GTV-based prescription in SBRT for lung lesions using advanced dose calculation algorithms

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Stereotactic body radiation therapy (SBRT) for lung lesions presents challenges in dose prescription.
• Advanced dose calculation algorithms, specifically type B (including electron transport), offer greater accuracy than type A algorithms.
• Type A algorithms tend to overestimate dose in lung lesions due to neglecting secondary electron transport, while type B algorithms lack standardized prescription protocols.

Purpose of the Study:

• To investigate optimal dose prescription methods for lung lesions during SBRT using type B dose calculation algorithms.
• To evaluate the impact of secondary electron transport on dose distribution and prescription accuracy.
• To establish a robust and consistent SBRT dose prescription strategy for lung lesions.

Main Methods:

• Dose calculation experiments were performed on three peripheral lung lesion cases of varying sizes across three treatment platforms.
• Prescription doses were evaluated using both type A and type B algorithms, with recalculations to assess secondary electron transport effects.
• Different prescription strategies were tested, including PTV-based and GTV dose-volume-based prescriptions.

Main Results:

• Prescribing to the PTV with a type A algorithm resulted in <10% median GTV dose variation across platforms and cases.
• Prescribing to the PTV with a type B algorithm showed higher variability (24-28%) in median GTV dose.
• Prescribing a median GTV dose of 54 Gy using a type B algorithm minimized observed dose variability.

Conclusions:

• Normalizing SBRT prescription dose to the median GTV dose for lung lesions effectively reduces inter-case and inter-platform variability when using type B algorithms.
• A combined approach, using type A for PTV optimization and type B for GTV median dose prescription, offers a robust SBRT treatment method for lung lesions.