Beam shaping for conformal fractionated stereotactic radiotherapy: a modeling study

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Fractionated stereotactic radiotherapy (SRT) presents unique challenges due to larger, less spherical lesions in critical CNS regions.
• Existing circular collimators may not optimally conform to these complex target shapes.

Purpose of the Study:

• To evaluate a simple, cost-effective beam shaping system using four independent jaws for conformal therapy in SRT.
• To compare its effectiveness against circular collimators and an ideal dynamically conforming system.

Main Methods:

• Modeled conformal arc therapy with a four-jaw system, adjusting jaw positions and collimator angles between arcs.
• Re-planned 11 SRT cases and compared tissue sparing at various dose levels (100%, 80%, 50%, 20%) against circular collimator plans and ideal conformal plans.

Main Results:

• Rectangular jaw plans reduced mean healthy tissue volume at the prescription dose by 57% compared to circular collimators for tumors >3.5 cm.
• Ideal conformal plans showed no significant further improvement at the prescription dose.
• At lower doses (20%), rectangular jaws offered equivalent sparing to circular collimators, while ideal plans provided better sparing.

Conclusions:

• The simple rectangular jaw system provides the beam shaping benefits of an ideal system at the prescription dose.
• This system offers significant advantages over circular collimators in high-dose regions for SRT.
• It is readily implementable in clinics and performs comparably to circular collimators in low-dose regions.