Manual reconstruction of tumor volumes from CT scans for radiotherapy planning

Using a computed tomographic scan to construct a tumor volume on a simulation film has become an important part of radiation therapy treatment planning. Techniques for reconstruction of brain tumor volumes from computed tomographic scans onto simulation films are discussed. A technique for reconstructing by hand the tumor volume projection at a different angle from the plane of the computed tomographic scan is outlined. Ignoring beam divergence simplifies reconstruction, allowing it to be done by hand but introduces an additional error of at most 0.06, 0.15, 0.26 and 0.42 cm for tumors with maximum diameters of 5, 7.5, 10 and 12.5 cm, respectively. This technique provides the capability for limited 3-dimensional volume reconstruction of small tumors without the use of the computer.     

Impact of FDG-PET on lung cancer delineation for radiotherapy

Purpose: The purpose of this study is to assess the impact of fused diagnostic F‐18 2‐fluoro‐2‐deoxy‐D‐glucose (FDG) positron emission tomography (PET)/computed tomography (CT) and planning FDG‐PET/CT scans on voluming of lung cancer for radiotherapy. Methods: Five radiation oncologists (ROs), five radiation oncology trainees and a radiologist contoured five cases of non‐small cell lung cancer. The CT alone, the diagnostic FDG‐PET/CT and planning FDG‐PET/CT each registered to the CT, were used to contour three volumes. The concordance index (CI) was used to compare each volume with a reference RO. Results: Although there was considerable inter‐observer variability in CT contouring, there was no significant difference between mean volumes of the gross tumour volume for the RO and radiation oncology trainees using any technique. There was no increase in CI with the addition of PET/CT, either diagnostic or planning, for the RO. However, the volumes of the radiation oncology trainees showed a significant increase in CI from 65.8% with CT alone to 68.0% and 72.3% with diagnostic PET/CT and planning PET/CT, respectively (P = 0.028). Mean variation at the tumour/mediastinum interface was significantly reduced with addition of registered PET/CT. Conclusions: The concordance of RO with the reference RO did not significantly increase with use of integrated FDG PET/CT images. However, the contouring of radiation oncology trainees' became more concordant with the reference.     

Functional anatomic imaging in radiation therapy planning

Improvements in techniques for the delivery of curative radiation have paralleled the advances in three-dimensional imaging devices, specifically, computed tomography and magnetic resonance imaging. These modalities supply the high-resolution image data which, when transferred to radiotherapy computers, allows the construction of a "virtual patient" and calculation of radiation dose that can be delivered within a three-dimensional volume. Although anatomic methods have long been the main stay of cancer imaging, it now clear that functional imaging, provided by positron emission tomography and other nuclear medicine techniques, provides additional critical information regarding tumor biologic activity. The additional step of fusion of functional and anatomic images further refines radiation treatment planning.     

Computational dosimetry and treatment planning for Boron Neutron Capture Therapy

The technology for computational dosimetry and treatment planning for Boron Neutron Capture Therapy (BNCT) has advanced significantly over the past few years. Because of the more complex nature of the problem, the computational methods that work well for treatment planning in photon radiotherapy are not applicable to BNCT. The necessary methods have, however, been developed and have been successfully employed both for research applications as well as human trials, although further improvements in speed are needed for routine clinical applications. Computational geometry for BNCT applications can be constructed directly from tomographic medical imagery and computed radiation dose distributions can be readily displayed in formats that are familiar to the radiotherapy community.     

Transarterial chemoembolisation and radioembolisation for the treatment of primary liver cancer and secondary liver cancer: A review of the literature

Liver‐directed therapies are continuing to evolve in the field of interventional oncology and are gaining increasing use in the treatment of unresectable primary and secondary liver cancers. In this article, we review two liver‐directed therapies that are currently used for the palliative treatment of primary and secondary hepatic tumours: transcatheter arterial chemoembolisation (TACE), including a new type of TACE with drug‐eluting beads (DEB‐TACE), and radioembolisation. The concept of these transcatheter intraarterial therapies is to selectively deliver high doses of anticancer treatment to the tumour. While TACE delivers one or more chemotherapeutic drugs into the hepatic arteries supplying the tumour, radioembolisation uses non‐embolic microspheres incorporating the radioactive isotope ⁹⁰Y. In this article, we discuss some technical aspects, patient selection, current clinical evidence, and future directions of TACE, TACE with drug‐eluting beads (DEB‐TACE) and radioembolisation for primary and secondary liver cancer.     

A multileaf collimator phantom for the quality assurance of radiation therapy planning systems and CT simulators

PURPOSE: The evolution of three-dimensional conformal radiation treatment has led to the use of multileaf collimators (MLCs) in intensity-modulated radiation therapy (IMRT) and other treatment techniques to increase the conformity of the dose distribution. A new quality assurance (QA) phantom has been designed to check the handling of MLC settings in treatment planning and delivery. METHODS AND MATERIALS: The phantom consists of a Perspex block with stepped edges that can be rotated in all planes. The design allows for the assessment of several MLC and micro-MLC types from various manufacturers, and is therefore applicable to most radiation therapy institutions employing MLCs. The phantom is computed tomography (CT) scanned as is a patient, and QA assessments can be made of field edge display for a variety of shapes and orientations on both radiation treatment planning systems (RTPS) and computed tomography simulators. RESULTS: The dimensions of the phantom were verified to be physically correct within an uncertainty range of 0-0.7 mm. Errors in leaf position larger than 1 mm were easily identified by multiple observers. CONCLUSIONS: The MLC geometry phantom is a useful tool in the QA of radiation therapy with application to RTPS, CT simulators, and virtual simulation packages with MLC display capabilities.     

Radiotherapeutic computed tomography with scanned photon beams

Radiotherapeutic computed tomography is a powerful technique to generate anatomical transversal tomograms of the patient in treatment position by using the therapy beam from the treatment unit. For this purpose the treatment unit has to be equipped with a detector array that can detect the beam transmitted through the patient and a computer that analyzes the data and performs the back projection. When the treatment unit uses scanned elementary photon beams, the only practical technique available for generating high quality high energy photon beams, the operation principle and, to some extent, the image quality is similar to that of a 3rd generation CT-scanner. The optimum choice of detection geometry and type of radiation detectors for radiotherapeutic computed tomography particularly at high photon energies are discussed indicating the merits of BGO (bismuthgermanate) or CWO (cadmiumtungstate) photodiod arrays. The first tomographic images of a thorax phantom at an acceleration potential of 50 MV using such detectors are presented. The image contrast is similar to that for 300 kV X rays mainly because the considerable influence of pair production at 50 MV. Line spread and modulation transfer functions are presented indicating a resolution of the order of two millimeters using a crystal thickness of 5 mm. The advantages with radiotherapeutic computed tomography, beside forming a new general communication channel between different diagnostic techniques, dose planning, and radiation delivery, are the elimination of position errors and the provision of exact attenuation data for dose planning.     

The imaging revolution and radiation oncology: use of CT, ultrasound, and NMR for localization, treatment planning and treatment delivery

The explosion of new imaging technologies such as X ray computed tomography (CT), ultrasound (US), positron emission tomography (PET), and nuclear magnetic resonance imaging (NMR) has forced a major change in radiation therapy treatment planning philosophy and procedures. Modern computer technology has been wedded to these new imaging modalities, making possible sophisticated radiation therapy treatment planning using both the detailed anatomical and density information that is made available by CT and the other imaging modalities. This has forced a revolution in the way treatments are planned, with the result that actual beam configurations are typically both more complex and more carefully tailored to the desired target volume. This increase in precision and accuracy will presumably improve the results of radiation therapy.     

Imaging characteristics following 90yttrium microsphere treatment for unresectable liver cancer

Selective internal radiation therapy (SIRT) with (90)yttrium microspheres - also known as radioembolisation - is a relatively new interventional radiology technique offering symptomatic and survival advantages for patients with unresectable liver cancer. However, in delivering both beta-particle brachytherapy and embolisation of tumour vasculature, SIRT produces biological sequelae and imaging characteristics distinct from other treatment modalities. Current CT interpretation criteria consistently under-report pathological responses to radioembolisation, diminishing both the prognosis and subsequent treatment choices for responding patients. However, newer criteria incorporating both tumour dimensions and enhancement characteristics improve the correlation with histopathology and provide substantially earlier confirmation of response. CT following radioembolisation may also identify parenchymal features that are often benign but may be mistaken for tumour progression. This review outlines imaging criteria specific to SIRT, including assessment of tumour response and interpretation of both lesion and parenchymal characteristics. The adjunctive role of additional modalities such as positron emission tomography is also addressed.     

The value of magnetic resonance imaging in treatment planning of nasopharyngeal carcinoma

Seven patients with AJCC Stage T4 nasopharyngeal carcinoma underwent both computed tomographic (CT) and magnetic resonance (MR) examinations prior to radiation therapy treatment planning. Lateral tumor extension into the infratemporal fossa was visualized by MR as less extensive in three cases than suggested by CT, as was inferior extension into the parapharyngeal soft tissues in three cases. MR clarified uncertainties on CT regarding involvement of the pontine cistern in three patients and of the cavernous sinus in two patients. Posterior extension of tumor was underestimated by CT in four of six cases shown by MR to involve the clivus. MR appeared superior in evaluating the presence of parenchymal brain involvement in three cases. The margins of the final boost treatment fields dictated by MR findings differed measurably from those derived from CT in six of seven cases. These findings lend support for greater utilization of MR in treatment planning of nasopharyngeal carcinoma.     

Four‐dimensional computed tomography (4DCT): A review of the current status and applications

The applications of conventional computed tomography (CT) have been widely researched and implemented in clinical practice. A recent technological innovation in the field of CT is the emergence of four‐dimensional computed tomography (4DCT), where a three‐dimensional computed tomography volume containing a moving structure is imaged over a period of time, creating a dynamic volume data set. 4DCT has previously been mainly utilised in the setting of radiation therapy planning, but with the development of wide field of view CT, 4DCT has opened major avenues in the diagnostic arena. The aim of this study is to provide a comprehensive narrative review of the literature regarding the current clinical applications of 4DCT. The applications reviewed include both routine diagnostic usage as well as an appraisal of the current research literature. A systematic review of the studies related to 4DCT was conducted. The Medline database was searched using the MeSH subject heading ‘Four‐Dimensional Computed Tomography’. After excluding non‐human and non‐English papers, 2598 articles were found. Further exclusion criteria were applied, including date range (since wide field of view CT was introduced in 2007), and exclusion of technical/engineering/physics papers. Further filtration of papers included identification of Review papers. This process yielded 67 papers. Of these, exclusion of papers not specifically discussing 4DCT (cone beam, 4D models) yielded 38 papers. As part of the review, the technique for 4DCT is described, with perspectives as to how it has evolved and its benefits in different clinical indications.     

Multimodality nuclear medicine imaging in three-dimensional radiation treatment planning for lung cancer: challenges and prospects

The purpose of this study was to determine the utility of quantitative single photon emission computed tomography (SPECT) lung perfusion scans and F-18 fluorodeoxyglucose positron emission computed tomography (PET) during X-ray computed tomography (CT)-based treatment planning for patients with lung cancer. Pre-radiotherapy SPECT (n = 104) and PET (n = 35) images were available to the clinician to assist in radiation field design for patients with bronchogenic cancer. The SPECT and PET scans were registered with anatomic information derived from CT. The information from SPECT and PET provides the treatment planner with functional data not seen with CT. SPECT yields three-dimensional (3D) lung perfusion maps. PET provides 3D metabolic images that assist in tumor localization. The impact of the nuclear medicine images on the treatment planning process was assessed by determining the frequency, type, and extent of changes to plans. Pre-radiotherapy SPECT scans were used to modify 11 (11%) treatment plans; primarily altering beam angles to avoid highly functioning tissue. Fifty (48%) SPECT datasets were judged to be 'potentially useful' due to the detection of hypoperfused regions of the lungs, but were not used during treatment planning. PET data influenced 34% (12 of 35) of the treatment plans examined, and resulted in enlarging portions of the beam aperture (margins) up to 15 mm. Challenges associated with image quality and registration arise when utilizing nuclear medicine data in the treatment planning process. Initial implementation of advanced SPECT image reconstruction techniques that are not typically used in the clinic suggests that the reconstruction method may influence dose response data derived from the SPECT images and improve image registration with CT. The use of nuclear medicine transmission computed tomography (TCT) for both SPECT and PET is presented as a possible tool to reconstruct more accurate emission images and to aid in the registration of emission data with the planning CT. Nuclear medicine imaging techniques appear to be a potentially valuable tool during radiotherapy treatment planning for patients with lung cancer. The utilization of accurate nuclear medicine image reconstruction techniques and TCT may improve the treatment planning process.     

Three-dimensional conformal radiation treatment planning and delivery for low- and intermediate-grade gliomas

Three-Dimensional conformal radiation treatment (3D-CRT) planning and delivery is an external beam radiation therapy modality that has the general goal of conforming the shape of a prescribed dose volume to the shape of a 3-dimensional target volume, simultaneously limiting dose to critical normal structures. 3-Dimensional conformal therapy should include at least one volumetric imaging study of the patient. This image should be obtained in the treatment position for visualizing the target and normal anatomic structures that are potentially within the irradiated volume. Most often, computed tomography (CT) and/or magnetic resonance imaging (MRI) are used; however, recently, other imaging modalities such as functional MRI, MR spectroscopy, and positron emission tomography (PET) scans have been used to visualize the clinically relevant volumes. This article will address the clinically relevant issues with regard to low- and intermediate-grade gliomas and the role of 3D-CRT planning. Specific issues that will be addressed will include normal tissue tolerance, target definition, treatment field design in regard to isodose curves and dose-volume histograms, and immobilization.     

Computed tomography for radiotherapy planning

Images obtained by X-ray transmission computed tomography (CT) assist in planning external beam radiation therapy. Quantitatively, contiguous transverse tomograms may be used to compute radiation dose distributions, based on patient-specific geometry and density of the tissues irradiated. We present here our clinical experience with a computerized treatment planning system modified for this purpose. The importance of performing a CT examination under conditions which simulate treatment is emphasized, particularly for radiotherapy in the thorax. An approximate method for determining tissue electron densities from CT data of a single scan has been verified for tissues in vivo. These tissue densities are used to compute dose distributions for Cobalt-60 and 25 MV X-ray beams, using the equivalent tissue-air ratio method. Predicted doses have been verified to an accuracy of 2%, using intra-rectal thermoluminescent dosimeters. Three clinical examples, dealing with radiotherapy of the esophagus, the rectum, and the upper half body are discussed. Comparison of dose distributions, corrected for tissue inhomogeneities, to those based on a water-like patient indicate differences in the dose to tumor or to surrounding healthy tissue, which are considered clinically significant.     

Target delineation and treatment planning in breast conserving therapy

The increased utilization of computed tomography based treatment planning and intensity modulated radiation therapy for treatment of breast cancer has yielded many potential advantages. Yet, a complete understanding of at risk tissues and avoidance structures is necessary to appropriately utilize such a conformal treatment design. Designing a treatment that maximizes dose homogeneity to the whole breast while minimizing dose to the lung parenchyma, coronary vessels, and myocardium has the potential to improve long-term morbidity and cosmetic outcome. In this review we discuss the utilization of three dimensional treatment planning and intensity modulation for the treatment of breast cancer. We focus on the delineation of target and avoidance structures in the setting of breast conserving therapy and the techniques utilized to maximize the therapeutic ratio.     

Optimising the dosimetric quality and efficiency of post-prostatectomy radiotherapy: a planning study comparing the performance of volumetric-modulated arc therapy (VMAT) with an optimised seven-field intensity-modulated radiotherapy (IMRT) technique

Purpose: The purpose of this study was to compare and evaluate radiotherapy treatment plans using volumetric modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT) for post‐prostatectomy radiotherapy. Methods and Materials: The quality of radiotherapy plans for 10 patients planned and treated with a seven‐field IMRT technique for biochemical failure post‐prostatectomy were subsequently compared with 10 prospectively planned single‐arc VMAT plans using the same computed tomography data set and treatment planning software. Plans were analysed using parameters to assess for target volume coverage, dose to organs at risk (OAR), biological outcomes, dose conformity and homogeneity, as well as the total monitor units (MU), planning and treatment efficiency. Results: The mean results for the study population are reported for the purpose of comparison. For IMRT, the median dose to the planning target volume, V_95% and D_95% was 71.1 Gy, 98.9% and 68.3 Gy compared with 71.2 Gy, 99.2% and 68.6 Gy for VMAT. There was no significant difference in the conformity index or homogeneity index. The VMAT plans achieved better sparing of the rectum and the left and right femora with a reduction in the median dose by 7.9, 6.3 and 3.6 Gy, respectively. The total number of monitor units (MU) was reduced by 24% and treatment delivery time by an estimated 3 min per fraction without a significant increase in planning requirements. Conclusions: VMAT can achieve post‐prostatectomy radiotherapy plans of comparable quality to IMRT with the potential to reduce dose to OAR and improve the efficiency of treatment delivery.     

Progress in the management of limited‐stage small cell lung cancer

Approximately 15% of lung cancer cases are of the small cell subtype, but this variant is highly aggressive and is often diagnosed at advanced stages. Outcomes after current treatment regimens have been poor, with 5‐year survival rates as low as 25% for patients with limited‐stage disease. Advances in therapy for small cell lung cancer have included the development of more effective chemotherapeutic agents and radiation techniques. For example, hyperfractionated radiotherapy given early in the course of the disease can reduce local recurrence and extend survival. Other technologic advances in radiation planning and delivery such as intensity‐modulated radiotherapy, image‐guided adaptive radiotherapy, and 4‐dimensional computed tomography/positron emission tomography have facilitated the design of treatment volumes that closely conform to the shape of the tumor, which allows higher radiation doses to be given while minimizing radiation‐induced toxicity to adjacent structures. Future improvements in outcomes will require clarifying the molecular basis for this disease. Cancer 2014;120:790–798 . © 2013 American Cancer Society.     

L’imagerie en radiothérapie

The goal of radiation therapy is to deliver a high-dose of radiation to the tumour or target region to improve local control of disease and a low-dose to normal soft tissues to limit side effects. Conformal radiation therapy, intensity modulated radiotherapy (IMRT), brachytherapy and stereotactic radiosurgery have been developed to achieve the desired dose distribution. They require precise imaging of internal anatomy so that it is well adapted to the tumour and organs at risk. Indeed, morphological imaging such as computed tomography is already recommended for radiotherapy planning. But radiation oncologists are also considering other imaging modalities for treatment planning and imaging tools capable of controlling patient motion during treatment. The aim of this article is to present and illustrate the place of imaging during treatment planning and delivery via techniques such as: 4D computed tomography, morphological and functional MRI, positron emission tomography, and imaging devices mounted on accelerators.     

PET and PET/CT in radiation treatment planning for prostate cancer

Molecular imaging by means of PET provides a method to study the metabolic activity of tumors in vivo. (18)F- or (11)C-choline and occasionally (18)F- or (11)C-acetate, are used as tracers for prostate cancer, reflecting the phospholipid metabolism. The hybrid technology PET/computed tomography significantly reduces image fusion mismatch. The role of molecular imaging is increasing in radiation treatment planning for prostate cancer. Local prostate cancer recurrence after primary radiation treatment usually originates at the location of the primary tumor. Focusing the dose escalation on the actual tumor is an option to increase tumor control without increasing toxicity. Image-guided radiotherapy and intensity-modulated radiotherapy are prerequisite technologies for applying the simultaneous boost concept. Clinical results are needed in the near future to support the effectiveness of the concept.