Robust optimization of VMAT for lung cancer: Dosimetric implications of motion compensation techniques

Abstract

In inverse planning of lung radiotherapy, techniques are required to ensure dose coverage of target disease in the presence of tumor motion as a result of respiration. A range of published techniques for mitigating motion effects were compared for dose stability across 5 breath cycles of ±2 cm. Techniques included planning target volume (PTV) expansions, internal target volumes with (OITV) and without tissue override (ITV), average dataset scans (ADS), and mini‐max robust optimization. Volumetric arc therapy plans were created on a thorax phantom and verified with chamber and film measurements. Dose stability was compared by DVH analysis in calculations across all geometries. The lung override technique resulted in a substantial lack of dose coverage (−10%) to the tumor in the presence of large motion. PTV, ITV and ADS techniques resulted in substantial (up to 25%) maximum dose increases where solid tissue travelled into low density optimized regions. The results highlight the need for care in optimization of highly heterogeneous where density variations may occur with motion. Robust optimization was shown to provide greater stability in both maximum (<3%) and minimum dose variations (<2%) over all other techniques.

Practical robustness evaluation in radiotherapy – A photon and proton-proof alternative to PTV-based plan evaluation

“…A scenario is commonly called 'error scenario', although in this work terminology 'treatment scenario' is used, see next section. Since becoming available in commercial treatment planning systems, robust optimisation has demonstrated the ability to improve target coverage robustness and/or organ at risk (OAR) sparing compared to PTV-based planning, in both proton [15][16][17][18][19][20][21] and photon therapy [22][23][24][25]. It must be noted however, that robust target coverage is generally one of many variables in the optimisation objective function and therefore is in competition with other objectives, such as OAR dose.…”

Volumetric modulated arc therapy with robust optimization for larynx cancer

“…The robust optimization plan for intensity-modulated proton therapy (IMPT) is widely used for several treatment sites [9][10][11]. The photon robust optimization plan also facilitates significantly more robust dose distribution to targets and OARs than the PTV-based optimization plan [12][13][14][15][16][17][18]. This approach has been investigated to achieve coverage of the breast CTV with setup variations [12,13], or to cover the dose to moving targets through breathing cycles in lung tissue [14,15].…”

“…The photon robust optimization plan also facilitates significantly more robust dose distribution to targets and OARs than the PTV-based optimization plan [12][13][14][15][16][17][18]. This approach has been investigated to achieve coverage of the breast CTV with setup variations [12,13], or to cover the dose to moving targets through breathing cycles in lung tissue [14,15]. The robust optimization plan using partial-arc VMAT has been shown to be effective for targets at the periphery of the body because when the setup error occurs in the lateral direction, the depth of the tumor either increases or decreases [16].…”

Composite minimax robust optimization of VMAT improves target coverage and reduces non-target dose in head and neck cancer patients

“…The agreement between the planned nominal dose and dose evaluated on the 4DCT was better for the CMRO-plans than the PTV-plans[6]. Archibald-Heeren et al compared CMRO VMAT of lung cancer on a thorax phantom[24]. The authors found fewer maximum and minimum dose variations compared to other current treatment techniques such as internal target volume based planning as evaluated on a 4DCT[24].…”

“…Archibald-Heeren et al compared CMRO VMAT of lung cancer on a thorax phantom[24]. The authors found fewer maximum and minimum dose variations compared to other current treatment techniques such as internal target volume based planning as evaluated on a 4DCT[24]. Zhang et al investigated the benefit of CMRO for five prostate cancer patients in which the CTV and OAR delineations were…”