Is daily computed tomography image guidance necessary for nasal cavity and nasopharyngeal radiotherapy? An investigation based on helical tomotherapy

Abstract

To analyze the magnitude of setup errors corrected by helical tomotherapy megavoltage computed tomography (MVCT) on a daily or weekly basis and the impact of those corrections on the delivered dose to the tumor and organs at risk (OARs), we retrospectively analyzed the setup errors for 6 nasal cavity and 4 nasopharyngeal cancer patients treated with helical tomotherapy for 25 – 33 fractions. Each patient had MVCT‐guided repositioning for all fractions of treatment. The new dose–volume histograms (DVHs) and equivalent uniform doses (EUDs) for the planning target volume (PTV) and OARs were calculated for hypothetical situations in which no imaging guidance (IG) or once‐weekly imaging guidance (WIG) took place. The mean total setup error for treatment without daily IG was 3.6±1.0 mm, which could be reduced to 1.7±0.6 mm if WIG were to be performed. The geometric uncertainties from the absence of IG resulted in a reduction of mean PTV EUD by 2.1%±1.0%, which could be reduced to 1.4%±1.0% with WIG. The EUDs of the OARs increased to 1.8±2.0 Gy or 0.8±1.3 Gy without and with WIG respectively. Without daily IG, the mean uncertainty in patient position has a relatively small effect on the mean dosimetry for PTV and OARs, and the use of WIG can further reduce those effects by approximately half. On the other hand, because of the large variance, with low probability, substantial deviation from the original planned dosimetry may occur without IG. Therefore, daily MVCT is preferred as an important safety measure in the delivery of intensity‐modulated radiation therapy.PACS number: 87.53.Dq

Comparative Analysis of an Image-Guided Versus a Non–Image-Guided Setup Approach in Terms of Delivered Dose to the Parotid Glands in Head-and-Neck Cancer IMRT

“…Our data are similar to the previously reported setup errors in cases of HT, ranging from 1 to 3 mm for the translational errors and from 0.8 to 1.5 for the roll rotation (23,24). There was no statistical difference in the vertical and longitudinal directions to the zero position; therefore no systematic errors in the positioning of the patient were present in those directions.…”

The ratio of weight loss to planning target volume significantly impacts setup errors in nasopharyngeal cancer patients undergoing helical tomotherapy with daily megavoltage computed tomography

“…Among IGRT modalities, helical tomotherapy with daily megavoltage computed tomography (MVCT) is the one most frequently used to evaluate and correct daily online interfraction setup errors. 11, 14 Using daily MVCT setup data, our aim was to determine which clinical and treatment factors (including tumor stage, body mass index [BMI], weight loss, and planning target volume [PTV]) predict setup errors in NPC patients treated with IMRT by tomotherapy.…”

An Evaluation of Inter-Fractional Set-Up Errors in Patients Treated with Distinct Immobilization Equipment for Varying Anatomical Regions

“…Currently, two-dimensional conventional RT has been replaced by three-dimensional conformal RT and intensity-modulated radiotherapy (IMRT). The latter offers a wide conformality for the dose distribution, reducing organs at risk (OAR) dose and toxicity [7]. Compared to conventional treatment modalities, geometric uncertainties are more critical, and also detection and reduction of set-up errors are more invaluable in IMRT [8].…”