Volume effects in radiosurgical spinal cord dose tolerance: how small is too small?
Spinal cord dose constraints are a critical feature for stereotactic body radiation therapy (SBRT). Spinal cord maximum point dose (Dmax) by Monte Carlo (MC) calculations is used as a critical cord tolerance limit for SBRT, but information is lacking about its reproducibility. This study examines uncertainty of MC dose calculations for small volumes in spine SBRT.
Seven consecutive spine radiosurgery cases were randomly selected to measure precision of the Dmax calculation in comparison to other volumes. Each plan was calculated five times using MC with a 2% uncertainty objective, and variabilities in dose-volume histogram (DVH) parameters across recalculations were evaluated with coefficient of variation (standard deviation divided by mean). The average ratio of D0.03 cc/Dmax was calculated across a larger series of 130 cases.
The variability of Dmax was twice as high for D0.03 cc and five times as high for D1 cc across recalculations for the seven cases. For larger volumes, the variability was lower. The standard deviation of Dmax was 0.1959 Gy, compared to 0.0931 Gy, 0.0569 Gy, and 0.0364 Gy for D0.03 cc, D0.1 cc, and D1 cc, respectively. The average D0.03 cc/Dmax among 130 cases was 0.93.
Dmax has greater variability compared to D0.03 cc, D0.1 cc, and D1 cc, potentially creating risks when used for guidance for spinal cord. D0.03 cc may be an attractive alternative with higher reliability while its limits could be obtained by scaling the reported Dmax limit by a factor of 0.93. This may help guide treatment planning and aid in discovering true dose constraints for spine SBRT.
KeywordsStereotactic body radiation therapy (SBRT) Spine Monte Carlo Dmax D0.03 cc Uncertainty
Compliance with ethical standards
Conflict of interest
Jimm Grimm designed and holds intellectual property rights to the DVH Evaluator software tool which is an FDA-cleared product in commercial use and which has been used for this analysis. Lawrence Kleinberg has received research grants from Novacure, Arbor, and Accuray. He also serves on the advisory board for Novacure. Ting Martin Ma, Bahman Emami, Jinyu Xue, Sucha O. Asbell, Gregory J. Kubicek, Rachelle Lanciano, James Welsh, Luke Peng, Chengcheng Gui, Indra J. Das, Howard Warren Goldman, Luther W. Brady, and Kristin J. Redmond declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
- 9.Sahgal A, Chou D, Ames C, Ma L, Lamborn K, Huang K, Chuang C, Aiken A, Petti P, Weinstein P, Larson D (2007) Image-guided robotic stereotactic body radiotherapy for benign spinal tumors: the University of California San Francisco preliminary experience. Technol Cancer Res Treat 6:595–604CrossRefGoogle Scholar
- 14.Sahgal A, Weinberg V, Ma L, Chang E, Chao S, Muacevic A, Gorgulho A, Soltys S, Gerszten PC, Ryu S, Angelov L, Gibbs I, Wong CS, Larson DA (2013) Probabilities of radiation myelopathy specific to stereotactic body radiation therapy to guide safe practice. Int J Radiat Oncol Biol Phys 85:341–347CrossRefGoogle Scholar
- 27.Chetty IJ, Curran B, Cygler JE, DeMarco JJ, Ezzell G, Faddegon BA, Kawrakow I, Keall PJ, Liu H, Ma CMC, Rogers DWO, Seuntjens J, Sheikh-Bagheri D, Siebers JV (2007) Report of the AAPM Task Group No. 105: issues associated with clinical implementation of Monte Carlo-based photon and electron external beam treatment planning. Med Phys 34:4818–4853CrossRefGoogle Scholar
- 29.Measurements TICoRUa. ICRU Report 91 (2014) Prescribing, recording, and reporting of stereotactic treatments with small photon beams. Int. Comm. Radiat. Unit and Meas. 14:1–160Google Scholar
- 36.Okoye CC, Patel RB, Hasan S, Podder T, Khouri A, Fabien J, Zhang Y, Dobbins D, Sohn JW, Yuan J, Yao M, Machtay M, Sloan AE, Miller J, Lo SS (2016) Comparison of ray tracing and Monte Carlo calculation algorithms for thoracic spine lesions treated with CyberKnife-based stereotactic body radiation therapy. Technol Cancer Res Treat 15:196–202CrossRefGoogle Scholar