3 research outputs found
New Eyeball Phantom for Verification of Patient Positioning and Eye Fixation at the IFJ PAN eye proton facility
Dose distribution comparison of cerebrospinal axis irradiation. Helical tomotherapy vs proton pencil beam scanning
Characterization of the HollandPTC proton therapy beamline dedicated to uveal melanoma treatment and an interinstitutional comparison
Purpose Eye dedicated proton therapy PT facilities are used to treat malignant intraocular lesions, especially uveal melanoma UM . The first commercial ocular PT beamline from Varian was installed in the Netherlands. In this work, the conceptual design of the new eyeline is presented. In addition, a comprehensive comparison against five PT centers with dedicated ocular beamlines is performed, and the clinical impact of the identified differences is analyzed. Material Methods The HollandPTC eyeline was characterized. Four centers in Europe and one in the United States joined the study. All centers use a cyclotron for proton beam generation and an eye dedicated nozzle. Differences among the chosen ocular beamlines were in the design of the nozzle, nominal energy, and energy spectrum. The following parameters were collected for all centers technical characteristics and a set of distal, proximal, and lateral region measurements. The measurements were performed with detectors available in house at each institution. The institutions followed the International Atomic Energy Agency IAEA Technical Report Series TRS 398 Code of Practice for absolute dose measurement, and the IAEA TRS 398 Code of Practice, its modified version or International Commission on Radiation Units and Measurements Report No. 78 for spread out Bragg peak normalization. Energy spreads of the pristine Bragg peaks were obtained with Monte Carlo simulations using Geant4. Seven tumor specific case scenarios were simulated to evaluate the clinical impact among centers small, medium, and large UM, located either anteriorly, at the equator, or posteriorly within the eye. Differences in the depth dose distributions were calculated. Results A pristine Bragg peak of HollandPTC eyeline corresponded to the constant energy of 75 MeV maximal range 3.97 g cm2 in water with an energy spread of 1.10 MeV. The pristine Bragg peaks for the five participating centers varied from 62.50 to 104.50 MeV with an energy spread variation between 0.10 and 0.70 MeV. Differences in the average distal fall offs and lateral penumbrae LPs over the complete set of clinically available beam modulations among all centers were up to 0.25 g cm2, and 0.80 mm, respectively. Average distal fall offs of the HollandPTC eyeline were 0.20 g cm2, and LPs were between 1.50 and 2.15 mm from proximal to distal regions, respectively. Treatment time, around 60 s, was comparable among all centers. The virtual source to axis distance of 120 cm at HollandPTC was shorter than for the five participating centers range 165 350 cm . Simulated depth dose distributions demonstrated the impact of the different beamline characteristics among institutions. The largest difference was observed for a small UM located at the posterior pole, where a proximal dose between two extreme centers was up to 20 . Conclusions HollandPTC eyeline specifications are in accordance with five other ocular PT beamlines. Similar clinical concepts can be applied to expect the same high local tumor control. Dosimetrical properties among the six institutions induce most likely differences in ocular radiation related toxicities. This interinstitutional comparison could support further research on ocular post PT complications. Finally, the findings reported in this study could be used to define dosimetrical guidelines for ocular PT to unify the concepts among institution