Fuzzy analytic hierarchy process-based risk priority number for risk assessments of commissioning process of a ring gantry LINAC.

PURPOSE: We propose a fuzzy analytic hierarchy process (AHP)-based risk priority number (RPN) method in failure modes and effects analysis (FMEA) to overcome the shortcomings of traditional RPN-based FMEA. Our research group has previously published the FMEA to mitigate the failure modes (FMs) for the commissioning process of a ring gantry LINAC. However, inter-relationships among FMs were observed in high ranked FMs due to a heavy reliance on imaging system. METHODS: Fuzzy AHP was applied to determine relative weights of risk impacts based on inter-relationships among FMs. Since the time sequence dependency is a major factor for risk factors, a hierarchical structure of AHP was used to reflect the directional impacts such as causal influence and feedback loop. Two fuzzy weighted RPNs, called (RPNW and FRPNW , were calculated depending on the input values of severity (S), occurrence (O), and probability of not being detected (D) from the evaluators. The RPNW used numerical values, whereas the fuzzy values were used for FRPNW . Both RPNs were calculated by multiplying the weighted O, S, and D using the fuzzy AHP method. RESULTS: The differences between the two fuzzy RPN rankings are due to inherent fuzzy uncertainty and deviations in O, S, and D values submitted by the evaluators. Considering all results of traditional and fuzzy-based FMEA, the two most highly ranked FMs were identified: errors in determining the non-isocentric SSD and SSD from MV images because of the unique features of the ring gantry LINAC. CONCLUSION: This study has demonstrated the feasibility of the use of a fuzzy AHP-based RPN to perform comprehensive analysis and prioritization of FMs. The risk analysis using fuzzy AHP can be improved and/or refined based on the department's specific workflow and clinical preferences taking various priority weighting approaches into account.

Genotoxic stress accelerates age-associated degenerative changes in intervertebral discs.

Intervertebral disc degeneration (IDD) is the leading cause of debilitating spinal disorders such as chronic lower back pain. Aging is the greatest risk factor for IDD. Previously, we demonstrated IDD in a murine model of a progeroid syndrome caused by reduced expression of a key DNA repair enzyme. This led us to hypothesize that DNA damage promotes IDD. To test our hypothesis, we chronically exposed adult wild-type (Wt) and DNA repair-deficient Ercc1(-/Δ) mice to the cancer therapeutic agent mechlorethamine (MEC) or ionization radiation (IR) to induce DNA damage and measured the impact on disc structure. Proteoglycan, a major structural matrix constituent of the disc, was reduced 3-5× in the discs of MEC- and IR-exposed animals compared to untreated controls. Expression of the protease ADAMTS4 and aggrecan proteolytic fragments was significantly increased. Additionally, new PG synthesis was reduced 2-3× in MEC- and IR-treated discs compared to untreated controls. Both cellular senescence and apoptosis were increased in discs of treated animals. The effects were more severe in the DNA repair-deficient Ercc1(-/Δ) mice than in Wt littermates. Local irradiation of the vertebra in Wt mice elicited a similar reduction in PG. These data demonstrate that genotoxic stress drives degenerative changes associated with IDD.

Synchrony--cyberknife respiratory compensation technology.

Studies of organs in the thorax and abdomen have shown that these organs can move as much as 40 mm due to respiratory motion. Without compensation for this motion during the course of external beam radiation therapy, the dose coverage to target may be compromised. On the other hand, if compensation of this motion is by expansion of the margin around the target, a significant volume of normal tissue may be unnecessarily irradiated. In hypofractionated regimens, the issue of respiratory compensation becomes an important factor and is critical in single-fraction extracranial radiosurgery applications. CyberKnife is an image-guided radiosurgery system that consists of a 6-MV LINAC mounted to a robotic arm coupled through a control loop to a digital diagnostic x-ray imaging system. The robotic arm can point the beam anywhere in space with 6 degrees of freedom, without being constrained to a conventional isocenter. The CyberKnife has been recently upgraded with a real-time respiratory tracking and compensation system called Synchrony. Using external markers in conjunction with diagnostic x-ray images, Synchrony helps guide the robotic arm to move the radiation beam in real time such that the beam always remains aligned with the target. With the aid of Synchrony, the tumor motion can be tracked in three-dimensional space, and the motion-induced dosimetric change to target can be minimized with a limited margin. The working principles, advantages, limitations, and our clinical experience with this new technology will be discussed.

Clinical implementation of tangential field intensity modulated radiation therapy (IMRT) using sliding window technique and dosimetric comparison with 3D conformal therapy (3DCRT) in breast cancer.

The purpose of this study was to evaluate the clinical implementation of tangential field IMRT using sliding window technique and to compare dosimetric parameters with 3-dimensional conformal radiation therapy (3DCRT). Twenty breast cancer patients were randomly selected for comparison of intensity modulated radiation therapy (IMRT)-based treatment plan with 3DCRT. Inverse treatment was performed using the sliding window technique, employing the Eclipse Planning System (version 7.1.59, Varian, Palo Alto, CA). The dosimetric parameters compared were V(95) (the percentage of target volume getting > or =95% of prescribed dose), V(105), V(110), and dose homogeneity index, DHI (percentage of target volume getting between 95% and 110% of prescribed dose). The mean V(95), DHI, V(105), and V(110) for target volume for IMRT vs. 3D were 90.6% (standard deviation [SD]: 3.2) vs. 91% (SD: 3.0), 87.7 (SD: 6.0) vs. 82.6 (SD: 7.8), 27.3% (SD: 20.3) vs. 49.4% (SD: 14.3), and 2.8 (SD: 5.6) vs. 8.4% (SD: 7.4), respectively. DHI was increased by 6.3% with IMRT compared to 3DCRT (p < 0.05). The reductions of V(105) and V(110) for the IMRT compared to 3DCRT were 44.7% and 66.3%, respectively (p < 0.01). The mean dose and V(30) for heart with IMRT were 2.3 (SD: 1.1) and 1.05 (SD: 1.5) respectively, which was a reduction by 6.8% and 7.9%, respectively, in comparison with 3D. Similarly, the mean dose and V(20) for the ipsilateral lung and the percentage of volume of contralateral volume lung receiving > 5% of prescribed dose with IMRT were reduced by 9.9%, 2.2%, and 35%, respectively. The mean of total monitor units used for IMRT and 3DCRT was about the same (397 vs. 387). The tangential field IMRT for intact breast using sliding window technique was successfully implemented in the clinic. We have now treated more than 1000 breast cancer patients with this technique. The dosimetric data suggest improved dose homogeneity in the breast and reduction in the dose to lung and heart for IMRT treatments, which may be of clinical value in potentially contributing to improved cosmetic results and reduced late treatment-related toxicity.