| Περίληψη: | Patient-specific quality assurance (PSQA) should ideally pick up errors that can lead to inaccurate patient dose, such as treatment planning errors, computational dosimetry errors, data transmission errors, and machine delivery errors (mechanical and dosimetry errors of the treatment machine)28. PSQA not only varies between different clinics but also depends on the type of treatment given. It is important that each clinic carefully considers which action level is suitable for their methods and quality assurance system.
The patient's QA is performed using a phantom. The deviation resulting from the phantom radiation from a material that mimics the tissue during irradiation is calculated and it is possible to detect radiation within it and the dose calculated through the treatment planning system. The measurements are collected and the resulting errors are calculated. This procedure is performed to confirm the treatment plans. The QA of each patient is done before his first treatment.
The purpose of the present study was to examine the ability of Delta4 phantom, which is a commercial system designed to perform patient specific QA for VMAT, to detect multiple delivery errors that were intentionally introduced into treatment plans, and we report on the sensitivity with which the device detected such errors and any limitations in error detection ability.
The lungs are one of the organs that are known to move with the breath. Patients’ breathing patterns can vary in magnitude, period and regularity during imaging and treatment sessions17. We did research in lung cancer patients on the movement of the lungs due to respiration and consequently the target tumor. We showed that respiration-induced tumor motion is small during irradiation and does not affect the validity of the treatment plan during normal treatment, when we suppose that patients breathe quietly.
Furthermore, we increased the monitor units in the lung cancer patient plans to see to what extent the γ-index is affected and consequently the validity of the treatment plan. To evaluate specific %Gamma Pass gradients for each type of error, the default gamma criterion (DD%/DTA mm) was set to 3%/3 mm.
Finally, the sensitivity of the gamma-index method to detect a disagreement between a VMAT plan and plan delivery varied according to the gamma criterion, therefore, a gamma criterion which makes the gamma evaluation most sensitive is recommended for use in the clinic.
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