. Abnormal citrate regions, termed the biologic tumor volume, were prescribed a dose of 130% of the target volume dose to dose escalate in the abnormal citrate regions while respecting the normal radiation tolerances of the surrounding areas. Three-dimensional treatment planning was used to perform the implant.

RESULTS

Of the 15 prostate cancer patients evaluated, all had successful three-dimensional MRSI acquisition before their scheduled PB procedure. In 14 of the 15 patients planned with MRSI, the data were successfully incorporated into their treatment planning and were used to increase the radiation dose prescription to 130% in the MRSI-defined volumes. In 1 patient, MRSI revealed significant background artifact that made a focal boost impractical. Postimplant dosimetry confirmed a median V100 of 95% (range 72%-100%) in the 15 evaluated patients for the prescription dose. Furthermore, the median BTV100 for the abnormal citrate region was 90% (range 80-100%) as determined by postimplant dosimetry. Urethral and rectal dose-volume histograms were within normal limits. Morbidity was comparable with that for conventionally treated patients.

CONCLUSION

MRSI offers a promising new approach for the delivery of ionizing radiation in PB. Although this series was small and with a short follow-up, MRSI-guided implants are feasible and warrant further investigation as a means of improving the therapeutic ratio in PB [corrected].

Trans-rectal ultrasonography (TRUS) with lipiodol injection for localization of the prostatic apex before radiotherapy planning

PURPOSE

To evaluate reliability of Trans-rectal ultra-sonography (TRUS) guidance with lipiodol injection for prostate localization before radiotherapy planning.

MATERIAL AND METHODS

From October 1997 to March 2000, 31 patients with prostatic adenocarcinoma and six patients with anastomotic recurrence after radical prostatectomy had TRUS-guided injection of lipiodol. Two milliliters of lipiodol were injected into each side of the prostate and 1 ml into both seminal vesicles with a 22 Gauge CHIBA needle and US probe guide before radiotherapy planning. We had established a contrast quality index (0 for no prostate enhancement to 5 for efficient pacification without any diffusion). On simulation films, we had performed anatomic measurements for comparison with other anatomic studies.

RESULTS

For all 37 patients, TRUS-guided injection was well tolerated. Among 31 patients with the prostate in situ, three had no apex opacification and 15 had no vesicle enhancement or peri-vesicle space diffusion. However, in 19 patients there was good contrast quality with an index score of > or =3. The majority of patients had prostatic apex between 1.5 and 3.5 cm from ischial tuberosities ligne (27 from 28 evaluable for apex). Among 19 evaluable patients, 15 had seminal vesicles 2-4 cm above the top of pubis. For six patients with anastomotic recurrence after radical prostatectomy, lipiodol was precious aid to locate it. We had only one failure because of a precocious bladder absorption relating to a delay which is too long between rectal probe locating and portal films.

CONCLUSION

TRUS injection of lipiodol is a simple, inexpensive, relatively safe technique for localization of prostatic apex, but not appropriate for seminal vesicles enhancement. This is also an interesting method to locate anastomotic recurrence.

Lymph node-positive prostate cancer: evaluation of the results of the combination of androgen deprivation therapy and radiation therapy

OBJECTIVE

To evaluate the outcome of patients with pathologic stage IV prostate cancer treated with androgen ablation plus external-beam radiation therapy.

PATIENTS AND METHODS

Sixty consecutive patients treated between August 1986 and February 1995 with androgen ablation plus radiation therapy for stage IV (T1-4 N1 M0) adenocarcinoma of the prostate were selected for outcome analysis in this retrospective study. Bilateral pelvic lymphadenectomy was performed in 56 patients (93%). The 4 remaining patients had pelvic adenopathy on computed tomography, which was confirmed histologically in all patients. The median pretreatment prostate-specific antigen (PSA) level was 28.8 ng/mL (mean, 55 ng/ mL; range, 0.1-428 ng/mL). All patients received radiation therapy to the prostate, and 29 (48%) had pelvic node radiation. Biochemical failure was defined according to the American Society for Therapeutic Radiology and Oncology criteria of 3 successive increases in the PSA level.

RESULTS

The median follow-up duration for surviving patients was 101.1 months (range, 20-134 months). Biochemical failure with (in 2 patients) or without (in 10 patients) clinically evident disease relapse was noted in 12 patients (20%). Four additional patients (7%) had clinical relapse without biochemical failure. Local recurrences were observed in 6 patients (10%), and this clinical impression was confirmed by biopsy in 4 patients. Thirteen patients (22%) died of causes related to prostate cancer. The biochemical relapse-free, clinical disease-free, overall, and cause-specific survival rates at 5 years were 82%, 84%, 76%, and 80%, respectively.

CONCLUSIONS

This observational case series of patients treated with the combination of external-beam radiation therapy and permanent androgen ablation for pathologic stage IV prostate cancer suggests that the addition of androgen deprivation therapy to radiation therapy may improve disease outcome. In the absence of randomized trial results, these observations may be beneficial in clinical decision making.

Postimplant dosimetry for (125)I prostate implants: definitions and factors affecting outcome

OBJECTIVE

An analysis of CT-based dosimetry was performed to assess the efficacy of the real time method of prostate implantation, explore the relationship of various dose descriptions and determine implant factors affecting outcome.

METHODS AND MATERIALS

Between 7/95 and 8/99, 297 patients underwent (125)I implants for T1-T2 prostate cancer and had CT-based dosimetry performed (TG43 formalism). Dosimetry was performed 1 month postimplant. Using a dose-volume histogram, doses delivered to 100%, 95%, 90%, and 80% of the prostate (D100, D95, D90, D80, respectively) as well as percentages of the gland receiving 240 Gy, 160 Gy, 140 Gy (V240, V160, V140, respectively) were reported. Correlations between the various dose parameters and D90 were generated. The effect of the number of seeds implanted, seeds/volume, prostate volume, experience as assessed by time (8/01/99-date of implant), ultrasound probe (mechanical sector vs. dual phased electronic), and the ratio of the CT dosimetry prostate volume/ultrasound implant volume (CT/US vol) were analyzed.

RESULTS

The median D100, D95, D90, and D80 values were 10,200 cGy, 15,655 cGy, 17,578 cGy, and 19,873 cGy, respectively. The median V240, V160, and V140 were 56%, 94%, and 98%, respectively. Correlations of dose descriptions found a close relationship of D95, D80, V240, V160, and V140 with D90 with r values of 0.928, 0.973, 0.911, 0.816, and 0.733, respectively. D100 correlated poorly with D90 (r = 0.099). Using a stepwise regression analysis, CT/US vol ratio, prostate volume, and seed number were the only significant factors affecting D90 with CT/US vol ratio having the greatest effect. The dual-phased electronic probe was associated with fewer D90 values of less than 140 Gy (2%) compared to the mechanical sector probe (14%) (p = 0.02).

CONCLUSION

CT-based dosimetry results reveal the real-time implant technique to be an effective method of prostate implantation. Factors associated with more precise implantation, such as decreased postimplant edema, new technology, and increased number of seeds will lead to higher D90 values.

The American Brachytherapy Society recommendations for permanent prostate brachytherapy postimplant dosimetric analysis

PURPOSE

The purpose of this report is to establish guidelines for postimplant dosimetric analysis of permanent prostate brachytherapy.

METHODS

Members of the American Brachytherapy Society (ABS) with expertise in prostate dosimetry evaluation performed a literature review and supplemented with their clinical experience formulated guidelines for performing and analyzing postimplant dosimetry of permanent prostate brachytherapy.

RESULTS

The ABS recommends that postimplant dosimetry should be performed on all patients undergoing permanent prostate brachytherapy for optimal patient care. At present, computed tomography (CT)-based dosimetry is recommended, based on availability cost and the ability to image the prostate as well as the seeds. Additional plane radiographs should be obtained to verify the seed count. Until the ideal postoperative interval for CT scanning has been determined, each center should perform dosimetric evaluation of prostate implants at a consistent postoperative interval. This interval should be reported. Isodose displays should be obtained at 50%, 80%, 90%, 100%, 150%, and 200% of the prescription dose and displayed on multiple cross-sectional images of the prostate. A dose-volume histogram (DVH) of the prostate should be performed and the D90 (dose to 90% of the prostate gland) reported by all centers. Additionally, the D80, D100, the fractional V80, V90, V100, V150 and V200 (i.e., the percentage of prostate volume receiving 80%, 90%, 100%, 150%, and 200% of the prescribed dose, respectively), the rectal, and urethral doses should be reported and ultimately correlated with clinical outcome in the research environment. On-line real-time dosimetry, the effects of dose heterogeneity, and the effects of tissue heterogeneity need further investigation.

CONCLUSION

It is essential that postimplant dosimetry should be performed on all patients undergoing permanent prostate brachytherapy. Guidelines were established for the performance and analysis of such dosimetry.

The contribution of magnetic resonance imaging to the three-dimensional treatment planning of localized prostate cancer

PURPOSE

To investigate whether the use of transaxial and coronal MR imaging improves the ability to localize the apex of the prostate and the anterior part of the rectum compared to the use of transaxial CT alone, and whether the incorporation of MR could improve the coverage of the prostate by the radiotherapy field and change the volume of rectum irradiated.

METHODS AND MATERIALS

Ten consecutive patients with localized prostate carcinoma underwent a CT and an axial and coronal MR scan in treatment position. The CT and MR images were mathematically aligned, and three observers were asked to contour independently the prostate and the rectum on CT and on MR. The interobserver variability of the prostatic apex location and of the delineation of the anterior rectal wall were assessed for each image modality. A dosimetry study was performed to evaluate the dose to the rectum when MR was used in addition to CT to localize the pelvic organs.

RESULTS

The interobserver variation of the prostatic apex location was largest on CT ranging from 0.54 to 1.07 cm, and smallest on coronal MR ranging from 0.17 to 0.25 cm. The interobserver variation of the delineation of the anterior rectum on MR was small and constant along the whole length of the prostate (0.09+/-0.02 cm), while for CT it was comparable to that for the MR delineation at the base of the prostate, but it increased gradually towards the apex, where the variation reached 0.39 cm. The volume of MR rectum receiving more than 80% of the prescribed dose was on average reduced by 23.8+/-11.2% from the CT to the MR treatment plan.

CONCLUSION

It can be concluded that the additional use of axial and coronal MR scans, in designing the treatment plan for localized prostate carcinoma, improves substantially the localization accuracy of the prostatic apex and the anterior aspect of the rectum, resulting in a better coverage of the prostate and a potential to reduce the volume of the rectum irradiated to a high dose.

American Brachytherapy Society (ABS) recommendations for transperineal permanent brachytherapy of prostate cancer

PURPOSE/OBJECTIVE

To develop and disseminate the American Brachytherapy Society (ABS) recommendations for the clinical quality assurance and guidelines of permanent transperineal prostate brachytherapy with 125I or 103Pd.

METHODS AND MATERIALS

The ABS formed a committee of experts in prostate brachytherapy to develop consensus guidelines through a critical analysis of published data supplemented by their clinical experience. The recommendations of the panels were reviewed and approved by the Board of Directors of the ABS.

RESULTS

Patients with high probability of organ-confined disease are appropriately treated with brachytherapy alone. Brachytherapy candidates with a significant risk of extraprostatic extension should be treated with supplemental external beam radiation therapy (EBRT). Patient selection guidelines were developed. Dosimetric planning of the implant should be carried out for all patients before seed insertion. A modified peripheral loading is preferred. The AAPM TG-43 recommendations requiring a change in prescription dose for 125I sources should be universally implemented. The recommended prescription doses for monotherapy are 145 Gy for 125I and 115-120 Gy for 103Pd. The corresponding boost doses (after 40-50 Gy EBRT) are 100-110 Gy and 80-90 Gy, respectively. Clinical evidence to guide selection of radionuclide (103Pd or 125I) is lacking. Post implant dosimetry and evaluation must be performed on all patients. It is suggested that the dose that covers 90% (D90) and 100% (D100) of the prostate volume and the percentage of the prostate volume receiving the prescribed dose (V100) be obtained from a dose-volume histogram (DVH) and reported.

CONCLUSION

Guidelines for appropriate patient selection, dose reporting, and improved quality of permanent prostate brachytherapy are presented. These broad recommendations are intended to be technical and advisory in nature, but the ultimate responsibility for the medical decisions rests with the treating physician. This is a constantly evolving field, and the recommendations are subject to modifications as new data becomes available.

Intraoperative optimized inverse planning for prostate brachytherapy: early experience

PURPOSE

To demonstrate the feasibility of an intraoperative inverse planning technique with advanced optimization for prostate seed implantation.

METHODS AND MATERIALS

We have implemented a method for optimized inverse planning of prostate seed implantation in the operating room (OR), based on the genetic algorithm (GA) driven Prostate Implant Planning Engine for Radiotherapy (PIPER). An integrated treatment planning system was deployed, which includes real-time ultrasound image acquisition, treatment volume segmentation, GA optimization, real-time decision making and sensitivity analysis, isodose and DVH evaluation, and virtual reality navigation and surgical guidance. Ten consecutive patients previously scheduled for implantation were included in the series.

RESULTS

The feasibility of the technique was established by careful monitoring of each step in the OR and comparison with conventional preplanned implants. The median elapsed time for complete image capture, segmentation, GA optimization, and plan evaluation was 4, 10, 2.2, and 2 min, respectively. The dosimetric quality of the OR-based plan was shown to be equivalent to the corresponding preplan.

CONCLUSION

An intraoperative optimized inverse planning technique was developed for prostate brachytherapy. The feasibility of the method was demonstrated through an early clinical experience.

The latest in ultrasound: three-dimensional imaging. Part II

INTRODUCTION

The three-dimensional (3D) reconstruction of ultrasound images has become a widespread option in ultrasound equipment. Specific softwares have become available and 3D reconstruction feasible since the early 1990s, particularly since 1994.

POSSIBLE CLINICAL APPLICATIONS

Several clinical applications are feasible in all parenchymatous organs (mainly the liver and prostate), hollow viscera (e.g. the bladder and gallbladder), peripheral vessels (supra-aortic trunks and limb vessels) and central (the aorta and iliac arteries) or cerebral vessels. Moreover, tumoral vessels in parenchymatous organs can be reconstructed, and even the fetus in the uterine cavity, with excellent detailing. The recent introduction of echocontrast agents and second harmonic imaging has permitted to study normal and abnormal peripheral, central and parenchymatous vessels, with similar patterns to those obtained with digital angiography. The spatial relationships between the vascular structures of the liver, kidney and placenta were studied with 3D ultrasound angiograms. The applications of this new technique include the analysis of vascular anatomy and the potential assessment of organ perfusion. THE LATEST APPLICATIONS--INTRAVASCULAR STUDIES: Some catheters with an ultrasound transducer in the tip have been tested for intravascular studies. Just like conventional transducers, they provide two-dimensional (2D) images which are then postprocessed into longitudinal 3D or volume reconstructions. The former resemble angiographic images and can be viewed 3D rotating the image along its longitudinal axis. Volume images, which are more complex and slower to obtain, can be rotated on any spatial plane and provide rich detailing of the internal vascular lumen. The clinical importance of intravascular ultrasound with 3D volume reconstructions lies in the diagnosis of vascular conditions and the assessment and monitoring of intravascular interventional procedures--e.g. to detect inaccurate deployment of intravascular stents and endoluminal grafts during the maneuver. Three-dimensional reconstructions involve geometric data assembly and volumetric interpolation of a spatially related sequence of tomographic cross sections generated by an ultrasound catheter withdrawn at a constant rate through a vascular segment of interest, resulting in the display of a straight segment. Therefore particular care is needed and there are some useful hints to avoid mistakes.

CONCLUSIONS

Three dimensional reconstructions of B-mode and color Doppler images are no longer a work in progress and their clinical importance and possible applications are both established and ever-increasing. On the other hand, independent of the different types of energy used, also computed tomography and magnetic resonance 3D reconstructions are very useful from a clinical viewpoint and they have become an established routine technique for both these methods. It is very likely that 3D volume reconstructions in ultrasound will find numerous applications in the near future. They may help to increase the diagnostic confidence and to facilitate diagnosis, intraprocedure monitoring in interventional radiology and follow-up and also to reduce the number of invasive examinations with iodinated contrast agents. This could result in cutting the cost and duration of the most expensive examinations. New, although invasive, applications can be hypothesized for intravascular or intraluminal catheters with an ultrasound transducer inside.

The latest in ultrasound: three-dimensional imaging. Part 1

OBJECTIVE

The state-of-the-art of three-dimensional ultrasound is reviewed to evaluate technological achievements and future possibilities in diagnosis and in the follow-up of medical or invasive therapy.

MATERIAL AND METHODS

The problems related to volumetric acquisitions in the tissues of interest to provide three-dimensional images are considered. Three-dimensional images are easier to achieve with computed tomography because the scanning system of this technique is automatic and thus provides sequential slices. The same is true for magnetic resonance imaging which can aquire volumes directly. The problem with ultrasound lies in the fact that the scans are manual and therefore less precise. To obtain three-dimensional images these devices are commonly used: manual scanning probes connected to spatial magnetic evidencers with remote processing; manual scanning probes connected to spatial magnetic evidencers placed on the patient's examination table with processing internal to the ultrasound unit; mechanical probes that can provide volumetric scans; 'matrix' probes. Recent contributions are discussed relative to three-dimensional applications to cardiology (cardiac valve studies), obstetrics (malformations), gynecology (uterine malformations and extensive ovarian disease studies), gastroenterology (diagnosis of pancreatic and hepatoabiliary tumor extent), uro-nephrology (detection of stones, prostatic tumors) and finally in the study of rectal carcinomas.

CONCLUSIONS

Nearly all the papers about three-dimensional ultrasound are works in progress because the technique has not been standardized yet and some of its future diagnostic possiblities are difficult to foresee. Moreover, 'matrix' probes are still in the experimental stage. Nevertheless, this technique seems to be able to yield the best results in: fetal malformations; calculating the volumes of normal and diseased organs; the follow-up of masses treated with irradiation/chemotherapy or with alcohol or chemoembolization; the spatial reconstruction of extensive lesions; the detection of small lesions (metastases); the study of some complex functions such as cardiac valve dynamics. But the real problem with three-dimensional sonography is not its efficiency but rather its efficacy, that is which actual role this technique can play in diagnosis and which information it can add to that obtained with two-dimensional imaging.