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SU‐GG‐T‐525: Quantification of the Peripheral Dose Components in Perfexion
Author(s) -
Nayebi N,
Ruschin M,
Nordström H,
Johansson J,
Eriksson M,
Kjäll P,
Jaffray D
Publication year - 2010
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 - 10.1118/1.3468922
Subject(s) - collimator , monte carlo method , dosimetry , imaging phantom , radiosurgery , nuclear medicine , collimated light , physics , radiation , photon , optics , materials science , mathematics , medicine , radiation therapy , radiology , laser , statistics
Purpose: To explore the possibility of separately quantifying the leakage and scatter components of the peripheral radiation dose resulting from Leksell GammaKnife R Perfexion™ radiotherapy. Methods and Materials: In this study, peripheral dose was defined as the dose arising at points outside the paths of the primary beams. Consider a spherical skull phantom centered at Leksell coordinates (100,100,100). Peripheral dose may arise from: (1) Inphantom scattered radiation originating from primary beams; (2) Radiation first scattered within the collimator structure (3) Photons undergoing multiple scattering and exiting through adjacent collimator openings and (4) Leakage radiation that passes directly through the collimator body. Contributions (1) and (2) were separately quantified via Monte‐Carlo simulations. Types (3) and (4) were measured using EBTII Gafchromic film inserts and placing the sources in“beam‐off” position (i.e. between collimator openings). Additionally, the total peripheral dose arising from a 16‐mm shot was measured using film. The combination of simulated type_1 and type_2 doses and measured type_3 and type_4 were compared to the measured total dose at 40 mm superior and inferior to the isocentre. Results: At the isocentre of the 16‐mm shot, the dose‐rate determined by Monte Carlo simulations agreed with measured dose‐rates to 0.8%, thereby establishing consistency between measurement and simulation. The simulated sum of Type_1 and Type_2 contributions at 40 mm inferior and superior to the isocentre was 0.40% and 0.35% of the isocentre dose‐rate, respectively. Of those totals, 87% was Type_1 a 13% came from Type 2. The measured total peripheral dose‐rate was 0.40% and 0.38% at 40 mm inferiorly and superiorly, respectively. The measured Type_3 and Type_4 dose‐rates were less than 0.01% of the isocentre dose‐rate in either direction. Conclusion: The results of this study indicate that peripheral dose arising from a single 16‐mm shot arises primarily from Type_1, with <0.01% contribution from leakage radiation.