ESTRO 2024 - Abstract Book

S4807

Physics - Quality assurance and auditing

ESTRO 2024

Melidis C, Bosch WR, Izewska J, Fidarova E, Zubizarreta E, Ulin K, et al. Global Harmonization of Quality Assurance Naming Conventions in Radiation Therapy Clinical Trials. International Journal of Radiation Oncology*Biology*Physics. 2014 Dec;90(5):1242–9.

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Digital Poster

Evaluating the impact of MLC models and beam qualities on PSQA in lung SBRT plans.

Fadhilah Ibrahim, Tan Hongqi, Ng Yan Yee

National Cancer Centre Singapore, Division of Radiation Oncology, Singapore, Singapore

Purpose/Objective:

This study investigates the plan quality, plan complexities and deliverability of lung Stereotactic Body Radiation Therapy (SBRT) Volumetric Modulated Arc Therapy (VMAT) treatment plans under two different flattening-filter-free (FFF) beam qualities, 6FFF and 10FFF, and two different multi-leaf collimator (MLC) models, Millennium 120 and HDMLC.

Material/Methods:

5 patients with lung adenocarcinoma treated previously with 60Gy in 5 fractions were randomly selected for this study. The clinically treated plan was done with 6MV FFF and Millennium 120 on a Varian Truebeam by an experienced planner. Three additional plans were subsequently generated for each patient using 10FFF and HDMLC, 6FFF and HDMLC, 10FFF and Millennium 120 by the same planner with the same planning objectives to reduce inter-planner variability. Anisotropic analytical algorithm (AAA) was used for dose calculation. The plans were optimised in accordance with RTOG 0813 and 0915 guidelines. Plans were evaluated based on 1) dosimetric indices (normal tissuing sparing and target coverage), 2) plan complexity metrics of modulation complexity score (MSC), cross axis score (CAS), Monitor Units (MU) together with MLC Width and 3) deliverability quantified by gamma passing rate (GPR) measured using SNC Stereophan with SRS MapCheck using a True Composite measurement geometry (TG 218).

Results:

There were no statistically significant differences observed for the dose to organs at risk such as spinal cord, oesophagus, heart, trachea, bronchus, lungs and skin between the two beam qualities and the two MLC models. Additionally, the conformity index (CI) between these plans were similar and met the criteria (Refer to Table 1). The GPR and plan complexity results are shown in Table 2. No statistically significant difference was observed in the 2%/2mm and 3%/2mm GPR when comparing the beam qualities and MLC models. 6FFF have a statistically higher MU/Gy compared to 10FFF, which is typical and expected from the percentage depth dose of the energies. The plan complexity comparison between the two MLC models suggests that Millennium 120 yields slightly more complex plan with both MCS (P =0.0039) and CAS (P = 0.0020)) demonstrating statistical significance.