IMRT patient-specific QA using the Delta4 dosimetry system and evaluation based on ICRU 83 recommendations

7th International Conference on 3D Radiation Dosimetry

Nilsson, J.^1 ; Hauer, A Karlsson^1 ; Bäck, A.^1

Department of Therapeutic Radiation Physics, Sahlgrenska University Hospital, Göteborg, Sweden^1

关键词: Absorbed dose distribution;    Dose distributions;    Measurements of;    Organs at risks;    Patient specific;    Tolerance levels;    Treatment planning systems;    Treatment plans;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/444/1/012048/pdf
DOI  :  10.1088/1742-6596/444/1/012048

来源: IOP

【 摘 要 】

Patient-specific IMRT QA is dependent on the dosimetry system and the evaluation procedure. The ICRU report 83 provides recommendations of tolerated deviations between measured and calculated absorbed dose distributions for QA of IMRT treatment plans. The result of doing IMRT patient-specific QA with the Delta4dosimetry system and using the ICRU recommendations for evaluation is studied. To be able to investigate the QA procedure the original IMRT treatment plans were modified in the treatment planning system to create calculated dose distributions with dosimetric deviations from the original treatment plans. The modified dose distributions were compared to the dose distributions from the Delta4measurements of the original treatment plans and the differences were evaluated with criteria and tolerance levels according to the recommendations from ICRU. The evaluation for all 28 modified dose distributions have gamma passing rates higher than the tolerance level recommended from ICRU and will therefore pass the patient-specific QA. More than half of the evaluations have a gamma passing rate of 100 %. Evaluation of the differences between the modified and the original calculated dose distributions revealed in several cases large unacceptable dose differences in the PTV volumes and the organs at risk, for example an increase in the near-maximum dose D2%to the spinal cord of 5.5 Gy. This study indicates that patient-specific QA with the Delta4dosimetry system and the ICRU recommendations for evaluation can not be used to distinguish differences between planned and measured dose of dosimetrical relevance.