mARC prostate treatment planning with Varian Eclipse for flat vs. FFF beams.

PURPOSE - The modulated arc (mARC) technique as an alternative to VMAT is a rotational IMRT irradiation with burst mode delivery. Varian has recently implemented an option for mARC-planning into the Eclipse treatment planning system (TPS) and so far mARC-planning with this TPS has not been evaluated systematically.

Therefore, for prostate treatment with Eclipse we compare mARC with IMRT using flat (6MV) and flattening-filter-free (FFF, 7MV) beam energies.

METHODS - For ten prostate cancer patients standardized re-contouring and re-planning was performed with a prescription of 76Gy to the complete planning-target-volume (PTV). IMRT and mARC plans (6MV vs. FFF 7MV) were compared pairwise considering indices for plan quality. All plans were delivered on an anthromorphic phantom equipped with thermoluminescent dosimeters to measure out-of-field dose and treatment times.

RESULTS - Regarding PTV coverage, there was no marked preference for either technique or energy. The evaluation of organs at risk showed improved bladder sparing of the mARC plans up to about 75Gy; above this dose the IMRT plans achieved significant better sparing. The use of the FFF-beam-energy and mARC-technique resulted in a significant decrease in out-of-field dose. This combination also led to a drastic reduction of treatment time by factor of three in comparison with 6MV IMRT.

CONCLUSIONS - While highly conformal treatment plans could be created by the use of all modalities, the combination of the high dose rate with mARC appears to be the preferable option as it benefits from a marked decrease in treatment time and out-of-field dose.

Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB). 2016 Apr 01 [Epub ahead of print]

Katharina Bell, Yvonne Dzierma, Jan Palm, Frank Nuesken, Norbert Licht, Christian Rübe

Department of Radiotherapy and Radiation Oncology, Saarland University Medical Centre, Kirrberger Str. Geb. 6.5, D-66421 Homburg/Saar, Germany.  Department of Radiotherapy and Radiation Oncology, Saarland University Medical Centre, Kirrberger Str. Geb. 6.5, D-66421 Homburg/Saar, Germany., Department of Radiotherapy and Radiation Oncology, Saarland University Medical Centre, Kirrberger Str. Geb. 6.5, D-66421 Homburg/Saar, Germany., Department of Radiotherapy and Radiation Oncology, Saarland University Medical Centre, Kirrberger Str. Geb. 6.5, D-66421 Homburg/Saar, Germany., Department of Radiotherapy and Radiation Oncology, Saarland University Medical Centre, Kirrberger Str. Geb. 6.5, D-66421 Homburg/Saar, Germany., Department of Radiotherapy and Radiation Oncology, Saarland University Medical Centre, Kirrberger Str. Geb. 6.5, D-66421 Homburg/Saar, Germany.