Measurement Techniques, Modeling Strategies and Pitfalls to Avoid when Implementing a Mini MLC in a Non Dedicated Planning System*

Abstract

The overall accuracy of the collapsed cone algorithm is within tolerances for single fraction stereotactic treatments.

Leakage reduction for the Siemens ModuLeaf

“…Nor did they report any problems with beam modeling in their treatment planning system. This was also the case for other reports on the ModuLeaf, and may be due to its use with other linear accelerators, ( 10 – 11 ) leakage films that were limited to , (1) , (12) different mounting methods, (1) , (12) or other planning systems (12) . The unusual leakage pattern we observed cost us many man‐hours of work that we could have saved if we had known its effects prior to commissioning.…”

NCS Report 22: Code of practice for the quality assurance and control for intensity modulated radiotherapy

“…Issues with leaf speed can also be monitored in the log files or are indicated by excessive beam holds. Leaf acceleration and deceleration have a negligible effect on the delivered intensity profiles (25,26).…”

“…• As the beam shape is made smaller, the total photon energy spectrum shifts to a spectrum determined by the thickness of the flattening filter (22,26) • The photon fluence will decrease with smaller fields due to the partial covering of the effective spot size (81) • The photon fluence will decrease with smaller fields due to the scattering in the flattening filter (81)…”

NCS Report 25: Process management and quality assurance for intracranial stereotactic treatment

“…Tolerances of 2 mm and 2% are often quoted [27,51,130], except for field sizes below 1x1 cm² where 5-6% dose differences are tolerated. Most recommendations of NCS15 remain valuable for the stereotactic treatment planning system, but the distance to agreement for individual beams is reduced to 1 mm or better [51,126]. Please notice that important issues on TPS are also handled in Chapter 6 of his report.…”