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Updated: Jan 21, 2026
Proton Therapy Delivery and Its Clinical Application in Select Solid Tumor Malignancies
Published on: February 6, 2019
Normal tissue complication probability models in plan evaluation of children with brain tumors referred to proton
Camilla H Stokkevåg1,2, Daniel J Indelicato3, Klaus Herfarth4
1Department of Oncology and Medical Physics, Haukeland University Hospital , Bergen , Norway.
Insights
Proton therapy (PT) significantly reduces radiation dose to healthy tissues in children with brain tumors compared to volumetric modulated arc therapy (VMAT). This leads to lower risks of long-term complications like auditory toxicity and secondary cancers.
Area of Science:
- Pediatric Oncology
- Radiation Oncology
- Medical Physics
Background:
- Children with brain tumors require radiotherapy, facing high risks of radiation-induced morbidity.
- Proton therapy (PT) is considered to minimize radiation dose to healthy tissues.
- Evaluating PT against volumetric modulated arc therapy (VMAT) using pediatric constraints and normal tissue complication probability (NTCP) models is crucial.
Purpose of the Study:
- To compare proton therapy (PT) and volumetric modulated arc therapy (VMAT) for pediatric brain tumors.
- To apply pediatric constraints and NTCP models to assess treatment differences.
- To evaluate the impact on various toxicity endpoints and secondary cancer risks.
Main Methods:
- Re-planning of 40 pediatric patients' VMAT using existing CT scans and target volumes.
- Comparison of delivered PT plans with re-planned VMAT plans.
- Analysis using dose/volume metrics and NTCP models for specific toxicities and secondary cancers.
Main Results:
- PT delivered lower mean doses to critical structures like hippocampi, cochleas, and optic nerves.
- Significant reductions in population median NTCP were observed for auditory toxicity, xerostomia, and secondary brain/salivary gland cancers with PT.
- PT showed a lower neurocognitive decline and reduced risk of secondary brain cancers compared to VMAT.
Conclusions:
- Proton therapy effectively reduces normal tissue exposure to radiation, especially at low-to-intermediate doses.
- PT demonstrates substantial reductions in NTCP for auditory complications, xerostomia, and secondary cancer risks.
- PT offers improved risk profiles for pediatric patients undergoing cranial radiotherapy.
Abstract:
Background: Children with brain tumors undergoing radiotherapy are at particular risk of radiation-induced morbidity and are therefore routinely considered for proton therapy (PT) to reduce the dose to healthy tissues. The aim of this study was to apply pediatric constraints and normal tissue complication probability (NTCP) models when evaluating the differences between PT and contemporary photon-based radiotherapy, volumetric modulated arc therapy (VMAT). Methods: Forty patients (aged 1-17 years) referred from Norwegian institutions to cranial PT abroad during 2014-2016 were selected for VMAT re-planning using the original CT sets and target volumes. The VMAT and delivered PT plans were compared by dose/volume metrics and NTCP models related to growth hormone deficiency, auditory toxicity, visual impairment, xerostomia, neurocognitive outcome and secondary brain and parotid gland cancers. Results: The supratentorial brain, temporal lobes, hippocampi, hypothalamus, pituitary glands, cochleas, salivary glands, optic nerves and chiasm received lower mean doses from PT. Reductions in population median NTCP were significant for auditory toxicity (VMAT: 3.8%; PT: 0.3%), neurocognitive outcome (VMAT: 3.0 IQ points decline at 5 years post RT; PT: 2.5 IQ points), xerostomia (VMAT: 2.0%; PT: 0.6%), excess absolute risk of secondary cancer of the brain (VMAT: 9.2%; PT: 6.7%) and salivary glands (VMAT: 2.8%; PT:0.5%). Across all patients, 23/38 PT plans had better or comparable estimated risks for all endpoints (within ±10% of the risk relative to VMAT), whereas for 1/38 patients all estimates were better or comparable with VMAT. Conclusions: PT reduced the volumes of normal tissues exposed to radiation, particularly low-to-intermediate dose levels, and this was reflected in lower NTCP. Of the included endpoints, substantial reductions in population medians were seen from the delivered PT plans for auditory complications, xerostomia, and risk of secondary cancers of the brain and salivary glands.
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