Spinal Cord Tolerance for Stereotactic Body Radiotherapy

PurposeThe aim of this study is to compare the dosimetric differences between four techniques for spine stereotactic body radiotherapy (SBRT): CyberKnife (CK), volumetric modulated arc therapy (VMAT), and helical tomotherapy (HT) with dynamic jaws (HT‐D) and fixed jaws (HT‐F).Materials/methodsData from 10 patients were utilized. All patients were planned for 24 Gy in two fractions, with the primary objectives being: (a) restricting the maximum dose to the cord to ≤ 17 Gy and/or cauda equina to ≤ 20 Gy, and (b) to maximize the clinical target volume (CTV) to receive the prescribed dose. Treatment plans were generated by separate dosimetrists and then compared using velocity AI. Parameters of comparison include target volume coverage, conformity index (CI), gradient index (GI), homogeneity index (HI), treatment time (TT) per fraction, and monitor units (MU) per fraction.Results PTV D2 and D5 were significantly higher for CK compared to VMAT, HT‐F, and HT‐D (P < 0.001). The average volume of CTV receiving the prescription dose (CTV D95) was significantly less for VMAT compared to CK, HT‐F and HT‐D (P = 0.036). CI improved for CK (0.69), HT‐F (0.66), and HT‐D (0.67) compared to VMAT (0.52) (P = 0.013). CK (41.86) had the largest HI compared to VMAT (26.99), HT‐F (20.69), and HT‐D (21.17) (P < 0.001). GI was significantly less for CK (3.96) compared to VMAT (6.76) (P = 0.001). Likewise, CK (62.4 min, 14059 MU) had the longest treatment time and MU per fraction compared to VMAT (8.5 min, 9764 MU), HT‐F (13 min, 10822 MU), and HT‐D (13.5 min, 11418 MU) (P < 0.001).ConclusionBoth CK and HT plans achieved conformal target coverage while respecting cord tolerance. Dose heterogeneity was significantly larger in CK. VMAT required the least treatment time and MU output, but had the least steep GI, CI, and target coverage.

Section: Discussionmentioning

confidence: 99%

Comparison of four techniques for spine stereotactic body radiotherapy: Dosimetric and efficiency analysis

Aljabab

Vellayappan

Vandervoort

et al. 2018

“…The risks of radiation myelopathy in spinal SRS/SBRT were very well studied6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 with Dmax been generally accepted as the parameter of dosimetric constraint. Kirkpatrick et al summarized nine published reports of spinal cord dose and myelopathy in 1,400 patients who received spinal SRS/SBRT 16.…”

Section: Discussionmentioning

confidence: 99%

Submillimeter alignment of more than three contiguous vertebrae in spinal SRS/SBRT with 6‐degree couch

Wang

Zhao

Luo

et al. 2017

The purpose of this study is to identify regions of spinal column in which more than three contiguous vertebrae can be reliably and quickly aligned within 1 mm using a 6‐degree (6D) couch and full body immobilization device. We analyzed 45 cases treated over a 3‐month period. Each case was aligned using ExacTrac x‐ray positioning system with integrated 6D couch to be within 1° and 1 mm in all six dimensions. Cone‐Beam computed tomography (CBCT) with at least 17.5 cm field of view (FOV) in the superior–inferior direction was taken immediately after ExacTrac positioning. It was used to examine the residual error of five to nine contiguous vertebrae visible in the FOV. The residual error of each vertebra was determined by expanding/contracting the vertebrae contour with a margin in millimeter integrals on the planning CT such that the new contours would enclose the corresponding vertebrae contour on CBCT. Submillimeter initial setup accuracy was consistently achieved in 98% (40/41) cases for a span of five or more vertebrae starting from T2 vertebra and extending caudally to S5. The curvature of spinal column along the cervical region and cervicothoracic junction was not easily reproducible between treatment and simulation. Fifty‐seven percent (8/14) of cases in this region had residual setup error of more than 1 mm in nearby vertebrae after alignment using 6D couch with image guidance. In conclusion, 6D couch integrated with image guidance is convenient and accurately corrects small rotational shifts. Consequently, more than three contiguous vertebrae can be aligned within 1 mm with immobilization that reliably reproduces the curvature of the thoracic and lumbar spinal column. Ability of accurate setup is becoming less a concern in limiting the use of stereotactic radiosurgery or stereotactic body radiation therapy to treat multilevel spinal target.

“…Our maximum doses at cervical and lumbar spinal cord in cervical and lumbar were 4.3 Gy and 9.3 Gy for carbon ion RT, as well as 8.1 Gy and 10.5 Gy for proton RT; dose to the spinal cord was considerably higher with IMRT (10.7 Gy–15.5 Gy). The maximum point dose for spine SBRT of 10 Gy is safe (29) . Reports of myelopathy from stereotactic radiosurgery to spinal lesions appear rare (

< 1 %

) when the maximum spinal cord dose is limited to the equivalent of 13 Gy in a single fraction (22) .…”

Section: Discussionmentioning

confidence: 99%

Intensity‐modulated radiotherapy versus proton radiotherapy versus carbon ion radiotherapy for spinal bone metastases: a treatment planning study

Rief

Chaudhri

Tonndorf-Martini

et al. 2015

Outcomes for selected patients with spinal metastases may be improved by dose escalation using stereotactic body radiotherapy (SBRT). As target geometry is complex, we compared SBRT plans using step‐and‐shoot intensity‐modulated radiotherapy (IMRT), carbon ion RT, and proton RT. We prepared plans treating cervical, thoracic, and lumbar metastases for three different techniques — IMRT, carbon ion, and proton plans — to deliver a median single 24 Gy fraction such that at least 90% of the planning target volume (PTV) received more than 18 Gy and were compared for PTV coverage, normal organ sparing, and estimated delivery time. PTV coverage did not show significant differences for the techniques, spinal cord dose sparing was lowered with the particle techniques. For the cervical lesion spinal cord maximum dose, dose of 1% (D1), and percent volume receiving 10 Gy (normalV10Gy) were 11.9 Gy, 9.1 Gy, and 0.5% in IMRT. This could be lowered to 4.3 Gy, 2.5 Gy, and 0% in carbon ion planning and to 8.1 Gy, 6.1 Gy, and 0% in proton planning. Regarding the thoracic lesion no difference was found for the spinal cord. For the lumbar lesion maximum dose, D1 and percent volume receiving 5 Gy (normalV5Gy) were 13.4 Gy, 8.9 Gy, and 8.9% for IMRT; 1.8 Gy, 0.7 Gy, and 0% for carbon ions; and 0 Gy,<0.01 Gy, and 0% for protons. Estimated mean treatment times were shorter in particle techniques (6–7 min vs. 12–14 min with IMRT). This planning study indicates that carbon ion and proton RT can deliver high‐quality PTV coverage for complex treatment volumes that surround the spinal cord.PACS number: 87.55.dk