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Erschienen in:
06.04.2017 | Technical Note
Modifying the planning target volume to optimize the dose distribution in dynamic conformal arc therapy for large metastatic brain tumors
Erschienen in: Japanese Journal of Radiology | Ausgabe 6/2017
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Purpose
When treating large metastatic brain tumors with stereotactic radiotherapy (SRT), high dose conformity to target is difficult to achieve. Employing a modified planning target volume (mPTV) instead of the original PTV may be one way to improve the dose distribution in linear accelerator-based SRT using a dynamic conformal technique. In this study, we quantitatively analyzed the impact of a mPTV on dose distribution.
Materials and methods
Twenty-four tumors with a maximum diameter of >2 cm were collected. For each tumor, two plans were created: one used a mPTV and the other did not. The mPTV was produced by shrinking or enlarging the original PTV according to the dose distribution in the original plan. The dose conformity was evaluated and compared between the plans using a two-sided paired t test.
Results
The conformity index defined by the Radiation Therapy Oncology Group was 1.34 ± 0.10 and 1.41 ± 0.13, and Paddick’s conformity index was 0.75 ± 0.05 and 0.71 ± 0.06, for the plans with and without a mPTV, respectively. All of these improvements were statistically significant (P < 0.05).
Conclusion
The use of a mPTV can improve target conformity when planning SRT for large metastatic brain tumors.