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Development, commissioning, and evaluation of a new intensity modulated minibeam proton therapy system
Author(s) -
Farr J. B.,
Moskvin V.,
Lukose R. C.,
Tuomanen S.,
Tsiamas P.,
Yao W.
Publication year - 2018
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 - 10.1002/mp.13093
Subject(s) - isocenter , proton therapy , ionization chamber , collimator , collimated light , nuclear medicine , imaging phantom , optics , physics , bragg peak , proton , percentage depth dose curve , materials science , beam (structure) , ionization , nuclear physics , medicine , laser , ion , quantum mechanics
Purpose To invent, design, construct, and commission an intensity modulated minibeam proton therapy system ( IMMPT ) without the need for physical collimation and to compare its resulting conformity to a conventional IMPT system. Methods A proton therapy system (Hitachi, Ltd, Hitachi City, Japan; Model: Probeat‐V) was specially modified to produce scanned minibeams without collimation. We performed integral depth dose acquisitions and calibrations using a large diameter parallel‐plate ionization chamber in a scanning water phantom ( PTW , Freiburg, Germany; Models: Bragg Peak ionization chamber, MP 3‐P). Spot size and shape was measured using radiochromic film (Ashland Advanced Materials, Bridgewater NJ ; Type: EBT 3), and a synthetic diamond diode type scanned point by point in air ( PTW Models: MicroDiamond, MP 3‐P). The measured data were used as inputs to generate a Monte Carlo‐based model for a commercial radiotherapy planning system ( TPS ) (Varian Medical Systems, Inc., Palo Alto, CA ; Model: Eclipse v13.7.15). The regular ProBeat‐V system (sigma ~2.5 mm) T PS model was available for comparison. A simulated base of skull case with small and medium targets proximal to brainstem was planned for both systems and compared. Results The spot sigma is determined to be 1.4 mm at 221 MeV at the isocenter and below 1 mm at proximal distances. Integral depth doses were indistinguishable from the standard spot commissioning data. The TPS fit the spot profiles closely, giving a residual error maximum of 2.5% in the spot penumbra tails (below 5% of maximum) from the commissioned energies 69.4 to 221.3 MeV. The resulting IMMPT plans were more conformal than the IMPT plans due to a sharper dose gradient (90‐10%) 1.5 mm smaller for the small target, and 1.3 mm for the large target, at a representative central axial water equivalent depth of 7 cm. Conclusions We developed, implemented, and tested a new IMMPT system. The initial results look promising in cases where treatments can benefit from additional dose sparing to neighboring sensitive structures.