SU-E-T-171: Missing Dose in Integrated EPID Images

PURPOSE

A dosimetric artifact has been observed with Varian EPIDs in the presence of beam interrupts. This work determines the root cause and significance of this artifact.

METHODS

Integrated mode EPID images were acquired both with and without a manual beam interrupt for rectangular, sliding gap IMRT fields. Simultaneously, the individual frames were captured on a separate computer using a frame-grabber system. Synchronization of the individual frames with the integrated images allowed the determination of precisely how the EPID behaved during regular operation as well as when a beam interrupt was triggered. The ability of the EPID to reliably monitor a treatment in the presence of beam interrupts was tested by comparing the difference between the interrupt and non-interrupt images.

RESULTS

The interrupted images acquired in integrated acquisition mode displayed unanticipated behaviour in the region of the image where the leaves were located when the beam interrupt was triggered. Differences greater than 5% were observed as a result of the interrupt in some cases, with the discrepancies occurring in a non-uniform manner across the imager. The differences measured were not repeatable from one measurement to another. Examination of the individual frames showed that the EPID was consistently losing a small amount of dose at the termination of every exposure. Inclusion of one additional frame in every image rectified the unexpected behaviour, reducing the differences to 1% or less.

CONCLUSIONS

Although integrated EPID images nominally capture the entire dose delivered during an exposure, a small amount of dose is consistently being lost at the end of every exposure. The amount of missing dose is random, depending on the exact beam termination time within a frame. Inclusion of an extra frame at the end of each exposure effectively rectifies the problem, making the EPID more suitable for clinical dosimetry applications. The authors received support from Varian Medical Systems in the form of software and equipment loans as well as technical support.

Short bowel syndrome: a practical pathway leading to successful enteral autonomy

BACKGROUND

Short bowel syndrome is a multisystemic disorder that results from the loss of a significant amount of small bowel. The goal of treatment in these patients is to achieve complete enteral autonomy while minimizing complications. Our unit has 30 years of experience in the management of short gut patients. During the past decade, our results have improved significantly, especially in children with severe short bowel syndrome. This brief communication looks at the algorithm presently used in our unit.

METHODS

In this communication, the principles in management of short bowel syndrome in our unit are discussed. In addition, our algorithm is published for the first time. A brief summary of our results is provided.

RESULTS

Twenty-seven children were enrolled from 2000 to 2009. In this cohort, two patients died because of significant liver disease: one after having two liver and bowel transplants. Overall, survival stands at 92%. All had autologous gastrointestinal reconstruction, and 19 patients underwent bowel lengthening (longitudinal intestinal lengthening and tailoring). The median residual length of bowel of this subgroup at first operation was 25 cm in those who had their gut measured. Two patients were lost to follow-up. Two patients remain on supplemental total parenteral nutrition (TPN), with an overall 91% of surviving patients off TPN at a median of 6 months after reconstruction.

CONCLUSIONS

We believe this improvement is related to the development-over many years-of a structured pathway for managing these patients.

Controlled tissue expansion in the initial management of the short bowel state

The treatment of short gut syndrome has evolved dramatically during the past decade. The combination of surgical techniques and medical management in the context of a multidisciplinary approach has improved the outcomes of these children. The authors describe in detail their technique of controlled tissue expansion of the bowel before lengthening procedures. Monitoring of the child and troubleshooting actions during the controlled tissue expansion program also are discussed.

Evaluating China's Slope Land Conversion Program as sustainable management in Tianquan and Wuqi Counties

Increased soil erosion on sloped land has become a significant environmental concern in China that has been attributed to human activities such as deforestation, over-cultivation, and over-grazing of livestock. In order to reduce soil erosion on sloped lands, the Chinese government has responded by implementing large-scale, ecological rehabilitation programs, including the "Grain for Green" reforestation project. This program involves financial incentives to transition farmers into other economic activities with the goal of reducing ecological pressures and degradation. Because of the scope and potential impacts from these programs, detailed research is needed to understand their social and ecological effects. This paper reports on research conducted in Tianquan County, Sichuan Province, and Wuqi County, Shaanxi Province, that evaluates the effects of the program upon local economies and household livelihood systems. The paper argues that the successful conversion of farmland under "Grain for Green" depends upon local government involvement, local economic development, and funding for local projects. Without economic development within rural economies, we conclude that farmers will remain dependent upon continued subsidy assistance to meet the policy's ambitious environmental restrictions, thereby undermining the program's long-term sustainability.