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. 2015 Apr 10;7(2):617-30.
doi: 10.3390/cancers7020617.

Predictive Risk of Radiation Induced Cerebral Necrosis in Pediatric Brain Cancer Patients after VMAT Versus Proton Therapy

Derek Freund  1   2 , Rui Zhang  3   4 , Mary Sanders  5 , Wayne Newhauser  6   7
Affiliations

Predictive Risk of Radiation Induced Cerebral Necrosis in Pediatric Brain Cancer Patients after VMAT Versus Proton Therapy

Derek Freund et al. Cancers (Basel). .

Abstract

Cancer of the brain and central nervous system (CNS) is the second most common of all pediatric cancers. Treatment of many of these cancers includes radiation therapy of which radiation induced cerebral necrosis (RICN) can be a severe and potentially devastating side effect. Risk factors for RICN include brain volume irradiated, the dose given per fraction and total dose. Thirteen pediatric patients were selected for this study to determine the difference in predicted risk of RICN when treating with volumetric modulated arc therapy (VMAT) compared to passively scattered proton therapy (PSPT) and intensity modulated proton therapy (IMPT). Plans were compared on the basis of dosimetric endpoints in the planned treatment volume (PTV) and brain and a radiobiological endpoint of RICN calculated using the Lyman-Kutcher-Burman probit model. Uncertainty tests were performed to determine if the predicted risk of necrosis was sensitive to positional errors, proton range errors and selection of risk models. Both PSPT and IMPT plans resulted in a significant increase in the maximum dose to the brain, a significant reduction in the total brain volume irradiated to low doses, and a significant lower predicted risk of necrosis compared with the VMAT plans. The findings of this study were upheld by the uncertainty analysis.

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Figures

Figure 1
Figure 1
Alternative risk models used to test the sensitivity of rNTCP to the shape of the model used. LNT is the linear no-threshold model, LT is the linear threshold model, LP(60) is the linear plateau model, and LQ is the linear quadratic model.
Figure 2
Figure 2
Patient 5 isodose distribution at isocenter CT slice location for (a) volumetric modulated arc therapy (VMAT), (b) passively scattered proton therapy (PSPT), and (c) intensity modulated proton therapy (IMPT).
Figure 3
Figure 3
The dose volume histograms (DVH) for patient 5. VMAT plans are represented with the solid lines, PSPT with the dotted lines and IMPT with the dash-dot lines. Different regions of interest are represented with different colored lines.
Figure 4
Figure 4
(a) The conformity of the dose to the PTV represented by the conformity index (CI) for VMAT, PSPT, and IMPT plans. (b) The homogeneity of the dose to the PTV represented by the homogeneity index (HI) for VMAT, PSPT, and IMPT plans.
Figure 5
Figure 5
The maximum dose to the brain for VMAT, PSPT, and IMPT plans.
Figure 6
Figure 6
(a) The ratio of risk (rNTCP) for PSPT plans compared to VMAT for all patients. (b) The ratio of risk (rNTCP) for IMPT plans compared to VMAT for all patients. The average value of rNTCP represented by the red circle with standard deviation error bar.
Figure 7
Figure 7
(a) The change in rNTCP with isocenter shifts and (b) with ±10% calibration curve errors for patient 5. (c) The change in rNTCP with isocenter shifts and (d) with ±10% calibration curve errors for patient 12.
Figure 8
Figure 8
The ratio of risk of necrosis for (a) PSPT plans and (b) IMPT plans compared to VMAT plans, calculated with baseline Lyman Kutcher Burman (LKB) model, the linear no threshold (LNT), linear threshold (LT), linear quadratic (LQ), and linear plateau (LP) models.
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