<scp>EPID</scp>‐based <i>in vivo</i> dosimetry using Dosimetry Check™: Overview and clinical experience in a 5‐yr study including breast, lung, prostate, and head and neck cancer patients

Purpose: Varian Halcyon linear accelerator version 2 (The Halcyon 2.0) was recently released with new upgraded features. The aim of this study was to report our clinical experience with Halcyon 2.0 for a dual-isocenter intensity-modulated radiation therapy (IMRT) planning and delivery for gynecological cancer patients and examine the feasibility of in vivo portal dosimetry. Methods: Twelve gynecological cancer patients were treated with extended-field IMRT technique using two isocenters on Halcyon 2.0 to treat pelvis and pelvic/or para-aortic nodes region. The prescription dose was 45 Gy in 25 fractions (fxs) with simultaneous integrated boost (SIB) dose of 55 or 57.5 Gy in 25 fxs to involved nodes. All treatment plans, pretreatment patient-specific QA and treatment delivery records including daily in vivo portal dosimetry were retrospectively reviewed. For in vivo daily portal dosimetry analysis, each fraction was compared to the reference baseline (1st fraction) using gamma analysis criteria of 4 %/4 mm with 90% of total pixels in the portal image planar dose.Results: All 12 extended-field IMRT plans met the planning criteria and delivered as planned (a total of 300 fractions). Conformity Index (CI) for the primary target was achieved with the range of 0.99-1.14. For organs at risks, most were well within the dose volume criteria. Treatment delivery time was from 5.0 to 6.5 min. Interfractional in vivo dose variation exceeded gamma analysis threshold for 8 fractions out of total 300 (2.7%). These eight fractions were found to have a relatively large difference in small bowel filling and SSD change at the isocenter compared to the baseline.Conclusion: Halcyon 2.0 is effective to create complex extended-field IMRT plans using two isocenters with efficient delivery. Also Halcyon in vivo dosimetry is feasible for daily treatment monitoring for organ motion, internal or external anatomy, and body weight which could further lead to adaptive radiation therapy. K E Y W O R D Sdual-isocenter, extended-field IMRT, gynecological cancer, Halcyon 2.0, In vivo portal dosimetry ---

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Early clinical experience with varian halcyon V2 linear accelerator: Dual‐isocenter IMRT planning and delivery with portal dosimetry for gynecological cancer treatments

Kim

Huq

Lalonde

et al. 2019

“…In those studies, the point dose was estimated based on the photon fluence using a back‐projection algorithm. In other studies, point dose and dose distributions were evaluated using integrated EPID images for various treatment sites, and gamma analyses were performed throughout VMAT. Kang et al assessed the relationship between interfractional setup error and integrated EPID images for postmastectomy radiation therapy.…”

Section: Introductionmentioning

confidence: 99%

Analyses of integrated EPID images for on‐treatment quality assurance to account for interfractional variations in volumetric modulated arc therapy

Matsushita

Nakamura

Sasaki

et al. 2020

Purpose: To investigate the effects of interfractional variation, such as anatomical changes and setup errors, on dose delivery during treatment for prostate cancer (PC) and head and neck cancer (HNC) by courses of volumetric modulated arc therapy (VMAT) aided by on-treatment electronic portal imaging device (EPID) images.Methods: Seven patients with PC and 20 patients with HNC who had received VMAT participated in this study. After obtaining photon fluence at the position of the EPID for each treatment arc from on-treatment integrated EPID images, we calculated the differences between the fluence for the first fraction and each subsequent fraction for each arc. The passing rates were investigated based on a tolerance level of 3% of the maximum fluence during the treatment courses and the correlations between the passing rates and anatomical changes.Results: In PC, the median and lowest passing rates were 99.8% and 95.2%, respectively. No correlations between passing rates and interfractional variation were found. In HNC, the median passing rate of all fractions was 93.0%, and the lowest passing rate was 79.6% during the 35th fraction. Spearman's correlation coefficients between the passing rates and changes in weight or neck volume were − 0.77 and − 0.74, respectively.Conclusions: Analyses of the on-treatment EPID images facilitates estimates of the interfractional anatomical variation in HNC patients during VMAT and thus improves assessments of the need for re-planning or adaptive strategies and the timing thereof.

“…Several studies have already investigated the dosimetric characteristics and performance of these devices. [21][22][23][24][25] A clear advantage of EPIDs is their availability which makes them suitable for large scale implementations. 16,17 Some EPID-based approaches already allow for patient specific QA by reconstructing 3D dose distributions within the patient or phantom anatomy.…”

Section: Introductionmentioning

confidence: 99%

“…[18][19][20] In 3D transit EPID dosimetry, the dose is reconstructed within the patient or phantom based on EPID measurements acquired behind the patient or phantom. [21][22][23][24][25] A clear advantage of EPIDs is their availability which makes them suitable for large scale implementations. When used for patient specific QA, non-transit 3D EPID dosimetry is easier and faster than transit 3D EPID dosimetry because it eliminates the need to position a phantom.…”

Section: Introductionmentioning

confidence: 99%

Transit and non‐transit 3D EPID dosimetry versus detector arrays for patient specific QA

Olaciregui-Ruiz

Vivas-Maiques

Kaas

et al. 2019

Purpose Despite their availability and simplicity of use, Electronic Portal Imaging Devices (EPIDs) have not yet replaced detector arrays for patient specific QA in 3D. The purpose of this study is to perform a large scale dosimetric evaluation of transit and non‐transit EPID dosimetry against absolute dose measurements in 3D. Methods After evaluating basic dosimetric characteristics of the EPID and two detector arrays (Octavius 1500 and Octavius 1000SRS), 3D dose distributions for 68 VMAT arcs, and 10 IMRT plans were reconstructed within the same phantom geometry using transit EPID dosimetry, non‐transit EPID dosimetry, and the Octavius 4D system. The reconstructed 3D dose distributions were directly compared by γ‐analysis (2L2 = 2% local/2 mm and 3G2 = 3% global/2 mm, 50% isodose) and by the percentage difference in median dose to the high dose volume (%∆HDVD50). Results Regarding dose rate dependency, dose linearity, and field size dependence, the agreement between EPID dosimetry and the two detector arrays was found to be within 1.0%. In the 2L2 γ‐comparison with Octavius 4D dose distributions, the average γ‐pass rate value was 92.2 ± 5.2%(1SD) and 94.1 ± 4.3%(1SD) for transit and non‐transit EPID dosimetry, respectively. 3G2 γ‐pass rate values were higher than 95% in 150/156 cases. %∆HDVD50 values were within 2% in 134/156 cases and within 3% in 155/156 cases. With regard to the clinical classification of alerts, 97.5% of the treatments were equally classified by EPID dosimetry and Octavius 4D. Conclusion Transit and non‐transit EPID dosimetry are equivalent in dosimetric terms to conventional detector arrays for patient specific QA. Non‐transit 3D EPID dosimetry can be readily used for pre‐treatment patient specific QA of IMRT and VMAT, eliminating the need of phantom positioning.