ABSTRACT
Quality assurance dosimetry often requires the comparison of measured doses with those calculated by a treatment-planning system for phantoms of density other than 1.000 g/cm3. The presence of an artifact in the Pinnacle3 treatment-planning system can lead to systematic errors in such cases. These errors are also present, although reduced in magnitude, in heterogeneous media.
Subject(s)
Artifacts , Quality Assurance, Health Care/methods , Radiometry/instrumentation , Radiotherapy Planning, Computer-Assisted/methods , Software , Data Interpretation, Statistical , Radiometry/methods , Radiotherapy Dosage , Reproducibility of Results , Sensitivity and Specificity , Software ValidationABSTRACT
The resolution of multileaf collimators (MLCs) is limited by their finite leaf width. A commercial package (HD-270) uses 3D couch translation and leaf adjustments to emulate smaller leaf widths. In this paper, we report on the commissioning of this feature using software testing, dial gauge measurements, and film dosimetry. We also identify a variety of limitations: software bugs and truncation artifacts, MLC leaf positioning uncertainties (random variations, systematic gantry dependence and backlash), and uncertainties in couch positioning. These reduce the capabilities of this implementation below that achievable theoretically.
Subject(s)
Quality Assurance, Health Care/methods , Radiotherapy Planning, Computer-Assisted/methods , Radiotherapy, Computer-Assisted/instrumentation , Radiotherapy, Computer-Assisted/methods , Radiotherapy, Conformal/instrumentation , Radiotherapy, Conformal/methods , Software , Equipment Design , Equipment Failure Analysis , Film Dosimetry , Miniaturization , Quality Assurance, Health Care/standards , Radiotherapy Dosage , Radiotherapy Planning, Computer-Assisted/instrumentation , Radiotherapy, Computer-Assisted/standards , Radiotherapy, Conformal/standards , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
PURPOSE: To investigate the therapeutic usefulness and cost-effectiveness of prophylactic cranial irradiation (PCI) in patients with limited-stage small-cell lung cancer (SCLC) who had achieved a complete remission. METHODS: A retrospective chart review was undertaken of all patients diagnosed in Saskatchewan with SCLC between 1987 and 1998 inclusive. Patients who achieved a complete remission were divided into two groups, depending on whether they underwent PCI (PCI+ and PCI-, respectively). The quality-of-life-adjusted survival was estimated by the Q-TWiST method (quality time without symptoms and toxicity). The mean incremental costs per month of incremental OS were calculated in a cost-effectiveness analysis. RESULTS: Among the 98 complete remission patients, the median OS for PCI+ and PCI- patients was 20.0 and 19.0 months, respectively (p > 0.05, nonsignificant). The median disease-free survival was 14.7 and 10.0 months, respectively (p < 0.05). The difference in the mean Q-TWiST survival was significant (p < 0.01). The mean marginal cost was $18,834/PCI+ patient and $17,885/PCI- patient (p > 0.05, nonsignificant). The cost-effectiveness ratio was $70/mo of incremental OS if u(tox) and u(rel) (the utility coefficients to reflect the value of time in health states of toxicity and relapse) were assumed to be 1.0. CONCLUSION: PCI is a cost-effective treatment that improves the quality-of-life-adjusted survival for patients with a complete remission of SCLC.
