Rotational IMRT techniques compared to fixed gantry IMRT and Tomotherapy: multi-institutional planning study for head-and-neck cases

Abstract

BackgroundRecent developments enable to deliver rotational IMRT with standard C-arm gantry based linear accelerators. This upcoming treatment technique was benchmarked in a multi-center treatment planning study against static gantry IMRT and rotational IMRT based on a ring gantry for a complex parotid gland sparing head-and-neck technique.MethodsTreatment plans were created for 10 patients with head-and-neck tumours (oropharynx, hypopharynx, larynx) using the following treatment planning systems (TPS) for rotational IMRT: Monaco (ELEKTA VMAT solution), Eclipse (Varian RapidArc solution) and HiArt for the helical tomotherapy (Tomotherapy). Planning of static gantry IMRT was performed with KonRad, Pinnacle and Panther DAO based on step&shoot IMRT delivery and Eclipse for sliding window IMRT. The prescribed doses for the high dose PTVs were 65.1Gy or 60.9Gy and for the low dose PTVs 55.8Gy or 52.5Gy dependend on resection status. Plan evaluation was based on target coverage, conformity and homogeneity, DVHs of OARs and the volume of normal tissue receiving more than 5Gy (V5Gy). Additionally, the cumulative monitor units (MUs) and treatment times of the different technologies were compared. All evaluation parameters were averaged over all 10 patients for each technique and planning modality.ResultsDepending on IMRT technique and TPS, the mean CI values of all patients ranged from 1.17 to 2.82; and mean HI values varied from 0.05 to 0.10. The mean values of the median doses of the spared parotid were 26.5Gy for RapidArc and 23Gy for VMAT, 14.1Gy for Tomo. For fixed gantry techniques 21Gy was achieved for step&shoot+KonRad, 17.0Gy for step&shoot+Panther DAO, 23.3Gy for step&shoot+Pinnacle and 18.6Gy for sliding window.V5Gy values were lowest for the sliding window IMRT technique (3499 ccm) and largest for RapidArc (5480 ccm). The lowest mean MU value of 408 was achieved by Panther DAO, compared to 1140 for sliding window IMRT.ConclusionsAll IMRT delivery technologies with their associated TPS provide plans with satisfying target coverage while at the same time respecting the defined OAR criteria. Sliding window IMRT, RapidArc and Tomo techniques resulted in better target dose homogeneity compared to VMAT and step&shoot IMRT. Rotational IMRT based on C-arm linacs and Tomotherapy seem to be advantageous with respect to OAR sparing and treatment delivery efficiency, at the cost of higher dose delivered to normal tissues. The overall treatment plan quality using Tomo seems to be better than the other TPS technology combinations.

A treatment planning study comparing Elekta VMAT and fixed field IMRT using the varian treatment planning system eclipse

“…This value is comparable to previous studies on step-and-shoot IMRT that reported reductions of 12% to 20% [10,31] and studies on sliding-window IMRT that reported reductions of 40% to 55% [11,16]. As the number of MUs per treatment is correlated with the amount of scatter dose and leakage radiation, which could be important based on the induction of secondary malignancies [32,33], a decrease in the number of MUs achieved with VMAT is desirable.…”

Treatment outcomes and patterns of radiologic appearance after hypofractionated image-guided radiotherapy delivered with helical tomotherapy (HHT) for lung tumours

“…Moreover, the helical radiation delivery method is associated with low-dose spread 6 to the normal lung and can potentially result in patterns of lung injury that might be different than those observed with conventional three-dimensional conformal radiotherapy or other SABR techniques (Figure 1). Lastly, HT requires an increased number of monitor units, as compared with a nonwedged conformal plan, 17 which might result in a substantial prolongation of the total treatment time. This can potentially impair the reproducibility and comfort of patients with abnormal breathing owing to coexisting chronic obstructive pulmonary disease (COPD).…”

Radiation dose escalation based on FDG-PET driven dose painting by numbers in oropharyngeal squamous cell carcinoma: a dosimetric comparison between TomoTherapy-HA and RapidArc

“…A higher degree of conformity was observed with the inhomogeneous dose prescription with HT than with nine fields step-and-shoot IMRT, although the authors concluded that both modalities were clinically suitable for dose painting. On the other hand, several studies comparing rotational IMRT systems without dose escalation in patients with HNSCC have been reported in the literature [25–30]. Most of them found significantly higher normal tissue dose sparing with HT than with RA [25, 28–30].…”

“…On the other hand, several studies comparing rotational IMRT systems without dose escalation in patients with HNSCC have been reported in the literature [25–30]. Most of them found significantly higher normal tissue dose sparing with HT than with RA [25, 28–30]. Regarding target coverage, Stromberger et al reported only small differences comparing both modalities for unilateral and bilateral simultaneous integrated boost plans [28].…”