Online

ESTRO 2020

Session Item

Physics track: Dose measurement and dose calculation
9319
Poster
Physics
00:00 - 00:00
End-to-end empirical validation of 3D dose distributions using an anthropomorphic pelvis phantom
Mathieu Marot, Germany
PO-1408

Abstract

End-to-end empirical validation of 3D dose distributions using an anthropomorphic pelvis phantom
Authors: Bettina Beuthien-Baumann.(German Cancer Research Center DKFZ, Radiology, Heidelberg, Germany), Alina Elter.(German Cancer Research Center DKFZ, Medical Physics in Radiation Oncology, Heidelberg, Germany), Clarissa Gillmann.(German Cancer Research Center DKFZ, Medical Physics in Radiation Oncology, Heidelberg, Germany), Wibke Johnen.(German Cancer Research Center DKFZ, Medical Physics in Radiation Oncology, Heidelberg, Germany), Stefan A. Körber.(University Hospital Heidelberg, Radiation Oncology and Radiotherapy, Heidelberg, Germany), Clemens Lang.(German Cancer Research Center DKFZ, Medical Physics in Radiation Oncology, Heidelberg, Germany), Philipp Mann.(German Cancer Research Center DKFZ, Medical Physics in Radiation Oncology, Heidelberg, Germany), Mathieu MAROT.(German Cancer Research Center DKFZ, Medical Physics in Radiation Oncology, Heidelberg, Germany), Andrea Schwahofer.(German Cancer Research Center DKFZ, Medical Physics in Radiation Oncology, Heidelberg, Germany)
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Purpose or Objective

To develop an end-to-end test for empirical validation of 3D dose distributions in prostate and rectum using an anthropomorphic pelvis phantom.

Material and Methods

Polymer dosimetry gel was filled into the 3D printed prostate organ shell of the phantom. A stack of nine thermoluminescent detectors (TLDs) mounted onto a specifically designed holder was placed into the rectum posterior to the prostate. The phantom was scanned in treatment position with an in-room CT (Somatom Emotion, Siemens Healthineers). Using Raystation8A (Raysearch Laboratories), a treatment plan simulating the clinical situation with seven beams aiming at a prescribed dose of 4.5 Gy to the whole prostate volume including a 4 mm margin was calculated. Phantom irradiation was performed on a 6 MV Linac (Artiste, Siemens). The dosimetry gel was evaluated using MRI and the TLDs were read out with a harshaw hot gas reader. For the dosimetry gel, the measured 3D dose distribution was compared to the calculated dose distribution with a 3D gamma analysis (Verisoft, PTW, passing criteria: 3% dose difference and 3 mm distance to agreement). The TLDs were used to evaluate punctual doses in the rectum and the measured doses were compared to calculated doses by the treatment planning software on a point-by-point basis.

Results

The 3D gamma index comparing measured and calculated dose distributions in the prostate was 97.7%. For the TLDs, the average dose difference between calculated and measured doses was 0.08 Gy (range: 0.02 – 0.21 Gy, with 0.08 Gy referring to 1.78 % of the prescribed dose). Table 1 summarizes the calculated and measured doses in the rectum.

Conclusion

Empirical validation of dose distributions in prostate and rectum is feasible using 3D dosimetry gel and TLD dose measurements. This study describes a novel method for absolute 3D dosimetry in a complex anthropomorphic phantom.