Prog Med Phys.  2019 Mar;30(1):14-21. 10.14316/pmp.2019.30.1.14.

Initial Experience of Patient-Specific QA for Wobbling and Line-Scanning Proton Therapy at Samsung Medical Center

• Jo K
• Ahn SH
• Chung K
• Cho S
• Shin EH
• Park S
• Hong CS
• Kim DH
• Lee B
• Lee W
• Choi DH
• Lim DH
• Pyo HR
• Han Y

• KMID: 2442417
• DOI: http://doi.org/10.14316/pmp.2019.30.1.14

Abstract

PURPOSE
To report the initial experience of patient-specific quality assurance (pQA) for the wobbling and line-scanning proton therapy at Samsung Medical Center.
MATERIALS AND METHODS
The pQA results of 89 wobbling treatments with 227 fields and 44 line-scanning treatments with 118 fields were analyzed from December 2015 to June 2016. For the wobbling method, proton range and spread-out Bragg peak (SOBP) width were verified. For the line-scanning method, output and two-dimensional dose distribution at multiple depths were verified by gamma analysis with 3%/3 mm criterion.
RESULTS
The average range difference was −0.44 mm with a standard deviation (SD) of 1.64 mm and 0.1 mm with an SD of 0.53 mm for the small and middle wobbling radii, respectively. For the line-scanning method, the output difference was within ±3%. The gamma passing rates were over 95% with 3%/3 mm criterion for all depths.
CONCLUSIONS
For the wobbling method, proton range and SOBP width were within the tolerance levels. For the line-scanning method, the output and two-dimensional dose distribution showed excellent agreement with the treatment plans.

Keyword

Proton therapy; Patient specific QA; Wobbling; Line-scanning

MeSH Terms

Methods
Proton Therapy*
Protons*
Protons

Figure

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  Fig. 1 One dimensional profile of wobbling beam is presented as an example. (a) The Gaussian beam size is small, the wobbling radius is small. (b) The Gaussian beam size is large, wobbling radius is large. The amplitude is normalized by the initial amplitude of Gaussian beam. The wobbling radius is fine-tuned in order to make flat central region.

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  Fig. 2 The difference of range and the SOBP width between the measurement and plan for a small WR and middle WR. (a, b) The difference in range for a small (middle) WR. (c, d) The difference in the SOBP width for a small (middle) WR. WR, wobbling radius; SOBP, spread out Bragg peak.

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  Fig. 3 The output difference between measurement depth and plan as a function of various factors. (a) Long-side field radius vs. output difference, (b) The histogram of output difference, (c) measurement depth vs. output difference, (d) The energy of the first layer with and without range shifter vs. output difference. Blue circle: field size <11 cm, red asterisk: field size >11 cm. Blue-plus sign, with range shifter; black diamond, without range shifter.

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  Fig. 4 Gamma index for line-scanning at three depths as a function of field radius. (a) shallow depth, (b) middle depth, (c) deep depth (Blue circle: gamma criterion of 3 mm/3%).

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