Background: This paper aimed to analyze the output constancy of a medical linear accelerator using PTW QUICKCHECK webline and studied the sensitivity of the PTW QUICKCHECK webline . Materials and Methods: The paper statistically analyzed the output doses of 6 MV and 10 MV of photons and 6 MeV, 9 MeV, and 12 MeV of electrons from a medical linear accelerator measured before the daily treatment to assess the output stability of a medical linear accelerator. Some modifications were introduced by artificially altering the external irradiation conditions, and the percent variations from baseline values were noted. The gantry angle was changed and some deviations were established in the vertical, longitudinal and lateral directions to study the sensitivity of the PTW QUICKCHECK webline . The beam flatness, symmetry, radiation quality and output energy of 6 MV of photon energy were statistically analyzed. Results: Among the measurements, no parameters exceeded the tolerance of ±3%. QUICKCHECK webline was capable of detecting the variations in the central axis dose, flatness, symmetry and radiation quality under the testing conditions. Similar to the photon energy, electron energy measurements also confirmed that the detector was sensitive to a small variation in output introduced by the testing conditions. An important application of accelerator performance prediction in this study confirms the irreplaceable and important function of morning quality checks of a linear accelerator. Conclusions: The output dose measured before daily treatment using PTW QUICKCHECK webline to analyze the linear accelerator output constancy helps to decrease the system error, effectively reduces the errors of the accelerator system, and avoids serious mistakes.

<p>Supplementary Figures 1 -7 and Supplementary Tables 1 - 3 legends</p>

Purpose/Objective(s): Radiotherapy related carries (RRCs) is one of the most common side effects for the patients with advanced nasopharyngeal carcinoma (NPC) following radiotherapy. The mechanism of RRC was still uncertain. How to precisely predict and treat effectively RRC remain controversial. Materials/Methods: A total of 138 patients with NPC receiving radiotherapy at our institute between June 2012 and December 2016 were enrolled in this study. There were 92 males and 46 females, and the median age was 48 (ranging from 12 to 72) years old. The median follow-up time was 30 (ranging from 12 to 60) months. Clinical characteristics, incidence of RRCs, radiation doses to OARs, oral pH values, and lifestyle of these patients were collected. Time-dependent Cox regression model, Cox regression tress, event-free Kaplan-Meier curve, Mann-Whitely U test were used to carry out statistical analysis. Results: 28 of 138 patients developed RRCs. We found that age (HRZ1.039, 95%CI: 1.004-1.075), oral pH value (HRZ0.352, 95%CI: 0.191-0.650), technique of radiotherapy (HRZ0.302, 95%CI: 0.135-0.678), degree of xerostomia (HRZ9.150,95%CI: 1.817-46.071), drinking habit (HRZ2.263,95% CI: 1.075-4.764), radiation dose of sublingual glands (HRZ1.045, 95%CI: 1.007-1.085) were potential risk factors of RRCs. Upon multivariate analysis, oral pH value (HR-Z0.390, 95%CI: 0.204-0.746) was shown to be an independent risk factor of RRCs. Patients with oral pH values 5.3 (HRZ33.68, p<0.001). Further, the cutoff value of radiation dose of sublingual glands was found to be 32.53Gy (ORZ 3.12, 95% CI: 1.16-8.42; P Z 0.02) upon Mann-Whitely U test and logistic regression tree analysis. Conclusion: Our results showed that age, pH value, technique of radiotherapy, degree of xerostomia, drinking habit and radiation dose of sublingual glands were potential risk factors for radiotherapy-related caries, in which oral pH value was an independent factor of RRCs. Limiting dose of sublingual gland might alleviate an acidic environment of the oral cavity and help decrease the risk of RRCs.

Intensity-modulated radiation therapy (IMRT) has replaced 3-dimensional conformal radiotherapy (3DCRT) because of its capacity to deliver a more conformal dose to the target and to spare normal structures. This helps the oncologist to escalate the dose to the tumor volume. It can improve the cure rate of cancer and better protect the organs at risk. A lot of scholars have reported that Intensity-modulated radiation therapy has an advantage over three-dimensional conformal radiation therapy (3DCRT) (1,2) . IMRT plans can be delivered by use of a static multi-leaf collimator (SMLC) and a dynamic multi-leaf collimator (DMLC)