Relative Biological Efficacy
From the viewpoint of radiation physics and radiobiology of low-energy X-rays reveals special characteristics association with this type of radiation. The relative biological effectiveness (RBE) of radiation increases with decreasing photon energy. As a result, the RBE of low-energy X-ray radiation, and consequently the ionization density of X-rays in the tissue is higher with INTRABEAM than with traditional linear accelerators.
Structures on the periphery are protected through the steep physical depth dose gradient of this type of radiation. Model calculations using clinical data show that the higher dose application of low energy X-ray radiation in the vicinity of the tumor compensates for the reduction of the local control at greater distances. Repairs in the normal tissue also take place in radiation with high RBE.
Models of normal tissue toxicity show that the breast wall thickness is an adequate barrier to prevent pneumonitis, and the risk of radiation-induced fibrosis of the breast is low. These postulates concur excellently with clinical observations that have been made to date.
Tumor cell sterilization
Dosing in treatment with INTRABEAM, is ideally performed on the applicator surface or at a defined distance. With an applied dosage of 20 Gy at the applicator surface, the physical dose achieved at 1 cm depth is about 6-7 Gy, depending on the size of the applicator. A one-time delivery of a 20 Gy dose is shown to reliably sterilize tumor cells, exceeding the local efficacy of a fractionated dose of 50?60 Gy. IORT with INTRABEAM demonstrates greater local tumor control than what is experienced with traditional external irradiation.
Spherical dose distribution of the X-rays. The steep drop in the dosage ensures that most of the radiation remains in the targeted tissue.
Sterilization of the tumor rim and influence on the would fluid
The surgical intervention activates numerous biological processes, including the expression of growth factors and cytokines which have a stimulating influence on tumor cells. Wound fluid seems to play a key in the promotion of proliferation, migration and invasion. In a study involving the wound fluid of patients receiving IORT compared to the wound fluid of patients receiving traditional irradiation, the growth-stimulating effect on tumor cells was lower in the IORT treated patients. In addition to the more efficient tumor cell sterilization of INTRABEAM low-energy radiation, the impact on wound fluid provides further pathophysiological explanation for the lower recurrence rate with INTRABEAM IORT compared to traditional irradiation.
More information about the INTRABEAM System you can get at Carl Zeiss.