Improved linac dose distributions for radiosurgery with elliptically shaped fields

Area of Science:

• Medical Physics
• Radiation Oncology
• Neurosurgery

Background:

• Stereotactic radiosurgery (SRS) commonly uses circular radiation fields from linear accelerators, aiming for spherical dose distributions.
• Irregularly shaped target volumes in SRS can lead to unintended irradiation of surrounding healthy tissues with high doses.
• Current SRS techniques involve multiple target points and optimized dose per arc to improve dose distribution.

Purpose of the Study:

• To evaluate the efficacy of elliptical radiation fields in SRS for improving dose distribution.
• To determine if elliptical fields can better conform radiation to irregular target volumes compared to traditional circular fields.
• To quantify the reduction in high-dose volume to normal tissues using elliptical SRS fields.

Main Methods:

• A retrospective review of 20 radiosurgery patients was conducted.
• Film measurements were performed using elliptical and circular radiation beams in a head phantom to assess dose distribution.
• Comparison of radiation dose distribution between elliptical and circular fields was analyzed.

Main Results:

• Elliptical radiation fields demonstrated a superior match to intended target volumes, particularly for irregular shapes.
• A significant reduction of 40% in the high-dose volume to surrounding tissues was achieved with elliptical fields.
• The therapeutic dose to the target volume was maintained without compromise when using elliptical fields.

Conclusions:

• Elliptical radiation fields represent a promising advancement in stereotactic radiosurgery technique.
• This method offers improved normal tissue sparing for irregular target volumes, enhancing treatment safety.
• Elliptical fields provide a more conformal dose distribution, potentially improving treatment outcomes in SRS.