Time filter

Source Type

Hsi W.C.,Proton Therapy | Hsi W.C.,Shanghai Proton and Heavy Ion Center | Law A.,ProCure Training and Development Center | Schreuder A.N.,ProCure Training and Development Center | And 2 more authors.
Medical Physics

Purpose: An optical tracking and positioning system (OTPS) was developed to validate the software-driven isocentric (SDI) approach to control the six-degrees-of-freedom movement of a robotic couch. Methods: The SDI approach to movements rotating around a predefined isocenter, referred to as a GeoIso, instead of a mechanical pivot point was developed by the robot automation industry. With robotic couch-sag corrections for weight load in a traditional SDI approach, movements could be accurately executed for a GeoIso located within a 500 mm cubic volume on the couch for treatments. The accuracy of SDI movement was investigated using the OTPS. The GeoIso was assumed to align with the proton beam isocenter (RadIso) for gantry at the reference angle. However, the misalignment between GeoIso and RadIso was quantitatively investigated by measuring the displacements at various couch angles for a target placed at the RadIso at an initial couch angle. When circular target displacements occur on a plane, a relative isocenter shift (RIS) correction could be applied in the SDI movement to minimize target displacements. Target displacements at a fixed gantry angle without and with RIS correction were measured for 12 robotic couches. Target displacements for various gantry angles were performed on three couches in gantry rooms to study the gantry-induced RadIso shift. The RIS correction can also be applied for the RadIso shift. A new SDI approach incorporating the RIS correction with the couch sag is described in this study. In parallel, the accuracy of SDI translation movements for various weight loads of patients on the couch was investigated during positioning of patients for proton prostate treatments. Results: For a fixed gantry angle, measured target displacements without RIS correction for couch rotations in the horizontal plane varied from 4 to 20 mm. However, measured displacements perpendicular to couch rotation plane were about 2 mm for all couches. Extracted misalignments of GeoIso and RadIso in the horizontal plane were about 10 mm for one couch and within 3 mm for the rest of couches. After applying the RIS correction, the residual target displacements for couch rotations were within 0.5 mm to RadIso for all couches. For various gantry angles, measured target location for each angle was within 0.5 mm to its excepted location by the preset RadIso shift. Measured target displacements for ±30° of couch rotations were within 0.5 mm for gantry angles at 0° and 180°. Overall, nearly 85% of couch movements were within 0.5 mm in the horizontal plane and 0.7 mm vector distance from required displacements. Conclusions: The authors present an optical tracking methodology to quantify for software-driven isocentric movements of robotic couches. By applying proper RIS correction for misaligned GeoIso and RadIso for each couch, and the RadIso shifts for a moving gantry, residual target displacements for isocentric couch movements around the actual RadIso can be reduced to submillimeter tolerance. © 2014 American Association of Physicists in Medicine. Source

Lin S.,Fujian Medical University | Lin S.,Fujian Provincial Key Laboratory of Translational Cancer Medicine | Pan J.,Fujian Medical University | Pan J.,Fujian Provincial Key Laboratory of Translational Cancer Medicine | And 9 more authors.
Radiotherapy and Oncology

Background and purpose To establish the minimally required margins in different directions measured from GTV in the definitive treatment of nasopharyngeal carcinoma (NPC) using IMRT based on the 5-year results. Methods and materials Between November 2003 and May 2007, 414 patients with non-metastatic NPC were treated with IMRT according to our institutional protocol. Treatment outcomes at 5 years were analyzed. Distances from GTV-T to CTV2 (i.e., CTV 59.4 Gy) in 6 directions (anterior, posterior, superior, inferior, and bilateral) were measured and analyzed. Results The 5-year estimated overall survival (OS), disease free survival (DFS), local control (LC) were 80%, 77% and 95%, respectively. For the margins measured from GTV-T to CTV2, margins used with T4 disease were significantly and uniformly smaller than the whole group in all the 6 directions (P = 0.000, 0.000, 0.000, 0.000 and 0.046, respectively). However, no increase of local recurrence was associated to this limited margins used. Conclusions Our 5-years' experience showed a very high LC rate. The strategy we used for CTV delineation was safe and reliable. Determined CTV through GTV expansion to a minimally required margin, using GTV + margin (used in our T4 patients) + the whole nasopharyngeal mucosa, especially for the patients with early T disease, might be feasible. © 2013 Elsevier Ireland Ltd. All rights reserved. Source

Purpose: Adequate evaluation of the results from multi-institutional trials involving light ion beam treatments requires consideration of the planning margins applied to both targets and organs at risk. A major uncertainty that affects the size of these margins is the conversion of x ray computed tomography numbers (XCTNs) to relative linear stopping powers (RLSPs). Various facilities engaged in multi-institutional clinical trials involving proton beams have been applying significantly different margins in their patient planning. This study was performed to determine the variance in the conversion functions used at proton facilities in the U.S.A. wishing to participate in National Cancer Institute sponsored clinical trials. Methods: A simplified method of determining the conversion function was developed using a standard phantom containing only water and aluminum. The new method was based on the premise that all scanners have their XCTNs for air and water calibrated daily to constant values but that the XCTNs for high density/high atomic number materials are variable with different scanning conditions. The standard phantom was taken to 10 different proton facilities and scanned with the local protocols resulting in 14 derived conversion functions which were compared to the conversion functions used at the local facilities. Results: For tissues within ±300 XCTN of water, all facility functions produced converted RLSP values within ±6% of the values produced by the standard function and within 8% of the values from any other facility's function. For XCTNs corresponding to lung tissue, converted RLSP values differed by as great as ±8% from the standard and up to 16% from the values of other facilities. For XCTNs corresponding to low-density immobilization foam, the maximum to minimum values differed by as much as 40%. Conclusions: The new method greatly simplifies determination of the conversion function, reduces ambiguity, and in the future could promote standardization between facilities. Although it was not possible from these experiments to determine which conversion function is most appropriate, the variation between facilities suggests that the margins used in some facilities to account for the uncertainty in converting XCTNs to RLSPs may be too small. © 2014 American Association of Physicists in Medicine. Source

Kong L.,Fudan University | Lu J.J.,Shanghai Proton and Heavy Ion Center
Chinese Clinical Oncology

Local or locoregional recurrence of nasopharyngeal carcinoma (NPC) after high-dose radiotherapy remains a significant clinical problem. This is especially important in regions of the world in which NPC is endemic, such as Southern China. In this review, we briefly present the evolution in the definitive treatment of NPC, but focus more so on the historical and contemporary treatment approaches and outcomes utilized in the recurrent setting. Specifically, we highlight the various treatment strategies (repeat surgery, brachytherapy, conventional re-irradiation, SRS/SBRT, and salvage IMRT), and their technical, physical and biological limitations. Special attention is given towards salvage IMRT, as this is becoming the standard of care for locally recurrent NPC. Further, it is the most commonly indicated modality, since it can be used to treat larger tumors and more extensive disease stages, which represent the majority of recurrent cases. Predictive and prognostic factors for the efficacy of repeat treatment are discussed as well. The toxicities brought about by repeat radiotherapy courses are also highlighted, with an emphasis on their impact on mortality and quality of life, which underscore the difficulty that this clinical entity presents. Lastly, the rationale for particle radiation therapy, which is potentially safer and more efficacious, for the treatment of locally recurrent NPC is presented. ©Chinese Clinical Oncology. Source

Qi W.-X.,Shanghai Proton and Heavy Ion Center | Fu S.,Shanghai Proton and Heavy Ion Center | Fu S.,Fudan University | Zhang Q.,Shanghai Proton and Heavy Ion Center | And 2 more authors.
BMC Medicine

Background: Anti-epidermal growth factor receptor (EGFR)-monoclonal antibodies (MoAbs) have been widely used in a variety of malignancies. Severe infections (≥grade 3) are potentially life-threatening adverse events with these drugs. However, the contribution of anti-EGFR MoAbs to infections is still unknown. We performed this meta-analysis to determine the overall incidence and risk of severe infections in cancer patients treated with these drugs. Methods: The databases of PubMed and abstracts presented at oncology conferences and published in the proceedings were searched for relevant studies from January 2000 to May 2014. Summary incidences, relative risks (RRs) and 95% confidence intervals (CIs) were calculated by using either random effects or fixed effect models according to the heterogeneity of included studies. Results: A total of 14,066 patients from 26 randomized controlled trials (RCTs) were included. The use of anti-EGFR-MoAbs significantly increased the risk of developing severe infections (RR 1.34, 95%CI: 1.10 to 1.62, P = 0.003) in cancer patients, but not for fatal infections (RR 1.62, 95%CI: 0.81 to 3.26, P = 0.18). Meta-regression indicated the infections might possibly occur early in the treatment with anti-EGFR MoAbs. On sub-group analysis, the risk of severe infections significantly varied with tumor type (P = 0.001). When stratified by specific anti-EGFR MoAbs, a significantly increased risk of infections with cetuximab was observed (P <0.001), but not for panitumumab (P = 0.98). Additionally, the use of anti-EGFR MoAbs significantly increased the risk of severe infections when used in conjunction with cisplatin (RR 1.48, 95%CI 1.22 to 1.79, P <0.001) or irinotecan (RR 1.53, 95%CI 1.12 to 2.10, P = 0.008). When stratified by specific infectious events, anti-EGFR-MoAbs significantly increased the risk of developing severe sepsis (RR 4.30, 95%CI: 1.80 to 10.27; P = 0.001). Conclusions: Anti-EGFR MoAbs treatment significantly increases the risk of developing severe infectious events in cancer patients. The risk may vary with tumor types. Clinicians should be aware of the risks of severe infections with the administration of these drugs in cancer patients. Source

Discover hidden collaborations