Proton Dose Distribution and its Biological Effect Distribution

• Project/Area Number: 10670822
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Radiation science
• Research Institution: University of Tsukuba
• Principal Investigator: MARUHASHI Akira Institute of Clinical Medicine (Proton Medical Research Center) University of Tsukuba Associate professor, 臨床医学系・陽子線医学利用開発センター, 助教授 (30114135)
• Co-Investigator(Kenkyū-buntansha): NOUTOMI Akihiro Institute of Applied Physics (Proton Medical Research Center) University of Tsukuba Assistant professor, 物理工学系・陽子線医学利用開発センター, 講師 (80243905) ; OKUMURA Toshiyuki Institute of Clinical Medicine (Proton Medical Research Center) University of Tsukuba Assistant professor, 臨床医学系・陽子線医学利用開発センター, 講師 (50241815)
• Project Period (FY): 1998 – 1999
• Project Status: Completed (Fiscal Year 1999)
• Budget Amount: ¥2,800,000 (Direct Cost: ¥2,800,000); Fiscal Year 1999: ¥1,700,000 (Direct Cost: ¥1,700,000); Fiscal Year 1998: ¥1,100,000 (Direct Cost: ¥1,100,000)
• Keywords: proton therapy / dose distribution / screen / CCD camera / imaging plat / Let dependency / faculty of proliferation / 発光LET依存性 / 細胞の増殖能分布 / Proton / Dose Distrebution / Biological Desimetry / CCD camera / Photoluminescence Microscope

Research Abstract

For an application to the dose-distribution measurement, response of an imaging plate (IP) has been studied with proton beams, which are routinely utilized for the radiation therapy. The upper limit of measurable proton dose by an IP system is almost controlled by the readout range of scanner used. Within this limit, reasonable linear response of an IP to proton dose to water is maintained. Fading curves are neither so sensitive to a small change of room temperature nor to a certain variation of proton dose (0.0108-0.132 Gy). Reproducibility of the PSL intensity is fairly good if both the fading characteristics and the lot-dependence of the sensitivity of each IP are taken into account carefully. Stopping power dependence of IP response has been measured at different positions in a Bragg curve. Tolerance of IP to radiation damage by proton irradiation has been examined.
In PMRC, dose distributions on the axis of proton beam and on the lines perpendicular to that in the water phantom hav e been measured by scanning Si semiconductor detector, under the same condition of a beam delivery system including bolus and patient collimator as that of patient treatment.
The purpose of this measurement is to verify that the width of high dose region (90%-95% to maximum on beam axis in the target volume in general) given by SOBP beam is coincident to that of planned target region as a result of the treatment planning. Now, we test the two dimensional dose distribution detector usable in water in place of the present detection system. For this purpose, a system composed of intensifying screen used for X-ray radiography and CCD camera was used. The screen stood vertically in water phantom was set to the axis of proton beam as 1) at small angle to mainly measure intensity distributions of its scintillation light on depth and 2) perpendicularly to measure 2-D light intensity distribution at given depth. In latter case, a miller set at 45 degrees to the proton beam direction was attached to the distal edge of the water phantom. Characteristics of the screen about efficiency converting the absorbed dose to light intensity were investigated on the basis of dose measured by Si semiconductor detector. We show LET dependency of light intensity generated from the screen and relationships between dose distributions by silicon dosimeter and light intensity distributions by the screen as experimental and analytical results on a poster.