Abstract
Stereotactic body radiation therapy (SBRT) involves the delivery of substantially larger doses over fewer fractions than conventional therapy. Therefore, SBRT treatments will strongly benefit patients using vivo patient dose verification, because the impact of the fraction is large. For in vivo measurements, a commercially available quality assurance (QA) system is the COMPASS system (IBA Dosimetry, Germany). For measurements, the system uses a new transmission detector (Dolphin, IBA Dosimetry). In this study, we evaluated the method for in vivo 3D dose reconstruction for SBRT using this new transmission detector. We confirmed the accuracy of COMPASS with Dolphin for SBRT using multi leaf collimator (MLC) test patterns and clinical SBRT cases. We compared the results between the COMPASS, the treatment planning system, the Kodak EDR2 film, and the Monte Carlo (MC) calculations. MLC test patterns were set up to investigate various aspects of dose reconstruction for SBRT: (a) simple open fields (2 × 2–10 × 10 cm2), (b) a square wave chart pattern, and (c) the MLC position detectability test in which the MLCs were changed slightly. In clinical cases, we carried out 6 and 8 static IMRT beams for SBRT in the lung and liver. For MLC test patterns, the differences between COMPASS and MC were around 3%. The COMPASS with the dolphin system showed sufficient resolution in SBRT. For clinical cases, COMPASS can detect small changes for the dose profile and dose–volume histogram. COMPASS also showed good agreement with MC. We can confirm the feasibility of SBRT QA using the COMPASS system with Dolphin. This method was successfully operated using the new transmission detector and verified by measurements and MC.
Highlights
There has been increased clinical use of stereotactic body radiation therapy (SBRT), where extremely large doses of radiation are delivered in 1–8 fractions to one or more small targets of diseased tissue
The SBRT approach of delivering a few large doses guarantees that any error made in treatment delivery has a greater radiological impact on the patient compared to the same error made during a conventional treatment regimen
We evaluate the method for in vivo 3D dose reconstruction with SBRT using the new transmission detector developed for in vivo dose verification in intensity-modulated radiotherapy (IMRT)
Summary
There has been increased clinical use of stereotactic body radiation therapy (SBRT), where extremely large doses of radiation are delivered in 1–8 fractions to one or more small targets of diseased tissue. The SBRT approach of delivering a few large doses guarantees that any error made in treatment delivery has a greater radiological impact on the patient compared to the same error made during a conventional treatment regimen. The ideal verification technique for SBRT is one that is applied during patient treatment by employing either entrance or exit dose measurements. For in vivo entrance dose measurements, the commercial QA platforms[3,4] which are able to correlate the delivered dose to the patient’s anatomy are available. The COMPASS system (IBA Dosimetry, Germany) is an in vivo dosimetry system, which provides dose–volume histograms (DVHs) based analysis for each structure.[5,6] For measurements, the system uses a new transmission detector (Dolphin, IBA Dosimetry) for in beam measurements
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