Fast dose algorithm for generation of dose coverage probability for robustness analysis of fractionated radiotherapy

Abstract

Abstract.A fast algorithm is constructed to facilitate dose calculation for a large number of randomly sampled treatment scenarios, each representing a possible realisation of a full treatment with geometric, fraction specific displacements for an arbitrary number of fractions. The algorithm is applied to construct a dose volume coverage probability map (DVCM) based on dose calculated for several hundred treatment scenarios to enable probabilistic evaluation of a treatment plan.For each treatment scenario, the algorithm calculates the total dose by perturbing a precalculated dose, separately for the primary and scatter dose components, for the nominal conditions. The ratio of the scenario specific accumulated fluence, and the average fluence for infinite number of fractions is used to perturb the pre-calculated dose. Irregularities in the accumulated fluence may cause numerical instabilities in the ratio, which is mitigated by regularisation through convolution with a dose pencil kernel.Compared to full dose calculations the algorithm demonstrates a speedup factor of ~1000. The comparisons to full calculations show 99% gamma index (2%/2mm) pass rate for a single highly modulated beam in a virtual water phantom subject to setup errors during five fractions. The gamma comparison show 100% pass rate in a moving tumour irradiated by a single beam in a lung-like virtual phantom. DVCM iso-probability lines computed with the fast algorithm, and with full dose calculations for each fraction, for a hypo-fractionated prostate case treated with rotational arc therapy treatment were almost indistinguishable.

Accuracy of the dose-shift approximation in estimating the delivered dose in SBRT of lung tumors considering setup errors and breathing motions

“…Its computational ease compared with the BSh method lends itself to such studies. Note that a more sophisticated alternative has been developed by Tilly et al [21]. The authors have developed a fast dose algorithm to account for dosimetric effects of geometrical uncertainties through applying setup uncertainties and intra-fractional motion to the pre-calculated primary and scatter dose components.…”

Practical robustness evaluation in radiotherapy – A photon and proton-proof alternative to PTV-based plan evaluation

“…Following the definition of Tilly [34], a treatment scenario describes a fractionated treatment with a systematic setup error and for each fraction a random setup error. In view of computational demands, sparse sampling is used, i.e.…”

Retrospective Cohort Study of Bronchial Doses and Radiation-Induced Atelectasis After Stereotactic Body Radiation Therapy of Lung Tumors Located Close to the Bronchial Tree

“…The time overhead for such calculations can be prohibitive and simplifications such as the dose-shift approximation are often used. However, Tilly and Ahnesjö (2015) have developed a fast dose algorithm of dose coverage probability, accounting for dosimetric effects of translational geometrical uncertainties. This algorithm repeatedly applies setup uncertainties and intra-fractional motion with random samples to the pre-calculated primary and scatter dose components, before the final dose calculation.…”