Impact of Geometric Uncertainties on Dose Distribution During Intensity Modulated Radiotherapy of Head-and-neck Cancer: The Need for a Planning Target Volume and A Planning Organ-at-Risk Volume

Abstract

We assessed the effect of geometric uncertainties on target coverage and on dose to the organs at risk (OARS) during intensity-modulated radiotherapy (IMRT) for head-and-neck cancer, and we estimated the required margins for the planning target volume (PTV) and the planning organ-at-risk volume (PRV). For eight headand- neck cancer patients, we generated IMRT plans with localization uncertainty margins of 0 mm, 2.5 mm, and 5.0 mm. The beam intensities were then applied on repeat computed tomography (CT) scans obtained weekly during treatment, and dose distributions were recalculated. The dose–volume histogram analysis for the repeat CT scans showed that target coverage was adequate (V100 ≥ 95%) for only 12.5% of the gross tumour volumes, 54.3% of the upper-neck clinical target volumes (CTVS), and 27.4% of the lower-neck CTVS when no margins were added for PTV. The use of 2.5-mm and 5.0-mm margins significantly improved target coverage, but the mean dose to the contralateral parotid increased from 25.9 Gy to 29.2 Gy. Maximum dose to the spinal cord was above limit in 57.7%, 34.6%, and 15.4% of cases when 0-mm, 2.5-mm, and 5.0-mm margins (respectively) were used for PRV. Significant deviations from the prescribed dose can occur during IMRT treatment delivery for headand- neck cancer. The use of 2.5-mm to 5.0-mm margins for PTV and PRV greatly reduces the risk of underdosing targets and of overdosing the spinal cord.

Accelerated radiotherapy with simultaneous integrated boost fractionation and intensity‐modulated radiotherapy for advanced head and neck cancer

“…A margin of 3 to 5 mm was added around the GTV and CTV to account for uncertainties in setup and organ motion and to obtain the planning target volume (PTV). We have previously reported that these margins are effective in preventing significant deviation from the prescribed dose in these patients 13 . The CT images and structure sets were then transferred to a commercially available inverse treatment planning system (CORVUS, V.5.0, NOMOS Corp) to generate IMRT plans.…”

“…We have previously reported that these margins are effective in preventing significant deviation from the prescribed dose in these patients. 13 The CT images and structure sets were then transferred to a commercially available inverse treatment planning system (CORVUS, V.5.0, NOMOS Corp) to generate IMRT plans.…”

Adaptive Volumetric-Modulated Arc Radiation Therapy for Head and Neck Cancer: Evaluation of Benefit on Target Coverage and Sparing of Organs at Risk

“…These modifications can be related to multiple factors, such as (1) shrinkage of large tumor and/or nodal masses; (2) weight loss; and (3) resolution of post-operative changes. Different studies have shown that the radiation dose to the target volume and organs at risk can vary significantly due to spatial and volume variability during treatment [ 6 , 7 ]; thus, the re-planning of treatment with adaptive radiotherapy may ensure adequate doses to the target volumes despite these anatomical changes [ 8 ]. Prospective trials are now evaluating the clinical benefit of adaptive radiotherapy.…”

A convolutional neural network for estimating cone-beam CT intensity deviations from virtual CT projections

“…Inter-fractional changes in patient anatomy constitute a significant source of error in external-beam radiotherapy. During the course of treatment, drastic changes in patient anatomy can occur due to weight loss (Müller et al (2015) found patients lost up to 12.8 kg over the course of a radiotherapy schedule), as well as tumor and surrounding tissue shrinkage (Ballivy et al 2006, Hansen et al 2006, Loo et al 2010, where (Barker et al 2004) showed head and neck (HN) tumors can shrink up to 69.5% over the course of treatment. Adaptive radiotherapy (ART) can reduce dosimetric errors linked to anatomical changes by re-optimizing treatment parameters based on patient anatomy of the day.…”