Radiation Therapy against Pediatric Malignant Central Nervous System Tumors : Embryonal Tumors and Proton Beam Therapy

Normal tissue tolerance amongst paediatric brain tumour patients- current evidence in proton radiotherapy

BACKGROUND

Proton radiotherapy (PT) is used increasingly for paediatric brain cancer patients. However, as demonstrated here, the knowledge on normal tissue dose constraints, to minimize side-effects, for this cohort is limited.

METHODS

A search strategy was systematically conducted on MEDLINE® database. 65 papers were evaluated ranging from 2013 to 2021.

RESULTS

Large variations in normal tissue tolerance and toxicity reporting across PT studies makes estimation of normal tissue dose constraints difficult, with the potential for significant late effects to go unmeasured. Mean dose delivered to the pituitary gland varies from 20 to 30 Gy across literature. Similarly, the hypothalamic dose delivery ranges from 20 to 54.6 Gy for paediatric patients.

CONCLUSION

There is a significant lack of radiobiological data for paediatric brain cancer patients undergoing proton therapy, often using data from x-ray radiotherapy and adult populations. The way forward is through standardisation of reporting in order to validate relevant dose constraints.

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

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.

BRAF V600E Detection in Liquid Biopsies from Pediatric Central Nervous System Tumors

Pediatric Central Nervous System (CNS) tumors are the most fatal cancer diseases in childhood. Due to their localization and infiltrative nature, some tumor resections or biopsies are not feasible. In those cases, the use of minimally invasive methods as diagnostic, molecular marker detection, prognostic or monitoring therapies are emerging. The analysis of liquid biopsies which contain genetic information from the tumor has been much more widely explored in adults than in children. We compare the detection of BRAF V600E targetable mutation by digital-PCR from cell-free-DNA and EV-derived DNA (ctDNA) in serum, plasma and cerebrospinal fluid (CSF) isolated from a cohort of 29 CNS pediatric patients. Here we demonstrate that ctDNA isolated from serum and plasma could be successfully analyzed to obtain tumor genetic information which could be used to guide critical treatment decisions.