Planning Target Volume Margin in Linac-Based Stereotactic Radiosurgery for Brain Metastases
- 1 Department of Radiation Oncology, International Medical Center (IMC), Cairo, Egypt
- 2 Department of Radiation Oncology, International Medical Center (IMC), Cairo, Egypt
- 3 Department of Medical Physics, Al Azhar University, Cairo, Egypt
- 4 Department of Medical Physics, International Medical Center (IMC), Cairo, Egypt
- 5 Department of Radiation Oncology, International Medical Center (IMC), Cairo, Egypt
- 6 Department of Medical Physics, International Medical Center (IMC), Cairo, Egypt
- 7 Department of Medical Physics, Department of Clinical Oncology, Faculty of Medicine, Zagazig University, Zagazig, Egypt
- 8 Department of Medical Physics, Al Azhar University, Cairo, Egypt
- 9 Department of Radiation Oncology, Armed Forces Medical Collogue (AFCM), Cairo, Egypt
Abstract
Background: The treatment of brain metastases with radiotherapy has shifted to the use of Stereotactic Radio-surgery (SRS). The technical issue of expanding the treatment volume around the Gross Tumor Volume (GTV) is a current debate. Radiotherapy centers use variable GTV-PTV margins, ranging from one to 2 mm. Material and Methods : We performed a dosimetric comparison in plans of twenty patients using three margins: PTV zero, PTV1, and PTV2. We also developed imaginary Peel volumes. These volumes are described as follows: Peel1 = PTV1 − GTV, Peel2 = PTV2 − GTV. Results: Our results showed that the mean PTV volume differed significantly across the different margins (p = 0.000). The V12 of the brain significantly varied as a function of PTV margin (p = 0.000). The target coverage and plan quality indices were not significantly different. The Peel volume dosimetric analysis showed that the mean dose was significantly higher in the nearby normal brain tissue: Peel1 (p = 0.022) and Peel 2 (p = 0.013). Conclusion: According to our dosimetric analysis, expanding the GTV into a PTV by 1 mm margin is more convenient than 2 mm.
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