Session Item

In recent years, a number of techniques for irradiation of patients with brain tumors enabling protection of the hippocampus have been developed. This advancement significantly improves quality of life of the patients after irradiation in terms of cognitive functions the affected organs are responsible for.

We investigated the feasibility of whole brain radiotherapy (WBRT) with using volumetric modulated arc therapy (VMAT) technique to spare the hippocampi and the other organs at risk (OARs). Ten patients previously treated with WBRT were analyzed. VMAT plans were generated for a prescription dose of 30 Gy in 10 fractions. Accurate localization of the hippocampus and other critical organs was possible based on additional examination using magnetic resonance (MR). Computed tomography (CT) simulation images of each patient’s head were co-registered with the T1-weighted cranial MR images with contrast medium-enhanced. Treatment plans were made on the Monaco Treatment Planning System (TPS) using photons with a nominal accelerating potential of 6MV and the Monte Carlo calculation algorithm. The VMAT technique with 6 double arcs and collimator angle set to 10 and 350 degrees, was used. Dosimetry treatment plans were analyzed according to the recommendations included in the NRGG-CC01 protocol. The brain area was defined as a planning treatment volume (PTV) where the maximum permissible dose, Dmax, was ≤37.5 Gy, D98% was above 25 Gy, while V30 Gy concerned the volume of ≥ 95%. Variation acceptable (VA) was defined for Dmax, D98% and V30 Gy within 37.5 and 40 Gy; 22.5 and 25 Gy; 90 and 95%, respectively. In the area of the hippocampus, the criteria for plan approval were defined consecutively for Dmax ≤16 Gy (VA from 16 to 17 Gy), and D100% ≤9 Gy (VA from 9 to 10 Gy). For the chiasma and the optic nerves, the maximum permissible dose was ≤30 Gy (VA from 30 to 37.5 Gy).

Properly defined objective functions during optimization in the TPS allowed to obtain the recommended dose levels in the PTV and OARs. In PTV, Dmax, D98% and V30 Gy were 35.3 ± 0.5 Gy, 25.02 ± 0.3 Gy and 95.6 ± 0.8%, respectively. For right and left hippocampus Dmax were 14.7 ± 0.9 Gy and 15.8 ± 0.8 Gy, respectively. For both optic nerves and chiasma Dmax were 35.7 ± 0.6 Gy and 34.2 ± 1.1 Gy, respectively.

The use of WBRT in patients with metastases reduces the risk of disease progression, helping to improve the quality of life of the patients. Our findings indicate that techniques currently available, such as VMAT irradiation, allow for the treatment of the PTV with simultaneously protecting the hippocampus in order to maintain the patient's normal mental processes.