Single-Arc IMRT?

Abstract

The idea of delivering intensity-modulated radiation therapy (IMRT) with a multileaf collimator in a continuous dynamic mode during a single rotation of the gantry has recently gained momentum both in research and industry. In this note we investigate the potential of this Single-Arc IMRT technique at a conceptual level. We consider the original theoretical example case from Brahme et al that got the field of IMRT started. Using analytical methods, we derive deliverable intensity 'landscapes' for Single-Arc as well as standard IMRT and Tomotherapy. We find that Tomotherapy provides the greatest flexibility in shaping intensity landscapes and that it allows one to deliver IMRT in a way that comes close to the ideal case in the transverse plane. Single-Arc and standard IMRT make compromises in different areas. Only in relatively simple cases that do not require substantial intensity modulation will Single-Arc be dosimetrically comparable to Tomotherapy. Compared with standard IMRT, Single-Arc could be dosimetrically superior in certain cases if one is willing to accept the spreading of low dose values over large volumes of normal tissue. In terms of treatment planning, Single-Arc poses a more challenging optimization problem than Tomotherapy or standard IMRT. We conclude that Single-Arc holds potential as an efficient IMRT technique especially for relatively simple cases. In very complex cases, Single-Arc may unduly compromise the quality of the dose distribution, if one tries to keep the treatment time below 2 min or so. As with all IMRT techniques, it is important to explore the tradeoff between plan quality and the efficiency of its delivery carefully for each individual case.

Volumetric Modulated Arc Therapy for Advanced Pancreatic Cancer

“…A recent paper questioned the ability to generate highly modulated treatment plans using volumetric arc therapy [3]. Our study as well as recent publications in a range of tumor sites [9,19,21,22,29,35,36] have clearly shown data to the contrary.…”

Comparative analysis of SmartArc‐based dual arc volumetric‐modulated arc radiotherapy (VMAT) versus intensity‐modulated radiotherapy (IMRT) for nasopharyngeal carcinoma

“…( 16 , 17 , 24 ) VMAT offers the potential for reduced delivery times and improved dose distributions for difficult cases when compared with IMRT. ( 6 , 7 , 15 , 16 , 25 , 30 , 49 – 50 ) However, VMAT has not been shown to provide general clinical advantages that can be translated to survival, tumor control, or normal tissue complications.…”

“…Thus, this provides a second reason that the dual arc method was selected, smoothing the process to sculpt the complex shaping of the NPC cases. Bortfeld et al ( 6 ) additionally reported that, due to the complex target volumes and the frequent use of multiple prescription levels, HN cancer cases are most likely to experience significant dosimetric improvement when using more than one single arc VMAT.…”

The effect of gantry spacing resolution on plan quality in a single modulated arc optimization

“…( 1 ) It allows simultaneous variation of dose rate, gantry speed, and multileaf collimator (MLC) segments. ( 2 ) The technique promises some dosimetric benefits ( 3 ) together with reduced treatment times ( 1 , 2 , 4 – 6 ) which, in turn, may have significant radiobiological impact. ( 7 – 9 ) …”