Abstract
IntroductionThe intracranial skull-base meningioma is in proximity to multiple critical organs and heterogeneous tissues. Steep dose gradients often result from avoiding critical organs in proton treatment plans. Dose uncertainties arising from setup errors under image-guided radiation therapy are worthy of evaluation.Patients and MethodsFourteen patients with skull-base meningioma were retrospectively identified and planned with proton pencil beam scanning (PBS) single-field uniform dose (SFUD) and multifield optimization (MFO) techniques. The setup uncertainties were assigned a probability model on the basis of prior published data. The impact on the dose distribution from nominal 1-mm and large, less probable setup errors, as well as the cumulative effect, was analyzed. The robustness of SFUD and MFO planning techniques in these scenarios was discussed.ResultsThe target coverage was reduced and the plan dose hot spot increased by all setup uncertainty scenarios regardless of the planning techniques. For 1 mm nominal shifts, the deviations in clinical target volume (CTV) coverage D99% was −11 ± 52 cGy and −45 ± 147 cGy for SFUD and MFO plans. The setup uncertainties affected the organ at risk (OAR) dose both positively and negatively. The statistical average of the setup uncertainties had <100 cGy impact on the plan qualities for all patients. The cumulative deviations in CTV D95% were 1 ± 34 cGy and −7 ± 18 cGy for SFUD and MFO plans.ConclusionIt is important to understand the impact of setup uncertainties on skull-base meningioma, as the tumor target has complex shape and is in proximity to multiple critical organs. Our work evaluated the setup uncertainty based on its probability distribution and evaluated the dosimetric consequences. In general, the SFUD plans demonstrated more robustness than the MFO plans in target coverages and brainstem dose. The probability-weighted overall effect on the dose distribution is small compared to the dosimetric shift during single fraction.
Highlights
The intracranial skull-base meningioma is in proximity to multiple critical organs and heterogeneous tissues
Physician-defined planning treatment volume (PTV) expands the clinical target volume (CTV) using a 5-mm margin, which can be reduced based on its extension into the organ at risk (OAR) and the extensiveness of the patientspecific disease
The min-max ranges of D0.03cc of brainstem among the 14 patients were [1278, 5657] cGy for single-field uniform dose (SFUD) plans and [1604, 5595] cGy for multifield optimization (MFO) plans; D0.03cc of optic nerves were [673, 5428] cGy for SFUD plans and [587, 5396] cGy for MFO plans; D0.03cc of optic chiasm were [3505, 5459] cGy for SFUD plans and [3703, 5408] cGy for MFO plans; D0.03cc of eyes were [~0, 5064] cGy for SFUD plans and [~0, 5099] cGy for MFO plan; D0.03cc/mean of the cochlea were [~0/0, 5507/5475] cGy for SFUD plans and [~0/0, 5503/5445] cGy for MFO plans
Summary
The intracranial skull-base meningioma is in proximity to multiple critical organs and heterogeneous tissues. Patients and Methods: Fourteen patients with skull-base meningioma were retrospectively identified and planned with proton pencil beam scanning (PBS) single-field uniform dose (SFUD) and multifield optimization (MFO) techniques. For 1 mm nominal shifts, the deviations in clinical target volume (CTV) coverage D99% was À11 6 52 cGy and À45 6 147 cGy for SFUD and MFO plans. Conclusion: It is important to understand the impact of setup uncertainties on skull-base meningioma, as the tumor target has complex shape and is in proximity to multiple critical organs. The SFUD plans demonstrated more robustness than the MFO plans in target coverages and brainstem dose. Proton pencil beam and dose painting methods were used for effective treatment of meningioma [16,17,18], where general dose reduction to brain, brainstem, and optic apparatus, as compared to IMRT plans, was observed
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