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WE‐D‐330A‐08: The Small‐Animal Radiation Research Platform (SARRP): Commissioning a 225 KVp “small‐Field” X‐Ray Source for Monte Carlo‐Based Treatment Planning
Author(s) -
Tryggestad E,
Armour E,
Deng H,
Ford E,
Huang J,
Iordachita I,
Kazanzides P,
Kennedy C,
McNutt T,
Verhaegen F,
Wong J
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2241749
Subject(s) - monte carlo method , medical physics , radiation treatment planning , dosimetry , radiation , x ray , nuclear medicine , physics , field (mathematics) , optics , radiation therapy , medicine , radiology , mathematics , statistics , pure mathematics
Purpose: To characterize the dosimetry of a small‐field 225 kVp x‐ray source and demonstrate the feasibility of the Pinnacle Monte Carlo Dose Computation engine (v7.9t alpha release) for treatment planning in the context of small‐animal radiation therapy. Method and Materials: The 225 kVp therapeutic x‐rays for the Small‐Animal Radiation Research Platform (SARRP) are produced by a GE 225 x‐ray tube (spot size 3 mm; Al filtration 4 mm). A simple small‐field collimation system was constructed; for commissioning purposes we machined a set of brass cutouts which define field sizes of 3×3, 5×5, 10×10, 30×30 and 60×60 mm 2 at the nominal SARRP source‐to‐axis distance of 33.5 cm. The x‐ray beams were characterized by irradiating Gafchromic EBT film in water. The film plane was oriented parallel to the central beam axis (z); measurements were made in the x‐z and y‐z planes for all field sizes. Dosimetric data were extracted from the films using a commercial flat‐bed document scanner. Profiles and percent depth‐dose (PDD) curves for depths from 0–9 cm (SSD = 33.5 cm) were imported into our research planning software for comparison with simulated data. Results: Preliminary simulated profiles for the 60×60 mm 2 cutout deviate, on average, by 1.7% and 2.8% in the high‐dose region (90% or greater) for depths of 0.5 and 3 cm, respectively. Average PDD discrepancies for depths from 0–3 cm and 3–6 cm are 4.3% and 18.4% for the 60×60 mm 2 cutout, respectively, and 6.6% and 29.2% for the 5×5 mm 2 cutout. Conclusion: These encouraging results identify the feasibility of using this planning system. Pinnacle supports the finer resolution required for modeling the small fields. Future development will involve incorporation of a measured photon energy spectrum. For purposes of comparison and validation, we will also incorporate an independently‐generated photon phase‐space file for the simulated x‐rays.