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MO‐EE‐A2‐06: Measurements and Comparison of Out‐Of‐Field Organ Doses From Varian Clinac IMRT Plans Using the Atom Phantom
Author(s) -
Han B,
Dorgu A,
Pavord D,
Bednarz B,
Xu X
Publication year - 2009
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 - 10.1118/1.3182258
Subject(s) - imaging phantom , thermoluminescent dosimeter , nuclear medicine , dosimeter , dosimetry , field size , medicine , radiation treatment planning , thermoluminescent dosimetry , radiation therapy , radiology
Purpose : To quantify and analyze the unwanted out‐of‐field organ doses during different IMRT prostate treatments and make a systematical comparison of previously reported organ doses. Method and Materials: The measurement involved an ATOM Phantom, thermoluminescent dosimeters (TLD) and a Varian 2100C Clinac. The ATOM phantom was scanned using CT machine to create virtual images for treatment planning. We developed two 6‐MV prostate IMRT plans of 5‐ and 9‐field with the same dose prescriptions, constraints to organs‐at‐risk, and similar in‐field dose distributions. A total of 162 TLDs were placed in the predefined holes to measure the average organ doses of 7 different organs. The results of the two treatment plans were compared to estimate the difference of the out‐of‐field doses. Results : The measurements showed that dose decreases as the distances from the measurement point to the radiation field increases for all treatment plans. The average out‐of‐field organ doses ranged from a maximum of 30.92 cGy to the small intestines to a minimum of 4.40 cGy to the thyroid. The 9‐field IMRT plan resulted in an absorbed dose up to 30% higher than the 5‐field plan which is mainly due to the increased accumulative scatter and lower MU efficiency of the 9‐field IMRT plan. The results were also compared with other studies and the discrepancies were mainly due to the different distances from organs to treatment fields. Conclusion: A method to use TLD and the ATOM physical phantom to measure out‐of‐field organ doses for IMRT has been presented. The measurement results demonstrated that the 9‐field IMRT treatment delivered higher photon doses than the 5‐field IMRT treatment to the out‐of‐field organs. Findings from this study involving the prostate treatments express the need to implement the out‐of‐field dose estimation to the treatment planning in order to minimize the secondary cancer and other radiation risk.