Validation of a method for in vivo 3D dose reconstruction in SBRT using a new transmission detector

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.

Clinical evaluation of a transmission detector system and comparison with a homogeneous 3D phantom dosimeter

“…It is therefore possible to make a 3D comparison between the TPS dose and Compass calculated and Compass reconstructed doses. Compass software can be employed as a secondary TPS [13][14][15][16] and the congruence between TPS involved in this study and Compass calculated dose has been verified at the stage of Dolphin acceptance.…”

“…Pre-clinical QA such as patient specific pre-treatment measurements are required for modern radiotherapy approaches, given the complexity of planning and treatment delivery, especially during the commissioning phase of a new machine, technique or software [10,11,[13][14][15][20][21][22][23][24]. In our study, we focused on two different platforms: a traditional 3D homogeneous phantom to be positioned on the couch and a new transmission detector inserted on the gantry.…”

“…This system can also be used as in vivo dosimetry even if, at present, there is no agreement with manufacturer companies in terms of patient safety. Many authors have studied the performances of the two devices employed in our comparative study, namely Delta 4 and Compass with transmission detector (Dolphin) [3][4][5][6][7][8][9][10][11][12][13][14][15]20]: all of them found the two instruments suitable for treatment verification. Of interest the study by Thoelking et al [13] that compared Dolphin with a 2D platform and analyzed 18 patients for only 3 clinical sites.…”

“…Our effort has been addressed to introduce a clinical perspective in strict collaboration with radiation oncologists, defining clinical criteria as normally done by physicians during plan approval. Nakaguchi et al [15] as well evaluated the performances of Dolphin (sensibility, detectability) using various methods but only tested the clinical behavior of the system for SBRT with no clinical considerations performed. The aim and the novelty of our study were to investigate the potential correlations between the two methods used for pre-treatment QA on a group of 50 patients with different tumors: gamma evaluation in a homogeneous phantom (Delta 4 ) and clinical DVHs analysis (Dolphin).…”

“…Several reports outline the characteristics and performances of the 2 systems [11,[13][14][15]20,21]; the reproducibility of the 2 detectors used in our study (Dolphin and Delta 4 ) was tested in a clinical context (lung case). The plan was measured 10 consecutive times with both Dolphin and Delta 4 .…”