The response of five commercially available thimble ionization chambers with various wall materials has been measured for 60Co,4 and 6 MV photon beams. Measurements were mada in air with build up cap of polymethyl methacrylate. To decrease the influence of photon beam fluctuations, a tip to tip calibration procedure was carried out. Responses were also calculated using a cavity theory. Experimental and calculated responses agree within the estimated total uncertainty.
Total skin electron beam irradiation is suitable for the treatment of widespread skin lesions. To reduce electron beam energy, the degrader is widely used in total skin electron beam irradiation. In this study the effects of source-degrader distance on dose distribution were investigated. Measurements include depth dose, photon contamination and dose rate at the depth of maximum dose for various source-degrader distances. A greater source-degrader distance resulted in lower x-ray contamination and a higher dose rate at the skin. It is concluded that the degrader should be placed closer to the patient.
Inhomogeneity correction factors for various field size and for various photon energies were demonstrated. Off center ratios in the inhomogeneous phantom for various photon energies were also shown. The influence of field size on dose distribution in an inhomogeneous material was considered to be important in planning irradiation of the thorax.
The purpose of this study was to evaluate the therapeutic effects on human tumors in situ using 31P-MR spectroscopy (P-MRS). Sixteen patients with tumor were selected for this study. Seven had brain tumors,2 had metastatic brain tumors,2 had lung cancers,3 had liver tumors, and 2 had superficial malignant tumors. P-MRS was performed using a 2.0 Tesla MRI/S system (MRT-200/RX, Toshiba Co., Tokyo). The acquisition parameters were fixed during this series. P-MR spectra were normalized with total adenosine tri phosphates (ATP) and phosphocreatine (PCr), and these peak ratios were evaluated in relation to therapeutic effects. The therapeutic effects were assessed 1 to 6 months after therapy. In this study, these changes in peak ratios were characterized with regard to the follwing three points.1) In the complete response group (CR), PCr/ATP did not change, and PME/PCr and PDE/PCr were significantly decreased.2) In the progressive disease group (PD), PME/ATP and PDE/ATP were significantly increased.3) In the partial response group (PR) and no change group (NC), no significant changes were observed. These results showed that PME/ATP, PDE/ATP, PME/PCr and PDE/PCr ratios are sensitive indicators of therapeutic effects on tumors and may contribute to therapeutic planning. In particular, PME/PCr and PDE/PCr ratios were able to demonstrate tumor viability.