Treatment plan evaluation using dose-volume histogram (DVH) and spatial dose-volume histogram (zDVH)

Objective: The dose–volume histogram (DVH) has been accepted as a tool for treatment-plan evaluation. However, DVH lacks spatial information. A new concept, the z-dependent dose–volume histogram (zDVH), is presented as a supplement to the DVH in three-dimensional (3D) treatment planning to provide the spatial variation, as well as the size and magnitude of the different dose regions within a region of interest.

Materials and Methods: Three-dimensional dose calculations were carried out with various plans for three disease sites: lung, breast, and prostate. DVHs were calculated for the entire volume. A zDVH is defined as a differential dose–volume histogram with respect to a computed tomographic (CT) slice position. In this study, zDVHs were calculated for each CT slice in the treatment field. DVHs and zDVHs were compared.

Results: In the irradiation of lung, DVH calculation indicated that the treatment plan satisfied the dose–volume constraint placed on the lung and zDVH of the lung revealed that a sizable fraction of the lung centered about the central axis (CAX) received a significant dose, a situation that warranted a modification of the treatment plan due to the removal of one lung. In the irradiation of breast with tangential fields, the DVH showed that about 7% of the breast volume received at least 110% of the prescribed dose (PD) and about 11% of the breast received less than 98% PD. However, the zDVHs of the breast volume in each of seven planes showed the existence of high-dose regions of 34% and 15%, respectively, of the volume in the two caudal-most planes and cold spots of about 40% in the two cephalic planes. In the treatment planning of prostate, DVHs showed that about 15% of the bladder and 40% of the rectum received 102% PD, whereas about 30% of the bladder and 50% of the rectum received the full dose. Taking into account the hollow structure of both the bladder and the rectum, the dose–surface histograms (DSH) showed larger hot-spot volume, about 37% of the bladder wall and 43% of the rectal wall. The zDVHs of the bladder revealed that the hot-spot region was superior to the central axis. The zDVHs of the rectum showed that the high-dose region was an 8-cm segment mostly superior to the central axis. The serial array-like of the rectum warrants a closer attention with regard to the complication probability of the organ.

Conclusions: Although DVH provides an averaged dose–volume information, zDVH provides differential dose–volume information with respect to the CT slice position. zDVH is a 2D analog of a 3D DVH and, in some situations, more superior. It provides additional information on plan evaluation that otherwise could not be appreciated. The zDVH may be used along with DVH for plan evaluation and for the correlation of radiation outcome.     

A novel method for the evaluation of uncertainty in dose-volume histogram computation

PURPOSE: Dose-volume histograms (DVHs) are a useful tool in state-of-the-art radiotherapy treatment planning, and it is essential to recognize their limitations. Even after a specific dose-calculation model is optimized, dose distributions computed by using treatment-planning systems are affected by several sources of uncertainty, such as algorithm limitations, measurement uncertainty in the data used to model the beam, and residual differences between measured and computed dose. This report presents a novel method to take them into account. METHODS AND MATERIALS: To take into account the effect of associated uncertainties, a probabilistic approach using a new kind of histogram, a dose-expected volume histogram, is introduced. The expected value of the volume in the region of interest receiving an absorbed dose equal to or greater than a certain value is found by using the probability distribution of the dose at each point. A rectangular probability distribution is assumed for this point dose, and a formulation that accounts for uncertainties associated with point dose is presented for practical computations. RESULTS: This method is applied to a set of DVHs for different regions of interest, including 6 brain patients, 8 lung patients, 8 pelvis patients, and 6 prostate patients planned for intensity-modulated radiation therapy. CONCLUSIONS: Results show a greater effect on planning target volume coverage than in organs at risk. In cases of steep DVH gradients, such as planning target volumes, this new method shows the largest differences with the corresponding DVH; thus, the effect of the uncertainty is larger.     

Analysis of dose-volume histogram parameters for radiation pneumonitis after definitive concurrent chemoradiotherapy for esophageal cancer

Purpose

To evaluate dose-volume histogram (DVH) parameters as predictors of radiation pneumonitis (RP) in esophageal cancer patients treated with definitive concurrent chemoradiotherapy.

Patients and methods

Thirty-seven esophageal cancer patients treated with radiotherapy with concomitant chemotherapy consisting of 5-fluorouracil and cisplatin were reviewed. Radiotherapy was delivered at 2 Gy per fraction to a total of 60 Gy. For most of the patients, two weeks of interruption was scheduled after 30 Gy. The percentage of lung volume receiving more than 5-50 Gy in increments of 5 Gy (V5-V50, respectively), and the mean lung dose (MLD) were analyzed.

Results

Ten (27%) patients developed RP of grade 2; 2 (5%), grade 3; 0 (0%), grade 4; and 1 (3%), grade 5. By univariate analysis, all DVH parameters (i.e., V5-V50 and MLD) were significantly associated with grade ?2 RP (p < 0.01). The incidences of grade ?2 RP were 13%, 33%, and 78% in patients with V20s of ?24%, 25-36%, and ?37%, respectively. The optimal V20 threshold to predict symptomatic RP was 30.5% according to the receiver operating characteristics curve analysis.

Conclusion

DVH parameters were predictors of symptomatic RP and should be considered in the evaluation of treatment planning for esophageal cancer.     

Prostate volume change after radioactive seed implantation: possible benefit of improved dose volume histogram with perioperative steroid

Purpose: To evaluate the changes in prostate volume associated with radioactive seed implantation and identify factors that influence prostate swelling.

Methods and Materials: Between June 1997 and August 1999, 161 patients implanted for prostate carcinoma at the University of California, San Francisco, had prostate volume measurements taken at 4 time points (preplan, preimplant, postimplant, postimplant dosimetry). Patient records were reviewed for treatment with perioperative steroids, hormone therapy (nHT), and external beam radiotherapy (EBRT). One and 2-way analysis of variance (ANOVA) methods were used to test differences in mean effects among patient subsets.

Results: A mean 20% volume increase was noted immediately postimplant overall (p < 0.0001), and even with EBRT and/or HT. Steroids were associated with a mean volume decrease of 19.9%, by 3–4 weeks post-procedure (p < 0.0001). Without steroids, only a 3.8% mean change was seen (p = ns). Steroid use resulted in a significant increase in mean dose-volume histogram (DVH) (p = 0.001); however, this benefit was only observed among patients who did not receive steroid. A consistently high DVH occurred with steroid use.

Conclusion: A significant decrease in prostate volume and improved DVH are associated with steroid use. The diminished benefit of steroid use and higher mean DVH achieved in later years suggests the existence of a significant “learning curve” for brachytherapy procedures.     

A practical evaluation of five dose-volume histogram reduction algorithms.

A unifying approach to cumulative dose-volume histogram (CDVH) reduction analysis is presented, utilising two weighted linear interpolation models (VWD, DWV), two weighted probability models (VWP, DWP) and a novel integral probability model (IPM). As a test of their predictive value these algorithms were applied to CDVH data generated from lung doses, measured by TLD arrays in a female anthropomorphic phantom. Three arbitrary configurations of breast size and location of "target volume" within the breast were "treated", using an appropriate electron field (Varian Clinac 1800) or double-plane iridium-192 implant. Calculated effective doses from each of the reduction algorithms showed the iridium implant to be dosimetrically the most favourable in two the three configurations. Likewise, complication probabilities, based on a logistic dose-volume response function showed lung complication probabilities to be lower for the interstitial technique in the same situations. All algorithms tested showed reasonable consistency, with the exception of the VWD. The rationale and value of comparative rather than absolute dose-volume histogram analyses are discussed.     

肺灌注显像联合剂量体积直方图参数预测放射性肺炎的临床研究

 目的　观察接受三维适形或调强放疗的肺癌患者放疗前后肺灌注显像的变化、肺受照射的剂量体积直方图（DVH）参数等,并结合临床因素,探讨其与放射性肺炎发生的相关性。方法　18例接受三维适形或调强放疗的肺癌患者放疗前后行肺灌注显像检查,比较照射前后肺灌注显像的变化。放射性肺炎的评价按美国肿瘤放疗协作组（RTOG）急性放射性肺炎标准评定。获得的CT与单光子发射CT（SPECT）肺灌注图像融合后,将等剂量曲线投影到SPECT图像,将传统的DVH转换成f-DVH。将f-DVH曲线中每例患者的V5、V10和V20所对应的灵敏度与特异度相加,取其最大值,寻找到曲线的界值。分析放疗前后肺灌注显像变化及肺受照射的DVH与放射性肺炎发生的相关性。结果　18例患者中,33.3 %（6／18）发生了2级以上放射性肺炎。放疗前后肺灌注受损加重者2级以上放射性肺炎发生率为62.5 %（5／8）,肺灌注受损改善者发生率为10.0 %（1／10）。f-DVH图曲线中V5、V10和V20的界值分别为53 %、41 %和27 %,以V5对中重度急性放射性肺炎的预测准确度最高。放疗前后肺灌注显像的变化联合全肺DVH参数V5是放射性肺炎最强的预测因素。结论　肺癌患者放疗前后肺灌注显像能反映患侧肺灌注功能的变化。放疗前后肺灌注显像的变化联合DVH参数V5有望作为预测放射性肺炎发生的指标。     

Improving soft-tissue contrast in four-dimensional computed tomography images of liver cancer patients using a deformable image registration method

PURPOSE: To investigate a deformable image registration method to improve soft-tissue contrast in four-dimensional (4D) computed tomography (CT) images of the liver. METHODS AND MATERIALS: Ten patients with hepatocellular carcinoma underwent 4D CT scan for radiotherapy treatment planning on a positron emission tomography/CT scanner. Four-dimensional CT images were binned into 10 equispaced phases. The exhale phase served as the reference phase, and images from the other nine phases were coregistered to the reference phase image using an intensity-based, automatic deformable image registration method. Then the coregistered images were combined to create a single, high-quality reconstructed CT image at exhale phase as the new reference for target delineation. The extent of image quality enhancement was quantified relative to the original CT by calculating the signal-to-noise ratio and the contrast-to-noise ratio. RESULTS: The soft tissue image contrast was noticeably better after deformable image registration than in the original scans. Signal-to-noise ratios inside the liver region of interest increased for all patients by a factor of 3.0 (range, 2.3-3.7). The improvement in image quality was not linearly proportionate to the number of images averaged. Using only 6 phases can achieve at least 85% of the contrast enhancement that can be achieved using all 10 phases. We also found that contrast enhancement was inversely proportional to the original image quality (p = 0.006), and the contrast enhancement is attained with little loss of spatial resolution. CONCLUSIONS: This deformable image registration method is feasible to improve soft-tissue image quality in 4D CT images.     

三维放疗前后血清心肌酶谱变化与心脏体积剂量相关性分析

目的 探讨胸部肿瘤患者三维放疗前后血清心肌酶谱改变与心脏体积剂量的相关性。方法 102例胸部肿瘤患者(肺癌 68例、食管癌 34例)放疗前后检测血清天冬氨酸氨基转移酶(AST)、肌酸激酶(CK)、CK同工酶(CK-MB)、乳酸脱氢酶(LDH)及α-羟丁酸脱氢酶(α-HBDH)水平。放疗前后各种酶水平比较行配对t检验,组间比较行成组t检验。采用剂量体积直方图(DVH)参数\[心脏接受≥x Gy照射体积占总体积百分比(Vx)\]评价心脏体积剂量,各种酶与DVH参数相关性行Pearson法分析。结果 放疗后血清AST、CK-MB、LDH、α-HBDH水平较放疗前明显增高(19.42∶27.89、14.72∶19.57、178.80∶217.57、140.32∶176.25,t=－3.39~－6.92,P均=0.000)。调强放疗前后AST变化与 V₂₀、V₂₅、V₃₀相关(r=0.302~0.431,P=0.039~0.003),CK变化与 V₃₀相关(r=0.345,P=0.013),CK-MB、LDH、α-HBDH变化与 V₂₅、V₃₀均相关(r=0.465~0.376,P=0.001~0.005);三维适形放疗前后CK-MB、LDH变化与 V₃₀相关(r=0.330、0.274,P=0.014、0.033),α-HBDH变化与 V₂₅、V₃₀、V₃₅相关(r=0.270~0.331,P=0.046~0.014)。当放疗剂量>50 Gy时AST、LDH、α-HBDH变化与 V₂₅、V₃₀相关(r=0.256~0.359,P=0.019~0.006),CK-MB变化与 V₃₀相关(r=0.233,P=0.037);≤50 Gy时仅 V₅、V₄₅与CK变化相关(r=0.581、0.536,P=0.023、0.043)。结论 心脏体积剂量与三维放疗前后心肌酶水平变化有一定相关性,提示心脏DVH参数有助于评价放疗诱导的心肌损伤。     

自研发变形配准软件在四维CT图像上确定靶体积的初步临床验证

目的 初步测试自研发变形配准软件在四维CT (4DCT)图像上快速确定临床靶体积(CTV)和呼吸运动内靶体积(ITV)精度,评估其临床应用可行性。
方法 选择临床治疗的 1例肺癌和 1例肝癌的4DCT图像进行实验。用变形配准软件以单一呼吸时相CT图像勾画的CTV为参考自动生成其余呼吸时相的CTV defm ,并与放疗医师在每个呼吸时相CT图像勾画的CTV manu 比较,分析CTV defm 精度与适用范围。用CTV defm 叠加形成复合ITV comp ,并与最大密度投影(MIP) CT图像勾画的ITV MIP 比较轮廓、体积和几何中心位置差异。
结果 肺癌病例10个呼吸时相4DCT图像序列的CTV defm 与CTV manu 体积偏差平均值为(－2.59±5.02)%。与CTV manu 相比,CTV defm 的几何中心三维矢量偏差为(1.04±0.89) mm。肝癌患者ITV comp 与ITV MIP 几何形状和位置几乎重合,体积差别<1%,几何中心三维矢量差别为1.4 mm。
结论 测试变形配准软件系统在4DCT图像上自动生成CTV和呼吸运动ITV精度可满足临床计划设计要求。     

High-dose preoperative chemoradiotherapy in esophageal cancer patients does not increase postoperative pulmonary complications: Correlation with dose-volume histogram parameters

Purpose

To investigate the association of high-dose preoperative chemoradiotherapy (CRT) and dose-volume histogram (DVH) parameters of lungs with incidence of postoperative pulmonary complications and to identify predictive clinical factors of pulmonary complications.

Methods

Data of 65 patients were collected retrospectively. Thirty-five patients underwent transthoracic esophagectomy (TTE) alone and 30 received cisplatin and 5-fluorouracil, concomitant with radiotherapy, median dose 66 Gy, and followed by TTE. From the DVH for each lung alone and for both lungs together as one organ we generated total lung volume, mean radiotherapy dose, relative and absolute volumes receiving more than a threshold dose, and relative and absolute volumes receiving less than a threshold dose. Postoperative pulmonary complications were defined as pneumonia or respiratory failure.

Results

Sixty percent of the patients in the TTE alone group had postoperative pulmonary complications versus 63% in the CRT + TTE group. Postoperative mortality was 8.6% and 16.7% in the respective patient groups (p = NS). None of the DVH parameters was associated with postoperative pulmonary complications. Squamous cell carcinoma was an adverse factor related to increased postoperative pulmonary complications.

Conclusion

High-dose preoperative CRT was not associated with increased postoperative pulmonary complications in this cohort of esophageal cancer patients.     

Assessing respiration-induced tumor motion and internal target volume using four-dimensional computed tomography for radiotherapy of lung cancer

PURPOSE: To assess three-dimensional tumor motion caused by respiration and internal target volume (ITV) for radiotherapy of lung cancer. METHODS AND MATERIALS: Respiration-induced tumor motion was analyzed for 166 tumors from 152 lung cancer patients, 57.2% of whom had Stage III or IV non-small-cell lung cancer. All patients underwent four-dimensional computed tomography (4DCT) during normal breathing before treatment. The expiratory phase of 4DCT images was used as the reference set to delineate gross tumor volume (GTV). Gross tumor volumes on other respiratory phases and resulting ITVs were determined using rigid-body registration of 4DCT images. The association of GTV motion with various clinical and anatomic factors was analyzed statistically. RESULTS: The proportions of tumors that moved >0.5 cm along the superior-inferior (SI), lateral, and anterior-posterior (AP) axes during normal breathing were 39.2%, 1.8%, and 5.4%, respectively. For 95% of the tumors, the magnitude of motion was less than 1.34 cm, 0.40 cm, and 0.59 cm along the SI, lateral, and AP directions. The principal component of tumor motion was in the SI direction, with only 10.8% of tumors moving >1.0 cm. The tumor motion was found to be associated with diaphragm motion, the SI tumor location in the lung, size of the GTV, and disease T stage. CONCLUSIONS: Lung tumor motion is primarily driven by diaphragm motion. The motion of locally advanced lung tumors is unlikely to exceed 1.0 cm during quiet normal breathing except for small lesions located in the lower half of the lung.     

应用4D-CT技术确定肝癌内靶体积及相关剂量学研究

背景与目的:由于肝脏肿瘤的位移受呼吸运动的影响显著,三维适形放射治疗(three-dimensionaI confomal radiotherapy,3D CRT)难以准确定位靶区.本研究应用4D-CT技术确定个体化肝癌内靶体积(internal target volume,ITV),比较3D计划与4D计划的计划靶体积(planning target volume,PTV)及相关剂量学差异,并评价4D-CT的优势.方法:选择7例原发性肝癌患者,行4D-CT门控扫描,在10个相位的CT图像中分别勾画大体肿瘤体积(gross tumor volume,GTV)和临床靶体积(clinical target volume,CTV).在20%呼吸时相CT图像中利用三维治疗计划系统根据PTV-3D、PTV-4D为每例患者设计两套放疗计划:3D计划与4D计划.PTV-3D由CTV外扩常规的安全边界得到;PTV-4D由10个时相的CTV融合形成的ITV-4D外扩摆位边界(SM)得到.两套计划的处方剂量、射野方式均相同.比较两套计划中靶区体积、靶区与危及器官的剂量学、正常组织并发症概率的差异.结果:PTV-3D、PTV-4D的体积分别为(417.60±197.70)cm3、(331.90±183.10)cm3,后者体积减少20.50%(12.60%～34.40%);两者靶区覆盖率与剂量分布均匀性无显著性差异;4D计划中危及器官(肝、肾、胃、小肠)的受照剂量均较3D计划降低,以肝最为显著.肝V30、V40分别由38.77%、27.32%降至33.59%、22.62%;正常肝平均剂量由24.13 Gy下降为21.50 Gy;肝并发症概率由21.57%下降为15.86%;在不增加正常组织并发症的前提下,4D计划的处方剂量可由(50.57±1.51)Gy提升至(54.86±2.79)Gy,平均提高9.72%(4.00%～16.00%).结论:3D计划存在遗漏靶区或过度扩大靶区的缺陷.应用4D-CT技术可在3D CRT的基础上准确定位肝癌靶区,进一步减少正常组织的受照剂量,并提升靶区剂量.     

Comparison of intensity-modulated radiotherapy planning based on manual and automatically generated contours using deformable image registration in four-dimensional computed tomography of lung cancer patients

PURPOSE: To evaluate the implications of differences between contours drawn manually and contours generated automatically by deformable image registration for four-dimensional (4D) treatment planning. METHODS AND MATERIALS: In 12 lung cancer patients intensity-modulated radiotherapy (IMRT) planning was performed for both manual contours and automatically generated ("auto") contours in mid and peak expiration of 4D computed tomography scans, with the manual contours in peak inspiration serving as the reference for the displacement vector fields. Manual and auto plans were analyzed with respect to their coverage of the manual contours, which were assumed to represent the anatomically correct volumes. RESULTS: Auto contours were on average larger than manual contours by up to 9%. Objective scores, D(2%) and D(98%) of the planning target volume, homogeneity and conformity indices, and coverage of normal tissue structures (lungs, heart, esophagus, spinal cord) at defined dose levels were not significantly different between plans (p = 0.22-0.94). Differences were statistically insignificant for the generalized equivalent uniform dose of the planning target volume (p = 0.19-0.94) and normal tissue complication probabilities for lung and esophagus (p = 0.13-0.47). Dosimetric differences >2% or >1 Gy were more frequent in patients with auto/manual volume differences > or =10% (p = 0.04). CONCLUSIONS: The applied deformable image registration algorithm produces clinically plausible auto contours in the majority of structures. At this stage clinical supervision of the auto contouring process is required, and manual interventions may become necessary. Before routine use, further investigations are required, particularly to reduce imaging artifacts.     

Utility of four-dimensional computed tomography for analysis of intrafractional and interfractional variation in lung volumes

PURPOSE: To assess the viability of four-dimensional (4D) computed tomography (CT) in describing intrafractional and interfractional changes in lung volumes and to determine which breathing phase, if any, produces the most highly reproducible lung volumes among fractions. METHODS AND MATERIALS: Weekly 4D CT scans were acquired for 13 patients with non-small-cell lung cancer during a course of radiotherapy. Contours delineating the right lung, left lung, and total lung were obtained by adapting library models of the anatomic structures to the CT images and propagating them to all 10 respiratory phases represented in the 4D CT image data set. Lung volumes were calculated using software tools in a commercial radiation treatment-planning system and analyzed for interfractional volume reproducibility using t tests and for phase reproducibility using a phase-dependent uncertainty curve across all patients. Probability (p) values of <0.05 were considered to indicate significant differences in all comparisons. RESULTS: The average mean coefficient of variation of tidal volume across all patients was 25.0%. The average standard deviation of tidal volumes was 5.7% relative to the lung volume at end-expiration. Total volumes measured at the 30% phase were 15% more consistent than those measured at end-inspiration (p = 0.03). CONCLUSIONS: Four-dimensional CT assesses lung volume with acceptable precision; but the technique was unable to accurately predict interfractional changes in lung volume because wide variations in intra- and interfractional breathing cause high uncertainties in 4D CT data acquisition. The most reproducible breathing phase seems to be at the 30-40% phase (just before end-expiration).     

Performance evaluation of automatic anatomy segmentation algorithm on repeat or four-dimensional computed tomography images using deformable image registration method

PURPOSE: Auto-propagation of anatomic regions of interest from the planning computed tomography (CT) scan to the daily CT is an essential step in image-guided adaptive radiotherapy. The goal of this study was to quantitatively evaluate the performance of the algorithm in typical clinical applications. METHODS AND MATERIALS: We had previously adopted an image intensity-based deformable registration algorithm to find the correspondence between two images. In the present study, the regions of interest delineated on the planning CT image were mapped onto daily CT or four-dimensional CT images using the same transformation. Postprocessing methods, such as boundary smoothing and modification, were used to enhance the robustness of the algorithm. Auto-propagated contours for 8 head-and-neck cancer patients with a total of 100 repeat CT scans, 1 prostate patient with 24 repeat CT scans, and 9 lung cancer patients with a total of 90 four-dimensional CT images were evaluated against physician-drawn contours and physician-modified deformed contours using the volume overlap index and mean absolute surface-to-surface distance. RESULTS: The deformed contours were reasonably well matched with the daily anatomy on the repeat CT images. The volume overlap index and mean absolute surface-to-surface distance was 83% and 1.3 mm, respectively, compared with the independently drawn contours. Better agreement (>97% and <0.4 mm) was achieved if the physician was only asked to correct the deformed contours. The algorithm was also robust in the presence of random noise in the image. CONCLUSION: The deformable algorithm might be an effective method to propagate the planning regions of interest to subsequent CT images of changed anatomy, although a final review by physicians is highly recommended.     

非小细胞肺癌三维适形放疗剂量体积直方图参数与放射性肺损伤CT分级的关系

目的 探讨剂量体积直方图(DVH)参数与非小细胞肺癌(NSCLC)三维适形放疗(3D-CRT)后放射性肺损伤CT分级的关系.方法 将3D-CRT治疗后CT随访6个月以上的169例Ⅰ～Ⅲ期NSCLC患者,按随访CT放射性肺损伤的表现分级(0～4级),并分为CT阳性组(2～4级)和CT阴性组(0～1级).从放疗计划中获取患者的DVH参数,分析DVH参数与放射性肺损伤CT分级的关系,评价DVH参数对放射性肺损伤的预测价值.结果 不同CT分级的全肺及患侧肺正常组织并发症概率(NTCP)值差异有统计学意义,随着CT分级的增加,NTCP相应增大.不同CT分级的全肺及患侧肺平均肺受照剂量(MLD)差异有统计学意义,随着CT分级的增加,全肺及患侧肺MLD相应增大.不同CT分级的全肺及患侧肺V20、V30和V40差异均有统计学意义,随着CT分级的增加,全肺及患侧肺V20、V30、V40相应增大.不同CT分级患者健侧肺的DVH参数差异无统计学意义.全肺、患侧肺DVH参数与患侧肺CT分级联系紧密,其中患侧肺NTCP与CT分级关联度最强(η=0.522).结论 NTCP、MID、V20、V30、V40等DVH参数与NSCLC 3D-CRT后放射性肺损伤的CT分级密切相关,可以作为评价及优化放疗计划的指标,以减少放疗后放射性肺损伤的发生.     

Deformable image registration for the use of magnetic resonance spectroscopy in prostate treatment planning

PURPOSE: There is now convincing evidence that prostate cancer cells lack the ability to produce and accumulate citrate. Using magnetic resonance spectroscopy imaging (MRSI), regions of absent or low citrate concentration in the prostate can be visualized at a resolution of a few mm. This new advancement provides not only a tool for early diagnosis and screening but also the opportunity for preferential targeting of radiation to regions of high tumor burden in the prostate. The differences in the shape and location of the prostate between MRSI imaging and treatment have been the major obstacle in integrating MRSI in radiation therapy treatment planning. The purpose of this study is to develop a reliable method for deforming the prostate and surrounding regions from the geometry of MRSI imaging to the geometry of treatment planning, so that the regions of high tumor burden identified by the MRSI study can be faithfully transferred to the images used for treatment planning. METHODS AND MATERIALS: Magnetic resonance spectroscopy imaging studies have been performed on 2 prostate cancer patients using a commercial MRSI system with an endorectal coil and coupling balloon. At the end of each study, we also acquired the MRI of the pelvic region at both the deformed state where the prostate is distorted by the endorectal balloon and the resting state with the endorectal balloon deflated and removed. The task is to find a three-dimensional matrix of transformation vectors for all volume elements that links the two image sets. We have implemented an optimization method to iteratively optimize the transformation vectors using a Newton-Ralphson algorithm. The objective function is based on the mutual information. The distorted images using the transformation vectors are compared with the images acquired at the resting conditions. RESULTS AND DISCUSSION: The algorithm is capable of performing the registration automatically without the need for intervention. It does not require manual contouring of the organs. By applying the algorithm to multiple image sets of different patients, we found a good agreement between the images transformed from those acquired at the deformed state and those acquired at resting conditions. The computation time required for achieving the registration is in the range of a half-hour (for image size: 256 pixels x 256 pixels x 25 slices). However, the space of registration can be restricted to speed up the process. CONCLUSION: In this article, we described a three-dimensional deformable image registration method to automatically transform images from the deformed imaging state to resting state. Our examples show that this method is feasible and useful to the treatment planning system.     

Reduce in variation and improve efficiency of target volume delineation by a computer-assisted system using a deformable image registration approach

PURPOSE: To determine whether a computer-assisted target volume delineation (CAT) system using a deformable image registration approach can reduce the variation of target delineation among physicians with different head and neck (HN) IMRT experiences and reduce the time spent on the contouring process. MATERIALS AND METHODS: We developed a deformable image registration method for mapping contours from a template case to a patient case with a similar tumor manifestation but different body configuration. Eight radiation oncologists with varying levels of clinical experience in HN IMRT performed target delineation on two HN cases, one with base-of-tongue (BOT) cancer and another with nasopharyngeal cancer (NPC), by first contouring from scratch and then by modifying the contours deformed by the CAT system. The gross target volumes were provided. Regions of interest for comparison included the clinical target volumes (CTVs) and normal organs. The volumetric and geometric variation of these regions of interest and the time spent on contouring were analyzed. RESULTS: We found that the variation in delineating CTVs from scratch among the physicians was significant, and that using the CAT system reduced volumetric variation and improved geometric consistency in both BOT and NPC cases. The average timesaving when using the CAT system was 26% to 29% for more experienced physicians and 38% to 47% for the less experienced ones. CONCLUSIONS: A computer-assisted target volume delineation approach, using a deformable image-registration method with template contours, was able to reduce the variation among physicians with different experiences in HN IMRT while saving contouring time.