放射性粒子治疗实体恶性肿瘤的进展

肿瘤放射治疗分外放疗和内放疗（也叫近距离治疗）。放射性粒子治疗是近距离治疗的一个重要分支。靶区勾画及处方剂量同样是粒子治疗的核心问题。国内外专家学者对不同瘤种的粒子治疗处方剂量已有相应推荐,但靶区勾画及相关定义少有报道。临床中,靶区勾画范围不精确是粒子治疗后肿瘤周边复发的主要原因。本文对几种粒子治疗常见实体恶性肿瘤亚临床病灶及外照射靶区进行描述,期望对目前粒子治疗的靶区勾画提供参考。     

MR/CT和18FDG PET/CT对鼻咽癌肿瘤区勾画比较研究

目的比较MRI/CT或PET/CT对鼻咽癌调强放射治疗患者肿瘤区(GTV)勾画的差异。方法2007年2~11月间,26例实施根治性调强放射治疗的鼻咽癌患者在放射治疗开始前1w内行PET/CT,MRI以及增强定位CT扫描,一组医师根据PET/CT勾画GTV,而另一组医师则根据MRI/CT勾画GTV,两组医师再共同评价肿瘤区间勾画部位差异。为便于研究,对于原发灶部位,GTV1C定义为MRI/CT基础上的GTV,GTV1P为PET/CT基础上的GTV,对于颈部区域淋巴结则分别定义为GTV2C及GTV2P,在此基础上,GTV1C和GTV1P的合并肿瘤区被定义为GTV1T,重叠肿瘤区则被定义为GTV1M,GTV2C和GTV2P的合并肿瘤区定义为GTV2T,重叠肿瘤区定义为GTV2M。结果GTV1P和GTV2P均明显小于GTV1C及GTV2C,GTV1T相较GTV1C无明显增大,但GTV2T则明显大于GTV2C,原发灶部位肿瘤区间勾画差异主要位于颅底,颈部淋巴结差异主要源于小淋巴结及淋巴结包膜外侵犯累及肌肉。结论PET/CT有助于鼻咽癌肿瘤区勾画,PET/CT基础上的肿瘤区明显小于MRI/CT基础上的肿瘤区,但PET/CT基础上的肿瘤区并不总是包含于MRI/CT基础上的肿瘤区,两者间的差异在颈部更为明显。     

An evaluation of the variability of tumor-shape definition derived by experienced observers from CT images of supraglottic carcinomas (ACRIN protocol 6658)

PURPOSE: Accurate target definition is considered essential for sophisticated, image-guided radiation therapy; however, relatively little information has been reported that measures our ability to identify the precise shape of targets accurately. We decided to assess the manner in which eight "experts" interpreted the size and shape of tumors based on "real-life" contrast-enhanced computed tomographic (CT) scans. METHODS AND MATERIALS: Four neuroradiologists and four radiation oncologists (the authors) with considerable experience and presumed expertise in treating head-and-neck tumors independently contoured, slice-by-slice, his/her interpretation of the precise gross tumor volume (GTV) on each of 20 sets of CT scans taken from 20 patients who previously were enrolled in Radiation Therapy Oncology Group protocol 91-11. RESULTS: The average proportion of overlap (i.e., the degree of agreement) was 0.532 (95% confidence interval 0.457 to 0.606). There was a slight tendency for the proportion of overlap to increase with increasing average GTV. CONCLUSIONS: Our work suggests that estimation of tumor shape currently is imprecise, even for experienced physicians. In consequence, there appears to be a practical limit to the current trend of smaller fields and tighter margins.     

International guideline for the delineation of the clinical target volumes (CTV) for nasopharyngeal carcinoma

Purpose

Target delineation in nasopharyngeal carcinoma (NPC) often proves challenging because of the notoriously narrow therapeutic margin. High doses are needed to achieve optimal levels of tumour control, and dosimetric inadequacy remains one of the most important independent factors affecting treatment outcome.

Validation of a Magnetic Resonance Imaging-based Auto-contouring Software Tool for Gross Tumour Delineation in Head and Neck Cancer Radiotherapy Planning

Aims

To carry out statistical validation of a newly developed magnetic resonance imaging (MRI) auto-contouring software tool for gross tumour volume (GTV) delineation in head and neck tumours to assist in radiotherapy planning.

Gradient-based delineation of the primary GTV on FDG-PET in non-small cell lung cancer: A comparison with threshold-based approaches, CT and surgical specimens

Purpose

The aim of this study was to validate a gradient-based segmentation method for GTV delineation on FDG-PET in NSCLC through surgical specimen, in comparison with threshold-based approaches and CT.

Materials and methods

Ten patients with stage I-II NSCLC were prospectively enrolled. Before lobectomy, all patients underwent contrast enhanced CT and gated FDG-PET. Next, the surgical specimen was removed, inflated with gelatin, frozen and sliced. The digitized slices were used to reconstruct the 3D macroscopic specimen. GTVs were manually delineated on the macroscopic specimen and on CT images. GTVs were automatically segmented on PET images using a gradient-based method, a source to background ratio method and fixed threshold values at 40% and 50% of SUV_max. All images were finally registered. Analyses of raw volumes and logarithmic differences between GTVs and GTV_macro were performed on all patients and on a subgroup excluding the poorly defined tumors. A matching analysis between the different GTVs was also conducted using Dice’s similarity index.

Results

Considering all patients, both lung and mediastinal windowed CT overestimated the macroscopy, while FDG-PET provided closer values. Among various PET segmentation methods, the gradient-based technique best estimated the true tumor volume. When analysis was restricted to well defined tumors without lung fibrosis or atelectasis, the mediastinal windowed CT accurately assessed the macroscopic specimen. Finally, the matching analysis did not reveal significant difference between the different imaging modalities.

Conclusions

FDG-PET improved the GTV definition in NSCLC including when the primary tumor was surrounded by modifications of the lung parenchyma. In this context, the gradient-based method outperformed the threshold-based ones in terms of accuracy and robustness. In other cases, the conventional mediastinal windowed CT remained appropriate.     

The utility of multimodality imaging with CT and MRI in defining rectal tumour volumes for radiotherapy treatment planning: a pilot study

Aims: This study compares the volumetric and spatial relationships of gross tumour volume (GTV) derived from CT (CT-GTV) and GTV derived from MRI (MR-GTV) to determine the utility of multi-modality imaging for radiotherapy treatment planning in rectal cancer. Methods and Materials: Fifteen patients with T3 rectal cancer were accrued over 18 months. The male : female ratio was 2:1. The average age was 60.3 years (range 38–79). All patients underwent a diagnostic MRI and CT and MRI simulation. Data sets were co-registered. A site specialised diagnostic radiologist contoured all volumes in consultation with a radiation oncologist. CT-GTV was contoured while blinded to MR data sets. MR-GTV was contoured independently 2–4 weeks later whilst blinded to its respective CT-GTV data. Tumour volumes were analysed for three anatomical subregions (sigmoid, rectal and anal). Reference points on tumour volumes were used for spatial comparison and analysis. Results: The mean CT-GTV/MR-GTV ratio was 1.2 (range 0.5–2.9). The tumour volume ratios for the rectal subregion were well correlated. CT-GTV provided adequate spatial coverage of tumour in reference to MR-GTV with the average mean discrepancy of 0.12 (range −0.08–0.38) or a maximum discrepancy of <0.4 cm (1.54 standard deviation). CT-GTV coverage was inadequate for tumours with MRI evidence of anal and sigmoid invasion. Conclusions: Conventional simulation CT imaging provided a reasonable estimate of the GTV. Multi-modality imaging with staging MRI can assist target volume definition where there is involvement of the sigmoid and anorectal region and avoid geographic misses. The role of a simulation MRI may aid in this process but remains investigational.     

Deviations in delineated GTV caused by artefacts in 4DCT

Background and purpose

Four-dimensional computed tomography (4DCT) is used for breathing-adapted radiotherapy planning. Irregular breathing, large tumour motion or interpolation of images can cause artefacts in the 4DCT. This study evaluates the impact of artefacts on gross tumour volume (GTV) size.

Material and methods

In 19 4DCT scans of patients with peripheral lung tumours, GTV was delineated in all bins. Variations in GTV size between bins in each 4DCT scan were analysed and correlated to tumour motion and variations in breathing signal amplitude and breathing signal period. End-expiration GTV size (GTVexp) was considered as reference for GTV size. Intra-session delineation error was estimated by re-delineation of GTV in eight of the 4DCT scans.

Results

In 16 of the 4DCT scans the maximum deviations from GTVexp were larger than could be explained by delineation error. The deviations were largest in the bins adjacent to the end-inspiration bin. The coefficient of variation of GTV size was significantly correlated to tumour motion in the cranio-caudal direction, but no significant correlation was found to breathing signal variations.

Conclusion

We found considerable variations in GTV size throughout the 4DCT scans. Awareness of the error introduced by artefacts is important especially if radiotherapy planning is based on a single 4DCT bin.     

Does enhanced CT influence the biological GTV measurement on FDG-PET images?

Objectives

To test the influence of media injection in PET/CT on the functional or gross tumour volume measurement.

Patients and methods

Thirty-three patients (56 ± 19 years) with non-Hodgkin’s lymphoma (n = 22) or Hodgkin’s disease (n = 11) were prospectively studied at staging. PET/CTs were performed 60 min after injection of FDG. Iopamiron 300 (Iopamidol, 1.5 cc/kg) was injected immediately after, followed 50 s later by a second craniocaudal CT (CT+). PET images were successively reconstructed using the unenhanced CT (PET−) and the CT+ (PET+) for attenuation correction using iterative reconstruction (4 iterations, 8 subsets, 5 mm post-filtering). The SUV_max, SUV_mean, SUV_peak and functional tumoural volume were measured in tumoural lymphadenopathies or malignant tissues (n = 56 VOIs) using 5 3D-thresholding methods on PET− and PET+ images: absolute SUV value of 2.5; 40% of SUV_max, and 3 adaptative thresholding methods (Vauclin, Black and Schaefer methods).

Results

The SUV_mean and the volume measurement were significantly different (p < 0.001) for the five segmentation methods for PET− (p < 0.001) and PET+ (p < 0.001). The SUV_max, SUV_mean and SUV_peak increased significantly in PET+ compared to PET− (2–5%). The SUV_peak was not significantly different for the five segmentation methods. The functional volume measurements were significantly different between PET− and PET+ only for the 2.5 segmentation method (+3%; p = 0.001), but not for the 40%, Vauclin, Black and Schaefer methods.

Conclusion

The functional volume could be measured in PET/CT when CT was performed with enhanced media. Caution should be taken when using the volume delineation method. Volume delineation methods using absolute threshold may artefactually increase the functional volume when enhanced CT is used for attenuation correction. The delineation volume using the relative or adaptative method should be preferred when contrast media are used for PET/CT.