The effects of using the aperture shape controller feature of photon optimizer algorithm in optimization of volumetric modulated ARC therapy plans in radiotherapy

Aim: In this study, it was aimed to investigate the effect of using "Aperture Shape Controller" (ASC) feature in the optimization with "Photon Optimizer" (PO) algorithm in "Volumetric Modulated Arc Therapy" (VMAT) RT plans of head and neck, lung, and prostate cancer patients in terms of treatment plan quality (TPQ), treatment delivery efficiency (TDE), and agreement between calculated and delivered dose distribution (QA). Hypothesis: The use of ASC feature in optimization will be superior in terms of TPQ, TDE, and QA. Material-Method: A total of 36 patients (each 12 with head and neck, lung, and prostate cancer) with a definitive RT plan were selected as the study group. Treatment plans were reprepared with full VMAT technique and optimized with the PO algorithm. In each case, optimization was performed by selecting 3 different levels of ASC feature (1. off, 2. medium, 3. very high). In order to test the dosimetric acceptability of each RT plan prepared, patient-specific Quality Assurance (QA) was evaluated with "ArcCheck". Comparisons of different ASC levels were performed using "Wilcoxon Signed-Rank" test (two related samples test) in terms of TPQ (Homogeneity Index (HI), OAR dose-volume parameters (DVP)), TDE (Average Open Aperture (AA), Modulation Complexity Score (MCS), Total Monitor Unit (MU)), and QA. Results: TPQ: The most homogeneous dose distribution in terms of HI for all PTVs in head and neck and prostate cancer is provided when the ASC level was off. OAR: As the ASC level was changed, significant differences were observed in the DVPs of brainstem, right cochlea, total parotid, right parotid, left and right optic nerve, lung, intestine, left femoral head and bladder. TDE: There was a significant difference only in MCS in head and neck cancer while in AA, MCS and total MU values in lung and prostate cancers.4 Conclusion: In the VMAT planning of patients with head and neck, lung and prostate cancer, the use of very high level of ASC is more favorable compared to the closed + medium level in terms of TDE and QA.