Respiratory gating for liver tumors: use in dose escalation

An internal target volume (ITV) accounting for respiratory‐induced tumor motion is best obtained using 4DCT. However, when 4DCT is not available, inspiratory/expiratory breath‐hold false(BHinsp, BHexpfalse) CT images have been suggested as an alternative. In such cases, an external fiducial on the abdomen can be used as a substitute for tumor motion and CT images are acquired when the marker position matches – as judged by the therapist/physicist ‐ its positions at previously determined free‐breathing (FB) respiratory extrema false(FBinsp, FBexpfalse). In this study we retrospectively determined the accuracy of these matches. Free breathing 4DCT images were acquired, followed by BHinsp and BHexp CT images for 25 patients with non‐small‐cell lung cancer. Respiration was monitored using a commercial external fiducial system, which generates positional information while CT studies are conducted. Software was written for statistically analyzing the displacement of the external fiducial during BHinsp and BHexp CT acquisition and comparing these displacements with corresponding mean FB extrema positions false(FBinsp and FBexp, respectivelyfalse) using a Student's t‐test. In 72% of patients, mean positions at BHinsp differed significantly from mean positions at FBinsp false(normalp<0.05: 0.13–1.40 cmfalse). In 92% of patients, mean positions at BHexp differed significantly from mean positions at FBexp false(normalp<0.05: 0.03–0.70 cmfalse), although this difference was smaller than 0.5 cm in many cases false(median=0.34 cmfalse). Our findings indicate that relying solely on abdominal external markers for accurate BH CT imaging in order to accurately estimate FB extrema positions may be subject to significant error.PACS numbers 87.53.bd, 87.57.C‐, 87.59.Fm, 87.55.Gh

{FB}_{insp}

SD is greater than the average

{FB}_{exp}

SD, suggesting that end‐expiration is the best phase for passive respiratory‐gated treatment where the patient is freely breathing, which is in agreement with previous observations 12 , 18 …”

Section: Discussionsupporting

confidence: 90%

Comparison of breath‐hold and free‐breathing positions of an external fiducial by analysis of respiratory traces

Hunjan

Starkschall

Rosen

et al. 2008

“…( 5 , 20 ) However, to reach this goal safely, radiation oncologists must first be able to precisely control treatment accuracy with respect to tumor location. Indeed, in the case of therapy with a reduced target volume, small geometric uncertainties could lead to large dosimetric errors—underdosage of tumor and overdosage of OARs.…”

Section: Introductionmentioning

confidence: 99%

Initial evaluation of a four‐dimensional computed tomography system, using a programmable motor

Simon

Giraud

Servois

et al. 2006

Self Cite

A dynamic lung tumor phantom was used to investigate the geometric reconstruction accuracy of a commercial four‐dimensional computed tomography (4D‐CT) system. A ball filled with resin, embedded in a cork cube, was placed on a moving platform. Various realistic antero‐posterior (AP) motions were programmed to reproduce the respiratory motion of a lung tumor. Several three‐dimensional (3D) CT and 4D‐CT images of this moving object were acquired and compared using different acquisition parameters. Apparent volume and diameter of the ball were measured and compared to the real values. The position of two points (the AP limits of the ball) during the motion in the coordinate system of the CT scanner were also compared with the expected values. Volume error was shown to increase with object speed. However, although the volume error was associated with intraslice artifacts, it did not reflect large interslice inconstancies in object position and should not be used as an indicator of image accuracy. The 3D‐CT gave a random position of the tumor along the phantom excursion; accuracy in the assessment of position by 4D‐CT ranged from 0.4 mm to 2.6 mm during extreme phases of breathing. We used average projection (AVE) and maximum intensity projection (MIP) algorithms available on the commercial software to create internal target volumes (ITVs) by merging gross tumor volume (GTV) images at various respiratory phases. The ITVs were compared to a theoretical value computed from the programmed ball excursion. The ITVs created from the MIP algorithm were closer to the theoretical value (within 12%) than were those created from the AVE algorithm (within 40%).PACS numbers: 87.53.Xd, 87.56.Mp, 87.57.Ce, 87.59.Fm

“…Christensen et al (8) reported that image registration and spirometry can reduce the radiation dose to normal tissue by minimizing the tumor treatment margins, although a model for predicting tumor motion should first be developed. Wagman et al (9) confirmed that the calculated dose of approximately 21% increased because the margin reduction in the gross tumor volume (GTV) to PTV decreased from 2 cm to 1 cm when using the RPM. Li et al (10) demonstrated that the Anzai gating system is robust and can compensate for respiration motion during radiation therapy.…”

Section: Introductionmentioning

confidence: 97%

“…Motion management requires both acquisition and correction techniques. Acquisition techniques incorporate the following tools: methods that acquire signals and images using a spirometer combined with artificial manipulation of the patient's respiration; 4 , 8 sensors that are used in real‐time position management (RPM), such as the Anzai, Calypso, and ExacTrac systems; fluoroscopy; and cone‐beam computed tomography (CBCT) 9 , 17 …”

Section: Introductionmentioning

confidence: 99%

“…The gating technique continuously monitors the respiration cycle of the patient and the tumor motion due to the patient's breathing during radiation therapy and compensates by turning the beam on and off. The respiratory gating technique has several disadvantages, including an increased treatment time caused by the intermittent beam application (9) . The radiation dose to patients may be increased due to the additional imaging dose, and pulmonary complications, such as pneumothorax, may occur because of the insertion of the fiducial marker.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Evaluation of mechanical accuracy for couch‐based tracking system (CBTS)

Lee

Chang

Shim

et al. 2012

This study evaluated the mechanical accuracy of an in‐house–developed couch‐based tracking system (CBTS) according to respiration data. The overall delay time of the CBTS was calculated, and the accuracy, reproducibility, and loading effect of the CBTS were evaluated according to the sinusoidal waveform and various respiratory motion data of real patients with and without a volunteer weighing 75 kg. The root mean square (rms) error of the accuracy, the reproducibility, and the sagging measurements were calculated for the three axes (X, Y, and Z directions) of the CBTS. The overall delay time of the CBTS was 0.251 sec. The accuracy and reproducibility in the Z direction in real patient data were poor, as indicated by high rms errors. The results of the loading effect were within 1.0 mm in all directions. This novel CBTS has the potential for clinical application for tumor tracking in radiation therapy.PACS number: 87.55.ne