Automatic registration of MR and SPECT images for treatment planning in prostate cancer

RATIONALE AND OBJECTIVES: To aid in surgical and radiation therapy planning for prostate adenocarcinoma, a general-purpose automatic registration method that is based on mutual information was used to align magnetic resonance (MR) images and single photon emission computed tomographic (SPECT) images of the pelvis and prostate. MATERIALS AND METHODS: The authors assessed the effects of various factors on alignment between pairs of MR and SPECT images, including the use of particular pulse sequences in MR imaging, image voxel intensity scaling, the use of different regions on the MR-SPECT histogram, spatial masking of nonoverlapping visual data between images, and multiresolution optimization. A mutual information algorithm was used as the cost function for automatic registration. Automatic registration was deemed acceptable when it resulted in a transformation with less than 2 voxel units (6 mm) difference in translation and less than 2 degree difference in rotation from that obtained with manual registration performed independently by nuclear medicine radiologists. RESULTS: Paired sets of MR and SPECT image volumes from four of five patients were successfully registered. For successful registration, MR images must be optimal and registration must be performed at full spatial resolution and at the full intensity range. Masking, cropping, and the normalization of mutual information, used to register partially overlapping MR-SPECT volumes, were not successful. Multiresolution optimization had little effect on the accuracy and speed of the registration. CONCLUSION: Automatic registration between MR and SPECT images of the pelvis can be achieved when data acquisition and image processing are performed properly. It should prove useful for prostate cancer diagnosis, staging, and treatment planning.     

Simulated required accuracy of image registration tools for targeting high-grade cancer components with prostate biopsies

Objectives

To estimate the required spatial alignment accuracy for correctly grading 95 % of peripheral zone (PZ) prostate cancers using a system for multiparametric magnetic resonance (MR)-guided ultrasound (US) biopsies.

Methods

PZ prostate tumours were retrospectively annotated on multiparametric MR series using prostatectomy specimens as reference standard. Tumours were grouped based on homogeneous and heterogeneous apparent diffusion coefficient (ADC) values using an automated ADC texture analysis method. The proportion of heterogeneous tumours containing a distinct, high Gleason grade tumour focus yielding low ADC values was determined. Both overall tumour and high-grade focal volumes were calculated. All high-grade target volumes were then used in a simulated US biopsy system with adjustable accuracy to determine the hit rate.

Results

An ADC-determined high-grade tumour focus was found in 63 % of the PZ prostate tumours. The focal volumes were significantly smaller than the total tumour volumes (median volume of 0.3 ml and 1.1 ml respectively). To correctly grade 95 % of the aggressive tumour components the target registration error (TRE) should be smaller than 1.9 mm.

Conclusions

To enable finding the high Gleason grade component in 95 % of PZ prostate tumours with MR-guided US biopsies, a technical registration accuracy of 1.9 mm is required.

Key Points

? MRI can identify foci of prostatic cancer with reduced apparent diffusion coefficients ? Sixty-three per cent of prostatic peripheral zone tumours contain high-grade tumour low ADC foci ? The median volume of such foci is 0.3 ml ? Biopsy targets are significantly smaller than whole tumour volumes ? Simulated registration accuracy is 1.9 mm for correctly grading 95 % of tumours     

Image segmentation in treatment planning for prostate cancer using the region growing technique

The purpose of this study was to evaluate the performance of a region growing technique for segmenting prostate, bladder and rectum in CT images of prostate cancer patients. Prostate, bladder and rectum were segmented in all CT images of 10 patients using the region growing technique and manual tracing. Volumes of the above organs computed with the region growing technique were compared with those from manually traced images on a slice-by-slice basis. Measurement reproducibility of both segmentation techniques was evaluated using the data obtained from four independent observers. The region growing technique was 1.5 times faster than manual tracing. There was no statistical difference between the slice volumes of prostate, bladder and rectum obtained by the two segmentation techniques (p > 0.05, paired Student's t-test). Correlation between slice volumes of all organs of interest provided both by region growing and by manual tracing was very good (prostate r2 = 0.84; bladder r2 = 0.93; rectum r2 = 0.85). An overall reasonable agreement was found between the two segmentation techniques. The intraobserver and interobserver variations for prostate, bladder and rectum volume segmentation were found to be lower with the region growing technique than with manual tracing. The suggested semi-automatic technique allows the possibility of generating accurate and reproducible segmentation of prostate, bladder and rectum from CT data with great saving in labour.     

Dosimetric evaluation of MRI-to-ultrasound automated image registration algorithms for prostate brachytherapy

PurposeIdentifying dominant intraprostatic lesions (DILs) on transrectal ultrasound (TRUS) images during prostate high-dose-rate brachytherapy treatment planning remains a significant challenge. Multiparametric MRI (mpMRI) is the tool of choice for DIL identification; however, the geometry of the prostate on mpMRI and on the TRUS may differ significantly, requiring image registration. This study assesses the dosimetric impact attributed to differences in DIL contours generated using commonly available MRI to TRUS automated registration: rigid, semi-rigid, and deformable image registration, respectively.Methods and MaterialsTen patients, each with mpMRI and TRUS data sets, were included in this study. Five radiation oncologists with expertise in TRUS-based high-dose-rate brachytherapy were asked cognitively to transfer the DIL from the mpMRI images of each patient to the TRUS image. The contours were analyzed for concordance using simultaneous truth and performance level estimation (STAPLE) algorithm. The impact of DIL contour differences due to registration variability was evaluated by comparing the STAPLE-DIL dosimetry from the reference (STAPLE) plan with that from the evaluation plans (manual and automated registration) for each patient. The dosimetric impact of the automatic registration approach was also validated using a margin expansion that normalizes the volume of the autoregistered DILs to the volumes of the STAPLE-DILs. Dose metrics including D₉₀, D_mean, V₁₅₀, and V₂₀₀ to the prostate and DIL were reported. For urethra and rectum, D₁₀ and V₈₀ were reported.ResultsSignificant differences in DIL coverage between reference and evaluation plans were found regardless of the algorithm methodology. No statistical difference was reported in STAPLE-DIL dosimetry when manual registration was used. A margin of 1.5 ± 0.8 mm, 1.1 ± 0.8 mm, and 2.5 ± 1.6 mm was required to be added for rigid, semi-rigid, and deformable registration, respectively, to mitigate the difference in STAPLE-DIL coverage between the evaluation and reference plans.ConclusionThe dosimetric impact of integrating an MRI-delineated DIL into a TRUS-based brachytherapy workflow has been validated in this study. The results show that rigid, semi-rigid, and deformable registration algorithms lead to a significant undercoverage of the DIL D₉₀ and D_mean. A margin of at least 1.5 ± 0.8 mm, 1.1 ± 0.8 mm, and 2.5 ± 1.6 mm is required to be added to the rigid, semi-rigid, and deformable DIL registration to be suitable for DIL-boosting during prostate brachytherapy.     

Clinical evaluation of an MRI-to-ultrasound deformable image registration algorithm for prostate brachytherapy

Purpose

Identifying dominant intraprostatic lesions (DILs) on transrectal ultrasound (TRUS) images during prostate high-dose-rate brachytherapy (HDR-BT) treatment planning is challenging. Multiparametric MRI (mpMRI) is the tool of choice for DIL identification; however, the geometry of the prostate on mpMRI and on the TRUS may differ significantly, requiring image registration. This study evaluates the efficacy of an in-house software for MRI-to-TRUS DIL registration (MR2US) and compares its results to rigid and B-Spline deformable registration.

CT-MRI image fusion for delineation of volumes in three-dimensional conformal radiation therapy in the treatment of localized prostate cancer

The objective of this study was to assess the utility of CT-MRI image fusion software and compare both prostate volume and localization with CT and MRI studies. We evaluated the differences in clinical volumes in patients undergoing three-dimensional conformal radiation therapy for localized prostate cancer. After several tests performed to ensure the quality of image fusion software, eight patients suffering from prostate adenocarcinoma were submitted to CT and MRI studies in the treatment position within an immobilization device before the start of radiotherapy. The clinical target volume (CTV) (prostate plus seminal vesicles) was delineated on CT and MRI studies and image fusion was obtained from the superimposition of anatomical fiducial markers. A comparison of dose-volume histograms relative to CTV, rectum, bladder and femoral heads was performed for both studies. Image fusion showed a mean overestimation of CTV of 34% with CT compared with MRI. Along the anterior-posterior and superior-inferior direction, CTV was a mean 5 mm larger with CT study compared with MRI. The dose-volume histograms resulting from CT and MRI comparison showed that it is possible to spare a mean 10% of rectal volume and approximately 5% of bladder and femoral heads, respectively. This study confirmed an overestimation of CTV with CT images compared with MRI. Because this finding only allows a minimal sparing of organs at risk, considering the organ motion during each radiotherapy session and the excellent outcomes of prostate cancer treatment with CT based target identification, we are still reluctant to reduce the CTV to that identified by MRI.     

Radiotherapy treatment planning for prostate cancer in patients with prosthetic hips.

Patients diagnosed with prostate cancer may also have a prosthetic hip. When planning radiotherapy for these patients, one must consider the attenuation of the dose when the beam passes through the prosthetic hip. It is best to avoid administration of radiation to the target through the prosthesis. Example treatment plans are evaluated. The potential advantages and disadvantages of each plan are reviewed.     

Quantitative evaluation of radiotherapy treatment planning using CT image

A method of computerized optimization system of radiotherapy treatment planning is presented. For the optimization of treatment planning, it is highly desirable to evaluate treatment planning quantitatively corresponding to a set of three-dimensional criteria. For this purpose, we introduce a set of criteria using some parameters defined as three-dimensional extension of those of ICRU report 29. The development of computer software has become feasible for clinical use of our criteria. This paper described some preliminary results of our criteria which was applied to some clinical cases. Our method was proved applicable to any type of treatment plannings, and the optimization of treatment plannings will surely be realized through our criteria.     

Target registration errors with surface imaging system in conformal radiotherapy for prostate cancer: study on 19 patients

Purpose

Accurate patient setup is a prerequisite for conformal radiotherapy (3D-CRT) and is based on various methods, including surface imaging systems. To evaluate the validity of a surface imaging system (AlignRT), we analysed setup reproducibility of a cohort of patients.

Materials and methods

Nineteen patients affected by prostate adenocarcinoma were enrolled in this study. We acquired 653 surface images and 99 digital portal images (DPI). Setup errors were found by matching surface images with computed tomography (CT) and DPI images.

Results

The setup errors from the threshold of 5 mm detected by AlignRT along the Y, Z and X axes occurred in 47.4%, 42.1% and 5.3% of patients, respectively. For the threshold of 3 mm, shifts along the Y, Z and X axes were observed in 68%, 69% and 10%, respectively. Comparing AlignRT and DPI, we found a statistically significant difference in the detection of shifts along the Y and Z axes. For a threshold ??5 mm, the two systems provided corresponding setup errors along the Y and Z axes, whereas along the X axis, the threshold was not necessary.

Conclusions

AlignRT is an accurate technique for setup in 3D-CRT prostate cancer patients, especially along the lateral direction.     

CT-image-based conformal brachytherapy of breast cancer. The significance of semi-3-D and 3-D treatment planning.

PURPOSE: To compare the conventional 2-D, the simulator-guided semi-3-D and the recently developed CT-guided 3-D brachytherapy treatment planning in the interstitial radiotherapy of breast cancer. PATIENTS AND METHODS: In 103 patients with T1-2, N0-1 breast cancer the tumor bed was clipped during breast conserving surgery. Fifty-two of them received boost brachytherapy after 46 to 50 Gy teletherapy and 51 patients were treated with brachytherapy alone via flexible implant tubes. Single, double and triple plane implant was used in 6, 89 and 8 cases, respectively. The dose of boost brachytherapy and sole brachytherapy prescribed to dose reference points was 3 times 4.75 Gy and 7 times 5.2 Gy, respectively. The positions of dose reference points varied according to the level (2-D, semi-3-D and 3-D) of treatment planning performed. The treatment planning was based on the 3-D reconstruction of the surgical clips, implant tubes and skin points. In all cases the implantations were planned with a semi-3-D technique aided by simulator. In 10 cases a recently developed CT-guided 3-D planning system was used. The semi-3-D and 3-D treatment plans were compared to hypothetical 2-D plans using dose-volume histograms and dose non-uniformity ratios. The values of mean central dose, mean skin dose, minimal clip dose, proportion of underdosaged clips and mean target surface dose were evaluated. The accuracy of tumor bed localization and the conformity of planning target volume and treated volume were also analyzed in each technique. RESULTS: With the help of conformal semi-3-D and 3-D brachytherapy planning we could define reference dose points, active source positions and dwell times individually. This technique decreased the mean skin dose with 22.2% and reduced the possibility of geographical miss. We could achieve the best conformity between the planning target volume and the treated volume with the CT-image based 3-D treatment planning, at the cost of worse dose homogeneity. The mean treated volume was reduced by 25.1% with semi-3-D planning, however, it was increased by 16.2% with 3-D planning, compared to the 2-D planning. CONCLUSION: The application of clips into the tumor bed and the conformal (semi-3-D and 3-D) planning help to avoid geographical miss. CT is suitable for 3-D brachytherapy planning. Better local control with less side effects might be achieved with these new techniques. Conformal 3-D brachytherapy calls for new treatment planning concepts, taking the irregular 3-D shape of the target volume into account. The routine clinical application of image-based 3-D brachytherapy is a real aim in the very close future.     

A graphical user interface for automatic image registration software designed for radiotherapy treatment planning

Medical imaging forms a vital component of radiotherapy treatment planning and its evaluation. The integration of the useful data obtained from multiple imaging modalities for radiotherapy planning is achieved by image registration softwares. In radiotherapy planning systems, normally the computed tomography (CT) slices are kept as a standard upon which other modality images (magnetic resonance imaging [MRI], single photon emission computed tomography [SPECT], positron emission tomography [PET], etc.) are aligned—automatically or interactively. Following validation of successful registration, they are resampled and reformatted, as per the requirements. This paper defines the minimum requirements of automatic image registration software for 3-dimensional (3D) radiotherapy planning and describes the implementation of a suitable graphical user interface developed in Visual Basic (version 5). The automatic image registration (AIR) routines freely available from Dr. Roger P. Woods, UCLA, (USA) were used in this software. This software could be easily implemented and was easy to use for image processing suitable for radiotherapy planning systems.     

三维适形放射治疗老年前列腺癌30例临床分析

目的探讨三维适形放射治疗前列腺癌的临床应用价值。方法 30例前列腺癌患者,26例放疗前行双侧睾丸切除术,20例同时服用内分泌治疗药物。全部采用WDVE-XKY808三维适形放射治疗系统照射前列腺靶区,5次/周,2 Gy次/,总剂量DT70～80 Gy。结果30例患者经三维适形放射治疗后3、6、12个月复查有效率分别为70%(21/30)、98%(29/30),90%(27/30),6个月时病灶缩小最明显。1、3、5年总生存率分别为100.0%、85.0%,75.1%。结论 三维适形放射治疗中晚期前列腺癌有较好的局部控制效果和较高的安全性,可作为前列腺癌姑息治疗的有效方法之一。     

A graphical user interface for automatic image registration software designed for radiotherapy treatment planning

Medical imaging forms a vital component of radiotherapy treatment planning and its evaluation. The integration of the useful data obtained from multiple imaging modalities for radiotherapy planning is achieved by image registration softwares. In radiotherapy planning systems, normally the computed tomography (CT) slices are kept as a standard upon which other modality images (magnetic resonance imaging [MRI], single photon emission computed tomography [SPECT], positron emission tomography [PET], etc.) are aligned—automatically or interactively. Following validation of successful registration, they are resampled and reformatted, as per the requirements. This paper defines the minimum requirements of automatic image registration software for 3-dimensional (3D) radiotherapy planning and describes the implementation of a suitable graphical user interface developed in Visual Basic (version 5). The automatic image registration (AIR) routines freely available from Dr. Roger P. Woods, UCLA, (USA) were used in this software. This software could be easily implemented and was easy to use for image processing suitable for radiotherapy planning systems.     

High-dose-rate brachytherapy in combination with conformal external beam radiotherapy in the treatment of prostate cancer

PurposeTo report long-term outcomes for treatment of prostate cancer using dose escalation with high-dose-rate (HDR) brachytherapy and 3-dimensional conformal external beam radiotherapy (3DCRT), and compare them with outcomes for treatment of prostate cancer with 3DCRT alone at the same institution.Methods and MaterialsFrom 1998 to 2003, 587 patients were treated for clinically localized prostate cancer. Patients received either 3DCRT (median, 46 Gy) with a single HDR brachytherapy implant (196 patients) delivering a fractionated dose of 18 Gy (combined group) or 3DCRT (median, 70 Gy; 387 patients; “3DCRT alone”). There were 41.9% patients with intermediate-risk and 42.6% with high-risk disease. In all, 441 patients (75.1%) received neoadjuvant and 116 patients (19.8%) received adjuvant androgen deprivation therapy. The American Society of Therapeutic Radiology and Oncology Phoenix definition for biochemical failure was used.ResultsThe median followup was 5.5 years. The 5- and 7-year biochemical control (BC) rates were 82.5% and 80.3%, respectively, for the combined group and 81.3% and 71%, respectively, for 3DCRT alone; for overall survival, they were 91.9% and 89.5% vs. 88.7% and 86.2%, respectively, whereas for cause-specific survival, they were 96.9% and 96.1% vs. 97.6% and 96.2%, respectively. Cox proportional hazard regression analysis for BC revealed that low Gleason grade, HDR brachytherapy combined with 3DCRT, and adjuvant androgen deprivation therapy were significant in predicting BC. Radiation Therapy Oncology Group Grade 3 late urinary and rectal morbidity rates were 7.1% and 0%, respectively. No Grade ≥4 reactions were detected.ConclusionsHDR brachytherapy combined with 3DCRT was associated with improved BC and minimal toxicity in patients with unfavorable prostate cancer compared with conventional 3DCRT.     

Accuracy of computerized radiation treatment planning

The accuracy of computerized dose planning depends essentially on the computer program. The quickest and simplest way to assess the accuracy of a commercial program is to compare the results of the computer calculations with measured values. The present report deals with the accuracy of the RADPLAN dose planning program in different situations easy to control. The test methods are also applicable to other corresponding systems.     

A unified set of analysis tools for uterine cervix image segmentation

Segmentation is a fundamental component of many medical image-processing applications, and it has long been recognized as a challenging problem. In this paper, we report our research and development efforts on analyzing and extracting clinically meaningful regions from uterine cervix images in a large database created for the study of cervical cancer. In addition to proposing new algorithms, we also focus on developing open source tools which are in synchrony with the research objectives. These efforts have resulted in three Web-accessible tools which address three important and interrelated sub-topics in medical image segmentation, respectively: the Boundary Marking Tool (BMT), Cervigram Segmentation Tool (CST), and Multi-Observer Segmentation Evaluation System (MOSES). The BMT is for manual segmentation, typically to collect “ground truth” image regions from medical experts. The CST is for automatic segmentation, and MOSES is for segmentation evaluation. These tools are designed to be a unified set in which data can be conveniently exchanged. They have value not only for improving the reliability and accuracy of algorithms of uterine cervix image segmentation, but also promoting collaboration between biomedical experts and engineers which are crucial to medical image-processing applications. Although the CST is designed for the unique characteristics of cervigrams, the BMT and MOSES are very general and extensible, and can be easily adapted to other biomedical image collections.