Feasibility Study of 3D CT Based Brachytherapy Planning for Accelerated Partial Breast Irradiation With Intraoperative Interstitial Implants (original) (raw)
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Strahlentherapie und Onkologie, 2007
To evaluate the precision of image-guided radiotherapy (IGRT) using cone-beam computed tomography (CB-CT) for volume imaging and a robotic couch for correcting setup errors in six degrees of freedom. Patients and Methods: 47 consecutive patients with 372 fractions were classified according to whether a patient fixation device was used (pat fix : n = 28) or not (pat non-fix : n = 19). Prior to treatment a CB-CT was acquired and translational and rotational setup errors were corrected online without an action level using a robotic couch (HexaPOD). A second CB-CT was acquired after the correction process and after treatment in 134 and 238 fractions, respectively. Results: In 17 fractions (4.6%) rotational errors > 3° exceeded the motion range of the HexaPOD. Errors (3D vector) after the correction process were significantly smaller for pat fix compared to pat non-fix (p < 0.001): 0.9 mm ± 0.5 mm and 1.6 mm ± 0.8 mm, respectively. For pat non-fix the correction of rotational errors resulted in displacements of the patients on the angled couch of 0.6 mm/1°. Intrafractional motion further decreased precision in pat non-fix but not in pat fix . Conclusion: Very high precision in cranial and extracranial treatment of immobilized patients was demonstrated. Without application of adequate immobilization the correction of rotational errors and intrafractional patient motion significantly decreased the accuracy of the online correction protocol.
International Journal of Radiation Oncology*Biology*Physics, 2012
Stereotactic body radiotherapy (SBRT) for spine tumors requires precise delivery in order to deposit high doses of radiation to the target while sparing the adjacent spinal cord. This paper describes a delivery technique with: near-rigid body immobilization; intrafraction cone-beam CT; corrections in all six degreesof-freedom with a robotic couch; and strict repositioning thresholds. Minimal Purpose: To evaluate the residual setup error and intrafraction motion following kilovoltage cone-beam CT (CBCT) image guidance, for immobilized spine stereotactic body radiotherapy (SBRT) patients, with positioning corrected for in all six degrees of freedom. Methods and Materials: Analysis is based on 42 consecutive patients (48 thoracic and/or lumbar metastases) treated with a total of 106 fractions and 307 image registrations. Following initial setup, a CBCT was acquired for patient alignment and a pretreatment CBCT taken to verify shifts and determine the residual setup error, followed by a midtreatment and posttreatment CBCT image. For 13 single-fraction SBRT patients, two midtreatment CBCT images were obtained. Initially, a 1.5-mm and 1 tolerance was used to reposition the patient following couch shifts which was subsequently reduced to 1 mm and 1 degree after the first 10 patients. Results: Small positioning errors after the initial CBCT setup were observed, with 90% occurring within 1 mm and 97% within 1. In analyzing the impact of the time interval for verification imaging (10 AE 3 min) and subsequent image acquisitions (17 AE 4 min), the residual setup error was not significantly different (p > 0.05). A significant difference (p Z 0.04) in the average three-dimensional intrafraction positional deviations favoring a more strict tolerance in translation (1 mm vs. 1.5 mm) was observed. The absolute intrafraction motion averaged over all patients and all directions along x, y, and z axis (AE SD) were 0.7 AE 0.5 mm and 0.5 AE 0.4 mm for the 1.5 mm and 1 mm tolerance, respectively. Based on a 1-mm and 1 correction threshold, the target was localized to within 1.2 mm and 0.9 with 95% confidence.
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 2014
Purpose: To determine the precision of our institution's current immobilization devices for spine SBRT, ultimately leading to recommendations for appropriate planning margins. Methods: We identified 12 patients (25 treatments) with spinal metastasis treated with spine Stereotactic Body Radiation Therapy (SBRT). The Body-FIX system was used as immobilization device for thoracic (T) and lumbar (L) spine lesions. The head and shoulder mask system was used as immobilization device for cervical (C) spine lesions. Initial patient setup used the infrared positioning system with body markers. Stereotactic X-ray imaging was then performed and correction was made if the initial setup error exceeded predetermined institutional tolerances, 1.5 mm for translation and 2˚ for rotation. Three additional sets of verification X-rays were obtained pre-, mid-, and post-treatment for all treatments. Results: Intrafraction motion regardless of immobilization technique was found to be 1.28 ± 0.57 mm. The mean and standard deviation of the variances along each direction were as follows: Superior-inferior, 0.56 ± 0.39 mm and 0.77 ± 0.52 mm, (p = 0.25); Anterior-posterior, 0.57 ± 0.43 mm and 1.14 ± 0.61 mm, (p = 0.01); Left-right, 0.48 ± 0.34 mm and 0.74 ± 0.40 mm, (p = 0.09) respectively. There was a significantly greater difference in the average 3D variance of the BodyFIX as compared to the head and shoulder mask immobilization system, 1.04 ± 0.46 mm and 1.71 ± 0.52 mm; (p = 0.003) respectively. Conclusions: Overall, our institution's image guidance system using stereotactic X-ray imaging verification provides acceptable localization accuracy as previously defined in the literature. We observed a greater intrafraction motion for the head and shoulder mask as compared with the BodyFIX immobilization system, which may be a result of greater C-spine mobility and/or the suboptimal mask immobilization. Thus, better immobilization techniques for C-spine SBRT are needed to reduce setup error and intrafraction motion. We are currently exploring alternative C-spine immobilization techniques to improve set up accuracy and decrease intrafraction motion during treatment.
Radiation Re-treatment of the Spine Using CyberKnife Radiosurgery
International Journal of Radiation Oncology*Biology*Physics, 2005
head. More recently wide bore (85 cm) CT scanners permit planning in both treatment positions. To determine whether arm position affects dosimetry and the relationship of target nodal groups to anatomic landmarks traditionally used for planning axillary node radiation treatment fields. Materials/Methods: Fourteen patients were scanned in a wide-bore CT in both the historic position with the ipsilateral arm held at 90 degrees by an arm board and in the narrow bore CT treatment planning position with both arms resting above the head in a custom vacuum-lock mold. Level I, II, III nodes were contoured on both CT's for each patient. Target depths and relationship to the coracoid process were measured for each nodal group and optimized dose distributions were compared. In addition, four patients had clips placed at the top of their Level I and II node dissections and the position of these clips relative to anatomic landmarks was compared in each position. Results: The average difference between the historic and narrow bore CT positions in target depth was 8.5 mm (range Ϫ4.7 mm to 24.9 mm) for level II nodes and 7.5 mm (range Ϫ2.2mm to 27.4 mm) for level III nodes. The depth of nodes relative to skin surface was usually greater in the CT position with arms above the head. The average distance from the lateral border of the coracoid process to the lateral anatomic boundary of level II nodes was 11.8 mm (range 1.6 mm to 20.2 mm) in the historic position and 8.1 mm (range of Ϫ4.7 mm to 25.7 mm) in the CT position. It was noted that standard historic posterior axillary boost fields that included only a small margin of lung tissue frequently excluded some Level II and III nodes. In plans optimized for adequate coverage of Level II and III, the mean dose for the deltopectoral nodal group, to which lymphatics of the arm drain, received 116.4% of the prescribed dose in the historical position and 112.4% in the narrow-bore CT position. Conclusions: Changes in arm position result in changes in the relationship between target nodes and anatomic landmarks used historically in treatment planning for breast cancer patients. Such changes could significantly impact the dose distribution unless treatment planning was based on 3D nodal contours. Clips placed at the top of Level I and II dissections are frequently lateral to the coracoid process in both treatment planning positions indicating that historical fields based on anatomic landmarks may well have underdosed or missed high level II and III nodes. The results of historical trials of postmastectomy radiation therapy may need reinterpretation as 3D treatment planning sheds light on the adequacy of historical treatment techniques.
Radiotherapy setup displacements in breast cancer patients: 3D surface imaging experience
Reports of practical oncology and radiotherapy : journal of Greatpoland Cancer Center in Poznan and Polish Society of Radiation Oncology
In this study, we intend to compare two different setup procedures for female breast cancer patients. Imaging in radiotherapy provides a precise localization of the tumour, increasing the accuracy of the treatment delivery in breast cancer. Twenty breast cancer patients who underwent whole breast radiotherapy (WBRT) were selected for this study. Patients were divided into two groups of ten. Group one (G1) was positioned by tattoos and then the patient positioning was adjusted with the aid of AlignRT (Vision RT, London, UK). In group two (G2), patients were positioned only by tattoos. For both groups, the first 15 fractions were analyzed, a daily kilovoltage (kV) cone beam computed tomography (CBCT) image was made and then the rotational and translational displacements and, posteriorly, the systematic () and random () errors were analyzed. The comparison of CBCT displacements for the two groups showed a statistically significant difference in the translational left-right (LR) directi...
Journal of applied clinical medical physics / American College of Medical Physics, 2014
The purpose of this study is to find the uncertainties in the reconstruction of MR compatible ring-tandem intracavitary applicators of high-dose rate image-based brachytherapy treatment planning using rigid registration of 3D MR and CT image fusion. Tandem and ring reconstruction in MR image based brachytherapy planning was done using rigid registration of CT and MR applicator geometries. Verifications of registration for applicator fusion were performed in six verification steps at three different sites of tandem ring applicator set. The first site consists of three errors at the level of ring plane in (1) cranio caudal shift (Cranial Shift) of ring plane along tandem axis, (2) antero-posterior shift (AP Shift) perpendicular to tandem axis on the plane containing the tandem, and (3) lateral shift (Lat Shift) perpendicular to the plane containing the tandem at the level of ring plane. The other two sites are the verifications at the tip of tandem and neck of the ring. The verificati...
Physics and Imaging in Radiation Oncology
Background and purpose: Spinal stereotactic ablative body radiotherapy (SABR) requires high precision. We evaluate the intrafraction motion during cone-beam computed tomography (CBCT) guided SABR with different immobilization techniques. Material and methods: Fifty-seven consecutive patients were treated for 62 spinal lesions with SABR with positioning corrected in six degrees of freedom. A surface monitoring system was used for patient set up and to ensure patient immobilization in 65% of patients. Intrafractional motion was defined as the difference between the last CBCT before the start of treatment and the first CT afterwards. Results: For all 194 fractions, the mean intrafractional motion was 0.1 cm (0-1.1 cm) in vertical direction, 0.1 cm (0-1.1 cm) in longitudinal direction and 0.1 cm (0-0.5 cm) in lateral direction. A mean pitch of 0.6 • (0-4.3 •), a roll of 0.5 • (0-3.4 •) and a rotational motion of 0.4 • (0-3.9 •) was observed. 95.5% of the translational errors and 95.4% of the rotational errors were within safety range. There was a significantly higher rotational motion for patients with arms along the body (p = 0.01) and without the use of the body mask (p = 0.05). For cervical locations a higher rotational motion was seen, although not significant (p = 0.1). The acquisition of an extra CBCT was correlated with a higher rotational (pitch) motion (p = 0 < 0.01). Conclusion: Very high precision in CBCT guided and surface-guided spinal SABR was observed in this cohort. The lowest intrafraction motion was seen in patients treated with arms above their head and a body mask. The use of IGRT with surface monitoring is an added value for patient monitoring leading to treatment interruption if necessary.
International Journal of Radiation Oncology*Biology*Physics, 2007
Purpose: To assess the feasibility of an online strategy for palliative radiotherapy (RT) of spinal bone metastasis, which integrates imaging, planning, and treatment delivery in a single step at the treatment unit. The technical challenges of this approach include cone-beam CT (CBCT) image quality for target definition, online planning, and efficient process integration. Methods and Materials: An integrated imaging, planning, and delivery system was constructed and tested with phantoms. The magnitude of CBCT image artifacts following the use of an antiscatter grid and a nonlinear scatter correction was quantified using phantom data and images of patients receiving conventional palliative RT of the spine. The efficacy of online planning was then assessed using corrected CBCT images. Testing of the complete process was performed on phantoms with assessment of timing and dosimetric accuracy. Results: The use of image corrections reduced the cupping artifact from 30% to 4.5% on CBCT images of a body phantom and improved the accuracy of CBCT numbers (water: ؎ 20 Hounsfield unit [HU], and lung and bone: to within ؎ 130 HU). Bony anatomy was clearly visible and was deemed sufficient for target definition. The mean total time (n ؍ 5) for application of the online approach was 23.1 min. Image-guided dose placement was assessed using radiochromic film measurements with good agreement (within 5% of dose difference and 2 mm of distance to agreement). Conclusions: The technical feasibility of CBCT-guided online planning and delivery for palliative single treatment has been demonstrated. The process was performed in one session equivalent to an initial treatment slot (<30 min) with dosimetric accuracy satisfying accepted RT standards.
Journal of Medical Physics, 2007
Conventional radiograph-based implant dosimetry fails to correlate the spatial dose distribution on patient anatomy with lack in dosimetry quality. Though these limitations are overcome in computed tomography (CT)-based dosimetry, it requires an algorithm which can reconstruct catheters on the multi-planner CT images. In the absence of such algorithm, we proposed a technique in which the implanted geometry and dose distribution generated from orthogonal radiograph were mapped onto the CT data using coordinate transformation method. Radiograph-based implant dosimetry was generated for five head and neck cancer patients on Plato Sunrise treatment planning system. Dosimetry was geometrically optimized on volume, and dose was prescribed according to the natural prescription dose. The final dose distribution was retrospectively mapped onto the CT data set of the same patients using coordinate transformation method, which was verified in a phantom prior to patient study. Dosimetric outcomes were evaluated qualitatively by visualizing isodose distribution on CT images and quantitatively using the dose volume indices, which includes coverage index (CI), external volume index (EI), relative dose homogeneity index (HI), overdose volume index (OI) and conformal index (COIN). The accuracy of coordinate transformation was within ±1 mm in phantom and ±2 mm in patients. Qualitative evaluation of dosimetry on the CT images shows reasonably good coverage of target at the expense of excessive normal tissue irradiation. The mean (SD) values of CI, EI and HI were estimated to be 0.81 (0.039), 0.55 (0.174) and 0.65 (0.074) respectively. The maximum OI estimated was 0.06 (mean 0.04, SD = 0.015). Finally, the COIN computed for each patient ranged from 0.4 to 0.61 (mean 0.52, SD = 0.078). The proposed technique is feasible and accurate to implement even for the most complicated implant geometry. It allows the physicist and physician to evaluate the plan both qualitatively and quantitatively. Dose volume indices derived from CT data set are useful for evaluating the implant and comparing different brachytherapy plans. COIN index is an important tool to assess the target coverage and sparing of normal tissues in brachytherapy.
Journal of radiosurgery and SBRT, 2016
In order to accurately assess positioning errors in spinal SBRT, many institutions employ bony-fusion based imaging techniques, such as the ExacTrac™ (Brain Lab) system, in conjunction with 3D verification (performed via CT-on-rails in our practice). We hypothesized that the use of implanted gold fiducial markers could improve the accuracy of patient positioning over bony fusion alone. We addressed this question prospectively, enrolling patients on an IRB-approved protocol. Gold seeds were implanted in the vertebral pedicles flanking the target level. At treatment, setup error was calculated using two methods-standard kV image fusion, and geometric fiducial-based projection, with independent CT-on-rails verification. Analyses of residual set-up error showed that fiducial-based setup agreed with fusion-based determination, but did not significantly reduce error. Offline 6D fusion of the treatment and planning CT illustrated residual rotational error using standard or fiducial based s...