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TH‐D‐210A‐09: Correlation Between Abdominal Organ Motion and An External Marker Toward Respiratory‐Gated Intensity‐Modulated Radiation Therapy for Pancreatic Carcinoma
Author(s) -
Shiinoki T,
Narita Y,
Nakamura M,
Shibuya K,
Sawada A,
Matsuo Y,
Mizowaki T,
Ito A,
Hiraoka M
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3182711
Subject(s) - medicine , nuclear medicine , stent , abdomen , radiology , correlation , radiation therapy , displacement (psychology) , intensity (physics) , physics , mathematics , geometry , optics , psychology , psychotherapist
Purpose: To attain the respiratory‐gated intensity‐modulated radiotherapy (IMRT) for pancreatic carcinoma by using an external marker as a surrogate for tumor motion, the correlation between a motion of an external marker and displacement of a stent around pancreas was investigated. Methods and Materials: Three patients who had undergone the ERCP for biliary decompression with placement of a stent were applied in this study. An anterior‐posterior motion of an external marker placed on the patient's abdomen was monitored by the Varian® RPM system for two minutes, this was synchronously displayed on the X‐ray fluoroscopic screen which acquired the stent's superior‐inferior displacement. For each patient, the above measurement was performed at four sessions during the treatment course. Both the displacements of an abdominal marker and a stent were automatically extracted by in‐house software based on the template‐matching algorithm. The cross‐correlation coefficients between displacement of an abdominal marker and a stent motion and their intra‐fractional variations were evaluated. The predicted stent positions at 30%, 40% and 50% of respiratory phase, which were traced the regression line from 0%‐phase (Exhalation), were compared with actual positions. Results: The correlation coefficients ( R 2 ) ranged from 0.77 to 0.97 and were inter‐fractionally reproducible. The predicted stent's positions at 30 %, 40 % and 50 % of respiratory phase were discrepant with actual positions with errors of 1.6 mm, 2.0 mm and 2.1 mm on average, respectively. Conclusions: The strong correlation between a motion of an external marker and a displacement of a stent around the pancreas was observed with a high reproducibility. An error of the predicted target position by an external marker was up to 3.1 mm for the expected‐gating duration (∼50 % respiratory phase) Our study demonstrated that the respiratory‐gated IMRT for pancreatic carcinoma may be clinically acceptable.