EFFICIENCY-CORRECTED DOSE VERIFICATION WITH THERMOLUMINESCENCE DOSEMETERS IN HEAVY-ION BEAMS

One of the most essential difficulties in heavy-ion dosimetry by means of thermoluminescence dosemeters (TLDs)—often seen as a serious disadvantage of TLD utilisation—regards the changing TL-efficiency with increasing linear energy transfer (LET) of the particle. This behaviour leads to a falsification of absorbed dose that can be significant for many applications, e.g. in space or radiotherapeutic dosimetry. The high-temperature TL emission of LiF:Mg,Ti TL detectors can be exploited to obtain information about the LET of the heavy-ion radiation field under study. The high-temperature ratio (HTR) is used as a parameter to determine average LET. To correct the absorbed dose according to the TL-efficiency, the detailed dependence of HTR- and TL-efficiency on LET was recorded. These investigations were accomplished at the Heavy Ion Medical Accelerator (HIMAC) in Chiba, Japan, with a variety of high-energy ion beams (helium, carbon, neon, silicon and iron) ranging in LET from 2.2 to 393 keV µm-1. The obtained relationships HTR vs. LET and TL-efficiency vs. LET were combined into a TL efficieny vs. HTR relationship. This enables correction of the absorbed dose (HTR-B method). The methodology is demonstrated by means of TLD 700 (7LiF:Mg,Ti) measurements in carbon beams of 290 and 400 MeV n-1 available from HIMAC