ESTRO 2022 - Abstract Book

S831

Abstract book

ESTRO 2022

the Wilms’ RT plans, the average absolute difference in mean and max dose, was 0.02Gy (0.00-0.11) and 0.03Gy (0.00- 0.21), respectively. For V 5 , V 10 , V 15 , and V 20 all absolute differences were within 1.6%. For D 1 , D 50 , and D 95 all absolute differences were within 2.9Gy. Conclusion We demonstrated that our colorectal statistical shape model can reconstruct unseen shapes with good accuracy and be used for accurate dose reconstruction. The model will be integrated (Fig. 1F-I) into the Late Effects Group computational phantom and be used to reconstruct colorectal doses for studies of RT-related colorectal late effects.

OC-0940 Independent Dosimetry Audits for Tomotherapy Machines in Korea

K.B. Kim 1 , K. Kim 2 , G. Cho 2 , S.H. Choi 2

1 Korea Institute of Radiological & Medical Sciences, Department of Radiation Oncology, Research Team of Radiological Physics & Engineering, Seoul, Korea Republic of; 2 Korea Institute of Radiological & Medical Sciences, Research Team of Radiological Physics & Engineering, Seoul, Korea Republic of Purpose or Objective We conducted an independent dosimetry audits to verify output dose and symmetry at the national level for all 27 Tomotherapy machines in Korea. Materials and Methods We were established an external dosimetry audit system using the radiophotoluminescent glass dosimeters (RPLD). A specific phantom was designed and fabricated according to the recommendations of AAPM TG-148 and IAEA TRS-398 using the water equivalents of plastic materials to measure output dose with RGDs (GD-302M, Asahi Techno Glass, Japan) [Figure 1]. Using this phantom, an independent dosimetry audit conducted for a total of 27 Tomotherapy machines operating in Korea for static output and symmetry at gantry 0 degree, and rotational output dose using the method of the end-to-end test. The output doses were analyzed by taking readings through a glass dosimeter reader (FGD-1000 SE, AGC Technology Solutions Co., Ltd., Japan) and applying several correction factors; scaling effect, energy dependence, and radio sensitivity. All dosimetry audits were performed according to the specific procedures. The output dose evaluation criteria were evaluated as an optimal level within ±3% (RGD uncertainty at 1 σ ) and a tolerance level within ±5% (ICRU recommendation). In addition, in the case of symmetry, within 2% (manufacturer acceptance criteria) as an optimal level and within 3% (RGD uncertainty at 1 σ ) as a tolerance level were evaluated.

Figure 1 Fabrication of phantom to measure using a RGDs; static output (left) and rotational output (right)

Results The static and rotational output dose were evaluated to be within the tolerance level (within ± 5%) for all machines. Additionally, the symmetry was also evaluated to be within the tolerance level (within 3%) for all machines. As a result of comparing PDD data collected from each institution for the independent dosimetry audits, it was confirmed that PDD 20,10 of beam quality was between 0.52 and 0.53 in most machines except for one machine [Figure 2].