Implementation and experimental validation of a robust hybrid direct aperture optimization approach for mixed‐beam radiotherapy

Abstract

The objectives of the work presented in this paper were to (1) implement a robust-optimization method for deliverable mixed-beam radiotherapy (MBRT) plans within a previously developed MBRT planning framework; (2) perform an experimental validation of the delivery of robust-optimized MBRT plans; and (3) compare PTV-based and robust-optimized MBRT plans in terms of target dose robustness and organs at risk (OAR) sparing for clinical head and neck and brain patient cases. Methods: A robust-optimization method, which accounts for translational setup errors, was implemented within a previously developed treatment planning framework for MBRT. The framework uses a hybrid direct aperture optimization method combining column generation and simulated annealing. A robust plan was developed and then delivered to an anthropomorphic head phantom using the Developer Mode of a TrueBeam linac. Planar dose distributions were measured and compared to the planned dose. Robust-optimized and PTV-based plans were developed for three clinical patient cases consisting of two head and neck cases and one brain case. The plans were compared in terms of the robustness to 5 mm shifts of the target volume dose as well as in terms of OAR sparing. Results: Using a gamma criterion of 3%/2 mm and a dose threshold of 10%,the agreement between film measurements and dose calculations was better than 97.7% for the total plan and better than 95.5% for the electron component of the plan. For the two head and neck patient cases, the average clinical target volume (CTV) dose homogeneity index (V95%-V107%) over all the considered setup error scenarios was on average 19% lower for the PTV-based plans and it had a larger standard deviation. The robust-optimized plans achieved, on average, a 20% reduction in the OAR doses compared to the PTV-based plans. For the brain patient case, the CTV dose homogeneity index was similar for the two plans,while the OAR doses were 22% lower,on average,for the robust-optimized plan.No clear trend in terms of electron contributions was found across the three patient cases, although robust-optimized plans tended toward higher electron beam energies. Conclusions: A framework for robust optimization of deliverable MBRT plans has been developed and validated. PTV-based MBRT were found to not be This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Robust mixed electron‐photon radiation therapy planning for soft tissue sarcoma

“…As all apertures were delivered at standard SAD, no intra‐fraction couch translation was required. This is in contrast to previous MBRT studies that have all reported the use of shortened SSD setups for deliveries of electron apertures 20–26,31 …”

“…For all patients, MBRT plans had either significantly lower or equivalent doses to normal tissue and bone. Being deliverable on current state‐of‐the‐art linacs without the use of electron applicators 26,31 or shortened SSD, 41 MBRT offers significant dosimetric benefits at reduced logistical cost.…”

“…The cost function can then be calculated as a weighted average of the cost function of each scenario. Accurate deliveries of robust MBRT plans have been experimentally validated on conventional linacs with excellent agreements between Monte Carlo‐calculated doses and ion chamber and film measurements 26,31 …”

“…This however comes at the cost of worse target dose homogeneity 18,19 . Mixed electron‐photon beam radiation therapy (MBRT) delivered using an existing pMLC is an emerging technique in which both external electron and photon beam are simultaneously optimized into a single treatment plan 20–26 . MBRT has been shown to provide superior sparing of normal tissue without sacrificing target coverage 20,22–24 .…”

Quality assurance for mixed electron–photon beam radiation therapy using treatment log files and MapCHECK

“…Heng et al 15 demonstrated the use of an ionization chamber and film dosimetry to perform PSQA for MBRT plans on a PMMA phantom and a Solid Water phantom. Heath et al 16 suggested the possibility of using log file-based dose calculation and EPID measurement for evaluating the delivery accuracy of MBRT. However, to our knowledge, no prior studies have examined the use of commercial QA devices for MBRT plan verification.…”