Characterization of the IDENTIFYTM surface scanning system for radiation therapy setup on a closed-bore linac.

PURPOSE: In radiation therapy, surface guidance can be used for patient setup and intra-fraction motion monitoring. The surface guided radiation therapy (SGRT) system from Varian Medical systems, IDENTIFYTM, consists of three pods, including cameras and a random pattern projector, mounted on the ceiling. The information captured by the cameras is used to make a reconstruction of the surface. The aim of the study was to assess the technical performance of this SGRT system on a closed-bore linac. METHODS: Phantom measurements were performed to assess the accuracy, precision, reproducibility and temporal stability of the system, both in align and in load position. Translations of the phantoms in lateral, longitudinal, and vertical direction, and rotations around three axes (pitch, roll and yaw) were performed with an accurate, in-house built, positioning stage. Different phantom geometries and different surface colors were used, and various ambient light intensities were tested. RESULTS: The accuracy of the IDENTIFYTM system at the closed-bore linac was 0.07 mm and 0.07 degrees at load position, and 0.06 mm and 0.01 degrees at align position for the white head phantom. The precision was 0.02 mm and 0.02 degrees in load position, and 0.01 mm and 0.02 degrees in align position. The accuracy for the Penta-Guide phantom was comparable to the white head phantom, with 0.06 mm and 0.01 degrees in align position. The system was slightly less accurate for translations of the CIRS lung phantom in align position (0.20 mm, 0.05 degrees). Reproducibility measurements showed a variation of 0.02 mm in load position. Regarding the temporal stability, the maximum drift over 30 min was 0.33 mm and 0.02 degrees in load position. No effect of ambient light level on the accuracy of the IDENTIFYTM system was observed. Regarding different surface colors, the accuracy of the system for a black phantom was slightly worse compared to a white surface, but not clinical relevant. CONCLUSION: The IDENTIFYTM system can adequately be used for motion monitoring on a closed-bore linac with submillimeter accuracy. The results of the performed measurements meet the clinical requirements described in the guidelines of the AAPM and the ESTRO.

Setup and intra-fractional motion measurements using surface scanning in head and neck cancer radiotherapy- A feasibility study.

Background and purpose: Surface-guided radiotherapy (SGRT) is applied to improve patient set-up and to monitor intra-fraction motion. Head and neck cancer (H&N) patients are usually fixated using 5-point thermoplastic masks, that are experienced as uncomfortable or even stressful. Therefore, the feasibility of irradiating H&N patients without a mask by using SGRT was examined. Material and methods: Nineteen H&N patients were included in a simulation study. Once a week, before the standard treatment, a maskless treatment was simulated, using SGRT for setup and intrafraction motion monitoring. Initial patient setup accuracy and intrafraction motion was determined using ConeBeam CT (CBCT) images as well as SGRT before and after the (simulated) treatment. The clinical target volume to planning target volume (CTV-PTV) margin for intrafraction motion was calculated. Using patient questionnaires, the patient-friendliness H&N irradiation with and without mask was determined. Results: Maskless setup with SGRT and CBCT was as accurate as with a mask. SGRT showed that intrafraction motion was gradual during the treatment. The CTV-PTV margin correcting for intrafraction motion was 1.7 mm for maskless treatment without interventions, and 1.2 mm if corrected for motions > 2 mm. For 19 % of fractions, the intrafraction motion, as detected by both SGRT and CBCT, was larger than 2 mm in at least one direction. Sixteen patients preferred maskless treatment, while 3 worried they would move too much. Conclusions: Using SGRT and a standard head rest resulted in a patient-friendly treatment with accurate patient setup and acceptably small intrafraction motion for H&N patients.

Dose coverage and breath-hold analysis of breast cancer patients treated with surface-guided radiotherapy.

BACKGROUND: Surface-guided radiotherapy (SGRT) is used to ensure a reproducible patient set-up and for intra-fraction motion monitoring. The arm position of breast cancer patients is important, since this is related to the position of the surrounding lymph nodes. The aim of the study was to investigate the set-up accuracy of the arm of patients positioned using SGRT. Moreover, the actual delivered dose was investigated and an extensive breath-hold analysis was performed. METHODS: 84 patients who received local or locoregional breast radiation therapy were positioned and monitored using SGRT. The accuracy of the arm position, represented by the clavicle position, was studied on the anterior-posterior kV-image. To investigate the effect of changes in anatomy and patient set-up, the actual delivered dose was calculated on cone-beam CT-scans (CBCT). A deformable registration of the CT to the CBCT was applied to deform the structures of the CT onto the CBCT. The minimum dose in percentage of the prescribed dose that was received by 98% of different CTV volumes (D98) was determined. An extensive breath-hold analysis was performed and definitions for relevant parameters were given. RESULTS: The arm position of 77 out of 84 patients in total was successful, based on the clavicle rotation. The mean clavicle rotation was 0.4° (± 2.0°). For 89.8% of the patients who were irradiated on the whole-breast D98 was larger than 95% of the prescribed dose (D98 > 95%). D98 > 95% applied for 70.8% of the patients irradiated on the chest wall. Concerning the lymph node CTVs, D98 > 95% for at least 95% of the patients. The breath-hold analysis showed a mean residual setup error of - 0.015 (± 0.90), - 0.18 (± 0.82), - 0.58 (± 1.1) mm in vertical, lateral, and longitudinal direction, respectively. The reproducibility and stability of the breath-hold was good, with median 0.60 mm (95% confidence interval (CI) [0.66-0.71] mm) and 0.20 mm (95% CI 0.21-0.23] mm), respectively. CONCLUSIONS: Using SGRT we were able to position breast cancer patients successfully, with focus on the arm position. The actual delivered dose calculated on the CBCT was adequate and no relation between clavicle rotation and actual delivered dose was found. Moreover, breath-hold analysis showed a good reproducibility and stability of the breath-hold. Trial registration CCMO register NL69214.028.19.

Geometrical analysis for motion monitoring of rigid bodies with optical surface scanning in radiation oncology.

BACKGROUND AND PURPOSE: Surface guided radiotherapy can be used to improve patient setup and for accurate intra-fraction motion monitoring in correspondence to the isocenter. For a clinical relevant motion analysis the actual displacement of the entire clinical target volume (CTV) is necessary. Therefore, the aim of this study was to develop a novel assessment method for intra-fraction motion for rigid body structures based on motion data and a geometrical analysis. MATERIALS AND METHODS: A threshold value on the volume coverage (VC(t)) of the CTV by the planning target volume (PTV) was proposed as online motion monitoring method. Moreover, offline analysis was performed by using heat maps and by calculating VCx, the volume coverage for at least x% of treatment time. The method was applied retrospectively to patient treatment data for whole brain radiation treatment without a thermoplastic mask. RESULTS: In 132 out of 142 fractions in total the proportion of the CTV that was inside the PTV for at least 99% of the time (VC99) was more than 95%, for a CTV-to-PTV margin of 5 mm. The source-voxel heat map showed which part of the CTV had a reduced coverage and the target heat map showed the movement of the CTV. CONCLUSION: Instead of using an action threshold on the movements of the isocenter, a threshold on the VC(t) of the CTV by the PTV was proposed. The heat maps and resulting values of VCx can be used to adapt the VC(t) threshold or the CTV-to-PTV margin for subsequent fractions.

Occurrence and mechanism of visual phosphenes in external photon beam radiation therapy and how to influence them.

BACKGROUND AND PURPOSE: Two plausible mechanisms to explain the appearance of visual phosphenes are: direct activation of the photochemicals in the retina and the generation of Cherenkov radiation in the vitreous humour. In this clinical trial we investigated the occurrence of visual phosphenes in external photon beam radiation therapy. MATERIAL AND METHODS: Logistic regression analysis is used to examine whether seeing light flashes and seeing steady light depended on the ambient light intensity and the dose. RESULTS: In total, 465 treatments of 25 patients were analysed. The odds of seeing light flashes multiply by 0,926 as the ambient light intensity increases by 10 lux. Similarly, the odds multiply by 1,604 as the dose to the retina increases by 10 cGy. The odds of seeing steady light multiply by 1,540 as the dose to the vitreous humour increases by 10 cGy. CONCLUSIONS: We postulate that one should reduce the dose rate, instruct patients to keep the eyes open and increase the illuminance in the treatment room to reduce the probability of experiencing visual phosphenes. We hypothesize that melanopsin is involved in the visual phosphenes and that fatigue of patients might be correlated with the observation of visual phosphenes.

Whole-brain radiation therapy without a thermoplastic mask.

The aim of the study was to investigate the clinical feasibility of whole-brain radiation therapy without a thermoplastic mask. Positioning and intra-fractional motion monitoring were performed using optical surface scanning. The motion threshold was 3 mm/3 degrees. The group mean vector deviation was 1.1 mm. The roll was larger compared to pitch and rotation. Two patients out of 30 were not able to lie still. All other patients completed their treatment successfully without a mask. With a probability of success of 93%, we concluded that irradiation without a mask is a clinically feasible method.

Sleep position trainer versus tennis ball technique in positional obstructive sleep apnea syndrome.

STUDY OBJECTIVE: Positional therapy (PT) is an effective therapy in positional obstructive sleep apnea syndrome (POSAS) when used, but the compliance of PT is low. The objective of this study was to investigate whether a new kind of PT is effective and can improve compliance. METHODS: 29 patients were treated with the Sleep Position Trainer (SPT), 26 patients with the Tennis Ball Technique (TBT). At baseline and 1 month polysomnography, Epworth Sleepiness Scale (ESS) and the Quebec Sleep Questionnaire (QSQ) were taken. Daily compliance was objectively measured in both groups. RESULTS: Both therapies prevent supine sleep position to a median of 0% (min-max: SPT 0.0% to 67%, TBT 0.0% to 38.9%), resulting in a treatment success (AHI <5) in 68.0% of the SPT and 42.9% of the TBT patients. The ESS at baseline was <10 in both groups. Sleep quality parameters as wake after sleep onset (WASO; p = 0.001) and awakenings (p = 0.006) improved more in the SPT group. Total QSQ scores (0.4±0.2, p = 0.03) and the QSQ domains nocturnal symptoms (0.7±0.2, p = 0.01) and social interactions (0.8±0.3, p = 0.02) changed in favor of the SPT group. Effective compliance (≥4 h/night + ≥5 days/week) was 75.9% for the SPT and 42.3% for the TBT users (p = 0.01). CONCLUSION: In mild POSAS with normal EES the new SPT device and the standard TBT are equally effective in reducing respiratory indices. However, compared to the TBT, sleep quality, quality of life, and compliance improved significantly more in the SPT group.