Errors in six degree-of-freedom pose estimation of spine tumors assessed by image guided radiotherapy / 北京大学学报(医学版)

ABSTRACT

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.