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Abstract: Positron emission tomography (PET) provides molecular information about the tumor microenvironment in addition to anatomical imaging. Hence, it seems to be highly beneficial to integrate PET data into radiotherapy (RT) treatment planning. Functional PET images can be used in RT planning following different strategies, with different orders of complexity. In a first instance, PET imaging data can be used for better target volume delineation. A second strategy, dose painting by contours (DPBC), consists of creating an additional PET-based target volume which will then be treated with a higher dose level. In contrast, dose painting by numbers (DPBN) aims for a locally varying dose prescription according to the variation of the PET signal. For both dose painting approaches, isotoxicity planning strategies should be applied in order not to compromise organs at risk compared to conventional modern RT treatment. In terms of physical dose painting treatment planning, several factors that may introduce limitations and uncertainties are of major importance. These are the PET voxel size, uncertainties due to image acquisition and reconstruction, a reproducible image registration, inherent biological uncertainties due to biological and chemical tracer characteristics, accurate dose calculation algorithms and radiation delivery techniques able to apply highly modulated dose distributions. Further research is necessary in order to investigate these factors and their influence on dose painting treatment planning and delivery thoroughly. To date, dose painting remains a theoretical concept which needs further validation. Nevertheless, molecular imaging has the potential to significantly improve target volume delineation and might also serve as a basis for treatment alteration in the future. [ABSTRACT FROM AUTHOR]

Background: Intensity-modulated radiation therapy (IMRT) was suggested as a suitable technique to protect the rectal wall, while maintaining a satisfactory planning target volume (PTV) irradiation in the case of high-dose radiotherapy of prostate cancer. However, up to now, few investigations tried to estimate the expected benefit with respect to conventional three-dimensional (3D) conformal radiotherapy (CRT).Purpose: Estimating the expected clinical gain coming from both 1D and 2D IMRT against 3DCRT, in the case of prostate cancer by mean of radiobiological models. In order to enhance the impact of IMRT, the case of concave-shaped PTV including prostate and seminal vesicles (P+SV) was considered.Materials and methods: Five patients with concave-shaped PTV including P+SV were selected. Two different sets of constraints were applied during planning: in the first one a quite large inhomogeneity of the dose distribution within the PTV was accepted (set (a)); in the other set (set (b)) a greater homogeneity was required. Tumor control probability (TCP) and normal tissue control probability (NTCP) indices were calculated through the Webb–Nahum and the Lyman–Kutcher models, respectively. Considering a dose interval from 64.8 to 100.8 Gy, the value giving a 5% NTCP for the rectum was found (D(NTCPrectum=5%)) using two different methods, and the corresponding TCP(NTCPrectum=5%) and NTCP(NTCPrectum=5%) for the other critical structures were derived. With the first method, the inverse optimization of the plans was performed just at a fixed 75.6 Gy ICRU dose; with the second method (applied to 2/5 patients) inverse treatment plannings were re-optimized at many dose levels (from 64.8 to 108 Gy with 3.6 Gy intervals). In this case, three different values of α/β (10, 3, 1.5)were used for TCP calculation. The 3DCRT plan consisted of a 3-fields technique; in the IMRT plans, five equi-spaced beams were applied. The Helios Inverse Planning software from Varian was used for both the 2D IMRT and the 1D IMRT inverse optimization, the last one being performed fixing only one available pair of leaves for modulation. A previously proposed forward 1D IMRT ‘class solution’ technique was also considered, keeping the same irradiation geometry of the inversely optimized IMRT techniques.Results: With the first method, the average gains in TCP(NTCPrectum=5%) of the 2D IMRT technique, with respect 3DCRT, were 10.3 and 7.8%, depending on the choice of the DVHs constraints during the inverse optimization procedure (set (a) and set (b), respectively). The average gain (ΔTCP(NTCPrectum=5%)) coming from the inverse 1D IMRT optimization was 5.0%, when fixing the set (b) DVHs constraints. Concerning the forward 1D IMRT optimization, the average gain in TCP(NTCPrectum=5%) was 4.5%. The gain was found to be correlated with the degree of overlapping between rectum and PTV. When comparing 2D IMRT and 1D IMRT, in the case of the more realistic set (b) constraints, ΔTCP(NTCPrectum=5%) was always less than 3%, excepting one patient with a very large overlap region. Basing our choice on this result, the second method was applied to this patient and one of the remaining. Through the inverse re-optimization of the treatment plans at each dose level, the gain in TCP(NTCPrectum=5%) of the inverse 2D technique was significantly higher than the ones obtained by applying the first method (concerning the two patients: +6.1% and +2.4%), while no significant benefit was found for inverse 1D. The impact of changing the α/β ratio was less evident in the patient with the lower gain in TCP(NTCPrectum=5%).Conclusions: The expected benefit due to IMRT with respect to 3DCRT seems to be relevant when the overlap between PTV and rectum is high. Moreover, the difference between the inverse 2D and the simpler inverse or forward 1D IMRT techniques resulted in being relatively modest, with the exception of one patient, having a very large overlap between rectum and PTV. Optimizing the inverse planning at each dose level to find TCP(NTCPrectum=5%) can improve the performances of inverse 2D IMRT, against a significant increase of the time for planning. These results suggest the importance of selecting the patients that could have significant benefit from the application of IMRT. [Copyright &y& Elsevier]

• Dysgeusia is a common side effect of radiotherapy for head & neck cancers. • Dosiomics and AI are applied for the first time to predict dysgeusia. • The central and anterior ⅔ regions of the tongue are associated with acute dysgeusia. • Dosiomics is comparable to conventional mean dose-based prediction of acute dysgeusia. • Dosiomics is superior to conventional mean dose-based prediction of chronic dysgeusia. To investigate the potential of dosiomics in predicting radiotherapy-induced taste distortion (dysgeusia) in head & neck (H&N) cancer. A cohort of 80 H&N cancer patients treated with radical or adjuvant radiotherapy and with a follow-up of at least 24 months was enrolled. Treatment information, as well as tobacco and alcohol consumption were also collected. The whole tongue was manually delineated on the planning CT and mapped to the dose map retrieved from the treatment planning system. For every patient, 6 regions of the tongue were examined; for each of them, 145 dosiomic features were extracted from the dose map and fed to a logistic regression model to predict the grade of dysgeusia at follow-up, with and without including clinical features. A mean dose-based model was considered for reference. Both dosiomics and mean dose models achieved good prediction performance for acute dysgeusia with AUC up to 0.88. For the dosiomic model, the central and anterior ⅔ regions of the tongue were the most predictive. For all models, a gradual reduction in the performance was observed at later times for chronic dysgeusia prediction, with higher values for dosiomics. The inclusion of smoke and alcohol habits did not improve model performances. The dosiomic analysis of the dose to the tongue identified features able to predict acute dysgeusia. Dosiomics resulted superior to the conventional mean dose-based model for chronic dysgeusia prediction. Larger, prospective studies are needed to support these results before integrating dosiomics in radiotherapy planning. [ABSTRACT FROM AUTHOR]

Abstract: Purpose: To assess anatomical, clinical and dosimetric pre-treatment parameters, possibly predictors of parotid shrinkage during radiotherapy of head and neck cancer (HNC). Materials: Data of 174 parotids from four institutions were analysed; patients were treated with IMRT, with radical and adjuvant intent. Parotid shrinkage was evaluated by the volumetric difference (ΔV) between parotid volumes at the end and those at the start of the therapy, as assessed by CT images (MVCT for 40 patients, KVCT for 47 patients). Correlation between ΔVcc/% and a number of dosimetric, clinical and geometrical parameters was assessed. Univariate as well as stepwise logistic multivariate (MVA) analyses were performed by considering as an end-point a ΔVcc/% larger than the median value. Linear models of ΔV (continuous variable) based on the most predictive variables found at the MVA were developed. Results: Median ΔVcc/% were 6.95cc and 26%, respectively. The most predictive independent variables of ΔVcc at MVA were the initial parotid volume (IPV, OR: 1.100; p =0.0002) and Dmean (OR: 1.059; p =0.038). The main independent predictors of ΔV% at MVA were age (OR: 0.968; p =0.041) and V40 (OR: 1.0338; p =0.013). ΔVcc and ΔV% may be well described by the equations: ΔVcc=−2.44+0.076 Dmean (Gy)+0.279 IPV (cc) and ΔV%=34.23+0.192 V40 (%)−0.2203 age (year). The predictive power of the ΔVcc model is higher than that of the ΔV% model. Conclusions: IPV/age and Dmean/V40 are the major dosimetric and clinical/anatomic predictors of ΔVcc and ΔV%. ΔVcc and ΔV% may be well described by bi-linear models including the above-mentioned variables. [Copyright &y& Elsevier]

Poster: Physics track: Imaging acquisition and processing PO-1768: A pre-treatment quality assurance survey on patients treated with the new Accuray Radixact platform M. Fusella, A. Scaggion, N. Pivato, M.A. Rossato, A. Roggio, M. Paiusco. [Extracted from the article]

Poster: Physics track: Dose measurement and dose calculation PO-1368: Clinical implementation of RayStation for Accuray Radixact tomotherapy platform M. Fusella, A. Scaggion, A. Roggio, M.A. Rossato, N. Pivato, R. Zandona, M. Paiusco. [Extracted from the article]

Abstract: Background and purpose: The purpose of this work was a comparison of realistic IMRT plans based on the same CT-image data set and a common predefined set of dose objectives for the planning target volume and the organs at risk. This work was part of the larger European QUASIMODO IMRT verification project. Materials and methods: Eleven IMRT plans were produced by nine different European groups, each applying a representative set of clinically used IMRT treatment planning systems. The plans produced were to be deliverable in a clinically acceptable treatment time with the local technical equipment. All plans were characterized using a set of different quality measures such as dose-volume histograms, number of monitor units and treatment time. Results: Only one plan was able to fulfil all dose objectives strictly; six plans failed some of the objectives but were still considered to be clinically acceptable; four plans were not able to reach the objectives. Additional quality scores such as the number of monitor units and treatment time showed large variations, which mainly depend on the delivery technique. Conclusion: The presented planning study showed that with nearly all presently available IMRT planning and delivery systems comparable dose distributions could be achieved if the planning goals are clearly defined in advance. [Copyright &y& Elsevier]

Background and purpose: An increasing number of radiotherapy centres is now aiming for clinical implementation of intensity modulated radiotherapy (IMRT), but – in contrast to conventional treatment – no national or international guidelines for commissioning of the treatment planning system (TPS) and acceptance tests of treatment equipment have yet been developed. This paper bundles the experience of five radiotherapy departments that have introduced IMRT into their clinical routine.Methods and materials: The five radiotherapy departments are using similar configurations since they adopted the commercially available Varian solution for IMRT, regarding treatment planning as well as treatment delivery. All are using the sliding window technique. Different approaches towards the derivation of the multileaf collimator (MLC) parameters required for the configuration of the TPS are described. A description of the quality control procedures for the dynamic MLC, including their respective frequencies, is given. For the acceptance of the TPS for IMRT multiple quality control plans were developed on a variety of phantoms, testing the flexibility of the inverse planning modules to produce the desired dose pattern as well as assessing the accuracy of the dose calculation. Regarding patient treatment verification, all five centres perform dosimetric pre-treatment verification of the treatment fields, be it on a single field or on a total plan procedure. During the actual treatment, the primary focus is on patient positioning rather than dosimetry. Intracavitary in vivo measurements were performed in special cases.Result and conclusion: The configurational MLC parameters obtained through different methods are not identical for all centres, but the observed variations have shown to be of no significant clinical relevance. The quality control (QC) procedures for the dMLC have not detected any discrepancies since their initiation, demonstrating the reliability of the MLC controller. The development of geometrically simple QC plans to test the inverse planning, the dynamic MLC modules and the final dose calculation has proven to be useful in pointing out the need to remodel the single pencil beam scatter kernels in some centres. The final correspondence between calculated and measured dose was found to be satisfactory by all centres, for QC test plans as well as for pre-treatment verification of clinical IMRT fields. An intercomparison of the man hours needed per patient plan verification reveals a substantial variation depending on the type of measurements performed. [Copyright &y& Elsevier]

Poster: Physics track: Treatment plan optimisation: algorithms PO-1434: Thorough assessment of a new commercial tool to reduce plan complexity A. Scaggion, M. Fusella, A. Bettinelli, F. Busato, N. Pivato, A. Roggio, M.A. Rossato, M. Sepulcri, R. ZandonÃ, M. Paiusco. [Extracted from the article]