D. Cusumano

Predicting tumour motion during the whole radiotherapy treatment: a systematic approach for thoracic and abdominal lesions based on real time MR

INTRODUCTIONnAim of this study was to investigate the ability of pre-treatment four dimensional computed tomography (4DCT) to capture respiratory-motion observed in thoracic and abdominal lesions during treatment. Treatment motion was acquired using full-treatment cine-MR acquisitions. Results of this analysis were compared to the ability of 30u202fseconds (s) cine Magnetic Resonance (MR) to estimate the same parameters.nnnMETHODSnA 4DCT and 30u202fs cine-MR (ViewRay, USA) were acquired on the simulation day for 7 thoracic and 13 abdominal lesions. Mean amplitude, intra- and inter-fraction amplitude variability, and baseline drift were extracted from the full treatment data acquired by 2D cine-MR, and correlated to the motion on pre-treatment 30u202fs cine-MR and 4DCT. Using the full treatment data, safety margins on the ITV, necessary to account for all motion variability from 4DCT observed during treatment, were calculated. Mean treatment amplitudes were 2u202f±u202f1u202fmm and 5u202f±u202f3u202fmm in the anteroposterior (AP) and craniocaudal (CC) direction, respectively. Differences between mean amplitude during treatment and amplitude on 4DCT or during 30u202fs cine-MR were not significant, but 30u202fs cine-MR was more accurate than 4DCT. Intra-fraction amplitude variability was positively correlated with both 30u202fs cine-MR and 4DCT amplitude. Inter-fraction amplitude variability was minimal.nnnRESULTSnMean baseline drift over all fractions and patients equalled 1u202f±u202f1u202fmm in both CC and AP direction, but drifts per fraction up to 16u202fmm (CC) and 12u202fmm (AP) were observed. Margins necessary on the ITV ranged from 0 to 8u202fmm in CC and 0 to 5u202fmm in AP direction. Neither amplitude on 4DCT nor during 30u202fs cine MR is correlated to the magnitude of drift or the necessary margins in both directions.nnnCONCLUSIONnLesions moving with small amplitude show limited amplitude variability throughout treatment, making passive motion management strategies seem adequate. However, other variations such as baseline drifts and shifts still cause significant geometrical uncertainty, favouring real-time monitoring and an active approach for all lesions influenced by respiratory motion.

Fractal-based radiomic approach to predict complete pathological response after chemo-radiotherapy in rectal cancer

The aim of this study was to propose a methodology to investigate the tumour heterogeneity and evaluate its ability to predict pathologically complete response (pCR) after chemo-radiotherapy (CRT) in locally advanced rectal cancer (LARC). This approach consisted in normalising the pixel intensities of the tumour and identifying the different sub-regions using an intensity-based thresholding. The spatial organisation of these subpopulations was quantified using the fractal dimension (FD). This approach was implemented in a radiomic workflow and applied to 198 T2-weighted pre-treatment magnetic resonance (MR) images of LARC patients. Three types of features were extracted from the gross tumour volume (GTV): morphological, statistical and fractal features. Feature selection was performed using the Wilcoxon test and a logistic regression model was calculated to predict the pCR probability after CRT. The model was elaborated considering the patients treated in two institutions: Fondazione Policlinico Universitario “Agostino Gemelli” of Rome (173 cases, training set) and University Medical Centre of Maastricht (25 cases, validation set). The results obtained showed that the fractal parameters of the subpopulations have the highest performance in predicting pCR. The predictive model elaborated had an area under the curve (AUC) equal to 0.77xa0±xa00.07. The model reliability was confirmed by the validation set (AUCxa0=xa00.79xa0±xa00.09). This study suggests that the fractal analysis can play an important role in radiomics, providing valuable information not only about the GTV structure, but also about its inner subpopulations.

Experimental evaluation of the impact of low tesla transverse magnetic field on dose distribution in presence of tissue interfaces

PURPOSEnAim of this study is to experimental evaluate the impact of a 0.35u202fT transverse magnetic field on dose distribution in presence of tissue-air and tissue-lung interfaces.nnnMETHODSnThe investigation was carried out using MRIdian (ViewRay, Cleveland, Ohio) and it consisted of comparing experimental measurements performed by Gafchromic EBT3 film dosimetry, to Montecarlo simulations, carried out in the presence and, as well as, the absence of the magnetic field. A preliminary dose calibration was planned on MRIdian, arranging 3u202f×u202f3u202fcm2 film pieces in a water slab phantom and exposing them at different beam-on times, in a dose range equal to 0.1-12.1u202fGy. All experimental measurements were then carried out using the calibrated films and delivering one single beam orthogonally to three different phantoms: without inhomogeneity, with an air gap and with a lung inhomogeneity. The dose distributions measured by EBT3 films in presence of magnetic field were compared to those calculated in the presence and, as well as, the absence of the magnetic field, in terms of gamma analysis. A quantification of electron return effect (ERE) was also performed.nnnRESULTSnAll the tested plans considering the magnetic field show a gamma-passing rate higher than 98% for 3%/3u202fmm gamma analysis. In presence of tissue-air interface, the electron return effect causes an over-dosage of +31.9% at the first interface and an under-dosage of -33% at the second interface. The dosimetric variations in presence of tissue-lung interface results to be smaller (+0.8% first interface, -1.3% second interface).nnnCONCLUSIONnThe impact of 0.35u202fT magnetic field is not negligible and it can be effectively modelled by the Montecarlo dose calculation platform available in the MRIdian TPS.

Use of Indirect Target Gating in Magnetic Resonance-guided Liver Stereotactic Body Radiotherapy: Case Report of an Oligometastatic Patient

The case of a 73-year-old woman affected by anal canal cancer with concomitant liver metastases is presented here. The patient was addressed to stereotactic body radiotherapy (SBRT) on two hepatic secondary lesions after the first radiochemotherapy treatment of the primary tumor. A Tri-60-Co magnetic resonance hybrid radiotherapy unit was used for SBRT treatment delivery. Both liver lesions were not clearly visible on the setup magnetic resonance imaging (MRI) due to their limited dimensions (maximum diameter 13 mm); however, the presence of two cysts adjacent to the metastases allowed the use of an indirect target gating approach. Treatment was delivered in deep inspiration breath-hold conditions using the visual feedback technique for breathing control optimization. Post radiotherapy imaging assessed the complete response.

Towards a modular decision support system for radiomics: A case study on rectal cancer

Following the personalized medicine paradigm, there is a growing interest in medical agents capable of predicting the effect of therapies on patients, by exploiting the amount of data that is now available for each patient. In disciplines like oncology, where images and scans are available, the exploitation of medical images can provide an additional source of potentially useful information. The study and analysis of features extracted by medical images, exploited for predictive purposes, is termed radiomics. A number of tools are available for supporting some of the steps of the radiomics process, but there is a lack of approaches which are able to deal with all the steps of the process. In this paper, we introduce a medical agent-based decision support system capable of handling the whole radiomics process. The proposed system is tested on two independent data sets of patients treated for rectal cancer. Experimental results indicate that the system is able to generate highly performant centre-specific predictive model, and show the issues related to differences in data sets collected by different centres, and how such issues can affect the performance of the generated predictive models.

Comparison of different treatment planning optimization methods for vaginal HDR brachytherapy with multichannel applicators: A reduction of the high doses to the vaginal mucosa is possible

PURPOSEnA direct planning approach with multi-channel vaginal cylinders (MVCs) used for HDR brachytherapy of vaginal cancers is particularly challenging. Purpose of this study was to compare the dosimetric performances of different forward and inverse methods used for the optimization of MVC-based vaginal treatments for endometrial cancer, with a particular attention to the definition of strategies useful to limit the high doses to the vaginal mucosa.nnnMETHODSnTwelve postoperative vaginal HDR brachytherapy treatments performed with MVCs were considered. Plans were retrospectively optimized with three different methods: Dose Point Optimization followed by Graphical Optimization (DPOu202f+u202fGrO), Inverse Planning Simulated Annealing with two different class solutions as starting conditions (surflPSA and homogIPSA) and Hybrid Inverse Planning Optimization (HIPO). Several dosimetric parameters related to target coverage, hot spot extensions and sparing of organs at risk were analyzed to evaluate the quality of the achieved treatment plans. Dose homogeneity index (DHI), conformal index (COIN) and a further parameter quantifying the proportion of the central catheter loading with respect to the overall loading (i.e., the central catheter loading index: CCLI) were also quantified.nnnRESULTSnThe achieved PTV coverage parameters were highly correlated with each other but uncorrelated with the hot spot quantifiers. HomogIPSA and HIPO achieved higher DHIs and CCLIs and lower volumes of high doses than DPOu202f+u202fGrO and surflPSA.nnnCONCLUSIONSnWithin the investigated optimization methods, HIPO and homoglPSA showed the highest dose homogeneity to the target. In particular, homogIPSA resulted also the most effective in reducing hot spots to the vaginal mucosa.

EP-1990: Comparison of dose optimisation methods for vaginal HDR brachytherapy with multichannel applicators

Results: Mean values and SD of calibration coefficients for each chamber type were calculated. For Standard Imaging HDR1000 Plus well chambers the mean calibration coefficient was 0.4669±0.0026. For Nucletron Holland well chambers (type 77091, 77092 and 77094) the mean calibration coefficient was 0.9472±0.0142 and for PTW33004 well chambers the mean calibration coefficient was 0.9655±0.0186. Some chambers were calibrated twice, what allowed for evaluation of their stability.