Abstract
PurposeThe purpose of this work is to develop fast deliverable step and shoot IMRT technique. A reduction in the number of segments should theoretically be possible, whilst simultaneously maintaining plan quality, provided that the reduction is accompanied by an increased number of gantry angles. A benefit of this method is that the segment shaping could be performed during gantry motion, thereby reducing the delivery time. The aim was to find classes of such solutions whose plan quality can compete with conventional IMRT.Materials/MethodsA planning study was performed. Step and shoot IMRT plans were created using direct machine parameter optimization (DMPO) as a reference. DMPO plans were compared to an IMRT variant having only one segment per angle ("2-Step Fast"). 2-Step Fast is based on a geometrical analysis of the topology of the planning target volume (PTV) and the organs at risk (OAR). A prostate/rectum case, spine metastasis/spinal cord, breast/lung and an artificial PTV/OAR combination of the ESTRO-Quasimodo phantom were used for the study. The composite objective value (COV), a quality score, and plan delivery time were compared. The delivery time for the DMPO reference plan and the 2-Step Fast IMRT technique was measured and calculated for two different linacs, a twelve year old Siemens Primus™ ("old" linac) and two Elekta Synergy™ "S" linacs ("new" linacs).Results2-Step Fast had comparable or better quality than the reference DMPO plan. The number of segments was smaller than for the reference plan, the number of gantry angles was between 23 and 34. For the modern linac the delivery time was always smaller than that for the reference plan. The calculated (measured) values showed a mean delivery time reduction of 21% (21%) for the new linac, and of 7% (3%) for the old linac compared to the respective DMPO reference plans. For the old linac, the data handling time per beam was the limiting factor for the treatment time reduction.Conclusions2-Step Fast plans are suited to reduce the delivery time, especially if the data handling time per beam is short. The plan quality can be retained or even increased for fewer segments provided more gantry angles are used.
Highlights
Fast delivery of radiation techniques sparing organs at risk (OAR) is desirable for several reasons
Materials and methods This work is closely related to the study of fast deliverable intensity modulated arc therapy (IMAT) methods that use the 2-Step Intensity modulated radiation therapy (IMRT) technique and which were compared to VMAT plans [18]
2-Step-Fast and 2-Step Fast* plans We propose fast versions of 2-Step IMRT technique: 2Step Fast and 2-Step Fast* IMRT, which
Summary
Fast delivery of radiation techniques sparing organs at risk (OAR) is desirable for several reasons. Some authors favor fast application due to biological effects [1]. Short delivery times reduce the problems related to patient movement. More patients can be treated with the same linear accelerator (linac). Intensity modulated radiation therapy (IMRT)[2] and improvement. Many hospitals are currently not equipped with linacs capable of IMAT delivery. A reduction of delivery times without compromising plan quality using less demanding IMRT-capable linacs could be useful [6]
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