Can Helium Ions Improve Particle Therapy?

Radiotherapy for paediatric patients is a double-edged sword: it has the potential to cure existing cancer and the potential to cause secondary cancers later in life. For this reason, a presentation about the potential use of helium ions to reduce radiation exposure generated much interest at the ESTRO 33 meeting, held last month in Vienna, Austria. Hermann Fuchs from the Medical University of Vienna presented a treatment planning study that showed how helium ions may provide superior dose distributions to proton-based radiotherapy. Fuchs and colleagues from the University’s Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology developed a method for calculating the optimal dose of helium ions for use in radiation treatment. They then used their dose calculation algorithm to create treatment plans for 10 paediatric patients.Fuchs and colleagues previously developed and validated a flexible pencil-beam algorithm for proton therapy and scanned helium ion beam therapy, based on the established theory of fluence-weighted elemental pencil-beam kernels (Med. Phys. 39 11 6726). Its flexible design allows for easy customization of measured depth-dose distributions and use of varying beam profiles, according to Fuchs. The algorithm was implemented in a customized development version of the Hyperion treatment planning system. The researchers created five paediatric neuroblastoma and five Hodgkin’s lymphoma treatment plans based on pencil-beam scanning. The same beam configurations (two beams from the anterior-posterior or lateral direction) were used for helium and proton therapy. The neuroblastoma clinical target volume (CTV) included the preoperative gross tumour volume and areas of local lymph node enlargement. The Hodgkin’s lymphoma CTV encompassed the involved lymph nodes at the time of diagnosis adapted to post-chemotherapy anatomy. The planning target volume (PTV) was 163–232 cm3 for neuroblastoma patients and 443–1521 cm3 for Hodgkin’s lymphoma patients. The dose prescription to the PTV was 21 Gy for neuroblastoma patients and 19.8 Gy for Hodgkin’s lymphoma patients. The liver, kidneys, heart, lungs and thyroid were considered as organs-at-risk (OARs) depending upon the tumour position. The researchers determined that more stringent OAR constraints could be employed for plan optimization using helium ions instead of protons. Helium ions provided improved PTV coverage and slightly lower doses for all OARs. The dose distribution outside the PTV was notably different between helium ions and protons, with reduced entrance doses for helium. Fuchs explained that due to the increased mass of helium ions compared to protons, spreading of the beam is reduced by a factor of two. Helium ions also have an increased biological effectiveness at the end of their range. “After three years of extensive research and validation efforts, we produced a treatment planning algorithm that enabled us to investigate the possibilities for using helium ion therapy in children treated with low-dose radiation, “Fuchs told medicalphysicsweb. “Our study offers the first step toward exploring the potential of helium ions for paediatric patients. We chose patients with low-dose radiation schemes for this first investigation, but would like to include patients treated with higher doses, like brain tumour patients, in a future study. The good results that we achieved are motivating us to take a more in-depth look at the clinical potential of helium ions.”

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