Evaluation of automated pre-treatment and transit in-vivo dosimetry in radiotherapy using empirically determined parameters

Abstract

Background and purpose: First reports on clinical use of commercially automated systems for Electronic Portal Imaging Device (EPID)-based dosimetry in radiotherapy showed the capability to detect important changes in patient setup, anatomy and external device position. For this study, results for more than 3000 patients, for both pre-treatment verification and in-vivo transit dosimetry were analyzed. Materials and methods: For all Volumetric Modulated Arc Therapy (VMAT) plans, pre-treatment quality assurance (QA) with EPID images was performed. In-vivo dosimetry using transit EPID images was analyzed, including causes and actions for failed fractions for all patients receiving photon treatment (2018)(2019). In total 3136 and 32,632 fractions were analyzed with pre-treatment and transit images respectively. Parameters for gamma analysis were empirically determined, balancing the rate between detection of clinically relevant problems and the number of false positive results. Results: Pre-treatment and in-vivo results depended on machine type. Causes for failed in-vivo analysis included deviations in patient positioning (32%) and anatomy change (28%). In addition, errors in planning, imaging, treatment delivery, simulation, breath hold and with immobilization devices were detected. Actions for failed fractions were mostly to repeat the measurement while taking extra care in positioning (54%) and to intensify imaging procedures (14%). Four percent initiated plan adjustments, showing the potential of the system as a basis for adaptive planning. Conclusions: EPID-based pre-treatment and in-vivo transit dosimetry using a commercially available automated system efficiently revealed a wide variety of deviations and showed potential to serve as a basis for adaptive planning.

Validation of virtual water phantom software for pre‐treatment verification of single‐isocenter multiple‐target stereotactic radiosurgery

“…In the context of PTV margins used for treatment, Bossuyt et al described to use the CTV-PTV margin as DTA for transit in-vivo PSQA based on EPID measurements. 43 The 2-mm DTA used in the present study coincides with the CTV-PTV margin implemented in our SIMT SRS policy. 44 So, a successful GPR using 2-mm DTA is compatible with an adequate dosimetric coverage of the lesions.…”

In vivo dosimetry for patients with prostate cancer to assess possible impact of bladder and rectum preparation

“…A disadvantage of the forward-projection method is that the dose in the patient cannot be reconstructed and interpretation of the difference in predicted and measured EPID images is challenging. In this study, all patients with prostate cancer were analyzed with a global gamma index (5% DD/5mm DTA) and 95% passing rate which was considered clinically relevant in avoiding too many FNs [11] .…”

“…Results were analyzed using a global gamma analysis with a threshold of 20%, a dose difference (DD) of 5%, a distance to agreement (DTA) of 5 mm and a passing level of 95%. These settings were the result of previous large scale evaluation to reduce the number of false positive (FP) results [11] . Irregularities were automatically detected and inspected by MPs to identify suspicious situations such as bladder and rectum filling that may have affected delivery.…”

“…Bedford et al showed that the EPID-based 2D and 3D IVD for prostate patients were not able to identify possible source of errors related to spatial shifts or bowel gas [10]. An automated EPID-based software platform (PerFRACTION TM , part of SunCHECK TM , Sun Nuclear Corporation) was introduced for patient-specific QA and IVD of all patients in our department [11] to detect major deviations and assess clinically relevant differences between planned and delivered dose. In this report a cohort of patients with prostate cancer was evaluated in more detail.…”

A Validation Method for EPID In Vivo Dosimetry Algorithms

“…Despite its wide availability and its simplicity of use, the clinical implementation of such a dosimetric technique is still challenging. Currently, only a few centers have reported wide statistics of IVD results [6,7]. One reason for the IVD implementation difficulty is the lack of guidelines around the validation and acceptance of an EPID IVD algorithm.…”