Stereotactic Body Radiation Therapy (SBRT) for adrenal metastases A Feasibility Study of Advanced Techniques with Modulated Photons and Protons

Purpose: To compare advanced treatment techniques with photons and protons as a stereotactic body radiation therapy (SBRT) for adrenal glands metastases. Materials and Methods: Planning computer tomographic (CT) scans of 10 patients were selected. A total dose of 45 Gy in 7.5 Gy fractions was prescribed. Organs at risk (OAR) were liver and kidneys. Dose–volume metrics were defined to quantify quality of plans assessing target coverage and sparing of organs at risk. Plans for RapidArc, intensity-modulated radiotherapy (IMRT), dynamic conformal arcs, 3D conformal static fields, and intensity modulated protons were compared. The main planning objective for the clinical target volume (CTV) was to cover 100% of the volume with 95% (V95% = 100%) and to keep the maximum dose below 107% of the prescribed dose (V107% = 0%). Planning objective for planning target volume (PTV) was V95% > 80%. For kidneys, the general planning objective was V15Gy < 35% and for liver V15Gy < (liver volume–700 cm3). Results: All techniques achieved the minimum and maximum dose objective for CTV and PTV, D5–95% ranged from 1 Gy (protons) to 1.6 Gy (conformal static fields) on CTV. Maximal organ at risk sparing was achieved by protons. RapidArc presented the second lowest dose bath (V10Gy and integral dose) after protons and the best conformality together with IMRT. Conclusions: Stereotactic body radiation therapy (SBRT) to adrenal glands metastases is achievable with several advanced techniques with either photons or protons. The intensity modulated approaches using either static fields, dynamic arcs or protons are superior to the other conformal solutions. For their simplicity, IMRT or RapidArc should be considered as the first option radiation treatment for those patients not eligible for proton treatment.