BackgroundCancer control outcomes of lung cancer are hypothesized to be affected by several confounding factors, including tumor heterogeneity and patient history, which have been hypothesized to mitigate the dose delivery effectiveness when treated with radiation therapy. Providing an accurate predictive model to identify patients at risk would enable tailored follow-up strategies during treatment.PurposeOur goal is to demonstrate the added prognostic value of including tumor displacement amplitude in a predictive model that combines clinical features and computed tomography (CT) radiomics for 2-year recurrence and survival in non-small-cell lung cancer (NSCLC) patients treated with curative-intent stereotactic body radiation therapy.MethodsA cohort of 381 patients treated for primary lung cancer with radiotherapy was collected, each including a planning CT with a dosimetry plan, 4D-CT, and clinical information. From this cohort, 101 patients (26.5%) experienced cancer progression (locoregional/distant metastasis) or death within 2 years of the end of treatment. Imaging data was analyzed for radiomics features from the tumor segmented image, as well as tumor motion amplitude measured on 4D-CT. A random forest (RF) model was developed to predict the overall outcomes, which was compared to three other approaches - logistic regression, support vector machine, and convolutional neural networks.ResultsA 6-fold cross-validation study yielded an area under the receiver operating characteristic curve of 72% for progression-free survival when combining clinical data with radiomics features and tumor motion using a RF model (72% sensitivity and 81% specificity). The combined model showed significant improvement compared to standard clinical data. Model performances for loco-regional recurrence and overall survival sub-outcomes were established at 73% and 70%, respectively. No comparative methods reached statistical significance in any data configuration.ConclusionsCombined tumor respiratory motion and radiomics features from planning CT showed promising predictive value for 2-year tumor control and survival, indicating the potential need for improving motion management strategies in future studies using machine learning-based prognosis models.

IntroductionThis study develops two new multi-institutional hippocampal-sparing whole-brain RapidPlan™ models (HLS-EC-WB and HMS-EC-WB) inspired by CCTG-CE.7 featuring enhanced target coverage with varying hippocampal sparing (limited and moderate).MethodsNew dosimetric scorecards were created to quantify the models’ clinical intent. The models were trained using a multi-institution dataset, and a recursive method was employed to generate consistent, high-quality plans. The models were validated using a five-case set and compared at 20- and 30-Gy prescriptions.ResultsEach model scored highest on its associated dosimetric scorecard. The new models achieved higher brain PTV prescription coverage (98%–99%) compared to the previous HSWBv2 model (95.12%), with some trade-off in hippocampal sparing.ConclusionsThree high-quality automated RapidPlan™ models for hippocampal-sparing whole brain are now available, each with a distinct dosimetric scorecard. The new models prioritize increased PTV coverage at some expense to hippocampal sparing. All models, example plans, scorecards, and scoring tools are freely available online.

Purpose/Objective(s) Stereotactic ablative body radiotherapy (SABR) is an emerging treatment option for lung cancer patients with interstitial lung disease (ILD). Identifying patients who are at greater risk of toxicity after SABR would help personalize their treatment. The aim of this study was to develop and validate methods to predict pulmonary toxicity in patients with ILD receiving SABR using radiomic and dosimetric-based machine learning methods. Materials/Methods This retrospective study used data from the ASPIRE-ILD clinical trial, currently the largest multi-centre trial investigating the use of SABR for the treatment of lung cancer patients with ILD. Dose-volume histogram features were calculated from the treatment plans and included the Vx, as both a percentage and volume, in steps of 5 Gy from 5 to 60 Gy, the mean and max lung dose, the D2cm, and the R50. Radiomic features were calculated from the lung volume of each patient's diagnostic pre-treatment CT scan using open source software. Additionally, deep learning-based features were extracted from each CT scan using a UNet convolutional neural network (CNN). The AdaBoost algorithm for boosted decision trees was used to train a prediction model for the binary prediction of grade ≥ 2 pulmonary toxicity, splitting the patient cohort into low and high-risk groups. Different combinations of feature sources were tested to determine the source of any predictive power and a leave-one-out cross-validation approach was applied to test over the full dataset. Results Baseline planning scans and diagnostic imaging was available from all 39 patients, of whom 11 developed grade ≥ 2 CTCAE v5 pulmonary toxicity with dyspnea (n=7) and pneumonitis (n=3) being the predominant toxicities. The best-performing model included dose, CT radiomic and CT deep learning features to achieve an AUC of 0.841 with a sensitivity of 81.8% and a specificity of 78.6%. This model correctly classified 9/15 patients as high-risk and 22/24 patients as low-risk giving a precision and negative predictive value of 60% and 92% respectively. Table 1 displays all model results. Conclusion A radiomic- and dosimetric-based machine learning method to predict the occurrence of pulmonary toxicity in lung cancer patients with ILD receiving SABR has been developed and validated. To our knowledge, this is the first study showing the benefit of radiomic and deep learning CT features, or to use of machine learning for stratifying these patients into low- and high-risk groups. Validation in a larger and more diverse dataset is needed.

Purpose/Objective(s) The SUNSET phase I trial investigated the maximum tolerated dose for ultracentral (UC) lung tumors treated with stereotactic body radiotherapy (SBRT). Here we report a detailed spatial and dosimetric secondary analysis of the treatment plan and assess relationships between doses to targets, organs-at-risk (OARs) and clinical outcomes. Materials/Methods Five Canadian institutions enrolled patients with UC primary lung cancer, cT1-3N0M0, and all received SBRT to a dose of 60 Gy in 8 daily fractions. Maximum dose (Dmax) was limited to 120% of prescription. Targets were delineated as internal target volume (ITV) (combining gross tumor volume (GTV) across respiratory phases) expanded by 5 mm to form planning target volume (PTV). All OARs including great vessels and bilateral proximal bronchial tree up to segmental bronchus were contoured at baseline. To evaluate OAR and target doses, planning datasets and treatment plans were imported into a central repository. Descriptive statistics were generated for baseline characteristics and dosimetry. Univariable logistic and Cox proportional hazards regression modelling were performed to identify significant dosimetric predictors for related grade ≥ 2 adverse events (CTCAE v4.0), overall survival (OS) and local control (LC). Results All 30 enrolled patients (13 males, 17 females) were included in this sub-study. At median follow-up of 36.5 months, 9 patients (30.0%) experienced grade 2 adverse events and 1 patient (3.3%) each with grade 3(dyspnea) and 5(infection) attributed to treatment. Median ITV and PTV sizes were 11.3 cc (IQR: 6.2-26.8) and 34.4 cc (IQR: 21.9-62.2), respectively. PTV overlapped with at least one OAR for all patients, most commonly the proximal bronchial tree (PBT) or trachea (27/30). Additionally, a second overlapping structure was identified in 26/30 patients, most commonly the pulmonary artery (14/26) and esophagus (9/26). The mean overlap of first and second OAR with PTV were 0.95 cc (range = 0-4.2) and 0.7 cc (range = 0-4.7), respectively. The mean Dmax was 69.4 Gy (range = 64-72.5 Gy); all were within the PTV. Mean (± SD) PTV D98 was 56.1 ± 7.8 Gy, while D0.1 cc of PBT, esophagus and pulmonary artery were 53.1 ± 12.6 Gy, 26.5 ± 10.5 Gy and 57 ± 8.6 Gy, respectively. On analysis, combined overlap volume (cc) of the two primary overlapping OARs with PTV was associated with statistically significant inferior LC (hazard ratio [HR] per 1 cc increase: 2.86, P = 0.012); however, overlap volume was not associated with an increase in grade ≥ 2 adverse events (odds ratio [OR] per 1 cc increase: 1.17, P = 0.49). There was no association between OAR doses (D1 cc/D0.1 cc) with toxicity. PTV under-coverage (D98) was not associated with worse LC (HR per 5 Gy increase: 1.54, P = 0.68). Conclusion Within the dose constraints used in the trial, there was no relationship identified between OAR doses and toxicity. Local control decreased with increasing overlap of PTV with OARs, however, this was not associated with dosimetric under-coverage of the target.

Abstract Background While IAEA's TRS‐483 code of practice is adapted for the calibration of CyberKnife machines, AAPM's TG‐51 is still the protocol recommended by the manufacturer for their calibration. The differences between both protocols could lead to differences in absorbed dose to water during the calibration process. Purpose The aims of this work are to evaluate the difference resulting from the application of TG‐51 (including the manufacturer's adaptations) and TRS‐483 in terms of absorbed dose to water for a CyberKnife M6, and to evaluate the consistency of TRS‐483. Methods Measurements are performed on a CyberKnife M6 unit under machine‐specific reference conditions using a calibrated Exradin A12 ionization chamber. Monte Carlo (MC) simulations are performed to estimate kQmsr,Q0fmsr,fref and kvol using a fully modeled detector and an optimized CyberKnife M6 beam model. The latter is also estimated experimentally. Differences between the adapted TG‐51 and TRS‐483 protocols are identified and their impact is quantified. Results When using an in‐house experimentally‐evaluated volume averaging correction factor, a difference of 0.11% in terms of absorbed dose to water per monitor unit is observed when applying both protocols. This disparity is solely associated to the difference in beam quality correction factor. If a generic volume averaging correction factor is used during the application of TRS‐483, the difference in calibration increases to 0.14%. In both cases, the disparity is not statistically significant according to TRS‐483's reported uncertainties on their beam quality correction factor (i.e., 1%). MC results lead to kQmsr,Q0fmsr,fref=1.0004±0.0002 and kvol=1.0072±0.0009. Results illustrate that the generic beam quality correction factor provided in the TRS‐483 might be overestimated by 0.36% compared to our specific model and that this overestimation could be due to the volume averaging component. Conclusions For clinical reference dosimetry of the CyberKnife M6, the application of TRS‐483 is found to be consistent with TG‐51.

Although this study demonstrates the presence of moderate IOV between 3 experienced head and neck ROs and one radiologist in an academic institution for the delineation of GTV on planning MRI, we observed a higher IOV between the 4 experts on mid-treatment MRI. We also experienced a higher IOV between the radiologist and RO on planning and mid-treatment images. These results show high degree of GTV volume variability on mid-treatment MRI. Therefore, peer review of contours is important and guidelines for MR adaptive tumor delineation are needed.

INTRODUCTION:To assess patterns of recurrence after stereotactic ablative radiotherapy (SABR) in patient ineligible to surgery with early-stage non-small cell lung cancer (ES-NSCLC), report survival and treatment after first recurrence. METHODS:We performed a retrospective analysis on 1068 patients with ES-NSCLC and 1143 lesions. Between group differences were estimated using competing risk analysis and cause-specific hazard ratios were calculated. Overall survival (OS) after first recurrence was calculated. RESULTS:Median follow-up was 37.6 months. Univariate analysis demonstrated that ultra-central location was associated with higher risk of regional recurrence (RR) and distant metastasis (DM) (p = 0.004 and 0.01). Central lesions were associated with higher risk of local recurrence (LR) and RR (p < 0.001). Ultra-central lesions were associated with shorter OS (p = 0.002) compared to peripheral lesions. In multivariate analysis, central location was the only factor associated with increased LR and RR risks (p = 0.016 and 0.005). Median OS after first recurrence was 14.8 months. There was no difference in OS after first recurrence between ultra-central, central, and peripheral lesions (p = 0.83). Patients who received a second SABR course had an OS of 51.3 months, compared to 19.5 months with systemic therapy and 8.1 months with supportive care (p < 0.0001). DISCUSSION:The main prognostic factor for LR and RR risks was central location. Ultra-central and central tumors might benefit from treatment intensification strategies such as dose escalation and/or addition of systemic therapy to improve radiotherapy outcomes. After a first recurrence post SABR, patients with contralateral lung recurrences and those who were eligible to receive a second course of SABR had improved OS.

The oligometastatic state refers to a clinical scenario where a cancer is no longer localized, but not yet widely metastatic. Although many trials define the oligometastatic state as 1 to 3 or 1 to 5 metastatic lesions, there is no universally accepted definition. 1 Palma DA Olson R Harrow S et al. Stereotactic ablative radiotherapy versus standard of care palliative treatment in patients with oligometastatic cancers (SABR-COMET): A randomized, phase 2, open-label trial. Lancet. 2019; 393: 2051-2058 Abstract Full Text Full Text PDF PubMed Scopus (920) Google Scholar , 2 Gomez DR Blumenschein Jr., GR Lee JJ et al. Local consolidative therapy versus maintenance therapy or observation for patients with oligometastatic non-small-cell lung cancer without progression after first-line systemic therapy: A multicentre, randomised, controlled, phase 2 study. Lancet Oncol. 2016; 17: 1672-1682 Abstract Full Text Full Text PDF PubMed Scopus (665) Google Scholar , 3 Iyengar P Wardak Z Gerber DE et al. Consolidative radiotherapy for limited metastatic non-small-cell lung cancer: A phase 2 randomized clinical trial. JAMA Oncol. 2018; 4:e173501 Crossref Scopus (528) Google Scholar , 4 Ruers T Punt C Van Coevorden F et al. Radiofrequency ablation combined with systemic treatment versus systemic treatment alone in patients with non-resectable colorectal liver metastases: A randomized EORTC Intergroup phase II study (EORTC 40004). Ann Oncol. 2012; 23: 2619-2626 Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar A recently published ESTRO-ASTRO consensus article, in defining oligometastasis, states that "the possibility to safely deliver curative intent metastasis-directed radiation therapy determines the maximum number." 5 Lievens Y Guckenberger M Gomez D et al. Defining oligometastatic disease from a radiation oncology perspective: An ESTRO-ASTRO consensus document. Radiother Oncol. 2020; 148: 157-166 Abstract Full Text Full Text PDF PubMed Scopus (175) Google Scholar However, the maximum number of metastases that can be safely treated is unknown.

Owing to its short computation time and simplicity, the Ray-Tracing algorithm (RAT) has long been used to calculate dose distributions for the CyberKnife system. However, it is known that RAT fails to fully account for tissue heterogeneity and is therefore inaccurate in the lung. The aim of this study is to make a dosimetric assessment of 219 non-small cell lung cancer CyberKnife plans by recalculating their dose distributions using an independent Monte Carlo (MC) method. For plans initially calculated by RAT without heterogeneity corrections, target coverage was found to be significantly compromised when considering MC doses. Only 35.4% of plans were found to comply to their prescription doses. If the normal tissue dose limits were respected in the treatment planning dose, the MC recalculated dose did not exceed these limits in over 97% of the plans. Comparison of RAT and recalculated-MC doses confirmed the overestimation of RAT doses observed in previous studies. An inverse correlation between the RAT/MC dose ratio and the target size was also found to be statistically significant (p < 10(-4)), consistent with other studies. In addition, the inaccuracy and variability in target coverage incurred from dose calculations using RAT without heterogeneity corrections was demonstrated. On average, no clinically relevant differences were observed between MC-calculated dose-to-water and dose-to-medium for all tissues investigated (<= 1%). Patients receiving a dose D-95(%) larger than 119 Gy in EQD2(10) (or approximate to 52 Gy in 3 fractions) as recalculated by MC were observed to have significantly superior loco-regional progression-free survival rates (p = 0.02) with a hazard ratio of 3.45 (95%CI: 1.14-10.5).

Background and Purpose: Previous literature suggests that the dose proximally outside the PTV could have an impact on the incidence of distant metastasis (DM) after SBRT in stage I NSCLC patients. We investigated this observation (along with local failure) in deliveries made by different treatment modalities: robotic mounted linac SBRT (CyberKnife) vs conventional SBRT (VMAT/CRT). Materials and methods: This study included 422 stage I NSCLC patients from 2 institutions who received SBRT: 217 treated conventionally and 205 with CyberKnife. The dose behavior outside the PTV of both sub-cohorts were compared by analyzing the mean dose in continuous shells extending 1, 2, 3,..., 100 mm from the PTV. Kaplan-Meier analysis was performed between the two sub-cohorts with respect to DM-free survival and local progression-free survival. A multivariable Cox proportional hazards model was fitted to the combined cohort (n = 422) with respect to DM incidence and local failure. Results: The shell-averaged dose fall-off beyond the PTV was found to be significantly more modest in CyberKnife plans than in conventional SBRT plans. In a 30 mm shell around the PTV, the mean dose delivered with CyberKnife (38.1 Gy) is significantly larger than with VMAT/CRT (22.8 Gy, p < 10(-8)). For 95% of CyberKnife plans, this region receives a mean dose larger than the 21 Gy threshold dose discovered in our previous study. In contrast, this occurs for only 75% of VMAT/CRT plans. The DM-free survival of the entire CyberKnife cohort is superior to that of the 25% of VMAT/CRT patients receiving less than the threshold dose (VMAT=CRT<21 Gy), with a hazard ratio of 5.3 (95% CI: 3.0-9.3, p < 10(-8)). The 2 year DM-free survival rates were 87% (95% CI: 81%-91%) and 44% (95% CI: 28%-58%) for CyberKnife and the below-threshold dose conventional cohorts, respectively. A multivariable analysis of the combined cohort resulted in the confirmation that threshold dose was a significant predictor of DM(HR = 0.28, 95% CI: 0.15-0.55, p < 10(-3)) when adjusted for other clinical factors. CyberKnife was also found to be superior to the entire VMAT/CRT with respect to local control (HR = 3.44, CI: 1.6-7.3). The 2-year local progression-free survival rates for the CyberKnife cohort and the VMAT/CRT cohort were 96% (95% CI: 92%-98%) and 88% (95% CI: 82%-92%) respectively. Conclusions: In standard-of-care CyberKnife treatments, dose distributions that aid distant control are achieved 95% of the time. Although similar doses could be physically achieved by conventional SBRT, this is not always the case with current prescription practices, resulting inworseDMoutcomes for 25% of conventional SBRT patients. Furthermore, CyberKnife was found to provide superior local control compared to VMAT/CRT. (C) 2020 Elsevier B.V. All rights reserved.

Accelerated partial breast irradiation is an option for some early stage breast cancer patients. The rationale of APBI consists of irradiating only the lumpectomy cavity and a margin that defines a volume where about 95% of the recurrence occurs after surgery. A smaller treated volume means a higher achievable dose per fraction and fewer fractions for a treatment with similar tumor control and toxicity rates. Its utilisation is increasing and a variety of technics can be used. The objective of this study is to compare the dosimetry of APBI plans delivered by high dose rate (HDR) brachytherapy and volumetric modulated arc therapy (VMAT). Twelve patients treated with brachytherapy were retrieved from our database. Eight patients were treated by APBI and received 33 Gy in 9 fractions BID (prescribed at V95≥5 %). Four patients received a boost as part of their treatment and their plans were adjusted to match the APBI prescription. All patients had a pre-implantation CT scan which was used to create VMAT plans following the OPAR protocol. The 30 Gy in 5 fractions prescription dose (prescribed at D100≥95%) was used to yield a biological equivalent dose similar to the HDR prescription. The t-test was used to compare HDR and VMAT dose distributions in terms of Dmax, Dmin, Dmean, and Vdose to targets and organs at risk. Firstly, the cavity's volumes were similar (VmeanVMAT=17.38±23.95 cc; VmeanHDR=18.40±20.13 cc) but not the CTV (VmeanVMAT=74.45±71.04 cc; VmeanHDR=18.40±20.13 cc). The HDR offers a higher cavity Dmean (DmeanVMAT=30.2±0.4 Gy; DmeanHDR=44.6±3.5 Gy). Small differences (p<0.001) were observed to the conformity index (CIVMAT=1.19±0.07 ; CIHDR=1.12±0.12), the ipsilateral lung V30 (V30VMAT=5.3±3.5 %; V30HDR=1.2±1.5 %) the contralateral breast Dmax (DmaxVMAT=0.622±0.236 Gy; DmaxHDR=0.246±0.163 Gy), and the heart Dmean (DmeanVMAT=0.433±0.193 Gy; DmeanHDR=0.624±0.355 Gy). No statistical difference were found in the dose to the contralateral lung, the contralateral breast Dmean (DmeanVMAT=0.141±0.063 Gy; DmeanHDR=0.047±0.029 Gy), the ipsilateral lung V10 (V10VMAT=12.8±5.6 %; V10HDR=12.7±9.3 %) and the heart Dmax (DmaxVMAT=0.472±0.633 Gy; DmaxHDR=0.324±0.280 Gy). Comparing VMAT and HDR APBI plans is complex due to their intrinsic differences, such as the prescription of the dose. That and the small number of patients included limit the conclusions that can be draw from our data. With that in mind, in this study, HDR brachytherapy allowed a higher dose at the cavity while effectively sparing OAR. Tough, both techniques offer a safe treatment, an adequate dose to the cavity and doses to the OAR well below the constraints, with minor dosimetric differences. Those nuances can guide the choice of a method to use for a specific patient considering some particularities such as the tumor location, the patient's comorbidities, previous irradiation and the preference of the patient.

L’objectif de cette étude était de quantifier les avantages dosimétriques de préservation cardiovasculaire de la tomothérapie hélicoïdale comparativement à des radiothérapies conformationnelle avec modulation d’intensité (RCMI) tangentielles. Des patientes atteintes d’un cancer du sein gauche ayant été pris en charge par une mastectomie partielle suivie d’une RCMI adjuvante de 42,5 Gy en 16 fractions tangentielle ont été incluses dans cette étude. Des plans de tomothérapie ont été rétrospectivement optimisés pour obtenir une couverture de volume cible prévisionnel (PTV) équivalente au plan de RCMI tangentielle. Un premier plan de tomothérapie (Tomo 1) a été optimisé selon les directives du Radiation Therapy Oncology Group (RTOG) 1005, qui limite la dose mammaire controlatérale maximale à 3,1 Gy. Un deuxième plan de tomothérapie (Tomo 2) a été optimisé sans contrôle de la dose mammaire controlatérale afin d’utiliser pleinement la capacité de modulation de la tomothérapie. Treize patientes ont été incluses dans cette étude rétrospective pour un total de 26 plans radiothérapie optimisés. La dose moyenne dans le cœur a été réduite de 3,6 Gy par RCMI tangentielle à 2,4 Gy pour Tomo 1 et 1,5 Gy pour Tomo 2. La dose moyenne dans l’artère interventriculaire antérieure et le V20 (V × Gy : volume recevant × Gy) du poumon gauche étaient respectivement de 26,3 Gy et 16,0 % par RCMI tangentielle, 12,9 Gy et 9,3 % pour Tomo 1 et 6,2 Gy et 5,5 % pour Tomo 2. En retour, le V3,1 du sein droit était de 0,1 × cm3 par RCMI tangentielle, 0,6 × cm3 pour Tomo 1 et 215,3 × cm3 pour Tomo 2 et le V5 du poumon droit de 0 %, 3,9 % et 5,8 % respectivement. La tomothérapie peut efficacement réduire la dose cardiaque pendant l’irradiation du cancer du sein gauche. Différents schémas d’optimisation sont possibles, permettant des traitements personnalisés. La tomothérapie hélicoïdale peut être une modalité de traitement particulièrement intéressante chez les patientes qui ne peuvent soutenir une inspiration profonde bloquée ou chez qui une réduction de la dose mammaire controlatérale peut être omise.

Purpose: Our preferred treatment for juxtapapillary choroidal melanoma is stereotactic radiotherapy. We aim to describe our immobilization system and quantify its reproducibility. Materials and Methods: Patients were identified in our radiosurgery database. Patients were imaged at computed tomography simulator with an in-house system which allows visual monitoring of the eye as the patient fixates a small target. All patients were reimaged at least once prior to and/or during radiotherapy. The patients were treated on the CyberKnife system, 60 Gy in 10 daily fractions, using skull tracking in conjunction with our visual monitoring system. In order to quantify the reproducibility of the eye immobilization system, computed tomography scans were coregistered using rigid 6-dimensional skull registration. Using the coregistered scans, x, y, and z displacements of the lens/optic nerve insertion were measured. From these displacements, 3-dimensional vectors were calculated. Results: Thirty-four patients were treated from October 2010 to September 2015. Thirty-nine coregistrations were performed using 73 scans (2-3 scans per patient). The mean displacements of lens and optic nerve insertion were 0.1 and 0.0 mm. The median 3-dimensional displacements (absolute value) of lens and nerve insertion were 0.8 and 0.7 mm (standard deviation: 0.5 and 0.6 mm). Ninety-eight percent of 3-dimensional displacements were below 2 mm (maximum 2.4 mm). The calculated planning target volume (PTV) margins were 0.8, 1.4, and 1.5 mm in the anterior–posterior, craniocaudal, and right–left axes, respectively. Following this analysis, no further changes have been applied to our planning margin of 2 to 2.5 mm as it is also meant to account for uncertainties in magnetic resonance imaging to computed tomography registration, skull tracking, and also contouring variability. Conclusion: We have found our stereotactic eye immobilization system to be highly reproducible (<1 mm) and free of systematic error.

INTRODUCTION:To assess laryngeal motion in early glottic cancer in order to determine safe margins for partial larynx volumetric modulated arc therapy (PL-VMAT), and to quantify dosimetric advantages of PL-VMAT.METHODS:This prospective study included T1-2N0 glottic cancers treated with whole larynx VMAT (WL-VMAT). Pre- and mid-treatment 4D-computed tomography (4D-CT) and dynamic magnetic resonance imaging (MRI) allowed for assessment of larynx swallowing and respiratory motion. For 10 patients with lateralized lesions, PL-VMAT plans were calculated using margins derived from 4D-CT analysis.RESULTS:Twenty patients were accrued from 2014 to 2016. Mean amplitude of larynx swallowing excursion was 23 mm and 6 mm in the superior and anterior directions, respectively. Mean respiratory motion reached 4 mm and 2 mm in superior-inferior and antero-posterior directions, respectively. Pre-treatment 4D-CT analysis identified one patient with planning CT acquired during swallowing. Mid-treatment 4D-CT revealed larynx shift relative to vertebrae in 30% of cases. PL-VMAT allowed for significant reduction of mean doses to ipsilateral carotid, contralateral carotid, thyroid gland, contralateral arytenoid and larynx. Using 8 mm internal margin for PL-VMAT, swallowing resulted in clinical target volume excursion beyond 95% isodose line during ≤1.5% of total treatment time in all patients.CONCLUSION:Although swallowing motion is rare, rapid and easily suppressed by patients, there is a risk of systematic miss-targeting if planning CT is acquired during swallowing. Larynx position shift relative to vertebrae occurs in 1/3 of patients over the course of radiotherapy. With soft-tissue image guidance and margins accounting for respiratory motion, PL-VMAT allows safe reduction of dose to organs at risk.

INTRODUCTION:The purpose of this study is quantify intrafraction motion (IFM) during lung volumetric-modulated arc therapy (VMAT) and evaluate the impact of mid-treatment cone beam computed tomography (CBCT)-guided patient repositioning on target coverage.METHOD:This analysis included lung tumours treated with VMAT to 50-60 Gy in 3-5 fractions. Treatment planning was based on four-dimensional CT scans from which internal tumour volumes (ITV) were derived. An isotropic 5 mm margin was added to obtain the final planning target volume (PTV). Patients were treated supine with a customized dual vacuum immobilization device (BodyFIX, Elekta, Sweden). All patients underwent pre and mid-treatment CBCTs. Following each CBCT, a rigid registration was performed by a radiation oncologist. IFM was defined as the target displacement from pre to mid-treatment CBCT. For patients with an IFM vector ≥5 mm, a post hoc dose calculation analysis was performed to assess the dosimetric impact of CBCT-guided repositioning.RESULTS:Ninety-seven patients (367 fractions) were included. Mean (±SD) overall treatment time was 53:02 ± 13:08 min. Mean time for mid-treatment CBCT scan acquisition and patient repositioning was 15:49 ± 4:14 min. Mean IFM vector was 1.5 ± 1.4 mm (max = 8.1 mm) and was <5 mm in 354/367 (96%) of fractions. For all 13 fractions with an IFM vector ≥5 mm, dose calculation analysis of worst-case scenario indicates that ITV coverage would have remained ≥95% without mid-treatment repositioning.CONCLUSION:For 96% of fractions, the IFM vector was within the 5 mm PTV margin. Mid-treatment CBCT-guided couch repositioning did not significantly impact ITV coverage and prolonged treatment duration.

OBJECTIVE Chest wall (CW) toxicity (rib fracture and/or pain) is a recognized complication of stereotactic ablative radiotherapy (SABR) for non-small-cell lung cancer. The aim of this study was to evaluate the frequency of CW toxicity following SABR and to propose a new dosimetric parameter. METHODS We reviewed the charts and SABR plans from patients treated for T1-T2N0 peripheral non-small-cell lung cancer between 2009 and 2015. The CW structure was created through a 3-cm expansion of the lung. The median dose delivered to the planning target volume was 60 Gy. SABR was delivered in three fractions for patients with CW V30 < 30 cm3. If the CW V30 exceeded 30 cm3, five fractions were used, and the plan was optimized based on CW V37 (biologically equivalent to the V30 of three-fraction plans). RESULTS In 6 years, 361 lesions from 356 patients were treated (3 fractions: 297; 5 fractions: 64). The median follow-up was 16 months. 23 patients (6.5%) developed CW toxicity after a median time of 10 months following treatment. The mean CW V30/V37 was 21 cm3 for patients with CW toxicity and 17 cm3 for patients without toxicity (p < 0.05). The 2-year local control and the CW toxicity rates were similar, whether patients received three or five fractions (97% vs 96% and 7% vs 5%). CONCLUSION When the CW V30 is >30 cm3, altered fractionation combined with V37 optimization can limit CW toxicity. Advances in knowledge: The CW V37 is a suggested dosimetric parameter adapted to fractionation that may potentially limit CW toxicity after lung SABR.

Purpose: To implement the new EBT-XD Gafchromic films for accurate dosimetric and geometric validation of stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) CyberKnife (CK) patient specific QA. Methods: Film calibration was performed using a triplechannel film analysis on an Epson 10000XL scanner. Calibration films were irradiated using a Varian Clinac 21EX flattened beam (0 to 20 Gy), to ensure sufficient dose homogeneity. Films were scanned to a resolution of 0.3 mm, 24 hours post irradiation following a well-defined protocol. A set of 12 QA was performed for several types of CK plans: trigeminal neuralgia, brain metastasis, prostate and lung tumors. A custom made insert for the CK head phantom has been manufactured to yield an accurate measured to calculated dose registration. When the high dose region was large enough, absolute dose was also measured with an ionization chamber. Dose calculation is performed using MultiPlan Ray-tracing algorithm for all cases since the phantom is mostly made from near water-equivalent plastic. Results: Good agreement (<2%) was found between the dose to the chamber and the film, when a chamber measurement was possible The average dose difference and standard deviations between film measurements and TPS calculations were respectively 1.75% and 3%. The geometric accuracy has been estimated to be <1 mm, combining robot positioning uncertainty and film registration to calculated dose. Conclusion: Patient specific QA measurements using EBT-XD films yielded a full 2D dose plane with high spatial resolution and acceptable dose accuracy. This method is particularly promising for trigeminal neuralgia plan QA, where the positioning of the spatial dose distribution is equally or more important than the absolute delivered dose to achieve clinical goals.