Prog Med Phys.  2014 Dec;25(4):242-247. 10.14316/pmp.2014.25.4.242.

Discrepancies between Calculated and Delivered Dose Distributions of Respiratory Gated IMRT Fields according to the Target Motion Ranges for Lung and Liver Cancer Patients

• Kim Y
• Lim S
• Choi JH
• Ma SY
• Jeung TS
• Ro TI

• KMID: 2315763
• DOI: http://doi.org/10.14316/pmp.2014.25.4.242

Abstract

To see the discrepancies between the calculated and the delivered dose distribution of IMRT fields for respiratory-induced moving target according to the motion ranges. Four IMRT plans in which there are five fields, for lung and liver patients were selected. The gantry angles were set to 0degrees for every field and recalculated using TPS (Eclipse Ver 8.1, Varian Medical Systems, Inc., USA). The ion-chamber array detector (MatriXX, IBA Dosimetry, Germany) was placed on the respiratory simulating platform and made it to move with ranges of 1, 2, and 3 cm, respectively. The IMRT fields were delivered to the detector with 30~70% gating windows. The comparison was performed by gamma index with tolerance of 3 mm and 3%. The average pass rate was 98.63% when there's no motion. When 1.0, 2.0, 3.0 cm motion ranges were simulated, the average pass rate were 98.59%, 97.82%, and 95.84%, respectively. Therefore, ITV margin should be increased or gating windows should be decreased for targets with large motion ranges.

Keyword

Gated radiation therapy; IMRT; Gamma index; Moving phantom

MeSH Terms

Humans
Liver
Liver Neoplasms*
Lung*

Figure

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  Fig. 1. To simulate the patients' respiratory motion, the moving platform was fabricated in laboratory. The solid water phantom with thickness of 1.3 cm and the MatriXX were placed on the simulating platform as shown figure. The SSD was 100 cm and the depth of measurement layer became 1.6 cm, which Dmax for 6 MV photon beams. We let the platform move with range of 0, 1, 2, and 3 cm and with cycle of 3.6 s.

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  Fig. 2. Example of five respiratory gated IMRT fields for case of A patient; the phantom simulated respiratory motion with four scenario (0, 1, 2, and 3 cm motion range and 3.6 s cycle). Gamma index were used with 3 mm/3% tolerance to compare calculated and measured dose distribution. White and black area in the figures represent pass and fail respectively.

Reference

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