Robustness and dosimetric verification of hippocampal-sparing craniospinal pencil beam scanning proton plans for pediatric medulloblastoma

Anneli Edvardsson; Jenny Gorgisyan; Karin M Andersson; Christina Vallhagen Dahlgren; Alexandru Dasu; Daniel Gram; Thomas Björk-Eriksson; Per Munck Af Rosenschöld

doi:10.1016/j.phro.2024.100555

Robustness and dosimetric verification of hippocampal-sparing craniospinal pencil beam scanning proton plans for pediatric medulloblastoma

Phys Imaging Radiat Oncol. 2024 Feb 15:29:100555. doi: 10.1016/j.phro.2024.100555. eCollection 2024 Jan.

Authors

Anneli Edvardsson^{1

2}, Jenny Gorgisyan^{1

2}, Karin M Andersson³, Christina Vallhagen Dahlgren³, Alexandru Dasu^{3

4}, Daniel Gram^{5

6

7}, Thomas Björk-Eriksson^{8

9}, Per Munck Af Rosenschöld^{1

2}

Affiliations

¹ Radiation Physics, Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Sweden.
² Medical Radiation Physics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
³ The Skandion Clinic, Uppsala, Sweden.
⁴ Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
⁵ Department of Clinical Oncology and Palliative Care, Radiotherapy, Zealand University Hospital, Næstved, Denmark.
⁶ Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark.
⁷ Department of Oncology - Section of Radiotherapy, Rigshospitalet, Copenhagen, Denmark.
⁸ Department of Oncology, Institute of Clinical Sciences, Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden.
⁹ Regional Cancer Centre West, Western Sweden Healthcare Region, Gothenburg, Sweden.

Abstract

Background and purpose: Hippocampal-sparing (HS) is a method that can potentially reduce late cognitive complications for pediatric medulloblastoma (MB) patients treated with craniospinal proton therapy (PT). The aim of this study was to investigate robustness and dosimetric plan verification of pencil beam scanning HS PT.

Materials and methods: HS and non-HS PT plans for the whole brain part of craniospinal treatment were created for 15 pediatric MB patients. A robust evaluation of the plans was performed. Plans were recalculated in a water phantom and measured field-by-field using an ion chamber detector at depths corresponding to the central part of hippocampi. All HS and non-HS fields were measured with the standard resolution of the detector and in addition 16 HS fields were measured with high resolution. Measured and planned dose distributions were compared using gamma evaluation.

Results: The median mean hippocampus dose was reduced from 22.9 Gy (RBE) to 8.9 Gy (RBE), while keeping CTV V_95% above 95 % for all nominal HS plans. HS plans were relatively robust regarding hippocampus mean dose, however, less robust regarding target coverage and maximum dose compared to non-HS plans. For standard resolution measurements, median pass rates were 99.7 % for HS and 99.5 % for non-HS plans (p < 0.001). For high-resolution measurements, median pass rates were 100 % in the hippocampus region and 98.2 % in the surrounding region.

Conclusions: A substantial reduction of dose in the hippocampus region appeared feasible. Dosimetric accuracy of HS plans was comparable to non-HS plans and agreed well with planned dose distribution in the hippocampus region.

Keywords: Craniospinal irradiation; Hippocampal-sparing; Medulloblastoma; Pediatrics; Proton therapy; Quality assurance.