pmp Progress in Medical Physics Progress in Medical Physics 2508-4445 2508-4453 Korean Society of Medical Physics 10.14316/pmp.2019.30.1.14 pmp-30-14 Original Article Initial Experience of Patient-Specific QA for Wobbling and Line-Scanning Proton Therapy at Samsung Medical Center JoKwanghyun AhnSung Hwan ChungKwangzoo ChoSungkoo ShinEun Hyuk ParkSeyjoon HonChae-Seon KimDae-Hyun LeeBoram LeeWoojin ChoiDoo Ho LimDo Hoon PyoHong Ryull HanYoungyih Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea Corresponding author Youngyih Han (youngyih@skku.edu) Tel: 82-2-3410-2604 Fax: 82-2-3410-2619 032019 19032019 30114 21 14122018 12032019 12032019 Copyright © 2019 Korean Society of Medical Physics 2019 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 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.

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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.

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.

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.

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%).

Patient statistics of wobbling and line-scanning proton therapy at Samsung Medical Center.

  Brain Eyeball H&N Thorax Pelvis Prostate CSI Liver Abd Spine Total
Wobbling
  Field 38 8 13 21 10 4   110 19 4 227
  Patient 14 3 6 9 5 2   36 12 2 89
  % of total field 16.7% 3.5% 5.7% 9.3% 4.4% 1.8%   48.5% 8.4% 1.8%  
Scanning
  Field 25 2 31 12 4 4 40       118
  Patient 11 1 13 6 2 2 9       44
  % of total field 21.2% 1.7% 26.3% 10.2% 3.4% 3.4% 33.9%        

H&N, head and neck; CSI, Cranio-Spinal Irradiation; Abd, abdomen.