Trends in the use of pre-operative radiation for adenocarcinoma of the pancreas in the United States.

BACKGROUND: The benefit and timing of radiation therapy (RT) for patients undergoing a resection for pancreatic adenocarcinoma remains unclear. This study identifies trends in the use of radiation over a 10-year period and factors associated with the use of pre-operative radiation, in particular. METHODS: The Surveillance, Epidemiology and End Results registry was used to identify patients aged ≥18 years with pancreatic adenocarcinoma who underwent a surgical resection between 2000 and 2010. Logistic regression was used to identify time trends and factors associated with the use of pre-operative radiation. RESULTS: The overall use of radiation decreased with time among the 8474 patients who met the inclusion criteria. However, the use of pre-operative radiation increased from 1.8% to 3.9% (P ≤ 0.05). Factors significantly associated with receipt of pre-operative radiation were younger age, treatment in more recent years and having an advanced T-stage tumour. The 5-year hazard of death was significantly less for those who received pre-operative radiation versus surgery alone [hazard ratio (HR) 0.64, 95% confidence interval (CI) 0.55-0.74] and for those who received post-operative radiation versus surgery alone (HR 0.69, 95% CI 0.65-0.73). DISCUSSION: The use of pre-operative radiation significantly increased during the study period. However, the overall use of pre-operative radiation therapy remains low in spite of the potential benefits.

Effect of lung and target density on small-field dose coverage and PTV definition.

We have studied the effect of target and lung density on block margin for small stereotactic body radiotherapy (SBRT) targets. A phantom (50 × 50 × 50cm(3)) was created in the Pinnacle (V9.2) planning system with a 23-cm diameter lung region of interest insert. Diameter targets of 1.6, 2.0, 3.0, and 4.0cm were placed in the lung region of interest and centered at a physical depth of 15cm. Target densities evaluated were 0.1 to 1.0g/cm(3), whereas the surrounding lung density was varied between 0.05 and 0.6g/cm(3). A dose of 100cGy was delivered to the isocenter via a single 6-MV field, and the ratio of the average dose to points defining the lateral edges of the target to the isocenter dose was recorded for each combination. Field margins were varied from none to 1.5cm in 0.25-cm steps. Data obtained in the phantom study were used to predict planning treatment volume (PTV) margins that would match the clinical PTV and isodose prescription for a clinical set of 39 SBRT cases. The average internal target volume (ITV) density was 0.73 ± 0.17, average local lung density was 0.33 ± 0.16, and average ITV diameter was 2.16 ± 0.8cm. The phantom results initially underpredicted PTV margins by 0.35cm. With this offset included in the model, the ratio of predicted-to-clinical PTVs was 1.05 ± 0.32. For a given target and lung density, it was found that treatment margin was insensitive to target diameter, except for the smallest (1.6-cm diameter) target, for which the treatment margin was more sensitive to density changes than the larger targets. We have developed a graphical relationship for block margin as a function of target and lung density, which should save time in the planning phase by shortening the design of PTV margins that can satisfy Radiation Therapy Oncology Group mandated treatment volume ratios.