Dose calculation and reporting with a linear Boltzman transport equation solver in vertebral SABR

Publication Name

Physical and Engineering Sciences in Medicine


Vertebral Stereotactic ablative body radiotherapy (SABR) involves substantial tumour density heterogeneities. We evaluated the impact of a linear Boltzmann transport equation (LBTE) solver dose calculation on vertebral SABR dose distributions. A sequential cohort of 20 patients with vertebral metastases treated with SABR were selected. Treatment plans were initially planned with a convolution style dose calculation algorithm. The plan was copied and recalculated with a LBTE algorithm reporting both dose to water (Dw) or dose to medium (Dm). Target dose as a function of CT number, and spinal cord dose was compared between algorithms. Compared with a convolution algorithm, there was minimal change in PTV D90% with LBTE. LBTE reporting Dm resulted in reduced GTV D50% by (mean, 95% CI) 2.2% (1.9–2.6%) and reduced Spinal Cord PRV near-maximum dose by 3.0% (2.0–4.1%). LBTE reporting Dw resulted in increased GTV D50% by 2.4% (1.8–3.0%). GTV D50% decreased or increased with increasing CT number with Dm or Dw respectively. LBTE, reporting either Dm or Dw resulted in decreased central spinal cord dose by 8.7% (7.1–10.2%) and 7.2% (5.7–8.8%) respectively. Reported vertebral SABR tumour dose when calculating with an LBTE algorithm depends on tumour density. Spinal cord near-maximum dose was lower when using LBTE algorithm reporting Dm, which may result in higher spinal cord doses being delivered than with a convolution style algorithm. Spinal cord central dose was significantly lower with LBTE, potentially reflecting LBTE transport approximations.

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