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Evaluation of New 2D Ripple Filters in Scanned Proton Therapy

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T Ringbæk

T P Ringbaek1,2*, U Weber3 , A Santiago2,4 , Y Simeonov1 , P Fritz5 , G Iancu4 , A Wittig2,4 , L Granska6,7 , N Bassler8 , R Engenhart-Cabillic2,4 , K Zink1,4 , (1) THM University of Applied Sciences, Giessen, Marburg, (2) Department of Radiotherapy and Oncology, Philipps-University, Marburg, Germany, (3) GSI Helmholtz Centre for Heavy Ion Research, Darmstadt, Germany, (4) Department of Radiotherapy and Oncology, University Medical Center Giessen-Marburg, Marburg, Germany, (5) St Marien-Krankenhaus, Siegen, Germany, (6) Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland, (7) AGH University of Science and Technology, Krakow, Poland, (8) Medical Radiation Physics, Department of Physics, Stockholm University, Sweden,


SU-I-GPD-T-195 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: We have shown previously that ripple filters (RiFis) of an improved 6 mm thick design with two-dimensional cone-structures can be used in scanned carbon ion therapy by widening the Bragg peak (BP) to reduce the accelerator energy shifts needed to cover the target volume and thus reduce the irradiation time. This design could potentially be used in proton therapy too, widening the BP to an extent which would be beneficial in treatment planning. RiFis are normally not used with protons due to larger scattering and straggling effects.

Methods: Measured proton Bragg curves confirm the functionality of the 2D RiFi. Base data for proton treatment planning in the form of depth-dose distributions and lateral profiles were generated with the Monte Carlo code SHIELD-HIT12A with and without the RiFi and imported in the treatment planning systems TRiP98 and proton Eclipse. Proton plans on simulated spherical targets in water were done in TRiP98 for a systematic analysis of the RiFi performance and for comparisons with carbon ion plans for the same respective energy step sizes. For a dosimetric evaluation of the RiFis on clinical cases, plans for selected NSCLC lung tumours fixated under high-frequency jet-ventilation were calculated in Eclipse.

Results: Slightly worse dose conformity and homogeneity for RiFis were found compared to no RiFis but with satisfactory dosimetric results for all cases. A general increase in conformity and homogeneity was found as a function of PTV size and isocenter depth. These effects are found to be more pronounced for protons than for carbon ions. For small superficial targets requiring low beam energies, the RiFi might result in an unacceptable large lateral beam broadening, which could be lowered by opting for a combined RiFi and range shifter setup.

Conclusion: Experimental and simulated data illustrate that 2D RiFis could be used in proton therapy.

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