Faculty Bibliography

Purpose: Rapid dose fall off from planning target volume (PTV) is required to spare organs at risk (OAR) that is hallmark of advanced treatment techniques (IMRT, VMAT, and SBRT). Along with conformity index (CI) and homogeneity index (HI) recently, gradient index (GI) was introduced to provide a measurable quality index for dose fall off from PTV. However, it is not clear if GI can be used in IMRT and if there are consistent differences between the two techniques. Methods: Dose volume histogram data for 700 patients equally divided between SBRT and IMRT were retrospectively analyzed. GI was calculated for each patient which is ratio of the volume of at half the prescription (PIV50%) to prescription isodose volume (PIV100%) which was calculated treatment plan and from PTV and CI. Physical distance ratio between OAR and PTV coverage was determined based on the cube root of the GI as an additional tool along with gradient measure distance (rPIV50%-rPIV100%) for the evaluation of SBRT and IMRT plans. Results: The GI varied widely between IMRT and SBRT patients due to inherent differences in techniques. The GIs are nearly constant 4.3 +/-1.1 and 12.8 +/-4.4 for SBRT and IMRT, respectively. The size of PTV is inversely related to GI with data more consistent in SBRT compared to IMRT. The gradient measure increases with PTV size in a well-defined way (0.5-1.5 cm) compared to IMRT where data is widely spread. This can be used as a surrogate for distance between PTV and OAR in IMRT and SBRT. Conclusion: Gradient index and measure are effective parameters in evaluating dose gradient that show consistent differences between treatment techniques. These tools could provide an opportunity for plan evaluation especially the distance from the PTV to OAR to optimize the dose to reduce complications

PURPOSE/OBJECTIVE:Ir-192 is the predominant source for high-dose-rate (HDR) brachytherapy in United States markets. Co-60, with longer half-life and fewer source exchanges, has piloted abroad with comparable clinical dosimetry but increased shielding requirements. We sought to identify practitioner knowledge of Co-60 and establish acceptable willingness-to-pay (WTP) thresholds for additional shielding requirements for use in future cost-benefit analysis. METHODS AND MATERIALS/METHODS:A nationwide survey of U.S. radiation oncologists was conducted from June to July 2015, assessing knowledge of HDR sources, brachytherapy unit shielding, and factors that may influence source-selection decision-making. Self-identified decision makers in radiotherapy equipment purchase and acquisition were asked their WTP on shielding should a more cost-effective source become available. RESULTS:Four hundred forty surveys were completed and included. Forty-four percent were ABS members. Twenty percent of respondents identified Co-60 as an HDR source. Respondents who identified Co-60 were significantly more likely to be ABS members, have attended a national brachytherapy conference, and be involved in brachytherapy selection. Sixty-six percent of self-identified decision makers stated that their facility would switch to a more cost-effective source than Ir-192, if available. Cost and experience were the most common reasons provided for not switching. The most common WTP value selected by respondents was <$25,000. CONCLUSIONS:A majority of respondents were unaware of Co-60 as a commercially available HDR source. This investigation was novel in directly assessing decision makers to establish WTP for shielding costs that source change to Co-60 may require. These results will be used to establish WTP threshold for future cost-benefit analysis.