Premium
SU‐D‐BRF‐02: In Situ Verification of Radiation Therapy Dose Distributions From High‐Energy X‐Rays Using PET Imaging
Author(s) -
Zhang Q,
Kai L,
Wang X,
Hua B,
Chui L,
Wang Q,
Ma C
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4887888
Subject(s) - imaging phantom , bremsstrahlung , nuclear medicine , irradiation , positron emission tomography , radiation , physics , radiation therapy , photon , medical imaging , dosimetry , materials science , nuclear physics , optics , medicine , radiology
Purpose: To study the possibility of in situ verification of radiation therapy dose distributions using PET imaging based on the activity distribution of 11C and 15O produced via photonuclear reactions in patient irradiated by 45MV x‐rays. Methods: The method is based on the photonuclear reactions in the most elemental composition 12 C and 16 O in body tissues irradiated by bremsstrahlung photons with energies up to 45 MeV, resulting primarily in 11 C and 15 O, which are positron‐emitting nuclei. The induced positron activity distributions were obtained with a PET scanner in the same room of a LA45 accelerator (Top Grade Medical, Beijing, China). The experiments were performed with a brain phantom using realistic treatment plans. The phantom was scanned at 20min and 2‐5min after irradiation for 11 C and 15 , respectively. The interval between the two scans was 20 minutes. The activity distributions of 11 C and 15 O within the irradiated volume can be separated from each other because the half‐life is 20min and 2min for 11 C and 15 O, respectively. Three x‐ray energies were used including 10MV, 25MV and 45MV. The radiation dose ranged from 1.0Gy to 10.0Gy per treatment. Results: It was confirmed that no activity was detected at 10 MV beam energy, which was far below the energy threshold for photonuclear reactions. At 25 MV x‐ray activity distribution images were observed on PET, which needed much higher radiation dose in order to obtain good quality. For 45 MV photon beams, good quality activation images were obtained with 2‐3Gy radiation dose, which is the typical daily dose for radiation therapy. Conclusion: The activity distribution of 15 O and 11 C could be used to derive the dose distribution of 45MV x‐rays at the regular daily dose level. This method can potentially be used to verify in situ dose distributions of patients treated on the LA45 accelerator.