Clinical applications of positron emission tomography/computed tomography treatment planning

Positron emission tomography/computed tomography (PET/CT) has provided an incremental dimension to the management of cancer patients by allowing the incorporation of important molecular images in radiotherapy treatment planning, ie, direct evaluation of tumor metabolism, cell proliferation, apoptosis, hypoxia, and angiogenesis. The CT component allows 4D imaging techniques, allowing improvements in the accuracy of treatment delivery by compensating for tumor/normal organ motion, improving PET quantification, and correcting PET and CT image misregistration. The combination of PET and CT in a single imaging system to obtain a fused anatomical and functional image data is now emerging as a promising tool in radiotherapy departments for improved delineation of tumor volumes and optimization of treatment plans. PET has the potential to improve radiotherapy planning by minimizing unnecessary irradiation of normal tissues and by reducing the risk of geographic miss. PET influences treatment planning in a high proportion of cases and therefore radiotherapy dose escalation without PET may be futile. This article examines the increasing role of hybrid PET/CT imaging techniques in process of improving treatment planning in oncology with emphasis on non small cell lung cancer.     

Technical aspects of positron emission tomography/computed tomography in radiotherapy treatment planning

The usage of functional data in radiation therapy (RT) treatment planning (RTP) process is currently the focus of significant technical, scientific, and clinical development. Positron emission tomography (PET) using ((18)F) fluorodeoxyglucose is being increasingly used in RT planning in recent years. Fluorodeoxyglucose is the most commonly used radiotracer for diagnosis, staging, recurrent disease detection, and monitoring of tumor response to therapy (Lung Cancer 2012;76:344-349; Lung Cancer 2009;64:301-307; J Nucl Med 2008;49:532-540; J Nucl Med 2007;48:58S-67S). All the efforts to improve both PET and computed tomography (CT) image quality and, consequently, lesion detectability have a common objective to increase the accuracy in functional imaging and thus of coregistration into RT planning systems. In radiotherapy, improvement in target localization permits reduction of tumor margins, consequently reducing volume of normal tissue irradiated. Furthermore, smaller treated target volumes create the possibility of dose escalation, leading to increased chances of tumor cure and control. This article focuses on the technical aspects of PET/CT image acquisition, fusion, usage, and impact on the physics of RTP. The authors review the basic elements of RTP, modern radiation delivery, and the technical parameters of coregistration of PET/CT into RT computerized planning systems.     

Motion management in positron emission tomography/computed tomography for radiation treatment planning

Hybrid positron emission tomography (PET)/computed tomography (CT) scanners combine, in a unique gantry, 2 of the most important diagnostic imaging systems, a CT and a PET tomograph, enabling anatomical (CT) and functional (PET) studies to be performed in a single study session. Furthermore, as the 2 scanners use the same spatial coordinate system, the reconstructed CT and PET images are spatially co-registered, allowing an accurate localization of the functional signal over the corresponding anatomical structure. This peculiarity of the hybrid PET/CT system results in improved tumor characterization for oncological applications, and more recently, it was found to be also useful for target volume definition (TVD) and treatment planning in radiotherapy (RT) applications. In fact, the use of combined PET/CT information has been shown to improve the RT treatment plan when compared with that obtained by a CT alone. A limiting factor to the accuracy of TVD by PET/CT is organ and tumor motion, which is mainly due to patient respiration. In fact, respiratory motion has a degrading effect on PET/CT image quality, and this is also critical for TVD, as it can lead to possible tumor missing or undertreatment. Thus, the management of respiratory motion is becoming an increasingly essential component in RT treatment planning; indeed, it has been recognized that the use of personalized motion information can improve TVD and, consequently, permit increased tumor dosage while sparing surrounding healthy tissues and organs at risk. This review describes the methods used for motion management in PET/CT for radiation treatment planning. The article covers the following: (1) problems caused by organ and lesion motion owing to respiration, and the artifacts generated on CT, PET, and PET/CT images; (2) data acquisition and processing techniques used to manage respiratory motion in PET/CT studies; and (3) the use of personalized motion information for TVD and radiation treatment planning.     

Evaluation of the role of computed tomography in radiotherapy treatment planning

The role of computed tomography (CT) in radiotherapy treatment planning was assessed in a series of 231 patients in whom treatment was planned with radical intent. For each patient, a treatment plan was produced by the best conventional techniques in use at the Middlesex Hospital. Each patient then underwent a CT scan in which the treatment conditions were closely simulated. As a result of the CT scan images, alteration was made to the planned treatment in 47% of 198 assessable patients. Large differences were seen in the usefulness of CT treatment planning for tumours in different sites, with the greatest contribution made to treatment of tumours of the sinuses and nasopharynx and of the bladder. Although its unit cost is high, computed tomography can be a very useful tool in radiotherapy treatment planning and can contribute uniquely to improved patient management for adequately selected patients.     

Use of computed tomography for a three-dimensional treatment planning system

Computed tomography (CT) can generate a set of serial contiguous slices which form a volume of medical image data. We have developed new techniques for creating computer synthesized 3-D images directly from a volume encoded as a three-dimensional array. The operator can place the eye anywhere in object space to selectively view a portion of the volume from any angle. A set of volume processing tools have been recently developed to allow interactive manipulation of image data within the volume. These tools allow the system to be used for surgical planning, and craniofacial implant design.     

Accuracy of implant treatment planning utilizing template-guided reformatted computed tomography

OBJECTIVES: To evaluate the magnitude of error in transferring the planned position of implants from reformatted CT scans to a surgical template. METHODS: The deviation between the position of the apex of the proposed implant in paraxial CT reformats and on the corresponding study cast was measured in 77 prospective sites in five maxillas and nine mandibles. RESULTS: The transfer error was 0.6 (s.d. 0.4) mm in the maxilla and 0.3 (s.d. 0.4) mm in the mandible. CONCLUSIONS: The transfer errors detected in this investigation are not clinically relevant. Other factors involved in transferring positional and angular measurements from reformatted CT to the surgical site may result in more significant errors.     

A method for integrating computed tomography into radiotherapy planning and treatment

A technique is described for accurate localisation and radiotherapy treatment planning for a wide range of intrathoracic, abdominal and pelvic tumours. It allows the patient to proceed in one step from a single examination by computed tomography (CT) to treatment and avoids the need for separate treatment simulation. Compatible laser-beam positioning systems between the CT scanner and treatment-machine rooms ensure accurate reproduction of patient position, so that CT data are directly applicable to treatment. The use of appropriate skin markers, which appear on the CT scan, allows accurate measurements of the distance of the centre of the planned volume from a tattoo placed on the patient at the time of the scan, and ensures that the planned treatment fields are accurately directed.     

Application of positron emission tomography/computed tomography in radiation treatment planning for head and neck cancers

18-fluorodeoxygluocose positron emission tomography/computed tomography (¹⁸FDG-PET/CT) provides significant information in multiple settings in the management of head and neck cancers (HNC). This article seeks to define the additional benefit of PET/CT as related to radiation treatment planning for squamous cell carcinomas (SCCs) of the head and neck through a review of relevant literature. By helping further define both primary and nodal volumes, radiation treatment planning can be improved using PET/CT. Special attention is paid to the independent benefit of PET/CT in targeting mucosal primaries as well as in detecting nodal metastases. The utility of PET/CT is also explored for treatment planning in the setting of SCC of unknown primary as PET/CT may help define a mucosal target volume by guiding biopsies for examination under anesthesia thus changing the treatment paradigm and limiting the extent of therapy. Implications of the use of PET/CT for proper target delineation in patients with artifact from dental procedures are discussed and the impact of dental artifact on CT-based PET attenuation correction is assessed. Finally, comment is made upon the role of PET/CT in the high-risk post-operative setting, particularly in the context of radiation dose escalation. Real case examples are used in these settings to elucidate the practical benefits of PET/CT as related to radiation treatment planning in HNCs.     

Role of whole-body 64-slice multidetector computed tomography in treatment planning for multiple myeloma

Purpose

The authors evaluated the role of whole-body 64-slice multidetector computed tomography (WB-MDCT) in treatment planning for multiple myeloma.

Material and methods

This was a prospective study of 28 consecutive patients with multiple myeloma (19 men, nine women; age range, 51–73 years; mean age, 60 years) who underwent WB-MDCT and conventional radiography (CR) of the skeleton. The images were interpreted for the presence of bony lesions, medullary lesions, fractures and extraosseous lesions. We evaluated any changes in treatment planning as a result of WB-MDCT findings.

Results

WB-MDCT was superior to CR for detecting bony lesions (p=0.001), especially of the spine (p=0.001) and thoracic cage (p=0.006). WB-MDCT upstaged 14 patients, with a significant difference in staging (p=0.002) between WB-MDCT and CR. Medullary involvement either focal (n=6) or diffuse (n=3) had a positive correlation with the overall score (r=0.790) and stage (r=0.618) of disease. Spine fractures were better detected at WB-MDCT (n=4) than at CR (n=2). Extraosseous soft tissue lesions (n=7) were detected only at WB-MDCT. Findings detected at the WB-MDCT led to changes in the patient’s treatment plan in 39% of cases. Upstaging of seven patients (25%) altered the medical treatment plan, and four of 28 (14%) patients required additional radiotherapy (7%) and vertebroplasty (7%).

Conclusions

We conclude that WB-MDCT has an impact on treatment planning and prognosis in patients with multiple myeloma, as it has high rate of detecting cortical and medullary bone lesions, spinal fracture and extraosseous lesions. This information may alter treatment planning in multiple myeloma due to disease upstaging and detection of spine fracture and extraosseous spinal lesions.     

Value of x-ray computed tomography in osteoid osteoma

Four cases of suspected osteoid osteoma were evaluated by computed tomography (CT). The authors relate the role of CT. As a key diagnostic tool: radionuclide imaging is helpful in directing subsequent CT scans, which allows the study of complex anatomical sites (spine) or the analysis of atypical lesions (invisible nidus, sclerosis or lytic lesions, double nidus...). CT provides the surgeon with the exact location and extent of the lesion, and thus, CT may allow a more limited surgical resection of the involved bone.     

Technical aspects of positron emission tomography/computed tomography fusion planning

Emerging technologies in radiation therapy computers and delivery systems allow surgically precise conformal radiation treatment that was not possible with previous generations of equipment. The newest treatment systems can compensate for tumor target motion as well as shape dose distributions to conform precisely to delineated target volumes. These sophisticated technologies now drive the development of imaging modalities able to generate equally high-resolution and lesion-specific roadmaps that are the foundation of these highly accurate radiation plans. Positron emission tomography/computed tomography (PET/CT) is currently becoming a routine imaging tool for radiation oncology because of its combined benefits of positron imaging and high-resolution anatomic display. The improved staging and lesion delineation provided by PET, combined with the 3D anatomic display provided by CT, now allows better treatment stratification and more precise targeting. Additionally, respiratory-gated 4D CT and 4D PET/CT have been used in the simulation process for respiratory-gated radiation therapy. Successful integration of PET/CT into the radiation therapy planning process requires an understanding of how therapy plans are derived and the process by which the patient receives therapy, because these dictate the method of image acquisition. The radiation oncologists, too, must understand the technology of positron imaging to adapt these functional images based on intensities rather than pixels to their targeting process. Modifications to the PET/CT scanner and room are necessary to image the patient in the reproducible position required for treatment planning. Although the impact of these efforts on patient outcome has yet to be determined, the benefit of better treatment choice, due to improved staging, and more precise targeting with less normal tissue exposure resulting in improved quality of life will likely promote PET/CT to the gold-standard for targeted therapies.     

Calcified herniations of the thoracic disk: role of magnetic resonance imaging and computed tomography in surgical planning.

Herniations of thoracic disks are uncommon, and their surgical management can be challenging. Magnetic resonance imaging (MRI) is rapidly becoming the method of choice for assessing degenerative disease in thoracic disks. However, calcification may be difficult to detect with MRI and plain films alone. The authors report a case in which MRI and myelography underestimated the true extent of disk calcification, the detection of which would have altered the initial surgical approach.     

Classification of calcaneal fractures by spiral computed tomography: implications for surgical treatment

The purpose of this study was to evaluate spiral computed tomography and multislice CT (SCT/MSCT) with multiplanar reconstructions (MPR) in the classification of calcaneal fractures according to a modified CT classification and to quantify fragment displacement to guide surgical treatment. Forty-eight calcaneal fractures were examined by spiral CT (1- to 2-mm slice thickness, pitch=1.5) with multiplanar reconstructions (MPR). Fractures were grouped according to a modified Munich classification scheme, differentiating six categories of fractures by joint involvement, number of fragments in the posterior facet, and the presence and extent of displacement. A qualitative and quantitative statement was made for the presence of clinical relevant displacement of the posterior articular facet (A: >2 mm), widening of the heel (B: crossing fibular reference line), reduction in calcaneal height (C: >10%), and axis shift of the calcaneocuboid angle (D: >10°). Treatment recommendations resulting from the CT classification were retrospectively compared with the treatment given by examining the patients' files. There were 10 extra-articular and 38 intra-articular fractures; 8 were in class I (extra-articular, nondisplaced), 2 in class II (extra-articular, displaced), 1 in class III (intra-articular, nondisplaced), 20 in class IV (two fragments), 9 in class V (three fragments), and 8 in class VI (>4 fragments), one of the latter being uncertain; 34 showed displacement of the articular facet, 35 widening of the heel, 35 reduction in calcaneal height, and 20 a shift of the axis. In 94% of the cases the procedure recommended by the Munich system of classification was followed; there was disagreement in 1 case in class I and 1 in class IV. Spiral CT allowed fracture classification and quantification of relevant displacement of fragments by radiologists. The implemented recommendations for treatment were adopted by surgeons in most cases.     

Influence of F-fluorodeoxyglucose-positron emission tomography on computed tomography-based radiation treatment planning for oesophageal cancer

The addition of positron emission tomography (PET) information to CT-based radiotherapy treatment planning has the potential to improve target volume definition through more accurate localization of the primary tumour and involved regional lymph nodes. This case report describes the first patient enrolled to a prospective study evaluating the effects of coregistered positron emission tomography/CT images on radiotherapy treatment planning for oesophageal cancer. The results show that if combined positron emission tomography/CT is used for radiotherapy treatment planning, there may be alterations to the delineation of tumour volumes when compared to CT alone. For this patient, a geographic miss of tumour would have occurred if CT data alone were used for radiotherapy planning.