Clinical target volume definition for glioblastoma radiotherapy planning: magnetic resonance imaging and computed tomography

Purpose

To assess the differences between the target delineation using computed tomography (CT) and imaging fusion CT/magnetic resonance imaging (MRI) for the radiotherapy planning of glioblastoma.

Methods

One hundred-twenty gross tumor volume and clinical target volume on CT and MRI (GTV_CT/CTV_CT, GTV_MRI/CTV_MRI, respectively) were contoured and evaluated. The treatments planning (total dose 60 Gy) based on CTV_CT were analysed in terms of percentage of CTV_CT and CTV_MRI receiving 95 % of the prescribed dose (V₉₅-CTV_CT, V₉₅-CTV_MRI).

Results

GTVs and CTVs contoured on MRI were significantly larger than those delineated on CT (p = 0.0003, p = 0.0006, respectively). Nighty-two percent of CTV_CT was coincident with the CTV_MRI and 8 % was normal tissue; 20 % of CTV_MRI, considered as tumor volume, was not included on CTV_CT. The V₉₅-CTV_MRI was significantly lower than the V₉₅-CTV_CT (p = 0.0005).

Conclusions

In the delineation of glioblastoma target volume, fusion CT/MRI was preferred. The CT only is insufficient for the CTV dose coverage.     

4D imaging for target definition in stereotactic radiotherapy for lung cancer

Stereotactic radiotherapy of Stage I lung tumors has been reported to result in high local control rates that are far superior to those obtained with conventional radiotherapy techniques, and which approach those achieved with primary surgery. Breathing-induced motion of tumor and target tissues is an important issue in this technique and careful attention should be paid to the contouring and the generation of individualized margins. We describe our experience with the use of 4DCT scanning for this group of patients, the use of post-processing tools and the potential benefits of respiratory gating.     

Histopathological correlation of C-choline PET scans for target volume definition in radical prostate radiotherapy

Background and purpose

To evaluate the accuracy of ¹¹C-choline PET scans in defining dominant intraprostatic lesions (DILs) for radiotherapy target volume definition.

Material and methods

Eight men with prostate cancer who had ¹¹C-choline PET scans prior to radical prostatectomy were studied. Several methods were used to contour the DIL on the PET scans: visual, PET Edge, Region Grow, absolute standardised uptake value (SUV) thresholds and percentage of maximum SUV thresholds. Prostatectomy specimens were sliced in the transverse plane and DILs were delineated on these by a pathologist. These were then compared with the PET scans. The accuracy of correlation was assessed by the Dice similarity coefficient (DSC) and the Youden index.

Results

The contouring method resulting in both the highest DSC and the highest Youden index was 60% of the maximum SUV (SUV_60%), with values of 0.64 and 0.51, respectively. However SUV_60% was not statistically significantly better than all of the other methods by either measure.

Conclusions

Although not statistically significant, SUV_60% resulted in the best correlation between ¹¹C-choline PET and pathology amongst all the methods studied. The degree of correlation shown here is consistent with previous studies that have justified using imaging for DIL radiotherapy target volume definition.     

Contrast enhanced 4D-CT imaging for target volume definition in pancreatic ductal adenocarcinoma

A procedure to improve target volume definition in pancreatic ductal adenocarcinoma by contrast enhanced 4D-CT imaging has been implemented for radiotherapy planning. The procedure allows good quality images to be obtained over the whole patient's breathing cycle in terms of anatomical details, pancreatic enhancement and vessel definition.     

Assessment of 18F PET signals for automatic target volume definition in radiotherapy treatment planning.

INTRODUCTION: Positron emission tomography (PET) alone or in combination with computer tomography (PET/CT) is increasingly used in target volume assessment. A standardized way of converting PET signals into target volumes is not available at present. MATERIALS AND METHODS: Assuming a uniform signal emission from a tumour and surrounding normal tissues, a model-based method was developed to determine a relative threshold level (Th(rel)) for gross tumour volume delineation. Two phantoms consisting of cylindrical and spherical sources of diameter ranging from 4.5 to 43 mm in a tank and (18)F activities ranging from 0.001 to 0.15 MBq/ml for tank and sources, respectively, were used for PET/CT imaging. A Th(rel) was calculated that best corresponded to the physical diameter of the cylindrical sources. Software (SW) was generated to automatically delineate volumes based on this threshold. The SW was validated for in vitro and in vivo PET signals. RESULTS: The Th(rel) best representing the source diameter was 41+/-2.5% (95% confidence level) of the background-subtracted signal. The mean deviation for sources of diameter > or =12.5 mm was < or =1.5 mm. The Th(rel) was constant for diameters > or =12.5 mm. For source diameters <12.5 mm, the 41% level over-estimated the real source diameter by a factor depending on the diameter. In an in vitro set-up the SW was capable of segmenting solitary PET volumes to within 1.4 mm (1SD). For non-homogeneous signals in a clinical set-up minimal manual intervention is presently required to separate target from non-target signals. The SW may slightly underestimate target volumes when compared with CT-based volumes, but works well as a first approximation. The volume can be manually adapted to give the ultimate target volume. CONCLUSIONS: SW-based automatic delineation of the volume of (18)F activity is feasible and highly reproducible. Volumes can be subsequently modified by the clinician if necessary. This approach will increase the efficiency of the planning process.     

Variation of clinical target volume definition among Japanese radiation oncologists in external beam radiotherapy for prostate cancer

Background: We investigated the interobserver variation in the prostatetarget volume and the trend toward the use of diagnostic computedtomography (CT) or magnetic resonance (MR) images for treatmentplanning. Methods: Twenty-five radiation oncologists were asked to draw the externalcontour of the prostate on CT images (0.3 cm spacing) of a patientwith localized prostate cancer. They also answered a questionnaireregarding the use of diagnostic CT or MR images for the contouring. Results: Of the 25 physicians, 28% rarely or never referred to the diagnosticCT images. In contrast, the physicians tended to refer to theMR images more frequently. Approximately 50% of the physiciansbelieved in the usefulness of contrast-enhanced images for thedelineation of the prostate. As for the variation of the prostatecontouring, the median craniocaudal prostate length was 36 mm(range, 21–54 mm), and the median prostate volume was43.5 cm³ (range, 23.8–98.3 cm³). The interobserver variabilitywas not significant in the duration as a radiation oncologist,the board certification status as radiation oncologists, andthe number of treatment plans developed for prostate cancerduring the last 1 year. Conclusion: A wide variety of the definitions of the prostate was foundamong Japanese radiation oncologists.     

An atlas of the pelvic lymph node regions to aid radiotherapy target volume definition

AimsThe implementation of advanced three-dimensional radiotherapy planning techniques requires accurate target volume localisation. We have previously developed guidelines to aid definition of the pelvic lymph node regions, and the aim of this study was to produce a CT atlas.Materials and methodsThe guidelines were applied to a CT scan of a patient to receive adjuvant radiotherapy.ResultsReference CT images of the pelvis were generated, illustrating the nodal regions and a typical target volume for adjuvant pelvic radiotherapy for gynaecological cancer.ConclusionThese images can be used as an aid for target volume definition of the pelvic nodal regions.     

An assessment of interfractional uterine and cervical motion: Implications for radiotherapy target volume definition in gynaecological cancer

PURPOSE: To assess interfractional movement of the uterus and cervix in patients with gynaecological cancer to aid selection of the internal margin for radiotherapy target volumes. METHODS AND MATERIALS: Thirty-three patients with gynaecological cancer had an MRI scan performed on two consecutive days. The two sets of T2-weighted axial images were co-registered, and the uterus and cervix outlined on each scan. Points were identified on the anterior uterine body (Point U), posterior cervix (Point C) and upper vagina (Point V). The displacement of each point in the antero-posterior (AP), supero-inferior (SI) and lateral directions between the two scans was measured. The changes in point position and uterine body angle were correlated with bladder volume and rectal diameter. RESULTS: The mean difference (+/-1SD) in Point U position was 7mm (+/-9.0) in the AP direction, 7.1mm (+/-6.8) SI and 0.8mm (+/-1.3) laterally. Mean Point C displacement was 4.1mm (+/-4.4) SI, 2.7mm (+/-2.8) AP, 0.3 (+/-0.8) laterally, and Point V was 2.6mm (+/-3.0) AP and 0.3mm (+/-1.0) laterally. There was correlation for uterine SI movement in relation to bladder filling, and for cervical and vaginal AP movement in relation to rectal filling. CONCLUSION: Large movements of the uterus can occur, particularly in the superior-inferior and anterior-posterior directions, but cervical displacement is less marked. Rectal filling may affect cervical position, while bladder filling has more impact on uterine body position, highlighting the need for specific instructions on bladder and rectal filling for treatment. We propose an asymmetrical margin with CTV-PTV expansion of the uterus, cervix and upper vagina of 15mm AP, 15mm SI and 7mm laterally and expansion of the nodal regions and parametria by 7mm in all directions.     

Computed tomography in definitive radiotherapy of prostatic carcinoma, part 2: definition of target volume

Pretreatment computed tomography (CT) scanning of the pelvis was performed in 100 consecutive patients with carcinoma of the prostate treated with external irradiation (82 patients) or interstitial I125 (18 patients). Treatment plan modifications prompted by CT scan findings were most frequent in patients with (clinical) involvement of the seminal vesicles in whom the conventional treatment planning often resulted in an underestimate of tumor volume. Seventeen of 32 (53%) such patients required an enlargement of treatment fields to adequately encompass the target volume. Using skeletal landmarks as reference, the dimensions of the prostate, seminal vesicles and the detectable tumor and their topographic relationships were systematically tabulated. These measurements provide a basis for the definition of the target volume in patients with carcinoma of the prostate in whom CT scans might not be available.     

Clinical target volume definition in the elderly patient

Elderly age is one of the main risk factors to be associated with the onset of different tumors. The tumor in the elderly almost always appears at a late, advanced stage for the lack of an accurate attention to symptoms-signs, as well as for the absence of involvement in mass screening campaigns. In the choice of a radiotherapy treatment in the elderly, the healthy tissues adjacent to the tumor may show a different ability for repair; this should be kept in mind in the definition of the target volume together with the possible presence of comorbidities specific to the elderly age.     

Portal imaging based definition of the planning target volume during pelvic irradiation for gynecological malignancies.

PURPOSE: Geometrical accuracy in patient positioning can vary substantially during external radiotherapy. This study estimated the set-up accuracy during pelvic irradiation for gynecological malignancies for determination of safety margins (planning target volume, PTV). METHODS AND MATERIALS: Based on electronic portal imaging devices (EPID), 25 patients undergoing 4-field pelvic irradiation for gynecological malignancies were analyzed with regard to set-up accuracy during the treatment course. Regularly performed EPID images were used in order to systematically assess the systematic and random component of set-up displacements. Anatomical matching of verification and simulation images was followed by measuring corresponding distances between the central axis and anatomical features. Data analysis of set-up errors referred to the x-, y-,and z-axes. Additionally, cumulative frequencies were evaluated. RESULTS: A total of 50 simulation films and 313 verification images were analyzed. For the anterior-posterior (AP) beam direction mean deviations along the x- and z-axes were 1.5 mm and -1.9 mm, respectively. Moreover, random errors of 4.8 mm (x-axis) and 3.0 mm (z-axis) were determined. Concerning the latero-lateral treatment fields, the systematic errors along the two axes were calculated to 2.9 mm (y-axis) and -2.0 mm (z-axis) and random errors of 3.8 mm and 3.5 mm were found, respectively. The cumulative frequency of misalignments < or =5 mm showed values of 75% (AP fields) and 72% (latero-lateral fields). With regard to cumulative frequencies < or =10 mm quantification revealed values of 97% for both beam directions. CONCLUSION: During external pelvic irradiation therapy for gynecological malignancies, EPID images on a regular basis revealed acceptable set-up inaccuracies. Safety margins (PTV) of 1 cm appear to be sufficient, accounting for more than 95% of all deviations.     

New imaging technologies: prospects for target definition.

Developments in medical imaging over the past 2 decades are providing significant improvement in tumor definition. Improvements in soft tissue visualization with tumor specific contrast combined with direct 3D data acquisition and millimetre spatial resolution set new standards in tumor definition. Such precision in tumor imaging provides a new level of challenge for precision radiation treatment. Significant further improvement over the next decade in geographic definition is unlikely. The challenge for imaging research is that of extracting tissue specific information about tumors such as perfusion and response to therapy rather than simply anatomical clarity.     

PET-CT定位图像上医生对肺癌大体肿瘤体积和临床靶体积定义的影响

目的 研究医生在PET-CT图像上对勾画肺癌大体肿瘤体积(GTV)和临床靶体积(CTV)的影响.方法 选取10例2008-2009年间PET-CT定位的肺癌患者,由本科胸组4位主任医生和副主任医生各自独立确定其GTV、CTV.比较每位患者GTV、CTV的平均值、最大值/最小值、变异系数(标准差/平均值);同时比较CTV外轮廓边界位置并计算其系统误差.结果 GTV、CTV最大值与最小值比的平均值分别为1.66、1.65,变异系数分别为0.20、0.17,体积差异较大原因主要为同侧肺门和纵隔淋巴结区域不同.CTV头脚方向与左右、前后方向系统误差分别为0.48 cm与0.37、0.32 cm (F=0.40、0.60、0.15,P=0.755、0.618、0.928).结论 不同放疗科医生在肺癌患者PET-CT定位图像上定义靶区存在差异,GTV、CTV最大值与最小值比的平均值均在1.7以下,差异较大主要原因为位于肺门或纵隔淋巴结区域.CTV头脚方向系统误差较左右和前后方向稍大但均<5 mm.

Abstract：

Objective To study the variation of gross tumor volume (GTV) and clinical target volume (CTV) definition for lung cancer between different doctors.Methods Ten lung cancer patients with PET-CT simulation were selected from January 2008 to December 2009.GTV and CTV of these patients were defined by four professors or associate professors of radiotherapy independently.Results The mean ratios of largest to smallest GTV and CTV were 1.66 and 1.65, respectively.The mean coefficients of variation for GTV and CTV were 0.20 and 0.17, respectively.System errors of CTV definition in three dimension were less than 5 mm, which was the largest in inferior and superior (0.48 cm,0.37 cm,0.32 cm;F=0.40,0.60,0.15,P=0.755,0.618,0.928).Conclusions The variation of GTV and CTV definition for lung cancer between different doctors exist.The mean ratios of largest to smallest GTV and CTV were less than 1.7.The variation was in hilar and mediastinum lymphanode regions.System error of CTV definition was the largest (<5 mm) in cranio-caudal direction.     

Guidelines for target volume definition in post-operative radiotherapy for prostate cancer, on behalf of the EORTC Radiation Oncology Group.

The appropriate application of 3-D conformal radiotherapy, intensity modulated radiotherapy or image guided radiotherapy for patients undergoing post-operative radiotherapy for prostate cancer requires a standardisation of the target volume definition and delineation as well as standardisation of the clinical quality assurance procedures. Recommendations for this are presented on behalf of the European Organisation for Research and Treatment of Cancer (EORTC) Radiation Oncology Group and in addition to the already published guidelines for radiotherapy as the primary treatment.     

FDG-PET/CT imaging for staging and target volume delineation in preoperative conformal radiotherapy of rectal cancer

PURPOSE: To investigate the potential impact of using (18)F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) on staging and target volume delineation for patients affected by rectal cancer and candidates for preoperative conformal radiotherapy. METHODS AND MATERIALS: Twenty-five patients diagnosed with rectal cancer T3-4 N0-1 M0-1 and candidates for preoperative radiotherapy underwent PET/CT simulation after injection of 5.18 MBq/kg of FDG. Clinical stage was reassessed on the basis of FDG-PET/CT findings. The gross tumor volume (GTV) and the clinical target volume (CTV) were delineated first on CT and then on PET/CT images. The PET/CT-GTV and PET/CT-CTV were analyzed and compared with CT-GTV and CT-CTV, respectively. RESULTS: In 4 of 25 cases (24%), PET/CT affected tumor staging or the treatment purpose. In 3 of 25 cases (12%) staged N0 M0, PET/CT showed FDG uptake in regional lymph nodes and in a case also in the liver. In a patient with a single liver metastasis PET/CT detected multiple lesions, changing the treatment intent from curative to palliative. The PET/CT-GTV and PET/CT-CTV were significantly greater than the CT-GTV (p = 0.00013) and CT-CTV (p = 0.00002), respectively. The mean difference between PET/CT-GTV and CT-GTV was 25.4% and between PET/CT-CTV and CT-CTV was 4.1%. CONCLUSIONS: Imaging with PET/CT for preoperative radiotherapy of rectal cancer may lead to a change in staging and target volume delineation. Stage variation was observed in 12% of cases and a change of treatment intent in 4%. The GTV and CTV changed significantly, with a mean increase in size of 25% and 4%, respectively.     

Transcranial sonography: integration into target volume definition for glioblastoma multiforme

PURPOSE: Recent studies indicate that transcranial sonography (TCS) reliably displays the extension of malignant brain tumors. The effect of integrating TCS into radiotherapy planning for glioblastoma multiforme (GBM) was investigated herein. METHODS AND MATERIALS: Thirteen patients subtotally resected for GBM underwent TCS during radiotherapy planning and were conventionally treated (54 to 60 Gy). Gross tumor volumes (GTVs) and stereotactic boost planning target volumes (PTVs, 3-mm margin) were created, based on contrast enhancement on computed tomography (CT) only (PTV(CT)) or the combined CT and TCS information (PTV(CT+TCS)). Noncoplonar conformal treatment plans for both PTVs were compared. Tumor progression patterns and preoperative magnetic resonance imaging (MRI) were related to both PTVs. RESULTS: A sufficient temporal bone window for TCS was present in 11 of 13 patients. GTVs as defined by TCS were considerably larger than the respective CT volumes: Of the composite GTV(CT+TCS) (median volume 42 ml), 23%, 13%, and 66% (medians) were covered by the overlap of both methods, CT only and TCS only, respectively. Median sizes of PTV(CT) and PTV(CT+TCS) were 34 and 74 ml, respectively. Addition of TCS to CT information led to a median increase of the volume irradiated within the 80% isodose by 32 ml (median factor 1.51). PTV(CT+TCS) volume was at median 24% of a "conventional" MRI(T2)-based PTV. Of eight progressions analyzed, three and six occurred inside the 80% isodose of the plans for PTV(CT) and for PTV(CT+TCS), respectively. CONCLUSION: Addition of TCS tumor volume to the contrast-enhancing CT volume in postoperative radiotherapy planning for GBM increases the treated volume by a median factor of 1.5. Since a high frequency of marginal recurrences is reported from dose-escalation trials of this disease, TCS may complement established methods in PTV definition.