Current status of stereotactic ablative body radiotherapy in the UK: six years of progress.

OBJECTIVE: To update the 2012 UK stereotacticablative radiotherapy (SABR) Consortium survey and assess the development of SABR services across the UK over the past 6 years. Use the results to share practice and continue to drive forward technique development, aid standardization and by highlighting issues, improve access to SABR services and trials across the UK. METHODS: In January 2018, an online questionnaire was sent by the UK SABR Consortium to 65 UK radiotherapy institutions covering current service provision and collecting data on immobilization, motion management, scanning protocols, target/OAR delineation, planning, image-guidance, quality assurance and future plans. RESULTS: 50 (77%) institutions responded, 38 ( vs 15 in 2012) indicated they had an active SABR programme with the remaining 12 centres intending to develop a SABR programmeDocumented changes include the development of Linac delivered SABR to non-lung sites, an increase in centres using abdominal compression (14 vs 2) and the introduction of four-dimensional cone beam CBCT. Current practice is broadly in line with UK SABR Consortium and European guidelines. CONCLUSION: This 2018 survey shows a welcome increase in SABR provision, surpassing 2012 projections. However, it is clear that the UK SABR program needs to continue to expand to ensure that patients with oligometastatic disease have access and SABR for early stage lung cancer is available in all centres. Updated guidance that addresses variability in target delineation, image guidance and reduces patient specific quality assurance is warranted. ADVANCES IN KNOWLEDGE: Documented progress of UK SABR across all treatment sites over the last six years, barriers to implementation and future plans.

A national dosimetry audit for stereotactic ablative radiotherapy in lung.

BACKGROUND AND PURPOSE: A UK national dosimetry audit was carried out to assess the accuracy of Stereotactic Ablative Body Radiotherapy (SABR) lung treatment delivery. METHODS AND MATERIALS: This mail-based audit used an anthropomorphic thorax phantom containing nine alanine pellets positioned in the lung region for dosimetry, as well as EBT3 film in the axial plane for isodose comparison. Centres used their local planning protocol/technique, creating 27 SABR plans. A range of delivery techniques including conformal, volumetric modulated arc therapy (VMAT) and Cyberknife (CK) were used with six different calculation algorithms (collapsed cone, superposition, pencil-beam (PB), AAA, Acuros and Monte Carlo). RESULTS: The mean difference between measured and calculated dose (excluding PB results) was 0.4±1.4% for alanine and 1.4±3.4% for film. PB differences were -6.1% and -12.9% respectively. The median of the absolute maximum isodose-to-isodose distances was 3mm (-6mm to 7mm) and 5mm (-10mm to +19mm) for the 100% and 50% isodose lines respectively. CONCLUSIONS: Alanine and film is an effective combination for verifying dosimetric and geometric accuracy. There were some differences across dose algorithms, and geometric accuracy was better for VMAT and CK compared with conformal techniques. The alanine dosimetry results showed that planned and delivered doses were within ±3.0% for 25/27 SABR plans.

Feasibility of using glass-bead thermoluminescent dosimeters for radiotherapy treatment plan verification.

OBJECTIVE: To investigate the feasibility of using glass beads as novel thermoluminescent dosemeters (TLDs) for radiotherapy treatment plan verification. METHODS: Commercially available glass beads with a size of 1-mm thickness and 2-mm diameter were characterized as TLDs. Five clinical treatment plans including a conventional larynx, a conformal prostate, an intensity-modulated radiotherapy (IMRT) prostate and two stereotactic body radiation therapy (SBRT) lung plans were transferred onto a CT scan of a water-equivalent phantom (Solid Water(®), Gammex, Middleton, WI) and the dose distribution recalculated. The number of monitor units was maintained from the clinical plan and delivered accordingly. The doses determined by the glass beads were compared with those measured by a graphite-walled ionization chamber, and the respective expected doses were determined by the treatment-planning system (TPS) calculation. RESULTS: The mean percentage difference between measured dose with the glass beads and TPS was found to be 0.3%, -0.1%, 0.4%, 1.8% and 1.7% for the conventional larynx, conformal prostate, IMRT prostate and each of the SBRT delivery techniques, respectively. The percentage difference between measured dose with the ionization chamber and glass bead was found to be -1.2%, -1.4%, -0.1%, -0.9% and 2.4% for the above-mentioned plans, respectively. The results of measured doses with the glass beads and ionization chamber in comparison with expected doses from the TPS were analysed using a two-sided paired t-test, and there was no significant difference at p < 0.05. CONCLUSION: It is feasible to use glass-bead TLDs as dosemeters in a range of clinical plan verifications. ADVANCES IN KNOWLEDGE: Commercial glass beads are utilized as low-cost novel TLDs for treatment-plan verification.