Magnetic resonance‐guided radiation therapy: A review

Magnetic resonance‐guided radiation therapy (MRgRT) is a promising approach to improving clinical outcomes for patients treated with radiation therapy. The roles of image guidance, adaptive planning and magnetic resonance imaging in radiation therapy have been increasing over the last two decades. Technical advances have led to the feasible combination of magnetic resonance imaging and radiation therapy technologies, leading to improved soft‐tissue visualisation, assessment of inter‐ and intrafraction motion, motion management, online adaptive radiation therapy and the incorporation of functional information into treatment. MRgRT can potentially transform radiation oncology by improving tumour control and quality of life after radiation therapy and increasing convenience of treatment by shortening treatment courses for patients. Multiple groups have developed clinical implementations of MRgRT predominantly in the abdomen and pelvis, with patients having been treated since 2014. While studies of MRgRT have primarily been dosimetric so far, an increasing number of trials are underway examining the potential clinical benefits of MRgRT, with coordinated efforts to rigorously evaluate the benefits of the promising technology. This review discusses the current implementations, studies, potential benefits and challenges of MRgRT.     

Radiation dose from cone beam computed tomography for image-guided radiation therapy

PURPOSE: To perform a comprehensive study on organ absorbed doses and effective doses from cone beam computed tomography (CBCT) for three different treatment sites. METHODS AND MATERIALS: An extensive set of dosimetric measurements were performed using a widely used CBCT system, the On-Board Imager (OBI). Measurements were performed using a female anthropomorphic phantom with thermoluminescent dosimeters (TLD). The effective doses to the body and the absorbed doses to 26 organs were reported using two different technical settings, namely, the standard mode and the low-dose mode. The measurements were repeated for three different scan sites: head and neck, chest, and pelvis. Comparisons of patient doses as well as image quality were performed among the standard mode CBCT, low-dose mode CBCT, and fan beam CT. RESULTS: The mean skin doses from standard mode CBCT to head and neck, chest and pelvis were 6.7, 6.4, and 5.4 cGy per scan, respectively. The effective doses to the body from standard mode CBCT for imaging of head and neck, chest, and pelvis were 10.3, 23.7, and 22.7 mSv per scan, respectively. Patient doses from low-dose mode CBCT were approximately one fifth of those from standard mode CBCT. CONCLUSIONS: Patient position verification by standard mode CBCT acquired by OBI on a daily basis could increase the secondary cancer risk by up to 2% to 4%. Therefore lower mAs settings for daily CBCT should be considered, especially when bony anatomy is the main interest.     

Post-prostatectomy image-guided radiation therapy: evaluation of toxicity and inter-fraction variation using online cone-beam CT

Purpose: The purpose of this study is to assess the acute and late genitourinary (GU) and gastrointestinal (GI) toxicities of cone‐beam computed tomography (CBCT) guided conformal adjuvant and salvage post‐prostatectomy radiotherapy (RT) compared with RT with port films. Materials and methods: Sixty‐eight patients (group 1) were treated with RT following radical prostatectomy (RP) using CBCT‐guided conformal RT to a median dose of 68.4 Gy. CBCT images were acquired three to five times weekly and were automatically co‐registered to a reference CT. A comparative group (group 2) included 150 patients who received post‐RP RT with weekly port films to a median dose of 64.8 Gy. GU and GI toxicities were graded in both the acute and late settings using Radiation Therapy Oncology Group criteria. Associations between toxicity and study variables were evaluated by odds ratios (ORs) estimated by logistic regression. Results: Grades 2 and 3 acute GU toxicity were experienced by 13% (n = 9) and 2% (n = 1) of patients in group 1, respectively, while 13% (n = 19) had grade 2 acute GU toxicity in the control group (group 2). Grade 2 acute GI toxicity was experienced by 13% (n = 9) and 15% (n = 23) in groups 1 and 2, respectively. Acute GU (P = 0.67) and GI (P = 0.84) toxicities were not significantly different between the two groups. There were no associations detected between CBCT and acute GI toxicity (OR 0.76, P = 0.57) or acute GU (OR 1.16, P = 0.75). Increased odds of acute GU toxicity were observed for doses > 68.4 Gy (OR 12.81, P = 0.04), which were only delivered in the CBCT group. CBCT mean variations (standard deviation) for 1053 fractions were 2.8 mm (2.8), 2.0 mm (2.4) and 3.1 mm (2.9) in the left‐to‐right, anterior‐to‐posterior (AP) and superior‐to‐inferior (SI) axes, respectively. Corrective shifts for variance ≥ 5 mm were required for 15%, 6% and 19% of fractions in the left‐to‐right, anterior‐to‐posterior and superior‐to‐inferior axes, respectively. Conclusions: Rates of acute toxicity with CBCT‐guided post‐RP RT to 68.4 Gy were similar to treatment to 64.8 Gy without image‐guidance RT. Acceptable early toxicity profiles suggest that CBCT is a reasonable strategy for image guidance, but the value of CBCT must be weighed against potential increased risk of secondary cancers due to increased radiation exposure.     

Implementation of daily image‐guided radiation therapy using an in‐room CT scanner for prostate cancer isocentre localization

The Tattersall’s Cancer Centre has been performing image‐guided radiation therapy (IGRT) using an in‐room CT on rails since 2003 to verify accurate patient setup position (relative to bony anatomy) immediately prior to treatment delivery for prostate cancer patients. While the concept of online correction for bony anatomy is well established, the use of an in‐room CT scanner also enables the collection and offline analysis of soft tissue volumetric data. Although initially IGRT was implemented under a research protocol, in‐room CT verification has continued to be used to measure and correct for patient setup variations for all patients undergoing intensity modulated radiation therapy (IMRT) treatments. The present paper outlines the protocol that was used to implement IGRT using an in‐room CT scanner at the Tattersall’s Cancer Centre. Online corrections that minimize patient setup uncertainties allow confidence in delivering dose escalation as well as decreasing the margins required around the target volume. With improvements in auto‐contouring tools, IGRT will also have the ability to measure and correct for variations in target and critical structure positioning online, rather than the current offline methods utilized.     

A survey of image‐guided radiation therapy use in the United States

BACKGROUND:

Image‐guided radiation therapy (IGRT) is a novel array of in‐room imaging modalities that are used for tumor localization and patient setup in radiation oncology. The prevalence of IGRT use among US radiation oncologists is unknown.

METHODS:

A random sample of 1600 radiation oncologists was surveyed by Internet, e‐mail and fax regarding the frequency of IGRT use, clinical applications, and future plans for use. The definition of IGRT included imaging technologies that are used for setup verification or tumor localization during treatment.

RESULTS:

Of 1089 evaluable respondents, 393 responses (36.1%) were received. The proportion of radiation oncologists using IGRT was 93.5%. When the use of megavoltage (MV) portal imaging was excluded from the definition of IGRT, the proportion using IGRT was 82.3%. The majority used IGRT rarely (in <25% of their patients; 28.9%) or infrequently (in 25%‐50% of their patients; 33.1%). The percentages using ultrasound, video, MV‐planar, kilovoltage (kV)‐planar, and volumetric technologies were 22.3%, 3.2%, 62.7%, 57.7%, and 58.8%, respectively. Among IGRT users, the most common disease sites treated were genitourinary (91.1%), head and neck (74.2%), central nervous system (71.9%), and lung (66.9%). Overall, 59.1% of IGRT users planned to increase use, and 71.4% of nonusers planned to adopt IGRT in the future.

CONCLUSIONS:

IGRT is widely used among radiation oncologists. On the basis of prospective plans of responders, its use is expected to increase. Further research will be required to determine the safety, cost efficacy, and optimal applications of these technologies. Cancer 2010. © 2010 American Cancer Society.     

Positron-emission tomography-guided radiation therapy: Ongoing projects and future hopes

Radiation therapy has undergone significant advances these last decades, particularly thanks to technical improvements, computer science and a better ability to define the target volumes via morphological and functional imaging breakthroughs. Imaging contributes to all three stages of patient care in radiation oncology: before, during and after treatment. Before the treatment, the choice of optimal imaging type and, if necessary, the adequate functional tracer will allow a better definition of the volume target. During radiation therapy, image-guidance aims at locating the tumour target and tailoring the volume target to anatomical and tumoral variations. Imaging systems are now integrated with conventional accelerators, and newer accelerators have techniques allowing tumour tracking during the irradiation. More recently, MRI-guided systems have been developed, and are already active in a few French centres. Finally, after radiotherapy, imaging plays a major role in most patients’ monitoring, and must take into account post-radiation tissue modification specificities. In this review, we will focus on the ongoing projects of nuclear imaging in oncology, and how they can help the radiation oncologist to better treat patients. To this end, a literature review including the terms “Radiotherapy”, “Radiation Oncology” and “PET-CT” was performed in August 2019 on Medline and ClinicalTrials.gov. We chose to review successively these novelties organ-by-organ, focusing on the most promising advances. As a conclusion, the help of modern functional imaging thanks to a better definition and new specific radiopharmaceuticals tracers could allow even more precise treatments and enhanced surveillance. Finally, it could provide determinant information to artificial intelligence algorithms in “-omics” models.     

MVCT图像引导调强放疗在线检验靶区位置及修正剂量分布的临床应用

目的利用在线高能X线计算机体层摄影术(MVCT)重建两组共45例调强放疗患者的三维图像,研究头颈部与前列腺肿瘤患者的治疗摆位在未经修正情况下的体位和靶区位置偏差,及其对照射剂量分布的影响,探索MVCT图像引导放疗的临床应用方法与意义。方法对实施切层调强放疗患者的计划分布分别以电离室和剂量胶片方法进行体模验证测量,在验证合格前提下用在线MVCT图像与模拟定位的CT图像进行三维融合比较,测量两组患者体位和靶区中心点的偏差,分析两组摆位的系统误差与随机误差。以测量的体位和靶区位移偏差值模拟体位偏差条件,比较模拟条件下测量得到的体模剂量分布与计划剂量分布和正常摆位时的剂量分布差别。结果头颈部和前列腺肿瘤治疗摆位未经修正时靶区的三维位移偏差值分别为(-3.0±2.8)、(-5.4±2.3)、(2.1±2.4)mm和(3.2±2.5)(、-6.4±5.3)、(8.7±3.6)mm。上述位移偏差条件下体模测量的头颈和前列腺照射剂量分布与计划剂量分布的误差分别为8.2%和6.9%。结论在线HVCT能精确快速测量患者体位和靶区位置空间误差,为修正摆位提供准确依据。未经修正时靶区位移误差导致的剂量分布误差可能超出临床允许范围,调强放疗应以在线图像引导验证基础上进行才能保证剂量分布精度。     

胸段食管癌IGRT中摆位误差分析

目的 使用CBCT测量食管癌IGRT中的摆位误差,为ART开展提供基础数据。方法 使用千伏级CBCT采集23例胸段食管癌治疗前、后摆位图像,探讨配准方法、病变部位以及不同治疗时间IGRT前摆位误差变化。单因素方差分析不同治疗时间的差异。结果 骨性及灰度匹配在x、z轴测量摆位误差有显著差异。不使用CBCT下PTV在x、y、z轴向胸上段癌分别外扩6、17、6 mm,胸中段癌分别外扩4、17、6 mm,胸下段癌分别外扩11、11、4 mm。每次使用CBCT行疗前摆位误差纠正则x、y、z轴向分别外扩2、2、4 mm。不同治疗时间IGRT前摆位误差在y轴上相近(P=0.858),在x、z轴上自第5周开始IGRT前摆位误差均高于其他几周(P=0.001, P=0.000)。结论 胸段食管癌IGRT中建议采用灰度配准。不同部位食管癌PTV在x、y、z轴向外扩范围应有所不同。IGRT可使PTV外放边界显著缩小。疗前期摆位误差可考虑用于指导后续治疗,治疗后期患者x、z轴向疗前摆位误差变大,建议自第5周时更换体膜进行模拟定位,重新制定治疗计划。     

胸段食管癌IGRT分次内误差对靶区剂量的影响

目的 使用CBCT测量食管癌IGRT分次内误差,评价其对靶区和周围OAR剂量的影响。方法 应用CBCT采集 23例胸段食管癌放疗前后摆位图像,获取分次内误差。将分次内误差模拟治疗计划2和计划3,与原始计划1比较,分析其对靶区和OAR剂量学影响,并用单因素方差分析和配对t检验。结果 胸上段、胸中段、胸下段食管癌IGRT分次内平均误差在左右方向分别为(1.2±1.5)、(1.0±1.0)、(1.0±1.0) mm (P=0.138),在上下方向分别为(1.2±1.0)、(1.1±1.0)、(1.2±1.0) mm (P=0.656),在前后方向分别为(1.3±1.1)、(1.2±1.0)、(0.8±0.7) mm (P=0.003)。全部患者3 mm内误差发生频率在左右、上下、前后方向分别占95.2%、94.5%、93.9%。计划3与计划1相比,GTV V_100%下降5.55%,有 3例患者PTV D_95%下降超过原始计划处方的5%。计划3中全肺 V₃₀为(15.24±2.24)%,低于计划1的(15.67±2.28)%(P=0.033)。计划2中 4例脊髓>4500 cGy (D_max为4517.2 cGy),计划3中 19例脊髓>4500 cGy (D_max为5045.2 cGy)。结论 IGRT分次内误差对患者靶区剂量分布有一定影响。脊髓为串行器官,对分次内误差相对敏感,可能会导致部分患者脊髓超过最大耐受量。     

四种不同配准方式对食管癌IGRT摆位误差的影响

目的:研究四种不同配准方法对食管癌图像引导放射治疗（IGRT）摆位误差的影响。方法:应用瑞典医科达Synergy直线加速器治疗食管癌患者100例,每位患者治疗前用锥形束CT（CBCT）扫描。将获得的CBCT图像与计划CT图像配准,分析左右（X）、头脚(Y)、上下(Z)方向上的平移误差,比较自动灰度配准、自动灰度+手动配准、自动骨性配准、自动骨性+手动配准四种配准间的差异。结果:100例食管癌患者共进行400次配准。自动灰度配准、自动灰度+手动配准、自动骨性配准、自动骨性+手动配准在左右(X)方向的平移误差分别为（2.70±2.20）mm、（3.04±2.36）mm、（2.76±2.24）mm、（3.04±2.45）mm,在头脚（Y）方向的平移误差分别为（2.82±2.15）mm、(2.95±2.31) mm、（2.74±1.78）mm、（2.66±1.82）mm,在上下（Z）方向的平移误差分别为（2.42±1.91）mm、（2.49±2.02）mm、（3.07±2.16）mm、（2.67±2.02）mm。其中自动灰度与自动灰度+手动配准在X、Z方向差异有统计学意义(P<0.05),自动骨性与自动骨性+手动配准在X方向差异有统计学意义（P<0.05),自动灰度与自动骨性、自动灰度+手动配准与自动骨性+手动配准在X、Y、Z方向上均差异无统计学意义(P>0.05)。结论:对于食管癌肿瘤的图像配准,加上手动配准是有必要的,骨性配准+手动配准精度和稳定性效果更好。     

医学图像融合技术在肿瘤放射治疗中的应用

医学图像融合技术一个非常重要的应用领域就是肿瘤的放射治疗,特别是对于精确放射治疗.本文简介医学图像融合技术的分类及主要方法和实施步骤,并综述各种图像融合技术在不同肿瘤放疗中的应用,对其在生物适形放射治疗中的应用前景作一展望.     

医学图像融合技术在肿瘤放射治疗中的应用

医学图像融合技术一个非常重要的应用领域就是肿瘤的放射治疗,特别是对于精确放射治疗。本文简介医学图像融合技术的分类及主要方法和实施步骤,并综述各种图像融合技术在不同肿瘤放疗中的应用,对其在生物适形放射治疗中的应用前景作一展望。     

Prostate bed localization with image-guided approach using on-board imaging: Reporting acute toxicity and implications for radiation therapy planning following prostatectomy

OBJECTIVES: To report our experience using Image-Guided Radiation Therapy (IGRT) in patients undergoing post-prostatectomy irradiation. METHODS: Twenty-six patients were treated with radiotherapy following radical prostatectomy using Intensity Modulated Radiation Therapy (IMRT). Prostate bed localization was done using image guidance to align surgical clips relative to the reference isocenter on the planning digitally reconstructed radiographs. Assuming surgical clips to be surrogate for prostate bed, daily shifts in their position were calculated after aligning with the bony anatomy. Shifts were recorded in three dimensions. The acute toxicity was measured during and after completion of treatment. RESULTS: The average (standard deviation) prostate bed motion in anterior-posterior, superior-inferior and left-right directions were: 2.7mm (2.1), 2.4mm (2.1) and 1.0mm (1.7), respectively. The majority of patients experienced only grade 1 symptoms, two patients had grade 2 symptoms and none had grade 3 or higher acute toxicity. CONCLUSIONS: Daily IGRT is recommended for accurate target localization during radiation delivery to improve efficacy of treatment and enhance therapeutic ratio. Larger studies with longer follow-up are necessary to make definitive recommendations regarding magnitude of margin reduction around clinical target volume.