I. Madani

Deformation field validation and inversion applied to adaptive radiation therapy.

Development and implementation of chronological and anti-chronological adaptive dose accumulation strategies in adaptive intensity-modulated radiation therapy (IMRT) for head-and-neck cancer. An algorithm based on Newton iterations was implemented to efficiently compute inverse deformation fields (DFs). Four verification steps were performed to ensure a valid dose propagation: intra-cell folding detection finds zero or negative Jacobian determinants in the input DF; inter-cell folding detection is implemented on the resolution of the output DF; a region growing algorithm detects undefined values in the output DF; DF domains can be composed and displayed on the CT data. In 2011, one patient with nonmetastatic head and neck cancer selected from a three phase adaptive DPBN study was used to illustrate the algorithms implemented for adaptive chronological and anti-chronological dose accumulation. The patient received three (18)F-FDG-PET/CTs prior to each treatment phase and one CT after finalizing treatment. Contour propagation and DF generation between two consecutive CTs was performed in Atlas-based autosegmentation (ABAS). Deformable image registration based dose accumulations were performed on CT1 and CT4. Dose propagation was done using combinations of DFs or their inversions. We have implemented a chronological and anti-chronological dose accumulation algorithm based on DF inversion. Algorithms were designed and implemented to detect cell folding.

Dose-painting intensity-modulated proton therapy for intermediate- and high-risk meningioma

BackgroundNewly diagnosed WHO grade II-III or any WHO grade recurrent meningioma exhibit an aggressive behavior and thus are considered as high- or intermediate risk tumors. Given the unsatisfactory rates of disease control and survival after primary or adjuvant radiation therapy, optimization of treatment strategies is needed. We investigated the potential of dose-painting intensity-modulated proton beam-therapy (IMPT) for intermediate- and high-risk meningioma.Material and methodsImaging data from five patients undergoing proton beam-therapy were used. The dose-painting target was defined using [68]Ga-[1,4,7,10-tetraazacyclododecane tetraacetic acid]– d-Phe1,Tyr3-octreotate ([68]Ga-DOTATATE)-positron emission tomography (PET) in target delineation. IMPT and photon intensity-modulated radiation therapy (IMRT) treatment plans were generated for each patient using an in-house developed treatment planning system (TPS) supporting spot-scanning technology and a commercial TPS, respectively. Doses of 66xa0Gy (2.2xa0Gy/fraction) and 54xa0Gy (1.8xa0Gy/fraction) were prescribed to the PET-based planning target volume (PTVPET) and the union of PET- and anatomical imaging-based PTV, respectively, in 30 fractions, using simultaneous integrated boost.ResultsDose coverage of the PTVsPET was equally good or slightly better in IMPT plans: dose inhomogeneity was 10u2009±u20093% in the IMPT plans vs. 13u2009±u20091% in the IMRT plans (pu2009=u20090.33). The brain Dmean and brainstem D50 were small in the IMPT plans: 26.5u2009±u20091.5xa0Gy(RBE) and 0.002u2009±u20090.0xa0Gy(RBE), respectively, vs. 29.5u2009±u20091.5xa0Gy (pu2009=u20090.001) and 7.5u2009±u200911.1xa0Gy (pu2009=u20090.02) for the IMRT plans, respectively. The doses delivered to the optic structures were also decreased with IMPT.ConclusionsDose-painting IMPT is technically feasible using currently available planning tools and resulted in dose conformity of the dose-painted target comparable to IMRT with a significant reduction of radiation dose delivered to the brain, brainstem and optic apparatus. Dose escalation with IMPT may improve tumor control and decrease radiation-induced toxicity.

SU‐E‐J‐49: Evaluation of Deformable Image Co‐Registration in Adaptive Dose Painting by Numbers for Head and Neck Cancer

Purpose: To evaluate the accuracy of automated contour deformation for head‐and‐neck cancer in adaptive treatment. Methods: Data from 13 head‐and‐neck patients in a phase I trial for adaptive treatment were used. Adaptation was based on [18F]FDG‐PET‐guided dose painting by numbers (DPBN) plans. Each patient had two DPBN plans based on: (i) a pretreatment PET/CT scan and (ii) a during‐treatment PET/CT scan acquired after 8 fractions. Contours manually drawn on the pretreatment CT scan were deformed using commercial deformable image registrationsoftware onto the during‐treatment CT scan. Deformed contours of regions of interest (ROIdef) were visually inspected by an experienced radiation oncologist and, if necessary, adjusted (ROIdef_ad) and both sets of contours were compared to manually redrawn ROIs (ROIm) using Jaccard (JI) and overlap indices (OI). ROI indices and volumes were compared for all contour sets used a paired t‐test and one‐way ANOVA pairwise comparison, respectively. Results: Almost all deformed ROIs in all patients required adjustment after visual inspection. The largest adjustments were made in GTVs when substantial tumor regression occured, e.g., ROIdef=9.2 cm3 vs. ROIdef_ad=2.2 cm3 vs. ROIm=2.1 cm3. The swallowing structures were the most frequently adjusted ROIs. The mandible was the most acurately propagated ROI requiring little or no adaptation: JI=0.7 and OI=0.8. The upper esophageal sphincter was the worst propagated ROI: JI=0.3 and OI=0.3 for the ROIdef, JI=0.5 and OI=0.6 for the ROIdef_ad. Despite the variation in indices, there was no statistically significant difference between ROIdef, ROIdef_ad and ROIm volumes. Generating ROIm took 4–6 hours, generating ROIdef took a few minutes and generating ROIdef_ad took less than 2 hours. Conclusions: Deformable image co‐registration followed by visual inspection does require adjustment of most deformed ROIs. Nevertheless, fast automatic ROI propagation followed by user‐driven adjustments appears to be more efficient than labor intensive de‐novo re‐contouring.

SP-0033: Adaptive dose painting early experiences

Despite attempts of treatment intensification, improvement of radio(chemo)therapy outcome in head-and-neck cancer remains marginal. Non-selective dose escalation in large planning volumes has not increased the rates of disease control and survival but severe debilitating treatment-induced toxicity. The use of biological imaging in radiotherapy allows detecting other than anatomical imaging-defined targets and enables tailoring dose prescription to tumor biology, .i.e. dose painting [1]. Dose painting can be employed in treatment intensification by non-uniformly escalating dose at no or minimal theoretical increase in the rates of treatment-induced toxicity relative to conventional or 3D-conformal radiotherapy [2]. Because of changes in tumor and non-tumor anatomy and biology throughout treatment, radiotherapy should not be based solely on pretreatment anatomical and biological imaging but adapted to occurring changes detected by pertreatment imaging. Combination of treatment adaptation with dose painting presents a new paradigm of treatment individualization with the promise of substantial improvement of treatment outcome. In Ghent University Hospital we tested dose painting in 41 head-and-neck cancer patients during 2003-2005 demonstrating feasibility of homogenous dose escalation up to 77.5 Gy in 18[F]FDG-PET-based subvolumes within the gross tumor volumes [3]. We introduced adaptive strategy in dose painting (18[F]FDG voxel intensity-based IMRT) in 2007 firstly in a clinical phase I trial with one per-treatment adaptation (21 patients) [4,5] and then in a clinical phase I trial with two per-treatment adaptations (10 patients) [6]. Significant non-homogenous dose escalation in the former trial (Normalized isoeffective dose equivalent to dose delivered in 2.0-Gy fractions [NID2Gy] of 91 Gy at the first level of dose escalation and 102 Gy at the second level of dose escalation) and adaptive procedures using deformable image co-registration in the latter trial were technically feasible and clinically tolerable. Update of clinical results of the trials will be presented at the meeting. The encouraging results of the only clinical trial on combined biologicalimage guided and adaptive IMRT [4,5] supported initiation of a clinical phase II randomized trial currently running in Ghent University Hospital [NCT01341535]. The trial compares adaptive dose painting against standard IMRT with increased loco-regional control and diminished treatment-induced toxicity as primary and secondary objectives, respectively.