Validation of a surface-based deformable MRI-3D ultrasound image registration algorithm toward clinical implementation for interstitial prostate brachytherapy

PURPOSEThe purpose of this study was to evaluate and clinically implement a deformable surface-based magnetic resonance imaging (MRI) to three-dimensional ultrasound (US) image registration algorithm for prostate brachytherapy (BT) with the aim to reduce operator dependence and facilitate dose escalation to an MRI-defined target.METHODS AND MATERIALSOur surface-based deformable image registration (DIR) algorithm first translates and scales to align the US- and MR-defined prostate surfaces, followed by deformation of the MR-defined prostate surface to match the US-defined prostate surface. The algorithm performance was assessed in a phantom using three deformation levels, followed by validation in three retrospective high-dose-rate BT clinical cases. For comparison, manual rigid registration and cognitive fusion by physician were also employed. Registration accuracy was assessed using the Dice similarity coefficient (DSC) and target registration error (TRE) for embedded spherical landmarks. The algorithm was then implemented intraoperatively in a prospective clinical case.RESULTSIn the phantom, our DIR algorithm demonstrated a mean DSC and TRE of 0.74 ± 0.08 and 0.94 ± 0.49 mm, respectively, significantly improving the performance compared to manual rigid registration with 0.64 ± 0.16 and 1.88 ± 1.24 mm, respectively. Clinical results demonstrated reduced variability compared to the current standard of cognitive fusion by physicians.CONCLUSIONSWe successfully validated a DIR algorithm allowing for translation of MR-defined target and organ-at-risk contours into the intraoperative environment. Prospective clinical implementation demonstrated the intraoperative feasibility of our algorithm, facilitating targeted biopsies and dose escalation to the MR-defined lesion. This method provides the potential to standardize the registration procedure between physicians, reducing operator dependence.     

Evaluating the accumulated dose distribution of organs at risk in combined radiotherapy for cervical carcinoma based on deformable image registration

ObjectiveTo evaluate the feasibility and value of deformable image registration (DIR) in calculating the cumulative doses of organs at risk (OARs) in the combined radiotherapy of cervical cancer.Patients and methodsThirty cervical cancer patients treated with external beam radiotherapy (EBRT) combined with intracavitary brachytherapy (ICBT) were reviewed. The simulation CT images of EBRT and ICBT were imported into Varian Velocity 4.1 for the DIR-based dose accumulation. Cumulative dose-volume parameters of D2cc for rectum and bladder were compared between the direct addition (DA) and DIR methods. The quantitative parameters were measured to evaluate the accuracy of DIR.ResultsThe three-dimensional cumulative dose distribution of the tumor and OARs were graphically well illustrated by composite isodose lines. In combined EBRT and ICBT, the mean cumulative bladder D2cc calculated by DIR and DA was 86.13 Gy and 86.27 Gy, respectively. The mean cumulative rectal D2cc calculated by DIR and DA was 72.97 Gy and 73.90 Gy, respectively. No significant differences were noted between these two methods (p > 0.05). As to the parameters used to evaluate the DIR accuracy, the mean DSC, Jacobian, MDA (mm) and Hausdorff distance (mm) were 0.79, 1.0, 3.84, and 22.01 respectively for the bladder and 0.53, 1.2, 7.31, and 29.58 respectively for the rectum. In this study, the DSC seemed to be slightly lower compared with previous studies.ConclusionDose accumulation based on DIR might be an alternative method to illustrate and evaluate the cumulative doses of the OARs in combined radiotherapy for cervical cancer. However, DIR should be used with caution before overcoming the relevant limitations.     

Deformable image registration–based contour propagation yields clinically acceptable plans for MRI-based cervical cancer brachytherapy planning

PurposeTo study the dosimetric impact of deformable image registration–based contour propagation on MRI-based cervical cancer brachytherapy planning.Methods and MaterialsHigh-risk clinical target volume (HRCTV) and organ-at-risk (OAR) contours were delineated on MR images of 10 patients who underwent ring and tandem brachytherapy. A second set of contours were propagated using a commercially available deformable registration algorithm. “Manual-contour” and “propagated-contour” plans were optimized to achieve a maximum dose to the most minimally exposed 90% of the volume (D₉₀) (%) of 6 Gy/fraction, respecting minimum dose to the most exposed 2cc of the volume (D_2cc) OAR constraints of 5.25 Gy and 4.2 Gy/fraction for bladder and rectum/sigmoid (86.5 and 73.4 Gy equivalent dose in 2 Gy fractions [EQD₂] for external beam radiotherapy [EBRT] + brachytherapy, respectively). Plans were compared using geometric and dosimetric (total dose [EQD₂] EBRT + brachytherapy) parameters.ResultsThe differences between the manual- and propagated-contour plans with respect to the HRCTV D₉₀ and bladder, rectum, and sigmoid D_2cc were not statistically significant (per-fraction basis). For the EBRT + brachytherapy course, the D_2cc delivered to the manually contoured OARs by the propagated-contour plans ranging 98–107%, 95–105%, and 92–108% of the dose delivered by the manual-contour plans (max 90.4, 70.3, and 75.4 Gy for the bladder, rectum, and sigmoid, respectively). The HRCTV dose in the propagated-contour plans was 97–103% of the dose in the manual-contour plans (maximum difference 2.92 Gy). Increased bladder filling resulted in increased bladder dose in manual- and propagated-contour plans.ConclusionsWhen deformable image registration–propagated contours are used for cervical brachytherapy planning, the HRCTV dose is similar to the dose delivered by manual-contour plans and the doses delivered to the OARs are clinically acceptable, suggesting that our algorithm can replace manual contouring for appropriately selected cases that lack major interfractional anatomical changes.     

形变配准在宫颈癌近距离放疗分次间剂量评估中的可行性研究

目的:比较近距离放疗分次间靶区和正常组织在形变配准(DIR)和简单累加剂量体积直方图(DVH)情况下,累积剂量的剂量学差异,分析在宫颈癌三维近距离放疗计划中,形变配准技术应用于靶区和正常组织剂量评估的可行性。方法:回顾性选取13例宫颈癌近距离放疗病例,每个病例均进行了4次CT定位的近距离放疗。对每个病例的4次CT进行形...     

左侧乳腺癌根治术后调强放疗中剂量累加的研究

目的 通过形变配准及刚性配准进行左侧乳腺癌放疗中靶区及危及器官剂量累加的研究,探讨二者受量的变化规律。方法 回顾分析16例女性左侧乳腺癌根治术后患者,靶区包括锁上淋巴结引流区加胸壁,均采用6 MV X射线调强放疗（IMRT）。所有患者均接受定位、二程CT扫描,在定位图像（CT1）上制定放疗计划为Plan1,在二程定位图像（CT2）上制定放疗计划为Plan2。利用Velocity软件将Plan2的剂量进行刚性、形变配准到CT1剂量累加后获得Plan-rigid、Plan-deform。比较4个计划中靶区及危及器官的剂量学差异。结果 CT2比CT1的CTV体积平均缩小6.64%;形变后靶区剂量均匀性指数（HI）提高23.05%,而形变后心脏、左、右肺戴斯相似系数（DSC）均低于形变前（0.94±0.01 vs.0.89±0.05、0.96±0.01 vs.0.91±0.03、0.96±0.01 vs.0.92±0.03）,且差异均有统计学意义（Z=-3.208、-3.533、-3.535,P<0.05）;心脏及左肺各剂量-体积指标在Plan2、Plan-rigid、Plan-deform与Plan1的组间差异均无统计学意义（P>0.05）;在Plan-rigid组各剂量-体积指标均高于Plan-deform组。结论 靶区及危及器官体积、剂量-体积指标变化较小的左乳癌根治术后患者在进行放疗剂量累加时,推荐使用刚性配准,且初次调强计划的剂量-体积指标可基本反映双肺及心脏的受量情况。     

变形配准与经验计算剂量累加法用于肺癌放疗计划累加剂量计算的研究

目的 应用变形配准功能评价肺癌患者放疗计划中正常组织和危及器官的累加剂量,并与经验计算剂量累加法进行比较.方法 回顾性分析10例肺癌患者,放疗前制定了三维适形或调强治疗计划,放疗过程中重新行CT模拟,并重新设计相同的治疗计划.采用Mimvista软件,运用变形配准,分别在2次CT图像上进行剂量累加.采用经验计算剂量累加法,计算2次放疗计划的正常组织和危及器官的累加剂量,分别对两种方法的双侧肺组织、心脏及脊髓的受照剂量体积以及平均剂量等参数,进行比较.结果 定位和复位图像采用相同的计划方式时,两种方法所得正常组织和危及器官的累积受照体积和剂量等参数差异无统计学意义,仅右肺的平均剂量除外(t=2.98,P＜0.05).结论 变形配准法可以准确评价肺癌患者多次放疗计划中正常组织和危及器官的累加剂量.肺癌患者的靶区变化不大并且采用相同的计划方式时,应用经验计算剂量累加法,可粗略评价肺和心脏等正常组织和危及器官的剂量体积.     

Evaluation of a novel software application for magnetic resonance distortion correction in cranial stereotactic radiosurgery

This study aimed to validate a novel commercially available software for correcting spatial distortion in cranial magnetic resonance (MR) images. This software has been used to assess the dosimetric impact of MR distortion in stereotactic radiosurgery (SRS) treatments of vestibular schwannomas (VSs). Five MR datasets were intentionally distorted. Each distorted MR dataset was corrected using the Cranial Distortion software, obtaining a new corrected MR dataset (MRcorr). The accuracy of the correction was quantified by calculating the target registration error (TRE) for 6 anatomical landmarks identified in the co-registered MRcorr and planning computed tomography (pCT) images. Nine VS cases were included to investigate the impact of the MR distortion in SRS plans. Each SRS plan was calculated on the pCT (1 × 1 × 1 mm³ voxel) with the target and organs at risk (OARs) delineated using the planning MR dataset. This MR dataset was then corrected (MRcorr) using the Cranial Distortion software. Geometrical agreement between the original target and the corresponding corrected target was assessed using several metrics: MacDonald criteria, mean distance to agreement (MDA), and Dice similarity coefficient (DSC). Target coverage (D99%) and maximum doses (D2%) to ipsilateral cochlea and brainstem resulting on the MRcorr dataset were compared with the original values. TRE values (0.6 mm ± 0.3 mm) and differences found in Macdonald criteria (0.3 mm ± 0.4 mm and 0.3 mm ± 0.3 mm) and MDA (0.8 mm ± 0.2 mm) were mostly within the voxel size dimension of the pCT scan (1 × 1 × 1 mm³). High similarity (DSC > 0.7) between the original and corrected targets was found. Small dose differences for the original and corrected structures were found: 0.1 Gy ± 0.1 Gy for target D99%, 0.2 Gy ± 0.3 Gy for cochlea D2%, and 0.1 Gy ± 0.1 Gy for brainstem D2%. Our study shows that Distortion Correction software can be a helpful tool to detect and adequately correct brain MR distortions. However, a negligible dosimetric impact of MR distortion has been detected in our clinical practice.     

Validation of MRI to TRUS registration for high-dose-rate prostate brachytherapy

PurposeThe objective of this study was to develop and validate an open-source module for MRI to transrectal ultrasound (TRUS) registration to support tumor-targeted prostate brachytherapy.Methods and MaterialsIn this study, 15 patients with prostate cancer lesions visible on multiparametric MRI were selected for the validation. T2-weighted images with 1-mm isotropic voxel size and diffusion weighted images were acquired on a 1.5T Siemens imager. Three-dimensional (3D) TRUS images with 0.5-mm slice thickness were acquired. The investigated registration module was incorporated in the open-source 3D Slicer platform, which can compute rigid and deformable transformations. An extension of 3D Slicer, SlicerRT, allows import of and export to DICOM-RT formats. For validation, similarity indices, prostate volumes, and centroid positions were determined in addition to registration errors for common 3D points identified by an experienced radiation oncologist.ResultsThe average time to compute the registration was 35 ± 3 s. For the rigid and deformable registration, respectively, Dice similarity coefficients were 0.87 ± 0.05 and 0.93 ± 0.01 while the 95% Hausdorff distances were 4.2 ± 1.0 and 2.2 ± 0.3 mm. MRI volumes obtained after the rigid and deformable registration were not statistically different (p > 0.05) from reference TRUS volumes. For the rigid and deformable registration, respectively, 3D distance errors between reference and registered centroid positions were 2.1 ± 1.0 and 0.4 ± 0.1 mm while registration errors between common points were 3.5 ± 3.2 and 2.3 ± 1.1 mm. Deformable registration was found significantly better (p < 0.05) than rigid registration for all parameters.ConclusionsAn open-source MRI to TRUS registration platform was validated for integration in the brachytherapy workflow.     

Integrating external beam and prostate seed implant dosimetry for intermediate and high-risk prostate cancer using biologically effective dose: Impact of image registration technique

PURPOSECombining external beam radiation therapy (EBRT) and prostate seed implant (PSI) is efficacious in treating intermediate- and high-risk prostate cancer at the cost of increased genitourinary toxicity. Accurate combined dosimetry remains elusive due to lack of registration between treatment plans and different biological effect. The current work proposes a method to convert physical dose to biological effective dose (BED) and spatially register the dose distributions for more accurate combined dosimetry.METHODS AND MATERIALSA PSI phantom was CT scanned with and without seeds under rigid and deformed transformations. The resulting CTs were registered using image-based rigid registration (RI), fiducial-based rigid registration (RF), or b-spline deformable image registration (DIR) to determine which was most accurate. Physical EBRT and PSI dose distributions from a sample of 91 previously-treated combined-modality prostate cancer patients were converted to BED and registered using RI, RF, and DIR. Forty-eight (48) previously-treated patients whose PSI occurred before EBRT were included as a “control” group due to inherent registration. Dose-volume histogram (DVH) parameters were compared for RI, RF, DIR, DICOM, and scalar addition of DVH parameters using ANOVA or independent Student's t tests (α = 0.05).RESULTSIn the phantom study, DIR was the most accurate registration algorithm, especially in the case of deformation. In the patient study, dosimetry from RI was significantly different than the other registration algorithms, including the control group. Dosimetry from RF and DIR were not significantly different from the control group or each other.CONCLUSIONSCombined dosimetry with BED and image registration is feasible. Future work will utilize this method to correlate dosimetry with clinical outcomes.     

Evaluation of intrafraction motion of the organs at risk in image-based brachytherapy of cervical cancer

Purpose/IntroductionTo assess the variation in the doses received by the organs at risk (OARs) that can occur during treatment planning of cervical cancer by image-based brachytherapy.Methods and MaterialsAfter intracavitary application, two sets of images—CT and MRI—were obtained. The two sets of images were fused together with respect to the applicator. Contouring was done separately on CT and MR images. Dose received by the OARs on CT images with respect to the plans made on the MR images was estimated and compared with those on the MR images.ResultsAlthough there was always a difference between the dose received by the OARs based on the CT and MRI contours, it was not significant for the bladder and rectum; 2 cc doses differed by 0.49 Gy (±0.44) p = 0.28 for the bladder and 0.30 Gy (±0.29) p = 0.16 for the rectum. The 1 cc and 0.1 cc differences were also not significant. However for the sigmoid colon, there was significant intrafraction variation in the 2 cc doses 0.61 (±0.6) p = 0.001, 1 cc doses 0.73 (±0.67) Gy p = 0.00, and 0.1 cc dose 0.97 (±0.93) Gy p = 0.009.ConclusionsThe variation in the doses to the OARs must be considered while weighing target coverage against overdose to the OARs. Although not significant for the bladder and rectum, it was significant for the sigmoid colon. Estimated doses to OARs on the planning system may not be the same dose delivered at the time of treatment.     

Configuration analysis of the injection position and shape of the gel spacer in gynecologic brachytherapy

PurposeIn this single-institution retrospective study, configuration analysis was performed to determine the optimal location and volume of hyaluronic acid gel spacer injection into the rectovaginal or vesicovaginal septum for effective dose reduction (DR) to the organs at risk (OARs), the rectum and bladder.Methods and materials70 and 50 intracavitary brachytherapy treatment plans used only vaginal cylinders with gel spacers for the rectal and bladder sides, respectively, whereas 28 did not use spacers. Correlation analysis was performed between the geometrical parameters and injection position of the gel spacers and the 2-cm³ covering doses of the OARs for each treatment.ResultsA higher DR was predicted for hyaluronic acid gel spacer injection within ±5 mm and ±2.5 mm in the lateral-medial direction from the midpoint on the rectal and bladder sides, and ±10 mm in the cranial–caudal direction from the midpoint on the rectal side. There were correlations between 2-cm³ covering doses and the gel spacer parameters: the volume on the rectal (p = 0.02) and bladder (p = 0.04) sides; the craniocaudal length on the rectal side (p << 0.05); and ventrodorsad thickness on each OAR (p << 0.05) sides. There was no significant difference in the DR between a volume of ～10 cm³ and that of a higher volume (p >> 0.05).ConclusionsA gel spacer volume of ～10 cm³ provides sufficient OAR DR if its gravity point is on the midpoint between the cylinder applicator and OAR, and its craniocaudal length covers the active length of the cylinder applicator.     

The influence of small field output factors simulated uncertainties on the calculated dose in VMAT plans for brain metastases: a multicentre study

Objectives:This multicentric study was carried out to investigate the impact of small field output factors (OFs) inaccuracies on the calculated dose in volumetric arctherapy (VMAT) radiosurgery brain plans.Methods:Nine centres, realised the same five VMAT plans with common planning rules and their specific clinical equipment Linac/treatment planning system commissioned with their OFs measured values (OFbaseline). In order to simulate OFs errors, two new OFs sets were generated for each centre by changing only the OFs values of the smallest field sizes (from 3.2 × 3.2 cm² to 1 × 1 cm²) with well-defined amounts (positive and negative). Consequently, two virtual machines for each centre were recommissioned using the new OFs and the percentage dose differences ΔD (%) between the baseline plans and the same plans recalculated using the incremented (OFup) and decremented (OFdown) values were evaluated. The ΔD (%) were analysed in terms of planning target volume (PTV) coverage and organs at risk (OARs) sparing at selected dose/volume points.Results:The plans recalculated with OFdown sets resulted in higher variation of doses than baseline within 1.6 and 3.4% to PTVs and OARs respectively; while the plans with OFup sets resulted in lower variation within 1.3% to both PTVs and OARs. Our analysis highlights that OFs variations affect calculated dose depending on the algorithm and on the delivery mode (field jaw/MLC‐defined). The Monte Carlo (MC) algorithm resulted significantly more sensitive to OFs variations than all of the other algorithms.Conclusion:The aim of our study was to evaluate how small fields OFs inaccuracies can affect the dose calculation in VMAT brain radiosurgery treatments plans. It was observed that simulated OFs errors, return dosimetric calculation accuracies within the 3% between concurrent plans analysed in terms of percentage dose differences at selected dose/volume points of the PTV coverage and OARs sparing.Advances in knowledge:First multicentre study involving different Planning/Linacs about undetectable errors in commissioning output factor for small fields.     

Factors associated with deformation accuracy and modes of failure for MRI-optimized cervical brachytherapy using deformable image registration

PurposeTo identify factors associated with MRI-to-CT image deformation accuracy and modes of failure for MRI-optimized intracavitary high-dose-rate treatment of locally advanced cervical cancer.Methods and MaterialsTwenty-six patients with locally advanced cervical cancer had preimplantation MRI registered and deformed to postimplantation CT images using anatomically constrained and biomechanical model–based deformable image registration (DIR) algorithms. Cervix (primary) and cervix plus 10-mm margin (secondary) were used as controlling regions of interest for deformation. High-risk clinical target volume defined on pre-MRI was propagated to CT and evaluated for clinical utility in optimizing target volumes using scores 0 (low performing) to 4 (high performing). Quantitative evaluation of deformation performance included Dice index, distance to agreement, center of mass (COM) differences, cervical/uterus volume, and geometric change in organ position for MR-projected structures. Statistical analysis was performed to identify predictors of clinical utility and modes of failure.ResultsAnatomically constrained and biomechanical model–based deformable image registration algorithms achieved clinical utility >3 in 65% and 81% of patients, respectively. This improved to 81% and 85%, respectively, if cervix plus margin was used to drive deformations. Total COM displacement (cervix plus uterus) had the highest sensitivity in predicting low from high clinical utility in optimizing target volumes. Deformation failure (low clinical utility) resulted from high COM displacement, high cervical volume change, and retroverted uterine anatomy.ConclusionsMRI-to-CT deformable image registration using a cervix-controlling region of interest can aid clinical target delineation in cervical brachytherapy and potentially improve brachytherapy implant quality and clinical workflow. Deformation failures warrant further study and prospective deformation validation.     

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.     

鼻咽癌放射治疗定位的CT/MRI图像配准辅助装置的研究

目的 研制用于鼻咽癌放射治疗定位的CT/MRI图像配准辅助装置,并且通过组织勾画差异分析使用该装置后所得配准融合图像在临床中的应用意义。方法 在普通的磁共振头颈线圈中设计特定形状的头枕,保持患者在扫描时与CT定位扫描时相同的体位。采用配对t检验分析CT图像与融合图像中腮腺、下颌骨的勾画差异。结果 患者的头颈部CT、MRI图像的配准精度较未使用该装置的图像具有明显的提高,使用该配准图像得到的融合图像、组织结构位置、细节显示准确清晰。左右腮腺体积在CT图像中较CT/MRI融合图像中偏小,左腮腺体积融合和CT图像中的体积分别为（17.78±6.89）cm³和（17.17±7.02）cm³（t=-2.715,P<0.05）;右腮腺体积融合和CT图像中的体积分别为（19.23±8.91）cm³和（17.47±7.42）cm³（t=-2.552,P<0.05）;下颌骨在CT图像中勾画体积较CT/MRI融合图像偏大,左下颌骨体积融合和CT图像中的体积分别为（33.7±5.59）cm³和（34.8±6.27）cm³（t=3.548,P<0.05）;右下颌骨体积融合和CT图像中的体积分别为（34.46±6.08）cm³和（35.38±6.72）cm³（t=3.14,P<0.05）。结论 使用该辅助装置,可以得到头颈部配准融合准确的CT/ MRI的图像,此融合图像对临床医师的组织和病灶勾画具有积极的参考价值。     

基于四分位距值的调强放疗计划剂量体积直方图分析

目的 提出一种基于四分位距值的调强放射治疗（IMRT）计划靶区及危及器官剂量体积直方图（DVH）差异分析方法。方法 回顾分析22例宫颈癌IMRT计划,将靶区和危及器官（膀胱、直肠和左右股骨头）5组DVH曲线从Pinnacle³计划系统中导出,对每组DVH曲线求出平均DVH曲线和四分位距值曲线。结果 计划靶区DVH在54.03 Gy处差异最大,四分位距值为6.95%,处方剂量包绕的靶区体积为（96.43±1.63）%。膀胱DVH在17.24 Gy处差异最大,四分位距值为14.62%,V₄₀和V₃₀分别为（32.79±7.06）% 和（56.47±9.94）%。直肠DVH在35.92 Gy处差异最大,四分位距值为19.94%,V₄₀和V₃₀分别为（30.17±10.80）%和（58.16±11.99）%。膀胱与直肠的四分位距值差异有统计学意义（z=-6.59, P<0.05）。左侧股骨头DVH在16.06 Gy处差异最大,四分位距值为31.47%。右侧股骨头DVH在17.47 Gy处差异最大,四分位距值为32.82%,左右股骨头间的四分位距值间差异无统计学意义（P>0.05）。结论 四分位距值曲线可以分析靶区和危及器官DVH曲线的变化趋势,为自动计划优化参数设置提供指导。     

Improvement in plan quality after Implementation of clinical goals in a large network of cancer centers

Clinical Goals (CG) is a tool available in the Varian Eclipse planning system to objectively and visually evaluate the quality of treatment plans based upon user-defined dose-volume parameters. We defined a set of CG for Stereotactic Radiosurgery (SRS) and Intensity-Modulated Radiotherapy (IMRT) based on published data and guidelines and implemented this in a network of cancer centers in India (American Institute of Oncology). A dosimetric study was performed to compare brain SRS and breast IMRT plan quality before and after CG implementation.The CG defined for SRS plans were target V_100% ≥ 98%, dose gradient measure (GM) ≤ 0.5 cm, conformity index (CI) 1.0 to 1.2. For breast IMRT plans, CG defined target V_100% ≥ 97%, V_95% ≥ 95%, V_107% ≤ 2%, V_105% ≤ 10%, and D_max ≤ 2.4 Gy. Dose limits to organs-at-risk (OAR) were summarize in supplemental materials. Twenty brain SRS and 10 breast IMRT treatment plans that were previously delivered on patients were selected and re-planned using CG. The pre and postoptimized plan parameters were compared using student t-tests.For brain SRS plans, the V₁₀₀, GM, and CI for the pre- and post-Clinical-Goals plans were 93.22% ± 7.2% vs 97.96% ± 0.29% (p = 0.009), 0.63 ± 0.16 vs 0.42 ± 0.05 (p < 0.001) and 1.07 ± 0.18 vs 1.06 ± 0.06 (p = 0.79), respectively. There were no differences in max dose to OARs. In breast IMRT plans, the target V_107% for pre and postimplemented plans were 16.50% ± 10.98% vs 0.32% ± 0.32%, respectively (p = 0.001). The average target V_105% were 44.00% ± 15.72% and 8.69% ± 4.53%, respectively (p < 0.001). No differences were found in the average target V_100% (p = 0.128) and V_95% (p = 0.205). The average target D_max were 112.28% ± 1.59% and 109.14% ± 0.73%, respectively (p < 0.001). There were only minor differences in doses to OARs.The implementation of CG in Varian Eclipse significantly improved SRS and IMRT plan quality with enhanced coverage, dose GM, and CI without increased dose to OARs.     

Validation of a dose warping algorithm using clinically realistic scenarios

Objective:

Dose warping following deformable image registration (DIR) has been proposed for interfractional dose accumulation. Robust evaluation workflows are vital to clinically implement such procedures. This study demonstrates such a workflow and quantifies the accuracy of a commercial DIR algorithm for this purpose under clinically realistic scenarios.

Methods:

12 head and neck (H&N) patient data sets were used for this retrospective study. For each case, four clinically relevant anatomical changes have been manually generated. Dose distributions were then calculated on each artificially deformed image and warped back to the original anatomy following DIR by a commercial algorithm. Spatial registration was evaluated by quantitative comparison of the original and warped structure sets, using conformity index and mean distance to conformity (MDC) metrics. Dosimetric evaluation was performed by quantitative comparison of the dose–volume histograms generated for the calculated and warped dose distributions, which should be identical for the ideal “perfect” registration of mass-conserving deformations.

Results:

Spatial registration of the artificially deformed image back to the planning CT was accurate (MDC range of 1–2 voxels or 1.2–2.4 mm). Dosimetric discrepancies introduced by the DIR were low (0.02 ± 0.03 Gy per fraction in clinically relevant dose metrics) with no statistically significant difference found (Wilcoxon test, 0.6 ≥ p ≥ 0.2).

Conclusion:

The reliability of CT-to-CT DIR-based dose warping and image registration was demonstrated for a commercial algorithm with H&N patient data.

Advances in knowledge:

This study demonstrates a workflow for validation of dose warping following DIR that could assist physicists and physicians in quantifying the uncertainties associated with dose accumulation in clinical scenarios.Modern radiotherapy aims to move towards a personalized treatment for each patient with cancer, requiring reliable predictions of an individual''s response to a particular therapy and accurate monitoring of treatment delivery, enabling adaptations to the treatment plan as required. To date, typical radiotherapy practice involves the preparation of a treatment plan based on an initial high resolution CT scan of the anatomy to be treated. However, since the treatment is optimized for the anatomy on planning CT (pCT), any changes in a patient''s anatomy during the treatment course itself (which may last for up to 8 weeks) could result in a suboptimal treatment. Currently, to account for interfraction movements, a low-resolution, low-dose CT image [typically cone beam CT (CBCT) or mega-voltage CT (MVCT), although other options exist] of the patient is often acquired prior to each treatment (daily images). This is termed image-guided radiotherapy (IGRT).¹In 1997, Yan et al² proposed the concept of adaptive radiotherapy (ART), suggesting the adaptation of the treatment plan to account for interfraction anatomical variations, based on these daily images. Such treatment adaptations are sometimes currently employed in routine clinical practice when significant anatomical changes are observed, such as substantial weight loss.³ State-of-the-art ART, on the other hand, aims to regularly monitor the treatment delivery and adapt when necessary (offline ART)² or even predict the result and alter it before the treatment of that day (online ART).⁴ The ability to determine the accumulated delivered dose to deforming anatomy is of vital importance not only for ART but also for the assessment and optimization of radiobiological models,⁵ since without it, these models are informed by less accurate estimates of delivered dose to each tissue or partial tissue volume. However, certain limitations such as inaccuracies in contour propagation and in reliable dose accumulation currently prevent efficient routine monitoring of delivered dose throughout the treatment.Deformable image registration (DIR) algorithms have been proposed as a method for facilitating these processes. The accuracy of DIR algorithms is therefore of critical importance and has been the subject of investigation by several researchers, with mechanical phantoms,^6–13 patient images^14–22 and digital phantoms (i.e. patient images artificially deformed with known deformations)^10,11,23 being extensively used for DIR assessment.An extension to these issues is the application of the underlying anatomical deformations to a calculated dose distribution, which is a necessary step in interfractional dose accumulation. Such dose warping process involves the direct deformation of a calculated dose distribution by applying the deformation matrix estimated during DIR between two anatomical scans, essentially warping the dose according to the reference anatomy. Dose warping and deformable dose accumulation have been employed in a number of clinical investigations, including a dose feedback technique in ART frameworks,²⁴ the assessment of planning target volume (PTV) margins²⁵ and the examination of parotid gland dose–effect relationships,²⁶ based on dose distributions recalculated on daily or weekly scans and the accumulation on a single frame of reference. Consequently, quality assurance and evaluation techniques have been investigated in order to validate the applicability of this dose warping concept. Previous work has investigated mathematical models to directly convert DIR errors into dose-warping uncertainties, through the use of patient images and mechanical or digital phantoms,^15,27–30 while a number of deformable dosimetric and non-dosimetric gel phantoms have been produced enabling the experimental evaluation of both DIR and dose warping.^31–35 Even though some of these studies revealed promising results, they have not convinced the radiotherapy community that these uncertainties are adequately understood.³⁶In one such study, Yeo et al³⁴ used a cylindrical deformable dosimetric gel phantom for the experimental validation of dose warping against actual three-dimensional (3D) measurements. The warped and measured dose distributions revealed an agreement of 3D γ_3%/3mm = 99.9%, after small deformations (approximately 9 mm), and γ_3%/3 mm = 96.7% after larger deformations (approximately 20 mm). The authors therefore concluded that “dose-warping may be justified for small deformations in particular and those that do not involve significant density changes”. On the other hand, Juang et al³⁵ exposed “substantial errors in a commercial DIR” used for dose-warping evaluation, utilizing another 3D deformable dosimetric gel, revealing a 3D γ_3%/3mm passing rate of 60%.Such studies, and especially the use of deformable dosemeters for the evaluation of dose warping, are very important as they can reveal the 3D dosimetric impact owing to the uncertainties of a given DIR algorithm. However, they possess three important limitations: first, typical physical dosimetric phantoms present limited image complexity and would not assess the performance limits of the DIR algorithm under evaluation in clinical scenarios. Second, plan delivery, intrinsic dosimetric and dose reading uncertainties are present when using any type of dosemeter in physical phantom measurements. The third limitation is the fact that even where such approaches can offer high precision dosimetric uncertainty evaluation, they cannot directly inform users about the potential extent of those uncertainties in practical clinical cases. All these issues will be addressed in this work.In the present study, a workflow for the robust validation of DIR and dose warping is presented, using patient images artificially deformed with clinically realistic deformations and clinically optimized Monte Carlo dose calculations of intensity-modulated radiotherapy (IMRT) plans, quantifying both the spatial errors in the deformable registration and their dosimetric impact when applied to dose accumulation. In contrast to previously proposed evaluation procedures, this method examines and reports dose-warping uncertainties under clinically relevant scenarios. Although the validation workflow is applicable for different DIRs and clinical indications, it is here employed specifically for the evaluation of a commercial software (OnQ rts^®; Oncology Systems Limited, Shropshire, UK) in head and neck (H&N) cancer patient cases.     

Automatic segmentation for adaptive planning in nasopharyngeal carcinoma IMRT: Time,geometrical, and dosimetric analysis

The aim of this study was to quantify the geometrical differences between manual contours and autocontours, the dosimetric impacts, and the time gain of using autosegmentation in adaptive nasopharyngeal carcinoma (NPC) intensity-modulated radiotherapy (IMRT) for a commercial system. A total of 20 consecutive Stages I to III NPC patients who had undergone adaptive radiation therapy (ART) re planning for IMRT treatment were retrospectively studied. Manually delineated organs at risks (OARs) on the replanning computed tomography (CT) were compared with the autocontours generated by VelocityAI using deformable registration from the original planning CT. Dice similarity coefficients and distance-to-agreements (DTAs) were used to quantify their geometric differences. IMRT test plans were generated with the assistance of RapidPlan based on the autocontours of OARs and manually segmented target volumes. The dose distributions were applied on the manually delineated OARs, their dose volume histograms and dose constraints compliances were analyzed. Times spent on target, OAR contouring, and IMRT replanning were recorded, and the total time of replanning using manual contouring and autocontouring were compared. The averaged mean DTA of all structures included in the study were less than 2 mm, and 90% of the patients fulfilled the mean distance agreement tolerance recommended by AAPM 132.¹ The averaged maximum DTA for brainstem, cord, optic chiasm, and optic nerves were all less than 4 mm, whereas temporal lobes and parotids have larger average maximum DTA of 4.7 mm and 6.8 mm, respectively. It was found that large contour discrepancies in temporal lobes and parotids were often associated with large magnitude of deformation (warp distance) in image registrations. The resultant maximum dose of manually segmented brainstem, cord, and temporal lobe and the median dose of manually segmented parotids were found to be statistically higher than those to their autocontoured counter parts in test plans. Dose constraints of the manually segmented OARs in test plans were only met in 15% of the cases. The average time of manual contouring and autocontouring were 108 and 10 minutes, respectively (p < 0.001). More than 30% of the total replanning time would be spent in manual OAR contouring. Manual OAR delineation takes up a significant portion of time spent in ART replanning and OAR autocontouring could considerably enhance ART workflow efficiency. Geometrical discrepancies between auto- and manual contours in head and neck OARs were comparable to typical interobserver variation suggested in various literatures; however, some of the corresponding dosimetric differences were substantial, making it essential to carefully review the autocontours.