Prog Med Phys.  2014 Jun;25(2):79-88. 10.14316/pmp.2014.25.2.79.

Evaluation of Dose Distributions Recalculated with Per-field Measurement Data under the Condition of Respiratory Motion during IMRT for Liver Cancer

• Song JY
• Kim YH
• Jeong JU
• Yoon MS
• Ahn SJ
• Chung WK
• Nam TK

• KMID: 1708174
• DOI: http://doi.org/10.14316/pmp.2014.25.2.79

Abstract

The dose distributions within the real volumes of tumor targets and critical organs during internal target volume-based intensity-modulated radiation therapy (ITV-IMRT) for liver cancer were recalculated by applying the effects of actual respiratory organ motion, and the dosimetric features were analyzed through comparison with gating IMRT (Gate-IMRT) plan results. The ITV was created using MIM software, and a moving phantom was used to simulate respiratory motion. The doses were recalculated with a 3 dose-volume histogram (3DVH) program based on the per-field data measured with a MapCHECK2 2-dimensional diode detector array. Although a sufficient prescription dose covered the PTV during ITV-IMRT delivery, the dose homogeneity in the PTV was inferior to that with the Gate-IMRT plan. We confirmed that there were higher doses to the organs-at-risk (OARs) with ITV-IMRT, as expected when using an enlarged field, but the increased dose to the spinal cord was not significant and the increased doses to the liver and kidney could be considered as minor when the reinforced constraints were applied during IMRT plan optimization. Because the Gate-IMRT method also has disadvantages such as unsuspected dosimetric variations when applying the gating system and an increased treatment time, it is better to perform a prior analysis of the patient's respiratory condition and the importance and fulfillment of the IMRT plan dose constraints in order to select an optimal IMRT method with which to correct the respiratory organ motional effect.

Keyword

Respiratory organ motion; IMRT; Internal target volume (ITV); Gating system; 3DVH

MeSH Terms

Kidney
Liver
Liver Neoplasms*
Prescriptions
Spinal Cord

Figure

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  Fig. 1. MapCHECK2 laid on the dynamic moving phantom for the per-field measurement of ITV-IMRT under the condition of respiratory motion.

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  Fig. 2. Diagram of the overall study process.

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  Fig. 3. Example of PTV and OARs in ITV-IMRT plan delineated in MIM program reflecting the respiratory motional effect.

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  Fig. 4. Volume increase rate of PTV and OARs in ITV-IMRT plan compared with the volume in Gate-IMRT plan.

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  Fig. 5. Example of the DVH comparison between the recalculated dose in the ITV-IMRT beam delivery and the DVH of Gate-IMRT plan.

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  Fig. 6. Differences of PTV's DVH values between the ITV-IMRT beam delivery and Gate-IMRT plan at the major points.

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  Fig. 7. Comparison of homogeneity index (HI) between the beam delivery of ITV-IMRT and Gate-IMRT plan.

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  Fig. 8. Differences of liver's DVH values between the ITV-IMRT beam delivery and Gate-IMRT plan at the major points.

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  Fig. 9. Differences of kidney's DVH values between the ITV-IMRT beam delivery and Gate-IMRT plan at the major points. (a) Left kidney. (b) Right kidney.

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  Fig. 10. Differences of maximum dose and mean dose of spinal cord between the ITV-IMRT beam delivery and Gate-IMRT plan.

Reference

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