pmp Progress in Medical Physics Progress in Medical Physics 2508-4445 2508-4453 Korean Society of Medical Physics 10.14316/pmp.2017.28.2.54 pmp-28-54 Original Article Feasibility Study of Patient Specific Quality Assurance Using Transit Dosimetry Based on Measurement with an Electronic Portal Imaging Device BaekTae Seong ∗ ChungEun Ji ∗ SonJaeman † YoonMyonggeun † Department of Radiation Oncology, National Health Insurance Co. Ilsan Hospital, Goyang, Korea Department of Bio-convergence Engineering, Korea University, Seoul, Korea Corresponding author Myonggeun Yoon (radioyoon@korea.ac.kr) Tel: 82-2-3290-5651 Fax: 82-2-921-6434 62017 1762017 282 5460 30062017 10062017 10062017 Copyright © 2017 Korean Society of Medical Physics 2017 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. Abstract

This study was designed to measure transit dose with an electronic portal imaging device (EPID) in eight patients treated with intensity modulated radiotherapy (IMRT), and to verify the accuracy of dose delivery to patients. The calculated dose map of the treatment planning system (TPS) was compared with the EPID based dose measured on the same plane with a gamma index method. The plan for each patient was verified prior to treatment with a diode array (MapCHECK) and portal dose image prediction (PDIP). To simulate possible patient positioning errors during treatment, outcomes were evaluated after an anthropomorphic phantom was displaced 5 and 10 mm in various directions. Based on 3%/3 mm criteria, the mean±SD passing rates of MapCHECK, PDIP (pre-treatment QA) for 47 IMRT were 99.8±0.1%, 99.0±0.7%, and, respectively. Besides, passing rates using transit dosimetry was 90.0±1.5% for the same condition. Setup errors of 5 and 10 mm reduced the mean passing rates by 1.3% and 3.0% (inferior to superior), 2.2% and 4.3% (superior to inferior), 5.9% and 10.9% (left to right), and 8.9% and 16.3% (right to left), respectively. These findings suggest that the transit dose-based IMRT verification method using EPID, in which the transit dose from patients is compared with the dose map calculated from the TPS, may be useful in verifying various errors including setup and/or patient positioning error, inhomogeneity and target motions.

 Linear accelerator Transit dose EPID Gamma index REFERENCES Langer M Brown R Urie M Leong J Stracher M Shapiro J Large scale optimization of beam weights under dose-volume restrictions Int J Radiat Oncol Biol Phys. 199018 88793 Langer M Leong J Optimization of beam weights under dose-volume restrictions Int J Radiat Oncol Biol Phys. 198713 125560 Morrill SM Lane RG Wong JA Rosen II Dose‐volume considerations with linear programming optimization Med Phys. 199118 120110 Low DA Moran JM Dempsey JF Dong L Oldham M Dosimetry tools and techniques for imrt Med Phys. 201138 131338 Olch AJ Dosimetric performance of an enhanced dose range radiographic film for intensity-modulated radiation therapy quality assurance Med Phys. 200229 215968 Ma C Jiang S Pawlicki T Chen Y Li J Deng J A quality assurance phantom for imrt dose verification Phys Med Biol. 200348 561 Berry SL Sheu R-D Polvorosa CS Wuu C-S Implementation of epid transit dosimetry based on a through-air dosimetry algorithm Med Phys. 201239 8798 Saitoh H Fujisaki T Sakai R Kunieda E Dose distribution of narrow beam irradiation for small lung tumor Int J Radiat Oncol Biol Phys. 200253 138087 Van Esch A Depuydt T Huyskens DP The use of an asi-based epid for routine absolute dosimetric pre-treatment verification of dynamic imrt fields Radiother Oncol. 200471 22334 McDermott L Wendling M Van Asselen B Stroom J Sonke J-J Van Herk M Clinical experience with epid dosimetry for prostate imrt pre-treatment dose verification Med Phys. 200633 392130 Van Esch A Vanstraelen B Verstraete J Kutcher G Huyskens D Pre-treatment dosimetric verification by means of a liquid-filled electronic portal imaging device during dynamic delivery of intensity modulated treatment fields Radiother Oncol. 200160 18190 McDermott LN Wendling M Sonke J-J van Herk M Mijnheer BJ Replacing pretreatment verification with in vivo epid dosimetry for prostate imrt Int J Radiat Oncol Biol Phys. 200767 156877 Berry SL Polvorosa C Cheng S Deutsch I Chao KC Wuu C-S Initial clinical experience performing patient treatment verification with an electronic portal imaging device transit dosimeter Int J Radiat Oncol Biol Phys. 201488 20409 Oldham M Sakhalkar H Guo P Adamovics J An investigation of the accuracy of an imrt dose distribution using two-and three-dimensional dosimetry techniques Med Phys. 200835 207280 Sabet M Rowshanfarzad P Vial P Menk FW Greer PB Transit dosimetry in imrt with an a-si epid in direct detection configuration Phys Med Biol. 201257 N295 Baek TS Chung EJ Koh EK Seo J Yoon M Evaluation of the accuracy of dose delivery for imrt based on transit dosimetry Health Phys. 2014107 2005 Baek TS Chung EJ Son J Yoon M Feasibility study on the verification of actual beam delivery in a treatment room using epid transit dosimetry Radiat Oncol. 20149 273 Low DA Harms WB Mutic S Purdy JA A technique for the quantitative evaluation of dose distributions Med Phys. 199825 65661 Figures and Tables

EPID measurements of transit doses during treatment at the posterior surfaces of Patients (a) 1 (maxillary sinus) and (b) 3 (prostate).

Transit doses in field 3 from Patient 1 (a) calculated from TPS and (b) measured using EPID.

Dose maps calculated in field 3 of Patient 2 by (a) MapCHECK and (b) PDIP and measured by transit dosimetry at (c) 3%/3 mm and (d) 5%/3 mm.

Demographic and radiologic characteristics of the eight patients analyzed in this study.

Patient number Treatment Site Photon Energy PTV (ml) Number of fields IMRT delivery technique
1 Maxillary sinus 6 MV 130.3 7 DMLC
2 Cervix 6 MV 171.4 5 DMLC
3 Prostate 6 MV 101.6 7 DMLC
4 Eye 6 MV 86.4 5 DMLC
5 Lung 6 MV 154.5 5 DMLC
6 Brain 6 MV 235.3 5 DMLC
7 Oropharynx 6 MV 228.8 7 DMLC
8 Brain 6 MV 122 6 DMLC

DMLC: Dynamic Multileaf collimator.

Pre-treatment passing rates (%) of results measured with MapCHECK (M) and PDIP (P) based on the gamma index for the eight included patients.

Patient No. Field number
Dosimetric tool 1 2 3 4 5 6 7 Mean
1 M 100.0 99.8 100.0 100.0 99.7 97.7 100.0 99.6
  P 99.5 99.3 96.0 99.4 99.6 98.6 95.7 98.3
2 M 99.1 100.0 100.0 99.6 100.0     99.7
  P 99.9 96.9 99.7 99.9 99.9     99.3
3 M 100.0 99.8 100.0 98.9 100.0 99.8 100.0 99.8
  P 99.9 99.8 100.0 97.0 98.9 97.9 99.9 99.1
4 M 100.0 100.0 100.0 100.0 100.0     100.0
  P 99.9 98.7 100.0 98.4 99.9     99.4
5 M 99.8 100.0 99.1 100.0 100.0     99.8
  P 99.7 100.0 98.5 99.9 99.9     99.6
6 M 100.0 100.0 100.0 100.0 100.0     100.0
  P 99.9 99.9 100.0 99.9 99.9     99.9
7 M 98.9 100.0 99.8 100.0 99.4 100.0 99.8 99.7
  P 97.7 100.0 99.0 99.4 98.8 98.9 97.4 98.7
8 M 99.1 98.9 100.0 100.0 100.0 99.4   99.6
  P 96.4 95.8 95.2 99.8 98.8 98.7   97.5

Passing rates of results measured using transit dosimetry based on the gamma index values for the eight patients.

Patient Field number
No. t 1 2 3 4 5 6 7 Mean
1 3%/3 mm 90.0 83.1 90.5 92.4 93.3 88.0 89.6 89.6
2 3%/3 mm 95.1 86.7 94.9 86.5 85.4 - - 89.7
3 3%/3 mm 96.5 96.4 86.8 79.4 84.9 91.6 95.3 90.1
4 3%/3 mm 94.9 95.3 92.4 95.9 87.3 - - 93.2
5 3%/3 mm 89.2 87.9 82.7 94.0 86.5 - - 88.1
6 3%/3 mm 94.9 93.4 81.4 92.9 94.1 - - 91.3
7 3%/3 mm 89.6 92.9 90.0 91.8 87.2 87.6 86.4 89.4
8 3%/3 mm 96.2 88.0 89.7 86.4 86.9 82.5 - 88.3

Decreases in passing rates for phantom movement compared with the original passing rate without movement.

Patient number IS   SI   LR   RL  
5 mm 10 mm 5 mm 10 mm 5 mm 10 mm 5 mm 10 mm
1 1.8 4.1 3.0 6.5 5.3 9.7 7.6 13.6
2 0.9 3.8 2.3 3.3 6.3 12.3 10.0 19.0
3 1.8 2.8 2.5 4.7 7.0 12.7 9.9 18.4
4 1.5 2.7 1.7 4.2 5.2 9.4 8.0 14.4
5 0.7 1.7 1.3 2.6 5.7 10.5 9.0 16.0
Mean 1.3 3.0 2.2 4.3 5.9 10.9 8.9 16.3
SD 0.5 0.9 0.6 1.3 0.7 1.3 1.0 2.1