Properties of unflattened photon beams shaped by a multileaf collimator

Journal Article · Thu Jun 15 04:00:00 EDT 2006 · Medical Physics

DOI:https://doi.org/10.1118/1.2201149· OSTI ID:20853187

Poenisch, Falk; Titt, Uwe; Vassiliev, Oleg N; Kry, Stephen F; Mohan, Radhe ^[1]

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1. Radiation Physics, University of Texas, M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Unit 94, Houston, Texas 77030 (United States)

Several studies have shown that removal of the flattening filter from the treatment head of a clinical accelerator increases the dose rate and changes the lateral profile in radiation therapy with photons. However, the multileaf collimator (MLC) used to shape the field was not taken into consideration in these studies. We therefore investigated the effect of the MLC on flattened and unflattened beams. To do this, we performed measurements on a Varian Clinac 21EX and MCNPX Monte Carlo simulations to analyze the physical properties of the photon beam. We compared lateral profiles, depth dose curves, MLC leakages, and total scatter factors for two energies (6 and 18 MV) of MLC-shaped fields and jaw-shaped fields. Our study showed that flattening filter-free beams shaped by a MLC differ from the jaw-shaped beams. Similar differences were also observed for flattened beams. Although both collimating methods produced identical depth dose curves, the penumbra size and the MLC leakage were reduced in the softer, unflattened beam and the total scatter factors showed a smaller field size dependence.

• OSTI ID: 20853187
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 6 Vol. 33; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
COLLIMATORS
COMPUTERIZED SIMULATION
DEPTH DOSE DISTRIBUTIONS
DOSE RATES
JAW
LINEAR ACCELERATORS
MONTE CARLO METHOD
PHOTON BEAMS
PHYSICAL PROPERTIES
RADIOTHERAPY