Set-up verification using portal imaging; review of current clinical practice

To analyze the magnitude of setup errors corrected by helical tomotherapy megavoltage computed tomography (MVCT) on a daily or weekly basis and the impact of those corrections on the delivered dose to the tumor and organs at risk (OARs), we retrospectively analyzed the setup errors for 6 nasal cavity and 4 nasopharyngeal cancer patients treated with helical tomotherapy for 25 – 33 fractions. Each patient had MVCT‐guided repositioning for all fractions of treatment. The new dose–volume histograms (DVHs) and equivalent uniform doses (EUDs) for the planning target volume (PTV) and OARs were calculated for hypothetical situations in which no imaging guidance (IG) or once‐weekly imaging guidance (WIG) took place. The mean total setup error for treatment without daily IG was 3.6±1.0 mm, which could be reduced to 1.7±0.6 mm if WIG were to be performed. The geometric uncertainties from the absence of IG resulted in a reduction of mean PTV EUD by 2.1%±1.0%, which could be reduced to 1.4%±1.0% with WIG. The EUDs of the OARs increased to 1.8±2.0 Gy or 0.8±1.3 Gy without and with WIG respectively. Without daily IG, the mean uncertainty in patient position has a relatively small effect on the mean dosimetry for PTV and OARs, and the use of WIG can further reduce those effects by approximately half. On the other hand, because of the large variance, with low probability, substantial deviation from the original planned dosimetry may occur without IG. Therefore, daily MVCT is preferred as an important safety measure in the delivery of intensity‐modulated radiation therapy.PACS number: 87.53.Dq

1.6 - 4.6 mm

and random errors of

1.1 - 2.5 mm

Section: Introductionmentioning

confidence: 87%

Section: Methodsmentioning

confidence: 99%

Is daily computed tomography image guidance necessary for nasal cavity and nasopharyngeal radiotherapy? An investigation based on helical tomotherapy

Sheng

Chow

Hunter

et al. 2008

“…In the case of a good setup, these projections look similar to each other; in the case of an incorrect setup, the projections should correspond to the misalignment of the phantom. This process is different from other image verification procedures that rely on either portal images, (2) ultrasound images, (13) or dual X‐ray verification (17) . In our system, the procedure of image verification is based solely on the images (contours) obtained during CT simulation and on the IR marker location comparison at CT and treatment.…”

Section: Methodsmentioning

confidence: 99%

“…With new advancements in treatment modalities and the increasing use of intensity‐modulated radiotherapy, the accuracy of patient positioning for the treatment becomes even more important. Lasers and field lights are routinely used for localizing an isocenter and positioning patients in the field, and portal imaging (electronic or radiographic) is used for more accurate setup verification (2) . However, these techniques are limited to 2D measurements and do not easily allow for a perfect setup due to the fact that the human body is nonrigid.…”

Section: Introductionmentioning

confidence: 99%

Performance and characteristics of an IR localizing system for radiation therapy

Lyatskaya¹,

Chin³

2006

We report the development of a new system for interactive patient posture, position, and respiratory control during radiation therapy treatment. The system consists of an infrared (IR) camera, retroreflective markers, and dedicated software that makes it practical to use in the clinic. The system is designed to be used with multiple retroreflective markers to monitor not only the position, but also the posture of the patient in real time. Specific features of the system include the following: (1) The system reports an absolute misalignment at several points on a patient and also provides feedback on any necessary adjustments in terms of site‐specific setup parameters, such as focus‐to‐surface distance (PIN), superior and inferior alignment, and chest‐wall angle. (2) The system is based on a set of predefined templates containing the number and position of control points and feedback parameters developed for different treatment sites. (3) A noninvasive IR‐based “virtual portal vision” procedure projects organ contours in the beam's‐eye‐view (BEV) based on the IR marker locations obtained in real time and compares them with digitally reconstructed radiographs (DRRs) from CT simulation. Assuming good correlation between external markers and internal anatomy, the system offers the possibility of mimicking a verification procedure without taking port‐films, which can potentially reduce the setup time. In this paper, we concentrate on the system properties and performance while initial applications on a number of clinical sites are ongoing. Accuracy and precision of this system are evaluated in the context of breast/chest treatments using rigid phantoms. The system has an intrinsic uncertainty of ±1.2emmm. When two systems in different rooms (CT and treatment rooms) are used for correlating positional information, the uncertainty is less than 2 mm.PACS number: 87.56.Da

“…It is mainly due to the fact that the reference geometry of the planning CT scan is actually a capture of an arbitrary random displacement. The random component, on the other side, can be defined as the fluctuation over the time around the systematic displacement (3) . The distinction between a systematic and a random component reflects a different impact on treatment dose.…”

Section: Introductionmentioning

confidence: 99%

Estimation of patient setup uncertainty using BrainLAB Exatrac X‐Ray 6D system in image‐guided radiotherapy

Infusino

Trodella

Ramella

et al. 2015

The purpose of this study was to evaluate setup uncertainties for brain sites with ExacTrac X‐Ray 6D system and to provide optimal margin guidelines. Fifteen patients with brain tumor were included in this study. Two X‐ray images with ExacTrac X‐Ray 6D system were used to verify patient position and tumor target localization before each treatment. The 6D fusion software first generates various sets of DRRs with position variations in both three translational and three rotational directions (six degrees of freedom) for the CT images. Setup variations (translation and rotation) after correction were recorded and corrected before treatment. The 3D deviations are expressed as mean±standard deviation. The random error false(normalΣfalse(σifalse)false), systematic error false(μifalse), and group systematic error false(Mfalse(μifalse)false) for the different X‐ray were calculated using the definitions of van Herk. (1) Mean setup errors were calculated from X‐ray images acquired after all fractions. There is moderate patient‐to‐patient variation in the vertical direction and small variations in systematic errors and magnitudes of random errors are smaller. The global systematic errors were measured to be less than 2.0 mm in each direction. Random component of all patients are smaller ranging from 0.1–0.3 mm small. The safety margin (SM) to the lateral, is 0.5 mm and 2.6 mm for van Herk (1) and Stroom et al., (2) respectively, craniocaudal axis is 1.5 mm and 3.4 mm, respectively, and with respect to the antero–posterior axis, 2.3 mm and 3.9 mm. Daily X‐ray imaging is essential to compare and assess the accuracy of treatment delivery to different anatomical locations.PACS number: 87.55.D