title: Evaluation of dose-volume metrics for microbeam radiation therapy dose distributions in head phantoms of various sizes using Monte Carlo simulations.
abstract: This work evaluates four dose-volume metrics applied to microbeam radiation therapy (MRT) using simulated dosimetric data as input. We seek to improve upon the most frequently used MRT metric, the peak-to-valley dose ratio (PVDR), by analyzing MRT dose distributions from a more volumetric perspective. Monte Carlo simulations were used to calculate dose distributions in three cubic head phantoms: a 2 cm mouse head, an 8 cm cat head and a 16 cm dog head. The dose distribution was calculated for a 4 × 4 mm² microbeam array in each phantom, as well as a 16 × 16 mm² array in the 8 cm cat head, and a 32 × 32 mm² array in the 16 cm dog head. Microbeam widths of 25, 50 and 75 µm and center-to-center spacings of 100, 200 and 400 µm were considered. The metrics calculated for each simulation were the conventional PVDR, the peak-to-mean valley dose ratio (PMVDR), the mean dose and the percentage volume below a threshold dose. The PVDR ranged between 3 and 230 for the 2 cm mouse phantom, and between 2 and 186 for the 16 cm dog phantom depending on geometry. The corresponding ranges for the PMVDR were much smaller, being 2-49 (mouse) and 2-46 (dog), and showed a slightly weaker dependence on phantom size and array size. The ratio of the PMVDR to the PVDR varied from 0.21 to 0.79 for the different collimation configurations, indicating a difference between the geometric dependence on outcome that would be predicted by these two metrics. For unidirectional irradiation, the mean lesion dose was 102%, 79% and 42% of the mean skin dose for the 2 cm mouse, 8 cm cat and 16 cm dog head phantoms, respectively. However, the mean lesion dose recovered to 83% of the mean skin dose in the 16 cm dog phantom in intersecting cross-firing regions. The percentage volume below a 10% dose threshold was highly dependent on geometry, with ranges for the different collimation configurations of 2-87% and 33-96% for the 2 cm mouse and 16 cm dog heads, respectively. The results of this study illustrate that different dose-volume metrics exhibit different functional dependences on MRT geometry parameters, and suggest that reliance on the PVDR as a predictor of therapeutic outcome may be insufficient.
authors.affiliation: Department of Oncology, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada. adaniell@ualberta.ca
authors.forename: Danielle
authors.initials: D
authors.lastname: Anderson
authors.forename: E Albert
authors.initials: EA
authors.lastname: Siegbahn
authors.forename: B Gino
authors.initials: BG
authors.lastname: Fallone
authors.forename: Raphael
authors.initials: R
authors.lastname: Serduc
authors.forename: Brad
authors.initials: B
authors.lastname: Warkentin
mesh_terms: D000818:Animals; D002415:Cats; D004285:Dogs; D006257:Head / Q000033:anatomy & histology* / Q000528:radiation effects; D051379:Mice; D009010:Monte Carlo Method; D009929:Organ Size; D019047:Phantoms, Imaging; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage