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Stem Cell Transplantation Strategies for the Restoration of Cognitive Dysfunction Caused by Cranial Radiotherapy
Published on: October 18, 2011
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Functional cranio-spinal irradiation: A hippocampal and hypothalamic-pituitary axis sparing radiation technique using
Jack Zheng1, Saif Aljabab2, Patricia Lacasse1
1Radiation Medicine Program, The Ottawa Hospital Cancer Centre, ON, Canada K1H 8L6.
Summary
This study introduces Functional Cranio-Spinal Irradiation (F-CSI) to reduce radiation dose to the brain in embryonal tumor patients. Both VMAT and Helical Tomotherapy F-CSI techniques significantly lowered hypothalamic-pituitary axis and hippocampal doses compared to standard CSI.
Area of Science:
- Radiation Oncology
- Pediatric Oncology
- Neuro-oncology
Background:
- Cranio-spinal irradiation (CSI) for embryonal tumors can lead to long-term endocrine and neuro-cognitive issues.
- Standard CSI (S-CSI) involves a prescribed dose of 23.4 Grays (Gy) followed by a 30.6Gy boost.
- The hypothalamic-pituitary axis (HPA) and hippocampi are critical organs at risk for radiation-induced toxicity.
Purpose of the Study:
- To evaluate a novel Functional Cranio-Spinal Irradiation (F-CSI) technique designed to reduce radiation dose to the HPA and hippocampi.
- To compare the efficacy of Volumetric Modulated Arc Therapy (VMAT) and Helical Tomotherapy (HT) in delivering F-CSI.
- To assess if F-CSI can achieve target dose coverage without compromising efficacy compared to S-CSI.
Main Methods:
- Treatment plans for F-CSI using VMAT and HT were created for 10 patients with embryonal tumors.
- Target volumes and organs at risk, including the HPA and hippocampi, were delineated according to established protocols.
- Dose metrics (D95% for target, Dmean for organs at risk) were analyzed, with a goal of Dmean ≤18Gy for HPA and hippocampi.
Main Results:
- Both VMAT and HT F-CSI techniques successfully achieved the prescribed D95% target coverage.
- Helical Tomotherapy demonstrated significantly lower hot spots (D2%) for both CSI and boost components (p = 0.03, p < 0.01).
- F-CSI significantly reduced the mean dose to the HPA and hippocampi compared to S-CSI (e.g., HPA Dmean reduced from ~23.9Gy to ~13.9Gy with VMAT).
- However, the composite dose (F-CSI plus boost) to the HPA and hippocampi often exceeded the 18Gy threshold.
Conclusions:
- F-CSI delivered via VMAT and HT can achieve adequate target coverage while significantly sparing the HPA and hippocampi compared to S-CSI.
- The addition of the boost dose frequently exceeded the 18Gy threshold for organs at risk.
- More conformal boost techniques, such as stereotactic radiotherapy or proton therapy, may be necessary to further reduce dose and mitigate long-term sequelae.
