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Radiosurgery with unflattened 6-MV photon beams
P F O'Brien1, B A Gillies, M Schwartz
1Toronto-Bayview Regional Cancer Centre, Sunnybrook Health Science Centre, Ontario, Canada.
Medical Physics
|May 1, 1991
Summary
Removing the flattening filter from a linear accelerator significantly speeds up stereotactic radiosurgery. This modification doubles the dose rate, reducing lengthy treatment times for cranial radiation therapy.
Area of Science:
- Medical Physics
- Radiation Oncology
Background:
- Stereotactic radiosurgery (SRS) using linear accelerators (LINACs) is challenged by prolonged treatment delivery times.
- High single doses (e.g., 25 Gy) for cranial SRS can exceed 15 minutes with standard LINAC dose rates (250 cGy/min).
Purpose of the Study:
- To investigate the feasibility of reducing SRS treatment time by modifying a LINAC.
- To evaluate the dosimetric characteristics of a flattened filter-free (FFF) beam for SRS applications.
Main Methods:
- A flattening filter was removed from an AECL Therac-6 linear accelerator.
- The resultant beam's characteristics, including flatness and dose rate, were measured.
- The modified LINAC was assessed for suitability in stereotactic radiosurgery.
Main Results:
- The modified linear accelerator demonstrated an increased dose rate by a factor of 2.75.
- The beam's flatness remained acceptable for the field sizes typically used in stereotactic radiosurgery.
- Treatment times can be substantially reduced.
Conclusions:
- Removing the flattening filter is a viable method to increase LINAC dose rate for SRS.
- This modification offers a practical approach to decrease treatment times in cranial radiosurgery.
- FFF beams are suitable for SRS, improving efficiency without compromising essential beam characteristics.