Multiple regions-of-interest analysis of setup uncertainties for head-and-neck cancer radiotherapy

Self Cite

The purpose of this study was to investigate the setup and positioning uncertainty of a custom cushion/mask/bite‐block (CMB) immobilization system and determine PTV margin for image‐guided head and neck stereotactic ablative radiotherapy (HN‐SABR). We analyzed 105 treatment sessions among 21 patients treated with HN‐SABR for recurrent head and neck cancers using a custom CMB immobilization system. Initial patient setup was performed using the ExacTrac infrared (IR) tracking system and initial setup errors were based on comparison of ExacTrac IR tracking system to corrected online ExacTrac X‐rays images registered to treatment plans. Residual setup errors were determined using repeat verification X‐ray. The online ExacTrac corrections were compared to cone‐beam CT (CBCT) before treatment to assess agreement. Intrafractional positioning errors were determined using prebeam X‐rays. The systematic and random errors were analyzed. The initial translational setup errors were −0.8±1.3 mm, −0.8±1.6 mm, and 0.3±1.9 mm in AP, CC, and LR directions, respectively, with a three‐dimensional (3D) vector of 2.7±1.4 mm. The initial rotational errors were up to 2.4° if 6D couch is not available. CBCT agreed with ExacTrac X‐ray images to within 2 mm and 2.5°. The intrafractional uncertainties were 0.1±0.6 mm, 0.1±0.6 mm, and 0.2±0.5 mm in AP, CC, and LR directions, respectively, and 0.0∘±0.5°, 0.0∘±0.6°, and −0.1∘±0.4∘ in yaw, roll, and pitch direction, respectively. The translational vector was 0.9±0.6 mm. The calculated PTV margins normalmPTVfalse(90,95false) were within 1.6 mm when using image guidance for online setup correction. The use of image guidance for online setup correction, in combination with our customized CMB device, highly restricted target motion during treatments and provided robust immobilization to ensure minimum dose of 95% to target volume with 2.0 mm PTV margin for HN‐SABR.PACS number(s): 87.55.ne

“…For example, tongue base or oral cavity targets may see up to 3 mm 3D shifts, while targets closer to skull base and more centrally located, including retropharyngeal nodes, typically require

< 1.5 mm

shifts and

< {1.5}^{\circ}

Section: Discussionsupporting

confidence: 92%

“…To account for positional uncertainty of the cervical spine as shown in prior studies, (11) results were also compared separately between skull base targets (Group 1, 11 patients, 55 sessions) and targets below C1 (Group 2, 10 patients, 50 sessions).…”

Section: Methodsmentioning

confidence: 99%

Improved setup and positioning accuracy using a three‐point customized cushion/mask/bite‐block immobilization system for stereotactic reirradiation of head and neck cancer

Wang

Tung

et al. 2016

Self Cite

“…Zhang et al (11) used a CT‐on‐Rails system to measure ∑ and

σ_{RMS} 3

times weekly throughout treatment at various anatomic landmarks. Another CT study by Guckenberger et al (9) used automated bony matching of cone‐beam CT to measure setup error in 8 head‐and‐neck patients.…”

Section: Discussionmentioning

confidence: 99%

“…The entire image was rigidly rotated, and the best match between the reference and OBI image was chosen. The measured rotational errors may therefore not be the same as non‐rigid “head rotation,” which has been measured as rotation around C2 in a recent paper by Zhang et al (11) …”

Section: Methodsmentioning

confidence: 99%

“…The former reflect setup differences from day to day, and the latter, changes in patient position during a treatment session. Setup verification studies more often measure the former ( 4 – 11 ) , but some measure the latter. ( 7 , 10 ) Measurement of interfractional and intrafractional setup error through the course of treatment therefore requires repeated imaging of the patient on the treatment table.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Using an onboard kilovoltage imager to measure setup deviation in intensity‐modulated radiation therapy for head‐and‐neck patients

Mechalakos

Hunt

Lee

et al. 2007

The purpose of the present study was to use a kilovoltage imaging device to measure interfractional and intrafractional setup deviations in patients with head‐and‐neck or brain cancers receiving intensity‐modulated radiotherapy (IMRT) treatment.Before and after IMRT treatment, approximately 3 times weekly, 7 patients were imaged using the Varian On‐Board Imager (OBI: Varian Medical Systems, Palo Alto, CA), a kilovoltage imaging device permanently mounted on the gantry of a Varian 21EX LINAC (Varian Medical Systems). Because of commissioning of the remote couch correction of the OBI during the study, online setup corrections were performed on 2 patients. For the other 5 patients, weekly corrections were made based on a sliding average of the measured data. From these data, we determined the interfractional setup deviation (defined as the shift from the original setup position suggested by the daily image), the residual error associated with the weekly correction protocol, and the intrafractional setup deviation, defined as the difference between the post‐treatment and pretreatment images. We also used our own image registration software to determine interfractional and intrafractional rotational deviations from the images based on the template‐matching method. In addition, we evaluated the influence of inter‐observer variation on our results, and whether the use of various registration techniques introduced differences. Finally, translational data were compared with rotational data to search for correlations.Translational setup errors from all data were 0.0±0.2 cm, −0.1±0.3 cm, and −0.2±0.3 cm in the right–left (RL), anterior–posterior (AP), and superior–inferior (SI) directions respectively. Residual error for the 5 patients with a weekly correction protocol was −0.1±0.2 cm (RL), 0.0±0.3 cm (AP), and 0.0±0.2 cm (SI). Intrafractional translation errors were small, amounting to 0.0±0.1 cm, −0.1±0.2 cm, and 0.0±0.1 cm in the RL, AP, and SI directions respectively. In the sagittal and coronal views respectively, interfractional rotational errors were −1.1±1.7 degrees and −0.5±0.9 degrees, and intrafractional rotational errors were 0.3±0.6 degrees and 0.2±0.5 degrees. No significant correlation was seen between translational and rotational data.The OBI image data were used to study setup error in the head‐and‐neck patients. Nonzero systematic errors were seen in the interfractional translational and rotational data, but not in the intrafractional data, indicating that the mask is better at maintaining head position than at reproducing it.PACS numbers:87.53.Kn, 87.53.Oq

Exploratory study of the association of volumetric modulated arc therapy (VMAT) plan robustness with local failure in head and neck cancer

Liu

Patel

Harrington

et al. 2017

This work is to show which is more relevant to cause local failures (LFs) due to patient setup uncertainty between the planning target volume (PTV) underdosage and the potential target underdosage subject to patient setup uncertainties in head and neck (H&N) cancer treated with volumetric‐modulated arc therapy (VMAT). Thirteen LFs in 10 H&N patients treated by VMAT were analyzed. Measures have been taken to minimize the chances of insufficient target delineation for these patients and the patients were clinically determined to have LF based on the PET/CT scan results by an experienced radiologist and then reviewed by a second experienced radiation oncologist. Two methods were used to identify the possible locations of LF due to underdosage: (a) examining the standard VMAT plan, in which the underdosed volume in the nominal dose distribution (UVN) was generated by subtracting the volumes receiving the prescription doses from PTVs, and (b) plan robustness analysis, in which in addition to the nominal dose distribution, six perturbed dose distributions were created by translating the CT iso‐center in three cardinal directions by the PTV margin. The coldest dose distribution was represented by the minimum of the seven doses in each voxel. The underdosed volume in the coldest dose distribution (UVC) was generated by subtracting the volumes receiving the prescription doses in the coldest dose distribution from the volumes receiving the prescription doses in the nominal dose distribution. UVN and UVC were subsequently examined for spatial association with the locations of LF. The association was tested using the binominal distribution and the Fisher's exact test of independence. We found that of 13 LFs, 11 were associated with UVCs (P = 0.011), while three were associated with UVNs (P = 0.99). We concluded that the possible target underdosage due to patient setup uncertainties appeared to be a more relevant factor associated with LF in VMAT for H&N cancer than the compromised PTV coverage at least for the patients included in this study.