Anatomic and dosimetric changes in patients with head and neck cancer treated with an integrated MRI-tri-⁶⁰Co teletherapy device

Abstract

Objective: Prior studies have relied on CT to assess alterations in anatomy among patients undergoing radiation for head and neck cancer. We sought to determine the feasibility of using MRI-based image-guided radiotherapy to quantify these changes and to ascertain their potential dosimetric implications. Methods: 6 patients with head and neck cancer were treated with intensity-modulated radiotherapy (IMRT) on a novel tri- 60Co teletherapy system equipped with a 0.35-T MRI (VR, ViewRay Incorporated, Oakwood Village, OH) to 66-70 Gy in 33 fractions (fx). Pre-treatment MRIs on Fx 1, 5, 10, 15, 20, 25, 30 and 33 were imported into a contouring interface, where the primary gross tumour volume (GTV) and parotid glands were delineated. The centre of mass (COM) shifts for these structures were assessed relative to Day 1. Dosimetric data were co-registered with the MRIs, and doses to the GTV and parotid glands were assessed.Results: Primary GTVs decreased significantly over the course of IMRT (median % volume loss, 38.7%; range, 29.5-72.0%; p , 0.05) at a median rate of 1.2%/ fx (range, 0.92-2.2%/fx). Both the ipsilateral and contralateral parotid glands experienced significant volume loss (p , 0.05, for all) and shifted medially during IMRT. Weight loss correlated significantly with parotid gland volume loss and medial COM shift (p , 0.05). Conclusion: Integrated on-board MRI can be used to accurately contour and analyze primary GTVs and parotid glands over the course of IMRT. COM shifts and significant volume reductions were observed, confirming the results of prior CT-based exercises. Advances in knowledge: The superior resolution of onboard MRI may facilitate online adaptive replanning in the future.

Head and Neck Cancer Adaptive Radiation Therapy (ART): Conceptual Considerations for the Informed Clinician

“…Consequently, interval OAR/GTV deformations during therapy are unincorporated, and dose is "forward projected" with increasingly large temporal and geometric differential(s) from the planning scan. This approach is currently the default implementation for the 0.35T ViewRay system for MRguided RT systems (as detailed by Raghavan et al (30), in a study where registration of the MRI Fraction to the initial MRI planning was performed prior to manual segmentation), and the initial 510k-compliant 1.5T Elekta MR-LinAc configuration (2ATL), which allows rigid registration of MRI planning to daily fractions, and either a "adapt-to-point" (virtual isocentric alignment) or "adapt-to-shape" (volume-based replanning).…”

Single-Institute Clinical Experiences Using Whole-Field Simultaneous Integrated Boost (SIB) Intensity-Modulated Radiotherapy (IMRT) and Sequential IMRT in Postoperative Patients With Oral Cavity Cancer (OCC)

“…Patients with OCC tend to experience changes in the soft tissue and flap throughout the course of RT, along with interfractional anatomic changes that may result in an unpredictable geographic miss. 5 - 8 , 30 Miyazaki et al reported that SIB with a sequential re-SIB plan had a significantly lower spinal cord Dmax than that of the initial SIB plan. 27 Additionally, the degree of dose inhomogeneity inside PTV1 was analyzed using the standard deviation parameter, demonstrating better homogeneity for the sequential technique and worse homogeneity for the SIB technique.…”

“…[1][2][3] In contrast, if different dose levels are delivered simultaneously during IMRT to different target volumes within a single treatment fraction, that procedure is known as the "SIB-IMRT" technique. 2,4 Patients with head and neck squamous cell carcinoma (HNSCC) tend to undergo changes in soft tissues and body weight throughout the course of radiotherapy (RT), 5,6 causing great deviation in the dose delivered to the planning target volume (PTV) and normal tissues outside the PTV, 7 which may result in an unpredictable geographic miss. 8 Additionally, SIB-IMRT might present a risk of locoregional failure due to the low marginal doses when the doses given to the adjacent critical structures or other normal tissues are the major concern in the high-dose region.…”

MR-Guided Radiotherapy for Head and Neck Cancer: Current Developments, Perspectives, and Challenges

“…Although there is a lack of prospective clinical trials evaluating the objective benefit of ART for HNC, several dosimetric studies have been published so far, e.g., demonstrating an underestimation of the cumulative dose to the parotids when using the original non-adapted plan only, leading to increased probability for xerostomia ( 15 , 18 ). Raghavan et al were one of the first groups to demonstrate both a migration of the center of mass of the parotids, as well as a bilateral volume shrinkage in 6 HNC-patients, using an MRgRT-dedicated platform ( 19 ). An example of parotid migration and volume reduction demonstrated with the help of longitudinal imaging on the MR-Linac is shown on Figure 1A .…”