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.     

Quantitative MR imaging assessment of prostate gland deformation before and during MR imaging-guided brachytherapy

RATIONALE AND OBJECTIVES: The authors performed this study to document the deformations that occur between pretreatment magnetic resonance (MR) imaging and intraoperative MR imaging during brachytherapy. MATERIALS AND METHODS: MR images obtained at 1.5 and 0.5 T in 10 patients with prostate cancer were analyzed for changes in the shape and substructure of the prostate. Three-dimensional models of the prostate were obtained. The authors measured anteroposterior dimension; total gland, peripheral zone, and central gland volumes; transverse dimension; and superoinferior height. RESULTS: Gland deformations were seen at visual inspection of the three-dimensional models. The anteroposterior dimension of the total gland, central gland, and peripheral zone increased from 1.5- to 0.5-T imaging (median dimension, 4.9, 1.5, and 1.8 mm, respectively), and the increase was greatest in the peripheral zone (P < .05, all comparisons). There was a decrease in the transverse dimension from 1.5- to 0.5-T imaging (median, 4.5 mm; P < .005). The total gland volume and the superoinferior height did not show a statistically significant change. CONCLUSION: There were significant deformations in the shape of the prostate, especially in the peripheral zone, between the two imaging studies. The likely causes of the shape change are differences in rectal filling (endorectal coil used in 1.5-T studies vs obturator in 0.5-T studies) and/or changes in patient position (supine vs lithotomy). These findings suggest that pretreatment images alone may not be reliable for accurate therapy planning. It may be useful to integrate pre-and intraoperative data.     

Online correction of catheter movement using CT in high-dose-rate prostate brachytherapy

PurposeTo present a clinical procedure that readjusts catheters to its planned positions based on pretreatment computed tomography (CT) for patients undergoing high-dose-rate (HDR) prostate brachytherapy, and evaluate the magnitude and dosimetric impact of the adjustments.Methods and MaterialsPatients received a pretreatment verification CT (vCT) before each fraction. The vCT dataset was imported to the treatment-planning system and fused to the planning CT (pCT) by rigid-body registration based on the implanted fiducials within the prostate. Catheter positions in the vCT were then compared with catheter positions in the pCT in a reconstructed plane through each catheter. Any catheter with difference in penetration larger than 3 mm was manually adjusted by a radiation oncologist before treatment. To evaluate treatment quality, the patient's plan was applied to the vCT off-line and dose delivered to prostate and normal structures were compared with their planned value.ResultsForty-four fractions of 13 consecutive patients were treated using this method. Thirty-nine fractions had at least one catheter adjusted before treatment. A total of 651 catheters were assessed, and 194 catheters (30%) were adjusted by an average amount of 5.8 ± 1.9 mm. In eight fractions the prostate D₉₀ would have decreased by more than 10% from the planned value (with a maximum of 32%) if the catheter displacements were not rectified. After the adjustment, the maximum deviation of D₉₀ was 10.6%. The improvement in D₉₀ is 24% per 1 cm of time-averaged adjustment.ConclusionsInterfraction catheter motion occurs without any particular pattern. Using pretreatment CTs and restoring each catheter to its planned position ensures that the delivered treatment closely matches the treatment plan and therefore enhances the overall quality of the HDR treatment. The procedure can be readily implemented in any clinical setting.     

Shape analysis of the prostate: Establishing imaging specifications for the design of a transurethral imaging device for prostate brachytherapy guidance

PurposeTo examine specific prostate and urethra dimensions and prostate shape to facilitate the design of a transurethral ultrasonographic imaging device.Methods and MaterialsComputed tomographic (CT) data sets were retrospectively evaluated from 191 patients who underwent permanent prostate brachytherapy at our institution. The prostate, rectum, urethra, and bladder were each segmented with imaging software. Collected data and calculations included prostate volume at specific distances from the urethra and rectum, distances from seeds to urethra (SU), distances from seeds to rectum (SR), prostate length, and curvilinear prostatic urethra length.ResultsThe CT-based, postimplant mean prostate volume was 49 cm³ (range, 22–106 cm³). Mean prostate length was 4.5 cm (range, 3.1–6.0 cm). The mean curvilinear length of the prostatic urethra was 4.5 cm. The mean (standard deviation) prostatic urethra bend was 29.0° (12.2°). The mean surface distance from the prostate to the urethra was 2.9 cm and from the prostate to the rectum w as 4.6 cm (p < 0.001, paired t test). The mean SU distance was 1.6 cm, and the mean SR distance was 2.3 cm (p < 0.001). In the largest prostate, the mean SU distance was 3.9 cm and the mean SR distance was 6.0 cm.ConclusionsA urethral imaging device for prostate brachytherapy and other minimally invasive prostate therapies should ideally have a 6-cm imaging field of view to image all the prostates in this series in a single image. The mean distance from the SU in permanent prostate brachytherapy is less than 70% of the mean SR distance.     

Evaluation of interobserver differences in postimplant dosimetry following prostate brachytherapy and the efficacy of CT/MRI fusion imaging

Purpose  

Interobserver differences in postimplant dosimetry based on computed tomography (CT) and CT/magnetic resonance imaging (MRI) fusion images were assessed to evaluate the efficacy of the fusion image. In addition, the part of the prostate contour responsible for the interobserver differences in CT was identified.     

Feasibility study of CT perfusion imaging for prostate carcinoma

Objective

The aim of this feasibility study was to obtain initial data with which to assess the efficiency of perfusion CT imaging (CTpI) and to compare this with magnetic resonance imaging (MRI) in the diagnosis of prostate carcinoma.

Materials and methods

This prospective study involved 25 patients with prostate carcinoma undergoing MRI and CTpI. All analyses were performed on T2-weighted images (T2WI), apparent diffusion coefficient (ADC) maps, diffusion-weighted images (DWI) and CTp images. We compared the performance of T2WI combined with DWI and CTp alone. The study was approved by the local ethics committee, and written informed consent was obtained from all patients.

Results

Tumours were present in 87 areas according to the histopathological results. The diagnostic performance of the T2WI+DWI+CTpI combination was significantly better than that of T2WI alone for prostate carcinoma (P?Conclusion CTp may be a valuable tool for detecting prostate carcinoma and may be preferred in cases where MRI is contraindicated. If this technique is combined with T2WI and DWI, its diagnostic value is enhanced.

Key Points

? Perfusion CT is a helpful technique for prostate carcinoma diagnosis. ? Colour maps allow easy and rapid visual assessment of the functional changes. ? Colour maps of prostate carcinoma provide information about in vivo tumoral vascularity. ? CTp images may be added into routine radiological examinations. ? CTp provides guidance for histopathological correlation if biopsy is scheduled.     

Image-guided brachytherapy for prostate cancer

Prostate brachytherapy offers and effective treatment for organ-confined prostate carcinoma. It is rapidly delivered compared with external beam radiation therapy or surgery and well tolerated by patients. Volumetric imaging and image guidance play critical roles in patient selection, treatment planning, treatment delivery, and postimplant assessment. Costs, availability and ease of use often dictate the local and regional differences in imaging approach, whether ultrasound, CT, or MR. Future volumetric image developments may permit multimodality image fusion to integrate tumor-specific imaging such as MR spectroscopy or positron emission tomography/CT into real-time ultrasound, CT, or MR.     

Parallel imaging compressed sensing for accelerated imaging and improved signal-to-noise ratio in MRI-based postimplant dosimetry of prostate brachytherapy

PurposeTo investigate the feasibility of using parallel imaging compressed sensing (PICS) to reduce scan time and improve signal-to-noise ratio (SNR) in MRI-based postimplant dosimetry of prostate brachytherapy.Methods and MaterialsTen patients underwent low-dose-rate prostate brachytherapy with radioactive seeds stranded with positive magnetic resonance-signal seed markers and were scanned on a Siemens 1.5T Aera. MRI comprised a fully balanced steady-state free precession sequence with two 18-channel external pelvic array coils with and without a rigid two-channel endorectal coil. The fully sampled data sets were retrospectively subsampled with increasing acceleration factors and reconstructed with parallel imaging and compressed sensing algorithms. The images were assessed in a blinded reader study by board-certified care providers. Rating scores were compared for statistically significant differences between reconstruction types.ResultsImages reconstructed from subsampling up to an acceleration factor of 4 with PICS demonstrated consistently sufficient quality for dosimetry with no apparent loss of SNR, anatomy depiction, or seed/marker conspicuity when compared to the fully sampled images. Images obtained with acceleration factors of 5 or 6 revealed reduced spatial resolution and seed marker contrast. Nevertheless, the reader study revealed that images obtained with an acceleration factor of up to 5 and reconstructed with PICS were adequate-to-good for postimplant dosimetry.ConclusionsCombined parallel imaging and compressed sensing can substantially reduce scan time in fully balanced steady-state free precession imaging of the prostate while maintaining adequate-to-good image quality for postimplant dosimetry. The saved scan time can be used for multiple signal averages and improved SNR, potentially obviating the need for an endorectal coil in MRI-based postimplant dosimetry.     

Quantitative CT assessment of a novel direction-modulated brachytherapy tandem applicator

PurposeThe purpose of this study was to quantitatively assess the CT metal-induced artifacts from a novel direction-modulated brachytherapy (DMBT) tandem applicator prototype, recently designed for cervical cancer treatments.Methods and materialsA water-based pelvic phantom was constructed for CT scanning. The DMBT applicator was imaged using our institutional protocol, one with higher kVp and mAs settings, and repetition of these protocols using 3-mm slices. A conventional stainless steel applicator was also scanned. In addition to the standard reconstructed images, applicator images were reconstructed using a commercial metal artifact-reduction (MAR) algorithm and an in-house–developed research algorithm. Subsequently, image quality and artifact severity were evaluated.ResultsArtifact severity, measured in terms of SDs in CT numbers, decreased asymptotically to background water levels with the distance away from the applicator. Artifact-reduction algorithms lead to significant and visible improvements in image quality, with >50% and >20% decrease in artifact severity achieved at a 10-mm distance for the DMBT and stainless steel applicators, respectively. Differences in artifact severity were minimal between the four imaging protocols. DMBT dimensions were the same on images with and without the commercial MAR algorithm, within <1 mm of the theoretical value. Both the commercial and in-house algorithms restored the CT numbers outside the applicator, albeit a better performance was achieved by the in-house algorithm.ConclusionsThe artifacts produced by both applicators were minimized with the use of MAR algorithms. Adoption of the DMBT and stainless steel applicators for CT-guided brachytherapy is anticipated as MAR algorithms are widely available on CT scanners.     

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 (125)I 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 (125)I 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; D(90)) and urethra (D(30)) were determined by CT-based dosimetry. RESULTS: The median prostate D(90) was 165 Gy (range, 16.5-260 Gy), and the median urethra D(30) 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 >or=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.     

前列腺癌近距离放射治疗的进展

前列腺癌近距离放射治疗是前列腺癌治疗的主要方法之一，由于其具有方法简便、微创及不需住院等优点，所以在临床应用中迅速普及，而所有的这些都要归功于放射性粒子制备技术、影像技术和三维放疗计划系统的发展，由于上述新技术的广泛应用，使得近距离放射治疗在提高疗效及降低周围组织毒副作用方面取得了重大进步。     

前列腺癌近距离放射治疗的进展

前列腺癌近距离放射治疗是前列腺癌治疗的主要方法之一,由于其具有方法简便、微创及不需住院等优点,所以在临床应用中迅速普及,而所有的这些都要归功于放射性粒子制备技术、影像技术和三维放疗计划系统的发展,由于上述新技术的广泛应用,使得近距离放射治疗在提高疗效及降低周围组织毒副作用方面取得了重大进步。     

Defining a magnetic resonance scan sequence for permanent seed prostate brachytherapy postimplant assessment

PurposeWe describe a magnetic resonance (MR) scan sequence for prostate brachytherapy postimplant assessment.Methods and MaterialsOne brachytherapy team at the British Columbia Cancer Agency has incorporated MR–CT fusion into their permanent seed prostate brachytherapy quality assurance procedure. Several attempts were required to ensure that the diagnostic MR scanner at the adjoining general hospital performed the desired sequence, providing many examples of suboptimal scans and underlining the pitfalls for a center trying to incorporate the use of MR scanning into their brachytherapy program.ResultsThe recommended sequence (Fast Spin Echo T2-weighted, repetition time [TR]/echo time [TE] 4500/90, echo train length [ETL] 10, 20 × 20 field of view [FOV], 80 bandwidth [BW]) is associated with superior edge detection when compared with those images in which a typical diagnostic sequence was used. The use of a low bandwidth sequence does not compromise edge detection or seed identification when compared with a higher bandwidth.ConclusionsWe have defined a magnetic resonance imaging sequence, which appears to optimize both prostate delineation and identification of seeds, lending itself to straightforward fusion with CT images and allowing for less uncertainty in permanent seed prostate brachytherapy quality assurance.     

Comparison of prostate distortion by inflatable and rigid endorectal MRI coils in permanent prostate brachytherapy imaging

PurposeTo study the deformation of the prostate by a rigid reusable endorectal coil and a balloon-type endorectal coil (BTC) during MRI of the prostate in brachytherapy imaging.Methods and MaterialsThe prostate gland was contoured on 157 MRI scans from 52 prostate cancer patients undergoing brachytherapy. The curvature of the posterior prostate surface deformation was computed as a measure of prostate distortion and compared between scans with a BTC, rigid endorectal coil (REC), or no endorectal coil. For the nine patients who had MRIs with all three endorectal scenarios, a mean prostate deformation vector was also calculated between scenarios using deformable image registration. These measures of prostate distortion were compared with the prostate anterior-to-posterior to left-to-right ratio (AP/LR) on the largest prostate axial slice.ResultsSignificant differences in prostate curvature were found between scans without an endorectal coil versus a REC versus a BTC (p < 0.001). The mean prostate deformation was 3.9 mm due to the BTC and 2.0 mm for the REC (p = 0.012). The mean AP/LR ratio was 0.62 with a BTC versus 0.76 without a coil or 0.73 with a REC (p < 0.001), but no difference existed between scans with a REC versus no coil (p = 0.7). The AP/LR ratio showed moderate correlation with prostate curvature (r = 0.48), and with mean prostate deformation (r = −0.64 to 0.68).ConclusionsThe REC caused minimal deformation of the prostate compared with a BTC with adequate MR image quality, and calculation of the cross-sectional AP/LR ratio on the largest axial prostate slice can serve as a simple measure of prostate distortion.     

Computed tomography versus magnetic resonance imaging in high-dose-rate prostate brachytherapy planning: The impact on patient-reported health-related quality of life

PurposeHigh-dose-rate (HDR) prostate brachytherapy uses volumetric imaging for treatment planning. Our institution transitioned from computed tomography (CT)-based planning to MRI-based planning with the hypothesis that improved visualization could reduce treatment-related toxicity. This study aimed to compare the patient-reported health-related quality of life (hrQOL) and physician-graded toxicity outcomes of CT-based and MRI-based HDR prostate brachytherapy.MethodsFrom 2016 to 2019, 122 patients with low- or intermediate-risk prostate cancer were treated with HDR brachytherapy as monotherapy. Patients underwent CT only or CT and MRI imaging for treatment planning and were grouped per treatment planning imaging modality. Patient-reported hrQOL in the genitourinary (GU), gastrointestinal (GI), and sexual domains was assessed using International Prostate Symptom Score and Expanded Prostate Cancer Index Composite Short Form-26 questionnaires. Baseline characteristics, changes in hrQOL scores, and physician-graded toxicities were compared between groups.ResultsThe median follow-up was 18 months. Patient-reported GU, GI, and sexual scores worsened after treatment but returned toward baseline over time. The CT cohort had a lower baseline mean International Prostate Symptom Score (5.8 vs. 7.8, p = 0.03). The other patient-reported GU and GI scores did not differ between groups. Overall, sexual scores were similar between the CT and MRI cohorts (p = 0.08) but favored the MRI cohort at later follow-up with a smaller decrease in Expanded Prostate Cancer Index Composite Short Form-26 sexual score from baseline at 18 months (4.9 vs. 19.8, p = 0.05). Maximum physician-graded GU, GI, and sexual toxicity rates of grade ≥2 were 68%, 3%, and 53%, respectively, with no difference between the cohorts (p = 0.31).ConclusionOur study shows that CT- and MRI-based HDR brachytherapy results in similar rates of GU and GI toxicity. MRI-based planning may result in improved erectile function recovery compared with CT-based planning.     

Regional treatment margins for prostate brachytherapy

PurposeThis study quantified the treatment margin (TM) around the prostate that received 100% of the prescribed dose and analyzed postimplant dosimetry in different regions of the prostate for ¹²⁵I seed implants.Methods and MaterialsAn average target volume (ATV) was created from postoperative MRI scan contours drawn independently by five radiation oncologists in 40 patients. The MRI was fused with the postoperative CT for dosimetry purposes. The TM, defined as the radial distance between the ATV and the 100% isodose line, was measured at 16 points at the base, midgland, and apex. The ATV was divided into four quadrants: anterior–superior, posterior–superior, anterior–inferior, and posterior–inferior quadrants. The values of the dose that covers 90% of the ATV (D₉₀) and the percentage of the ATV receiving the prescribed dose (V₁₀₀) received by the whole prostate and its four quadrants were documented.ResultsThe range of the mean TM, in millimeter, was ?8.88 to 3.68, 1.12 to 10.42, and 6.27 to 18.25 at the base, midgland, and apex, respectively. The mean D₉₀ was 135.8, 162.8, 191.0, and 194.6 Gy for the anterior–superior, posterior–superior, anterior–inferior, and posterior–inferior quadrants, respectively.ConclusionsDespite having a relatively uniform preoperative planning target volume, this study identified variable TMs postoperatively in different regions of the prostate. In particular, the anterior base is most underdosed, whereas the lateral regions of the midgland and apex have generous TMs. Postimplant dosimetric parameters were lowest in the anterior–inferior quadrant.