Comparison of three strategies in management of independent movement of the prostate and pelvic lymph nodes. Med Phys

Department of Radiation Oncology, University of California-San Francisco, San Francisco, California 94143, USA.
Medical Physics (Impact Factor: 2.64). 09/2010; 37(9):5006-13. DOI: 10.1118/1.3480505
Source: PubMed


Concurrent irradiation of the prostate and pelvic lymph nodes is technically challenging due to treating one moving target and one immobile target. The purposes of this article are to propose a new management strategy and to compare this strategy to the conventional isocenter shift method and the previously proposed MLC-shifting method.
To cope with two target volumes (one moving and one immobile), the authors propose a new management strategy referred to as multiple adaptive plans (MAPs). This strategy involves the creation of a pool of plans for a number of potential prostate locations. Without requiring any additional hardware or software, the MAP strategy is to choose a plan from the pool that most closely matches the "prostate position of the day." This position can be determined by dual image registrations: One aligned to the implant markers in the prostate and the other aligned to the pelvic bones. This strategy was clinically implemented for a special patient with high risk prostate cancer and pathologically confirmed positive pelvic lymph nodes, requiring concurrent IMRT treatment of the prostate and pelvic lymph nodes. Because this patient had an abdominal kidney, small planning margins around the both targets were desired. Using 17 daily acquired megavoltage cone beam CTs (CBCTs), three sets of validation plans were calculated to retrospectively evaluate the MAP strategy as well as the isoshifting and MLC-shifting strategies.
According to the validation plans, MAP, isoshifting, and MLC-shifting strategies resulted in D95 of the prostate > 95% of the daily dose on 65%, 100%, and 100% treatment days, respectively. Similarly, D95 of the pelvic lymph nodal was > 95% of the daily dose on 100%, 75%, and 94% of treatment days, respectively.
None of the above strategies simultaneously achieved all treatment goals. Among the three strategies, the MLC shifting was most successful. Validation plans based on daily CBCTs are useful to evaluate the effectiveness of the motion management strategies and to provide additional dose guidance if further dose compensation is needed.

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    • "Des plans sont préparés sur la base de modifications « a priori » du volume et le choix du plan est réalisé en temps réel en présence du patient. Ce type de radiothérapie adaptative a été appliqué par Xia et al. et Qi et al. pour l'irradiation de la prostate et des ganglions pelviens [11] [12]. Ces deux volumes ayant des mouvements très différents et indépendants, neuf plans de traitement différents étaient calculés a priori [12]. "
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    ABSTRACT: The development of both image-guided and intensity-modulated radiotherapy has underlined the question of treatment adaptation to anatomical and/or biological changes occurring during radiotherapy course and modifying delivered dose to the patient. Adaptive radiotherapy has been introduced when several plans are used to treat a patient during radiotherapy. Adaptation may be performed online, offline or in a hybrid way. New images of the patient are needed for adaptive radiotherapy to perform many processes: image registration, segmentation and evaluation of cumulative dose. Deformable image registration methods are generally used to image registration and contours propagation. Fraction and cumulative dose evaluations use deformable image registration methods or more complex methods based on Monte-Carlo calculation. These methods have uncertainties and have to be evaluated. However, evaluation and validation tools are still being developed. The physicist's mission is to ensure that every new technology, such as adaptive radiotherapy, is deployed with highest safety, by technical validation and by implementing a specific quality assurance program. Adaptive radiotherapy implementation still raises many questions, so its potential clinical application requires great caution and should be carefully explored in prospective clinical trials.
    No preview · Article · Sep 2015 · Cancer/Radiothérapie
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    • "These treatments may be compounded by independent motion and deformation of the involved targets. Depending on which target is being used for image-guidance, the uncertainties due to the residual, uncorrected motion should be accounted for the appropriate margin forming the planning target volume (PTV) [1] [2]. In radiotherapy of locally advanced prostate cancer – with the prostate as the primary target (CTV-p), and the elective targets consisting of the seminal vesicles (CTV-sv) and the pelvic lymph nodes (CTV-ln) – the different motion patterns present a considerable challenge. "
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    ABSTRACT: To determine the advantages and disadvantages of daily online adaptive image-guided radiotherapy (RT) compared with conventional RT for muscle-invasive bladder cancer. Twenty-seven patients with T2-T4 transitional cell carcinoma of the bladder were treated with daily online adaptive image-guided RT using cone-beam computed tomography (CBCT). From day 1 daily soft tissue-based isocenter positioning was performed using CBCT images acquired before treatment. Using a composite of the initial planning CT and the first five daily CBCT scans, small, medium, and large adaptive plans were created. Each of these adaptive plans used a 0.5-cm clinical target volume (CTV) to planning target volume expansion. For Fractions 8-32, treatment involved daily soft tissue-based isocenter positioning and selection of suitable adaptive plan of the day. Treating radiation therapists completed a credentialing program, and one radiation oncologist performed all the contouring. Comparisons were made between adaptive and conventional treatment on the basis of CTV coverage and normal tissue sparing. All 27 patients completed treatment per protocol. Bladder volume decreased with time or fraction number (p < 0.0001). For the adaptive component (Fractions 8-32) the small, medium, large, and conventional plans were used in 9.8%, 49.2%, 39.5%, and 1.5% of fractions, respectively. For the adaptive strategy, 2.7% of occasions resulted in a CTV V95 <99%, compared with 4.8% of occasions for the conventional approach (p = 0.42). Mean volume of normal tissue receiving a dose >45 Gy was 29% (95% confidence interval, 24-35%) less with adaptive RT compared with conventional RT. The mean volume of normal tissue receiving >5 Gy was 15% (95% confidence interval, 11-18%) less with adaptive RT compared with conventional RT. Online adaptive radiotherapy is feasible in an academic radiotherapy center. The volume of normal tissue irradiated can be significantly smaller without reducing CTV coverage.
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