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Investigation of intracranial peripheral dose arising from the treatment of large lesions with Leksell GammaKnife ® Perfexion™
Author(s) -
Ruschin Mark,
Nordström Håkan,
Kjäll Per,
Cho YoungBin,
Jaffray David
Publication year - 2009
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 - 10.1118/1.3125133
Subject(s) - collimator , nuclear medicine , dosimetry , imaging phantom , radiosurgery , sagittal plane , linear particle accelerator , physics , materials science , optics , medicine , beam (structure) , radiation therapy , radiology
This investigation involves quantifying the extent of intracranial peripheral dose arising from simulated targets situated in the skull‐base or upper‐spine region using the Leksell GammaKnife ® Perfexion™ treatment unit. For each of three spherical target volumes—denoted asV S( 4 cm 3 ) ,V M( 18 cm 3 ) , andV L( 60 cm 3 ) —three treatment plans were manually generated, one for each of the three collimator sizes—4, 8, and 16 mm. Each of the plans was delivered to a spherical dosimetry phantom with an insert containing EBT Gafchromic film. The total dose at 70 mm from the targets’ edges, % D ( 70 mm ) , was measured as a function of elevation angle and expressed as a percentage of the prescription dose. The film insert was placed centered in the median sagittal plane (Leksell X = 100 ) and % D ( 70 mm )was measured for the angular range from 0° (superior/along Z axis) to 90° (anterior/along Y axis). For a given collimator i , the irradiation timet ito treat a spherical target of volume V using the 50% isodose line was observed to follow a power‐law relationship of the formt i = A i( V / V i ) nwhereA iwas the maximum dose divided by collimator dose rate andV iwas the volume encompassed by the 50% isodose line for a single shot. The mean value of n was 0.61 (range: 0.61–0.62). Along the superior( Z )direction( angle = 0 ° )and up to angles of around 30°, the % D ( 70 mm )was always highest for the 4 mm plans, followed by the 8 mm, followed by the 16 mm. In this angular range, the maximum measured % D ( 70 mm )was 1.7% of the prescription dose. The intracranial peripheral dose along the superior direction (combined scatter and leakage dose) resulting from irradiation of upper‐spine or base‐of‐skull lesions is measured to be less than 2% of the prescription dose, even for very large( 60 cm 3 )targets. The results of this study indicate that, for a given target volume, treatment plans consisting of only 4 mm shots yield larger peripheral dose in the superior direction than 8 mm shot only plans, which in turn yield larger peripheral dose than 16 mm shot only plans.