High precision stereotactic radiation therapy (SRT) deliveries involve complex processes with multiple interdependent steps that rely on a series of decisions by clinical staff. Routine physics quality assurance (QA) generally ensures the proper functioning of each individual step of a SRT treatment process. However, these tests may not guarantee an accurate treatment delivery. For this reason, end-to-end (E2E) QA, performed from start to finish under real treatment conditions, could prove useful in validating the treatment process.
E2E QA methods are typically used when establishing SRT techniques by using simple in-house physics QA phantoms and dosimeters or by external credentialing institutes, such as the Imaging and Radiation Oncology Core (IROC), which manufactures purpose-built anthropomorphic phantoms and dosimeters.
In this virtual project gallery, we describe a process for regular clinical E2E QA for fractionated stereotactic radiation therapy (FSRT) for brain metastases using an in‑house developed head phantom. Our motivation is to ensure that the FSRT process established and tested at implementation is faithfully adhered to in the regular clinical delivery of FSRT.
A purpose-built anthropomorphic head phantom (based on an Rando head CT scan) was manufactured by 3D printing a skull (using iron-filled PLA), filling the brain region with water, and covering the surface with a polydoh plastic. The head phantom was designed to accommodate a variety of dosimeters, including a Capintec PR-05P 0.07cc ion chamber, EBT3 Gafchromic film, and leuco-crystal violet micelle or Fricke-xylenol orange gel dosimeters.
The head phantom (with a specific dosimeter in place) was given to radiation therapy staff for CT imaging, treatment planning, and VMAT FSRT delivery as per our clinical protocol. Dose delivery measurements were performed by Medical Physics staff. The film and gel measurements were analyzed using the film or gel dosimetry slicelet developed in 3D Slicer.
The phantom closely resembled a human head under imaging and set-up. It was easy for staff to use and enabled E2E QA testing. Phantom manufacture was economical with a materials cost of ~$300. The therapists treated the head phantom exactly as a patient and performed CT simulation, treatment planning, phantom set-up, CBCT imaging and alignment, and radiation delivery. The multi-dosimeter approach enabled treatment dose delivery validation in multiple dimensions. Measurements indicated excellent agreement with the planned dose delivery.
E2E tests that mimic the real patient image-guided radiation therapy process with relevant staff performing each step in the clinical workflow are feasible using in-house manufactured phantoms. This E2E testing provided a complete evaluation of our VMAT FSRT radiation therapy process and gives us confidence that our clinical workflow is safe, accurate, and effective at treating small targets.