Influence of Target Location, Size, and Patient Age on Normal Tissue Sparing- Proton and Photon Therapy in Paediatric Brain Tumour Patient-Specific Approach

SIMPLE SUMMARY: This manuscript investigates the latest proton and photon radiation delivery techniques and the delivered dose distribution dependence on age and brain tumour location for simulated paediatric patients. Brain tumors are the leading cause of cancer-related burden in childhood cancer survivors. Standard treatment regimens include radiotherapy, and whilst photon therapy is commonly prescribed, proton particles (where available) have been proven to reduce the risk of long-term illness and morbidities. Differences between the two modalities are not fully quantified in paediatric patients for various intracranial tumour sites or age. Ependymoma proton plans demonstrated greater dose reduction for the 9 vs. 13-year-old patients (pituitary gland p < 0.001). Whilst medulloblastoma proton plans achieved greater maximum dose sparing to optic structures (4.8–12.6 Gy optic chiasm), brainstem sparing was limited (~0.5 Gy). Understanding these differences may help clinicians estimate the benefit and improve referral across available centres. ABSTRACT: Background: Proton radiotherapy produces superior dose distributions compared to photon radiotherapy, reducing side effects. Differences between the two modalities are not fully quantified in paediatric patients for various intracranial tumour sites or age. Understanding these differences may help clinicians estimate the benefit and improve referral across available centres. Our aim was to compare intensity-modulated proton therapy (IMPT) and intensity-modulated photon radiotherapy (IMRT) radiation doses for select paediatric intracranial tumours. Methods: IMPT and IMRT dose distributions for gender-matched paediatric cranial CT-datasets (ages 5, 9 and 13 years) were retrospectively calculated to simulate irradiation of supratentorial (ependymoma) and infratentorial (medulloblastoma) target volumes diameters (1–3 cm) and position (central and 1–2 cm shifts). Results: Clinical dosimetric objectives were achieved for all 216 treatment plans. Whilst infratentorial IMPT plans achieved greater maximum dose sparing to optic structures (4.8–12.6 Gy optic chiasm), brainstem sparing was limited (~0.5 Gy). Mean dose difference for optic chiasm was associated with medulloblastoma target position (p < 0.0197). Supratentorial IMPT plans demonstrated greater dose reduction for the youngest patients (pituitary gland p < 0.001). Conclusions: Normal tissue sparing was achieved regardless of patient age for infratentorial tumours. However, for supratentorial tumours, there was a dosimetric advantage of IMPT across 9 vs. 13-year-old patients.