Interfractional Variations in the Setup of Pelvic Bony Anatomy and Soft Tissue, and Their Implications on the Delivery of Proton Therapy for Localized Prostate Cancer

Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA 02114, USA.
International journal of radiation oncology, biology, physics (Impact Factor: 4.26). 10/2010; 80(3):928-37. DOI: 10.1016/j.ijrobp.2010.08.006
Source: PubMed


To quantify daily variations in the anatomy of patients undergoing radiation therapy for prostate carcinoma, to estimate their effect on dose distribution, and to evaluate the effectiveness of current standard planning and setup approaches employed in proton therapy.
We used series of computed tomography data, which included the pretreatment scan, and between 21 and 43 in-room scans acquired on different treatment days, from 10 patients treated with intensity-modulated radiation therapy at Morristown Memorial Hospital. Variations in femur rotation angles, thickness of subcutaneous adipose tissue, and physical depth to the distal surface of the prostate for lateral beam arrangement were recorded. Proton dose distributions were planned with the standard approach. Daily variations in the location of the prescription isodose were evaluated.
In all 10 datasets, substantial variation was observed in the lateral tissue thickness (standard deviation of 1.7-3.6 mm for individual patients, variations of >5 mm from the planning computed tomography observed in all series), and femur rotation angle (standard deviation between 1.3° and 4.8°, with the maximum excursion exceeding 10° in 6 of 10 datasets). Shifts in the position of treated volume (98% isodose) were correlated with the variations in the lateral tissue thickness.
Analysis suggests that, combined with image-guided setup verification, the range compensator expansion technique prevents loss of dose to target from femur rotation and soft-tissue deformation, in the majority of cases. Anatomic changes coupled with the uncertainties of particle penetration in tissue restrict possibilities for margin reduction in proton therapy of prostate cancer.

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Available from: Hsiao-Ming Lu,
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    • "This entails a heavier workload at the CT scanner, additional appointments for the patient and may not capture patient positioning differences between the CT and treatment couches. The use of a CT-on-rail, investigated in the context of passively scattered proton therapy of the prostate (Trofimov et al 2011), would offer the optimal data for dose recalculation, although such installations are not common and increase the complexity of the delivery procedure. "
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    ABSTRACT: The ability to perform dose recalculation on the anatomy of the day is important in the context of adaptive proton therapy. The objective of this study was to investigate the use of deformable image registration (DIR) and cone beam CT (CBCT) imaging to generate the daily stopping power distribution of the patient. We investigated the deformation of the planning CT scan (pCT) onto daily CBCT images to generate a virtual CT (vCT) using a deformable phantom designed for the head and neck (H & N) region.
    Physics in Medicine and Biology 12/2014; 60(2):595-613. DOI:10.1088/0031-9155/60/2/595 · 2.76 Impact Factor
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    • "In addition, a proton beam is sensitive to tissue density and heterogeneity and may be perturbed by passage through very inhomogeneous tissue, such as bone, and then muscle of the pelvis. This becomes more of an issue if the bone is not fully immobilised as can be the case with the hips due to anatomical variation in femur angle (Trofimov et al, 2011). Similarly, targeting of dose can be affected significantly when organs move over the course of therapy (Wang et al, 2011). "
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    ABSTRACT: Proton therapy is a promising, but costly, treatment for prostate cancer. Theoretical physical advantages exist; yet to date, it has been shown only to be comparably safe and effective when compared with the alternatives and not necessarily superior. If clinically meaningful benefits do exist for patients, more rigorous study will be needed to detect them and society will require this to justify the investment of time and money. New technical advances in proton beam delivery coupled with shortened overall treatment times and declining device costs have the potential to make this a more cost-effective therapy in the years ahead.
    British Journal of Cancer 03/2013; 108(6). DOI:10.1038/bjc.2013.100 · 4.84 Impact Factor
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    • "The newer, higher energy, linear accelerators increasingly used in conventional radiotherapy also produce significantly elevated neutron environments that cause electronic failures [17]. Added to this is the fact that interest in applying image-guided techniques to proton therapy is growing rapidly, bringing the issue of radiation hardness of commercial units of this type to the forefront [18]. "
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    ABSTRACT: Secondary neutron induced single event burnouts (SEB) in power MOSFETs to be installed in an X-ray generator located in a proton therapy treatment vault are characterized. This is done using both accelerated and in situ testing. Experimental techniques and schematics are presented that allow non-destructive testing of multiple MOSFETs in parallel for in situ real time measurements.
    IEEE Transactions on Nuclear Science 12/2012; 59(6):3154-3159. DOI:10.1109/TNS.2012.2221741 · 1.28 Impact Factor
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