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Objective To investigate the precision of full six-degree target shift corrections using the ArcCHECK system.Metbods Fourteen patients receiving intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) in Fujian Medical University Cancer Hospital from May to September,2015 were selected.The first treatment setup errors were obtained using cone-beam computed tomography.The setup errors were simulated in ArcCHECK,and the full six-degree target shift corrections was used to correct the errors.The plans without and with setup errors and the plan with corrected setup errors were taken.The paired t-test was used to compare dose to agreement (DTA) and Gamma passing rates between the plan without setup errors and the plan with setup errors and plan with corrected setup errors.Results The DTA and Gamma passing rates were (96.76± 1.57)％ and (98.35±0.92)％ for the plan without setup errors,(59± 21.42) ％ and (62.86± 21.63) ％ for the plan with setup errors,and (91.41± 4.82) ％ and (94.11±4.33)％ for the plan with corrected setup errors.There were significant differences between the plan without setup errors and the plan with setup errors and plan with corrected setup errors in DTA passing rate (t=6.64 and 5.13,both P＜0.05) and Gamma passing rate (t=6.15 and 4.19,both P＜0.05).Conclusions The full six-degree target shift corrections can be used in IMRT for NPC,with good results in correcting setup errors and improving the precision for IMRT dose distribution.
ABSTRACT
Objective:The purpose of this paper is to introduce a method of using compensate angles to eliminate rotation set-up errors without six-degree of freedom couch. Methods: To detect six-degree of freedom set-up errors, cone-beam computed tomography (CBCT) scans were acquired. These set-up errors were defined as a matrix to transform from accelerator coordinate system to patient coordinate system. Two independent vectors were defined to describe angles of gantry, collimator and couch in accelerator machine. Transformation of vectors were determined by transformation matrix and re-calculated back to the machine angles. Results:It was found that compensate angles can fully corrected the rotation angles in set-up with limited time consuming. It is feasible to implement compensate angles in routinely radiation procedure. Conclusion:With this method, it is possible to implement the complete corrections of set-up errors in radiotherapy without six-degree of freedom couch and it is convenient in operation as well.
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Objective To study the ExacTrac X-ray image guide system for patients with head and neck cancer.Methods Ten patients were chosen foe this study.It was immoblized using the head mask and frame fixtures.The two KV X-ray units were matched with the digitally reconstructed radiographs after positioning with the infrared markers.Then the setup errors on x (horizontal axis),y (vertical axis) and z (up-down) directions and rotation errors were obtained.Paired t-test between any two direction difference errors.Results The setup errors with ExacTrac X-ray image guide system for the patients in x,y,z directions and rotation errors were (0.57 ± 0.24) mm,(0.68 ± 0.19) mm,(1.54 ± 0.29) mm,(0.54 ±0.13) °,(0.60 ± 0.23) °,(0.51 ± 0.15) °.The z-axis direction have slightly larger error (P =0.02,0.01).The others have not statistical significance (P =0.06,0.10-0.41).Conclusions To use ExacTrac X-ray image guide system cooperating with the six degree of freedom treatment couch in image guided radiotherapy for is feasible,the motion errors ＜ 2 mm,the rotation errors ＜ 2°.Reduced of the setup errors with replace the sphere or to reduce pollution of the sphere,improve the accuracy,it could provide a better quality assurance in radiation therapy.
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Objective:To evaluate the six-degree setup errors of tumors of cervical vertebra, thoracic vertebra and lumbar vertebra by image guided radiotherapy. Methods:From May 2013 to June 2014, 30 patients with spinal malignant tumors(10 patients of cervical vertebra, thoracic vertebra and lumbar verte-bra respectively) were treated with Elekata Synergy accelerator(Elekta company,Sweden). Six-degree set up errors were corrected using HexaPODTM evoRT bed under image of on board cone beam computed tomography ( CBCT) guided. All the patients received kilovoltage CBCT before receiving radiotherapy and after correction. The acquired images were co-registered with planning CT with bone window. The data of 838 CT images were analyzed and the errors of translational directions X ( lateral ) , Y ( lngitudi-nal),Z(vertical)and rotational directions RX(pitch), RY(roll), RZ(yaw) were recorded. The data were compared by t-test using SPSS 13. 0. Results:The absolute translational setup errors in X, Y and Z axes of cervical vertebra before correction were (1. 71 ± 0. 10) mm, (1. 81 ± 0. 11) mm and (1. 94 ± 0. 09) mm respectively:(3. 17 ± 0. 19) mm, (4. 26 ± 0. 28) mm and (2. 18 ± 0. 12) mm for thoracic vertebra, and (2. 69 ± 0. 24) mm, (3. 33 ± 0. 26) mm and (2. 86 ± 0. 21) mm for lumbar vertebra. The residual setup errors in X, Y and Z axes of cervical vertebra were (0. 5 ± 2. 4) mm,(0. 01 ± 2. 4) mm and (2. 4 ± 1. 4) mm, respectively after correction;(1. 17 ± 0. 11) mm,(0. 26 ± 0. 30) mm and (0. 08 ± 0. 12) mm for thoracic vertebra and (1. 09 ± 0. 24) mm,(2. 03 ± 1. 26) mm and (0. 06 ± 0. 51) mm for lumbar vertebra. The t-test of paired data of set up errors before and after CBCT showed significant difference in three translational directions of cervical vertebra and thoracic vertebra, only Z (t= -3. 518,P<0. 001) for lumbar vertebra. The absolute rotational setup errors in RX,RY and RZ axes of cervical vertebra before correction were 0 . 67 ° ± 0 . 04 ° ,1 . 06 ° ± 0 . 06 ° and 0 . 78 ° ± 0 . 05 ° respec-tively. 0. 62° ± 0. 05°, 0. 75° ± 0. 06°, and 0. 84° ± 0. 06° for thoracic vertebra, 0. 59° ± 0. 06°, 0. 80° ± 0. 07°, and 0. 73° ± 0. 06°for lumbar vertebra. The rotational directions RX, RY and RZ axes of cervical vertebra were 0 . 27 ° ± 0 . 14 ° , 1 . 20 ° ± 0 . 04 ° and 0 . 28 ° ± 0 . 05 ° respectively;0 . 02 ° ± 0 . 20 ° , 0. 05° ± 0. 26°and 0. 64° ± 0. 16°for thoracic vertebra and 0. 09° ± 0. 26°, 0. 50° ± 0. 05°,and 0. 03° ± 0. 16°for lumbar vertebra. The t-test of paired data of set up errors before and after CBCT showed signifi-cant difference in three rotational directions of cervical vertebra and lumbar vertebra, only RY(t=7. 106, P<0. 001)for thoracic vertebra. All the patients acquired pain relief and there was no radiation-induced toxicity detected clinically during a median follow-up of 6 months. Conclusion:Six-degree set up errors of spine tumors were corrected effectively with HexaPODTM evoRT bed under CBCT image guided and its feasibility in day-to-day clinical practice has been demonstrated.
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Objective To scrutinize the positioning accuracy and reproducibility of the cone-beam computed tomography system in combination with the six-degree couch table (Hexapod Robot Treatment Table, HRTT). Methods The mechanical stability of the X-ray volume imaging (XVI) system was tested,in terms of the reproducibility. And the influence of the moveable parts, including the KV panel and the source arm, on the accuracy of the XVI image registration was analyzed. The accuracy between the bone and grey value registration was compared using a head-and-neck phantom. The accuracy of the HRTT for translational, rotational, and a combination of translational and rotational corrections was investigated in consecutive measurements. Results The performance of XVI system itself was stable with translational and rotational error of below 0. 4 mm and below 0. 3°, respectively. The mean position accuracy of the XVI system in combination with the HRTT summarized over all measurements was below 0. 6 mm and below 0. 4° for translational and rotational corrections, respectively. The grey value match was more accurate than the bone match. Conclusions The XVI image acquisition and registration procedure were highly reproducible.Both translational and rotational positioning errors can be corrected very precisely with the HRTT. The HRTT is therefore well suited to complement CBCT to take full advantage of position correction in six degrees of freedom for image guided radiotherapy.