Publication: Investigation of gamma index parameters in patient specific quality assurance (PSQA) for radiotherapy treatment planning technique: retrosective study
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Date
2024-06
Authors
Mukhtar, Siti Yuni Sara
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Abstract
The patient specific quality assurance (PSQA) is a pre-treatment procedure performed to evaluate the validity of the inversed treatment plans, before the actual radiotherapy (RT) treatment delivery, to ensure the patient’s safety. The current method applied for the PSQA assessment in Hospital Universiti Sains Malaysia (HUSM) department is the ArcCHECK phantom based measurement using 3%/3mm gamma index (GI) analysis and currently, there is no standard procedure to perform the PSQA assessment. The aim of this study is to investigate the GI parameters (3%/3mm, 3%/2mm, 2%/2mm, 2%/1mm and 1%/1mm) in Volumetric modulated arc therapy (VMAT), intensity-modulated radiation therapy (IMRT) and Stereotactic body radiation therapy (SBRT) across various treatment regions retrospectively. The gamma passing rate (GPR) of 95% is the universal tolerance limit provide by the American Association of Physicist in Medicine Task Group 218 (AAPM TG-218). The GPR result indicated the PSQA cases were able to fulfill the 95% limit when 3%/3mm 3%/2mm and 2%/2mm GI parameter were applied with the result of 92.5% (99 cases), 100% (29 cases) and 87.5% (14 cases) for 3%/3mm, 82 cases (82.8%),18 cases (62.1%) and 8 cases (57.1%) for 3%/2mm, meanwhile for 2%/2mm, 46 cases (46.5%), 6 cases (20.7%) and 6 cases (42.9%) respectively for VMAT, IMRT and SBRT. Consequently, the GPR tolerance limit were also evaluated and reflected that 3%/2mm (≥95%), and 2%/2mm (>90%) is applicable for IMRT, VMAT and SBRT as the tolerance limit aligns with the suggestion by the previous study. Subsequently, The GPR tolerance limit for different treatment technique indicates a significant difference (p<0.05) in tolerance limit between IMRT and VMAT when applied using 3%/2mm (≥97.19%) and (≥94.85%), 2%/2mm (≥93.74%) and (≥90.39%). Moreover, The GPR tolerance limit for different treatment region reflect a significant different (p<0.05) when VMAT 3%/2mm is applied for HN (≥97 %), Pelvic (≥ 96%) and Chest (≥ 98%). In conclusion this study proves that apart from 3%/3mm (≥95%), 3%/2mm (≥95%) and 2%/2mm (>90%) are suitable for IMRT, VMAT and SBRT cases for all treatment region to be applied in HUSM, except for IMRT and VMAT when applied on HN region, as well as for VMAT when applied on HN, pelvic and chest region using 3%/2mm.