Development, treatment planning, and dosimetric verification of volumetric modulated arc therapy for total marrow irradiation

[Truncated] Total body irradiation (TBI) is a radiotherapy conditioning regimen for bone marrow transplantation, a procedure used in the treatment of diseases such as leukaemia and lymphoma. TBI is conventionally delivered at an extended source to surface distance (SSD), with large field static, unmodulated, parallel-opposed beams. At Royal Perth Hospital (RPH) (Perth, Western Australia), a largely uniform dose of 12 Gy is delivered in six fractions, with an anterior-posterior/posterior-anterior modality. Whilst this method achieves clinical goals of tumour control and immunosuppression, healthy tissues and organs are also irradiated, increasing the risk of acute and delayed toxicities.

Recent years have seen a growing number of institutions implementing linear accelerator (linac) based intensity modulated radiotherapy (IMRT) TBI regimens. IMRT techniques can shape the beam to cover bone marrow whilst simultaneously reducing dose to healthy tissue, with reported organ at risk (OAR) dose reductions from 30%. Targeted bone marrow techniques are often labelled ‘total marrow irradiation’ (TMI) to distinguish themselves from traditional whole body irradiation methods. Volumetric modulated arc therapy (VMAT) is an arc rotational IMRT technique that delivers radiation with variable gantry speed, dose rate, and multileaf collimator aperture shape to achieve target dose coverage based upon an optimised treatment plan.

It was proposed that VMAT-TMI could be implemented on Elekta linacs at Royal Perth Hospital. The aim of this project was to assess the feasibility of planning, and accurately delivering, a targeted TMI regimen at this institution.

TMI treatment plans were created using the SmartArc module of the Pinnacle treatment planning system (TPS). An existing patient computed tomography (CT) data set (from head to femur) was sourced as a base for developing the treatment. From this patient CT, the current RPH TBI regimen was approximated within the TPS to obtain comparative dosimetric statistics for treatment targets. The TMI regimen was then planned on this patient CT, with dosimetry performed on an ArcCHECK diode array, along with Gafchromic EBT2 film, and ion chamber measurements in an IMRT thorax phantom.