International Journal of Radiation Oncology*Biology*Physics
Physics ContributionHead and Neck Margin Reduction With Adaptive Radiation Therapy: Robustness of Treatment Plans Against Anatomy Changes
Introduction
Current planning and delivery techniques for head and neck cancer (HNC), such as intensity modulated radiation therapy and volumetric modulated arc therapy (VMAT), offer dose distributions conformal to the tumor with steep dose gradients, with superior sparing of organs at risk (OARs) (1). During treatment planning, safety margins around the targets are applied to account for geometric uncertainties such as delineation errors, uncorrected setup errors, and/or anatomy changes during treatment (2). With large margins, robust plans are created that ensure correct target dosage in case of large errors; however, substantial amounts of normal tissue may be irradiated. A reduction in geometric uncertainties would allow smaller safety margins and thereby increase the therapeutic window.
Image guided radiation therapy reduces geometric uncertainties. In-room imaging (eg, cone beam computed tomography [CBCT]) allows one to visualize (a surrogate of) the target volume in relation to OARs and derive a couch correction for alignment of the target volume or volumes with the treatment beams. In offline protocols, the systematic component of target positioning errors is estimated and corrected. Online protocols allow for near perfect correction of errors (3).
To further reduce uncertainties arising from nonrigid setup errors and anatomy changes (deformations), adaptive radiation therapy (ART) can be considered (4). Commonly, ART for HNC is based on a second computed tomography (CT) scan and used to address ad hoc observed treatment response (tumor regression, weight loss) 5, 6. Recently, however, ART based on an average anatomy model derived from CBCT has been proposed to reduce the impact of systematic deformations (7).
To improve the therapeutic ratio, we propose to use small margins, evaluate delivered dose with CBCT, and use adaptive strategies in case of target underdosage when needed. To test the feasibility of such an approach, we investigated (1) changes in dose to clinical target volumes (CTVs) and OARs from deformations in HNC patients as a function of applied safety margins; and (2) a CBCT-based adaptive strategy with an average anatomy model to overcome loss of coverage in selected patients.
Section snippets
Patient group
We retrospectively selected 19 patients with oropharyngeal cancers that were treated with curative intent. Patient data were accessed according to institutional guidelines. The T category distribution was T1 in 2 patients, T2 in 7, T3 in 8, and T4 in 2. Three patients did not have nodal involvement. The planning computed tomography (pCT) scan (Somatom Sensation Open; Siemens, Erlangen, Germany) had a voxel size of 1 × 1 × 3 mm3. Daily CBCT scans (Elekta Synergy; Elekta Oncology Systems,
Results
For the 19 selected patients, plans with 5-, 3-, and 0-mm margins were generated that fulfilled minimal requirements (Supplementary Material; available online at www.redjournal.org). A total of 651 CBCT scans underwent deformable registration to the corresponding pCT scans, and DVFs were visually inspected.
Discussion
In this study the potential of ART for anatomy changes during radiation therapy (RT) of HNC was assessed based on accumulated dose in daily CBCT scans. For 73 CTVs in 19 patients, VMAT treatment plans with 5-mm safety margins were adequate in all but 1 CTV. When margins were reduced, loss of target coverage (D99%<95% prescribed dose) increased to 27% of all CTVs (at 0-mm margins) but discrepancies with planned dose were small. Margin reduction led to sparing of approximately 1 Gy/mm in
Conclusions
In this study, the potential of ART for anatomy changes during RT of HNC was assessed based on accumulated dose in daily CBCT scans. For 73 target volumes in 19 patients, VMAT treatment plans with 5-mm safety margins were adequate in all but 1 target volume. Modest extra OAR dose was present. Margin reduction led to an improvement in OAR dose of approximately 1 Gy/mm. With 3- and 0-mm margins, dose to 2 targets and 20 targets, respectively, was compromised, although large discrepancies (>2 Gy)
References (27)
- et al.
Volumetric intensity-modulated arc therapy vs. conventional IMRT in head-and-neck cancer: A comparative planning and dosimetric study
Int J Radiat Oncol Biol Phys
(2009) Errors and margins in radiotherapy
Semin Radiat Oncol
(2004)- et al.
Evaluation of image-guidance protocols in the treatment of head and neck cancers
Int J Radiat Oncol Biol Phys
(2007) - et al.
Adaptive radiotherapy for head-and-neck cancer: Initial clinical outcomes from a prospective trial
Int J Radiat Oncol Biol Phys
(2012) - et al.
Adaptive radiotherapy with an average anatomy model: Evaluation and quantification of residual deformations in head and neck cancer patients
Radiother Oncol
(2013) - et al.
Automated VMAT treatment planning for head and neck cancer
Radiother Oncol
(2013) - et al.
Deformable Image Registration for Adaptive Radiation Therapy of Head and Neck Cancer: Accuracy and Precision in the Presence of Tumor Changes
Int J Radiat Oncol Biol Phys
(2014) - et al.
Automatic segmentation and online virtualCT in head-and-neck adaptive radiation therapy
Int J Radiat Oncol Biol Phys
(2012) - et al.
Setup uncertainties of anatomical sub-regions in head-and-neck cancer patients after offline CBCT guidance
Int J Radiat Oncol Biol Phys
(2009) - et al.
First clinical experience with a multiple region of interest registration and correction method in radiotherapy of head-and-neck cancer patients
Radiother Oncol
(2010)
Adaptive replanning strategies accounting for shrinkage in head and neck IMRT
Int J Radiat Oncol Biol Phys
Anatomic and dosimetric changes during the treatment course of intensity-modulated radiotherapy for locally advanced nasopharyngeal carcinoma
Med Dosim
Weekly volume and dosimetric changes during chemoradiotherapy with intensity-modulated radiation therapy for head and neck cancer: A prospective observational study
Int J Radiat Oncol Biol Phys
Cited by (41)
Adaptive radiation therapy: When, how and what are the benefits that literature provides?
2022, Cancer/RadiotherapieCitation Excerpt :In general, larger deviations were reported in the nodal GTV compared to the primary GTV. In nine studies (9/85) CTV volume deviations were reported [27,33,40,51,66,82,85,87,97] and in two studies (2/55) deviations in PTV volume [30,38]. Apparently, PTV volume deviations considered to be larger even though the margins of CTVs were the same as in the initial plan.
Human-level comparable control volume mapping with a deep unsupervised-learning model for image-guided radiation therapy
2022, Computers in Biology and Medicine
Supported by a grant from the Dutch Cancer Society (NKI:2005-3378).
Conflict of interest: none.