Prog Med Phys.  2015 Dec;26(4):250-257. 10.14316/pmp.2015.26.4.250.

Development of Manual Multi-Leaf Collimator for Proton Therapy in National Cancer Center

• Lee N
• Kim TY
• Kang DY
• Choi JH
• Jeong JH
• Shin D
• Lim YK
• Park J
• Kim TH
• Lee SB

• KMID: 2151759
• DOI: http://doi.org/10.14316/pmp.2015.26.4.250

Abstract

Multi-leaf collimator (MLC) systems are frequently used to deliver photon-based radiation, and allow conformal shaping of treatment beams. Many proton beam centers currently make use of aperture and snout systems, which involve use of a snout to shape and focus the proton beam, a brass aperture to modify field shape, and an acrylic compensator to modulate depth. However, it needs a lot of time and cost of preparing treatment, therefore, we developed the manual MLC for solving this problem. This study was carried out with the intent of designing an MLC system as an alternative to an aperture block system. Radio-activation and dose due to primary proton beam leakage and the presence of secondary neutrons were taken into account during these iterations. Analytical calculations were used to study the effects of leaf material on activation. We have fabricated tray model for adoption with a wobbling snout (30x40 cm2) system which used uniform scanning beam. We designed the manual MLC and tray and can reduce the cost and time for treatment. After leakage test of new tray, we upgrade the tray with brass and made the safety tool. First, we have tested the radio-activation with usually brass and new brass for new manual MLC. It shows similar behavior and decay trend. In addition, we have measured the leakage test of a gantry with new tray and MLC tray, while we exposed the high energy with full modulation process on film dosimetry. The radiation leakage is less than 1%. From these results, we have developed the design of the tray and upgrade for safety. Through the radio-activation behavior, we figure out the proton beam leakage level of safety, where there detects the secondary particle, including neutron. After developing new design of the tray, it will be able to reduce the time and cost of proton treatment. Finally, we have applied in clinic test with original brass aperture and manual MLC and calculated the gamma index, 99.74% between them.

Keyword

Proton treatment; Manual multileaf collimator

MeSH Terms

Film Dosimetry
Neutrons
Proton Therapy*
Protons*
Protons

Figure

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  Fig. 1. Brass aperture and snout in national cancer center. (a) Brass aperture for proton therapy and (b) Snout of proton therapy center (IBA, PROTEIS 235) in NCC.

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  Fig. 2. Designed manual MLC and adaptor. (a) Design of manual multi-leaf collimator (MLC) which made by brass leaf and (b) manual MLC with wobbling snout (30 cm×40 cm).

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  Fig. 3. Radio-activation test. Equivalent dose rate vs. time (a) Al, brass (Cu57%-Zn39%) block and leaves brass (Cu60%-Zn37%) and (b) radio-activation test for reuse of brass (Cu 60%-Zn 37%).

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  Fig. 4. Proton beam leakage test. (a) Set up for leakage test at surface, (b) measurement results of films at surface, (c) line profile of vertical direction and (d) line profile of horizontal direction at surface. (e) Set up for leakage test at mid of SOBP, (f) result of film at mid of SOBP, (g) line profile of vertical direction and (h) line profile of horizontal direction at mid of SOBP.

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  Fig. 5. Treatment planning system. Brass aperture (a) general block and (b) manual MLC, (c) Dose volume histogram (DVH) between brass aperture and manual MLC (eclipse, V. 10.0).

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  Fig. 6. Gamma index analysis between brass aperture and manual MLC. (a) general brass aperture and (b) manual MLC, and (c) gamma index between (a) and (b). 99.7% (RIT113, v.5.2).

Reference

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