Abstract

CyberKnife is a robotic stereotactic body radiotherapy (SBRT) system that precisely delivers large radiation doses to a target. Tissue heterogeneity and shape can be problems. The treatment -planning system allows for use of the Monte Carlo (MC) or fundamental Ray Tracing (RyTc) algorithms for ultimate dose calculation. The MC is more accurate but consumes more computer resources and time. We compared radiation dose calculations for lung targets between the MC and RyTc algorithms. We placed a prosthetic marker at different thorax sites in a Rando phantom to compare the calculation results. The peripheral sites followed by the diaphragm showed the greatest significant differences in parameters for evaluating the treatment quality. For gross tumor volume dose, peripheral lung targets were the most critical for the calculation algorithm. The MC mean doses were lower than the RyTc mean doses and generally demonstrated better conformity. However, the deviation between conformal index (CI) and new CI at the peripheral location was large. The coverage differences between the RyTc and MC were most obvious at the peripheral lung site. The MC algorithm for radiation dose calculation in the lungs was indispensable in SBRT using CyberKnife for accurate dose evaluation, especially at the peripheral and diaphragm locations.

Highlights

  • Stereotactic radiosurgery is a precision form of radiation therapy that focuses energy on a small area of the body

  • The coverage percentages for the gross tumour volume (GTV) were 100% except for the lesion located at the periphery of the lung for both the Ray Tracing (RyTc) and Monte Carlo (MC) algorithms

  • A paired t-test for the treatment plan parameters demonstrated a significant difference in the mean GTV doses, minimal planning target volume (PTV) doses, mean PTV doses and the conformal index (CI) and new conformal index (nCI) of both the GTV and PTV(Table2)

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Summary

Introduction

Stereotactic radiosurgery is a precision form of radiation therapy that focuses energy on a small area of the body. With a Linac, the patient lies on a gantry and treatment couch that moves in space to change the radiation delivery angle. These treatments use a thermoplastic cast to fix the patient and align the x-ray beam for imaging. The cast is both comfortable for the patient and accurate, and radiosurgery can be used to treat body lesions, including fractionally, besides skull lesions

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