Performance evaluation of respiratory motion‐synchronized dynamic IMRT delivery

S.A. Yoganathan,K.J. Maria Das,Arpita Agarwal,Shaleen Kumar

doi:10.1120/jacmp.v14i3.4103

Abstract

The purpose of this study was to evaluate the capabilities of DMLC to deliver the respiratory motion‐synchronized dynamic IMRT (MS‐IMRT) treatments under various dose rates. In order to create MS‐IMRT plans, the DMLC leaf motions in dynamic IMRT plans of eight lung patients were synchronized with the respiratory motion of breathing period 4 sec and amplitude 2 cm (peak to peak) using an in‐house developed leaf position modification program. The MS‐IMRT plans were generated for the dose rates of 100 MU/min, 400 MU/min, and 600 MU/min. All the MS‐IMRT plans were delivered in a medical linear accelerator, and the fluences were measured using a 2D ion chamber array, placed over a moving platform. The accuracy of MS‐IMRT deliveries was evaluated with respect to static deliveries (no compensation for target motion) using gamma test. In addition, the fluences of gated delivery of 30% duty cycle and non‐MS‐IMRT deliveries were also measured and compared with static deliveries. The MS‐IMRT was better in terms of dosimetric accuracy, compared to gated and non‐MS‐IMRT deliveries. The dosimetric accuracy was observed to be significantly better for 100 MU/min MS‐IMRT. However, the use of high‐dose rate in a MS‐IMRT delivery introduced dose‐rate modulation/beam hold‐offs that affected the synchronization between the DMLC leaf motion and target motion. This resulted in more dose deviations in MS‐IMRT deliveries at the dose rate of 600 MU/min.PACS numbers: 87.53.kn, 87.56.N‐

Highlights

It is revealed from these figures that the velocities of DMLC leafs are increased as the dose rate is increased
The impact of collimator rotation in motion-synchronized intensity-modulated radiation therapy (MS-IMRT) delivery was not included in our study because we considered target motion only along the DMLC leaf motion direction
The performance of MS-IMRT delivery was evaluated for various dose rates and compared with gated and non-MS-IMRT deliveries

Summary

Introduction

Intrafractional motion caused by respiration is an important concern in upper abdomen and thoracic sites and it results geometric, as well as dosimetric, uncertainties in radiation therapy treatments.[1,2,3,4,5] Advanced techniques, such as stereotactic body radiation therapy, utilizes delivery of higher dose to the target in a fewer fractions and this highlights the importance of managing these intrafractional uncertainties.[6] Techniques such as active or passive breath-hold[7,8,9] and respiratory gating[10,11,12] are commonly employed to account the intrafractional motion and reduce the internal margin in planning target volume. McQuaid and Webb,(33) McClelland et al,(34) and Webb et al[35,36,37] demonstrated an approach to deliver the dynamic IMRT treatments to moving targets; these studies considered the regular, as well as differential, target motions

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