Dosimetric Evaluation of the Aldo Function for Multiple Brain Metastases in Automated Stereotactic Radiosurgery Treatment Planning 📝

Author: Hsiao-Mei Fu, Shih-Ming Hsu, Chia-Ting Lee, Shih-Hua Liu, Tsung-Yu Yen 👨‍🔬

Affiliation: National Yang Ming Chiao Tung University, Mackay Memorial Hospital 🌍

Abstract:

Purpose: The Automatic Lower Dose Objective (ALDO) is a unique function designed to achieve 98% relative coverage across all targets in automated SRS treatment planning (HyperArc planning). This study examines the ALDO function in automated SRS planning for multiple brain metastases and its relationship with tumor distribution. A phantom-based approach was utilized to simulate tumors and analyze dose distribution.

Methods: Using CT images of a Rando phantom, two 1 cm spherical tumors were simulated with edge-to-edge distances of 1, 2, 3, 4, and 6 cm. Automated SRS plans (HyperArc) were generated with and without the use of the ALDO function, which does not allow for setting a maximum dose limitation. Dose distribution was analyzed using RTOG Conformity Index (CI), Paddick CI, Gradient Index (GI), and ICRU 83 Homogeneity Index (HI).

Results: Plans with ALDO demonstrate superior RTOG CI for individual tumors compared to non-ALDO plans (1.05-1.15 and 1.07-1.26, respectively). In terms of Paddick CI, ALDO plans show consistent performance across all distances, ranging from 0.74 to 0.76, while non-ALDO plans exhibited a wider range as 0.67 to 0.75. For GI, non-ALDO plans have a wider range compared to ALDO-plans (3.62-5.0 and 3.45-3.99, respectively). Regarding ICRU HI, non-ALDO plans display more uniformity due to a maximum dose constraint of 130%. In contrast, ALDO plans lack a maximum dose constraint, leading to hotspots of up to 158.9% of the prescribed dose for inter-tumor distances less than 3 cm.

Conclusion: The ALDO function facilitates improved dose gradients for each intracranial tumor in automated SRS planning. However, the absence of a maximum dose constraint can result in excessive hotspot doses inside tumor, particularly when inter-tumor distances are less than 3 cm. These findings underscore the need to balance dose conformity with hotspot management when utilizing the ALDO function for multiple brain metastases.

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