Abstract
Purpose/objectivesThe complex planning and quality assurance required for spine SBRT are a barrier to implementation in time-sensitive or limited resource clinical situations. We developed and validated an automated inverse planning algorithm designed to streamline planning and allow rapid delivery of conformal single fraction spine SBRT using widely available technology.Materials/methodsThe Rapid Spine (RaSp) automated script successfully generated single fraction SBRT plans for fourteen complex spinal lesions previously treated at a single high-volume institution. Automated RaSp plans were limited to 5 beams with a total of 15 segments (allowing calculation-based verification) and optimized based on RTOG 0631 objectives. Standard single fraction (16 Gy) stereotactic IMRT plans were generated for the same set of complex spinal lesions and used for comparison. A conservative 2 mm posterior isocenter shift was used to simulate minor set-up error.ResultsAutomated plans were generated in under 5 min from target definition and had a mean dose to the PTV of 1663 cGy (SD 131.5), a dose to 90 % of PTV (D90) of 1358 cGy (SD 111.0), and a maximum point dose (Dmax) to the PTV of 2055 cGy (SD 195.2) on average. IMRT plans took longer to generate but yielded more favorable dose escalation with a mean dose to the PTV of 1891 cGy (SD 117.6), D90 of 1731 cGy (SD 126.5), and Dmax of 2218 cGy (SD 195.7). A 2 mm posterior shift resulted in a 20 % (SD 10.5 %) increase in cord dose for IMRT plans and a 10 % (SD 5.3 %) increase for RaSp plans. The 2 mm perturbation caused 3 cord dose violations for the IMRT plans and 1 violation for corresponding RaSp plans.ConclusionThe Rapid Spine plan method yields timely and dosimetrically reasonable SBRT plans which meet RTOG 0631 objectives and are suitable for rapid yet robust pretreatment quality assurance followed by expedited treatment delivery. RaSp plans reduce the tradeoff between rapid treatment and optimal dosimetry in urgent cases and limited resource situations.
Highlights
Spine metastases are a common complication of malignancy, leading to diminished performance status, pain, and neurologic compromise
A 2 mm posterior shift resulted in a 20 % (SD 10.5 %) increase in cord dose for intensity modulated radiotherapy (IMRT) plans and a 10 % (SD 5.3 %) increase for Rapid Spine (RaSp) plans
The Rapid Spine plan method yields timely and dosimetrically reasonable stereotactic body radiation therapy (SBRT) plans which meet RTOG 0631 objectives and are suitable for rapid yet robust pretreatment quality assurance followed by expedited treatment delivery
Summary
Spine metastases are a common complication of malignancy, leading to diminished performance status, pain, and neurologic compromise. Conformal radiotherapy methods employing stereotactic set-up have allowed precise and safe delivery of higher doses of radiation to the tumor volume with durable local control rates approaching 90 % (Gerszten et al 2007). A growing body of clinical data suggests stereotactic body radiation therapy (SBRT) is well tolerated and provides rapid and durable pain relief (Ryu et al 2011; Amdur et al 2009; Schipani et al 2012). SBRT has the added benefit of shortened overall treatment course and smaller treatment volumes with less radiation exposure to adjacent normal tissues, potentially maximizing access to the systemic therapies important in this group of patients. Recent prospective trials including an ongoing cooperative group study (RTOG 0631) are further investigating whether clinical outcome measures such as pain control are improved with stereotactic radiotherapy compared to conventional radiation therapy
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