Dosimetric verification of SRS/SBRT planning for spinal metastases using conventional QA devices and discussion of existing problems(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2021年第12期
- Page:
- 1464-1471
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Dosimetric verification of SRS/SBRT planning for spinal metastases using conventional QA devices and discussion of existing problems
- Author(s):
- GUO Yixiao1; LIU Zhiqiang 2; LI Hongyan3; FENG Weigui 1; ZHANG Zhiyuan 1; LI Shuping1
- 1. Department of Radiation Oncology, Gansu Provincial Hospital, Lanzhou 730000, China 2. Radiation Medicine Center, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China 3. Key Laboratory of Heavy Ion Radiation Biology and Medicine, Chinese Academy of Sciences, Lanzhou 730000, China
- Keywords:
- Keywords: spinal metastases asi-1200 EPID Octavius 1500 dosimetric verification transmission factor dosimetric leaf gap
- PACS:
- R811.1
- DOI:
- DOI:10.3969/j.issn.1005-202X.2021.12.003
- Abstract:
- Abstract: Objective To compare the applications of asi-1200 EPID and Octavius 1500 matrix in the dosimetric verification for 6 MV flattening filter free plan of spinal metastases, and to explore potential problems. Methods Under global normalization, a total of 23 plans were evaluated by 2D gamma passing rates (GPR) at different criteria with different thresholds, and the patient data from treatment planning system (TPS) were imported into Verisoft software for dose reconstruction. Errors of different types and magnitudes including the errors from MLC transmission factor (TF), dosimetric leaf gap (DLG), treatment iso-center and MU were introduced. The sensitivity of Octavius 1500 matrix indentifying these errors was quantified by GPR method, and the clinical significance of TF and DLG errors was studied by evaluating the dosimetric deviations of target areas and organs-at-risk (OAR). Results Compared with Octavius 1500 matrix, EPID had a higher mean GPR at the same criteria with different thresholds and achieved a smaller dispersion degree of data. The dose-volume histogram (DVH) analysis between reconstruction and calculation showed that the percentage dose differences (DD%) of the minimum dose (Dmin), maximum dose (Dmax) and mean dose (Dmean) to clinical target volume (CTV) and planning target volume (PTV) were relatively larger, in which the maximum DD% of CTV were 50.00%, 11.31% and 8.71%, respectively, and the maximum DD% of PTV were -25.86%, 9.31% and -8.22%, respectively. Errors from treatment iso-centor and MU of +3%, +5% could be detected. TF error couldnt be detected at all criteria, and only +0.3 mm DLG error was detectable at 2%/3 mm criteria. A 0.023 6％increase of TF and +0.3 mm DLG error resulted in dose increase to target areas and OAR, among which the dose increase of OAR was obvious, especially V20 of the healthy lungs which was increased by 9.80% and 8.85%, and D0.1 cc to the spinal cord which was increased by 5.35%. Conclusion The inadequate reliability of using GPR to distinguish error-introducing MLC models suggests that more effective independent quality assurance methods are needed to identify the root cause of TPS problems, thereby ensuring the confidence of steep dose gradients calculated by TPS. The independent verification research on software algorithms of the dosimetric verification system is necessary for determining the uncertainty of reconstructed dose due to algorithm limits.
Last Update: 2021-12-24