A prospective study of weekly intensity modulated radiation therapy plan adaptation for head and neck cancer: improved target coverage and organ at risk sparing.

This prospective study of weekly CT scanning and plan adaption during H&N IMRT reports on the frequency of plan adaptations based on dosimetric differences between original and re-optimised IMRT plans. The volumetric and geometric change occurring in target volumes and salivary glands is also described. Ten H&N cancer patients underwent weekly planning CT imaging and re-optimisation of the IMRT plan if PTV or OAR coverage was unacceptable. Comparisons of PTV and parotid gland dosimetry between the original and adaptive plans were made. Parotid and submandibular gland volume changes and shift were calculated. Eight of ten patients required one or more plan adaptations, with 41% of adaptations occurring by fraction ten. Salivary glands reduced in volume, with a medial shift of the lateral border of the parotid gland and a superior shift of the submandibular gland. Change in PTV coverage did not correlate with weight loss or nutritional score. Inadequate PTV coverage, requiring plan adaptation, occurs early in the course of IMRT. A weekly Adaptive RT (ART) protocol results in significant improvement of PTV coverage. Implementation of a clinical ART protocol should include imaging and dose calculation within the first ten fractions.

Correlations between contouring similarity metrics and simulated treatment outcome for prostate radiotherapy.

Many similarity metrics exist for inter-observer contouring variation studies, however no correlation between metric choice and prostate cancer radiotherapy dosimetry has been explored. These correlations were investigated in this study. Two separate trials were undertaken, the first a thirty-five patient cohort with three observers, the second a five patient dataset with ten observers. Clinical and planning target volumes (CTV and PTV), rectum, and bladder were independently contoured by all observers in each trial. Structures were contoured on T2-weighted MRI and transferred onto CT following rigid registration for treatment planning in the first trial. Structures were contoured directly on CT in the second trial. STAPLE and majority voting volumes were generated as reference gold standard volumes for each structure for the two trials respectively. VMAT treatment plans (78 Gy to PTV) were simulated for observer and gold standard volumes, and dosimetry assessed using multiple radiobiological metrics. Correlations between contouring similarity metrics and dosimetry were calculated using Spearman's rank correlation coefficient. No correlations were observed between contouring similarity metrics and dosimetry for CTV within either trial. Volume similarity correlated most strongly with radiobiological metrics for PTV in both trials, including TCPPoisson (ρ = 0.57, 0.65), TCPLogit (ρ = 0.39, 0.62), and EUD (ρ = 0.43, 0.61) for each respective trial. Rectum and bladder metric correlations displayed no consistency for the two trials. PTV volume similarity was found to significantly correlate with rectum normal tissue complication probability (ρ = 0.33, 0.48). Minimal to no correlations with dosimetry were observed for overlap or boundary contouring metrics. Future inter-observer contouring variation studies for prostate cancer should incorporate volume similarity to provide additional insights into dosimetry during analysis.

Interobserver variability in clinical target volume delineation in tangential breast irradiation: a comparison between radiation oncologists and radiation therapists.

AIMS: The delineation of target volumes has been radiation oncologist led. If radiation therapists were to undertake this task, work processes may be more efficient and the skills set of radiation therapy staff broadened. This study was undertaken to quantify interobserver variability of breast target volumes between radiation oncologists and radiation therapists. MATERIALS AND METHODS: The planning computed tomography datasets of 30 patients undergoing tangential breast radiotherapy were utilised. Four radiation oncologists and four radiation therapists independently contoured the clinical target volume (CTV) of the breast on planning computed tomography using a written protocol. The mean CTV volumes and the mean distance between centres of volume (COV) were determined for both groups to determine intergroup variation. Each of the radiation oncologists' readings in turn has been used as the gold standard and compared with that of the radiation therapists. The concordance index for each patient's CTV was determined relative to the gold standard for each group. A paired t-test was used for statistical comparison between the groups. An intraclass correlation coefficient was calculated to measure the agreement between the radiation oncologist and radiation therapist groups. RESULTS: The mean concordance index was 0.81 for radiation oncologists and 0.84 for radiation therapists. The intraclass correlation coefficient for the mean volume was 0.995 (95% confidence interval 0.981-0.998) between radiation oncologist- and radiation therapist-contoured volumes. The intraclass correlation for the mean difference between radiation oncologists' and radiation therapists' COV was 0.999 (95% confidence interval 0.999-1.000). CONCLUSIONS: Interobserver variability between radiation oncologists and radiation therapists was found to be low. Radiation therapists could potentially assume the role of CTV voluming for breast radiotherapy provided a standardised contouring protocol is in place.

Physicians and American political leadership.

Physicians have actively participated in the political processes of American democracy throughout the nation's history. The purpose of this study was to compare physicians' participation in public office during the first and second centuries of American democracy. Following the commencement of the US Congress, physicians were active members of the legislative branch. However, physicians' membership in Congress has diminished significantly in modern times. The executive and judicial branches of the federal government have recorded only marginal representation by physicians and none during the 20th century.