Pain relief after a short course of palliative radiotherapy in pancreatic cancer, the Academic Medical Center (AMC) experience

Pain relief after a short course of palliative radiotherapy in pancreatic cancer, the Academic Medical Center (AMC) experienc

Dosimetric advantages of a clinical daily adaptive plan selection strategy compared with a non-adaptive strategy in cervical cancer radiation therapy

<p><b>Background:</b> Radiation therapy (RT) using a daily plan selection adaptive strategy can be applied to account for interfraction organ motion while limiting organ at risk dose. The aim of this study was to quantify the dosimetric consequences of daily plan selection compared with non-adaptive RT in cervical cancer.</p> <p><b>Material and methods:</b> Ten consecutive patients who received pelvic irradiation, planning CTs (full and empty bladder), weekly post-fraction CTs and pre-fraction CBCTs were included. Non-adaptive plans were generated based on the PTV defined using the full bladder planning CT. For the adaptive strategy, multiple PTVs were created based on both planning CTs by ITVs of the primary CTVs (i.e., GTV, cervix, corpus-uterus and upper part of the vagina) and corresponding library plans were generated. Daily CBCTs were rigidly aligned to the full bladder planning CT for plan selection. For daily plan recalculation, selected CTs based on initial similarity were deformably registered to CBCTs. Differences in daily target coverage (D_98% > 95%) and in V_0.5Gy, V_1.5Gy, V_2Gy, D_50% and D_2% for rectum, bladder and bowel were assessed.</p> <p><b>Results:</b> Non-adaptive RT showed inadequate primary CTV coverage in 17% of the daily fractions. Plan selection compensated for anatomical changes and improved primary CTV coverage significantly (<i>p</i> < 0.01) to 98%. Compared with non-adaptive RT, plan selection decreased the fraction dose to rectum and bowel indicated by significant (<i>p</i> < 0.01) improvements for daily V_0.5Gy, V_1.5Gy, V_2Gy, D_50% and D_2%. However, daily plan selection significantly increased the bladder V_1.5Gy, V_2Gy, D_50% and D_2%.</p> <p><b>Conclusions:</b> In cervical cancer RT, a non-adaptive strategy led to inadequate target coverage for individual patients. Daily plan selection corrected for day-to-day anatomical variations and resulted in adequate target coverage in all fractions. The dose to bowel and rectum was decreased significantly when applying adaptive RT.</p

Interfractional renal and diaphragmatic position variation during radiotherapy in children and adults: is there a difference?

<p><b>Background:</b> Pediatric safety margins are generally based on data from adult studies; however, adult-based margins might be too large for children. The aim of this study was to quantify and compare interfractional organ position variation in children and adults.</p> <p><b>Material and methods:</b> For 35 children and 35 adults treated with thoracic/abdominal irradiation, 850 (range 5–30 per patient) retrospectively collected cone beam CT images were registered to the reference CT that was used for radiation treatment planning purposes. Renal position variation was assessed in three orthogonal directions and summarized as 3D vector lengths. Diaphragmatic position variation was assessed in the cranio-caudal (CC) direction only. We calculated means and SDs to estimate group systematic (Σ) and random errors (σ) of organ position variation. Finally, we investigated possible correlations between organ position variation and patients’ height.</p> <p><b>Results:</b> Interfractional organ position variation was different in children and adults. Median 3D right and left kidney vector lengths were significantly smaller in children than in adults (2.8, 2.9 mm vs. 5.6, 5.2 mm, respectively; <i>p</i> < .05). Generally, the pediatric Σ and σ were significantly smaller than in adults (<i>p</i> < .007). Overall and within both subgroups, organ position variation and patients’ height were only negligibly correlated.</p> <p><b>Conclusions:</b> Interfractional renal and diaphragmatic position variation in children is smaller than in adults indicating that pediatric margins should be defined differently from adult margins. Underlying mechanisms and other components of geometrical uncertainties need further investigation to explain differences and to appropriately define pediatric safety margins.</p

Dosimetric advantages of proton therapy compared with photon therapy using an adaptive strategy in cervical cancer

<p><b>Background</b> Image-guided adaptive proton therapy (IGAPT) can potentially be applied to take into account interfraction motion while limiting organ at risk (OAR) dose in cervical cancer radiation therapy (RT). In this study, the potential dosimetric advantages of IGAPT compared with photon-based image-guided adaptive RT (IGART) were investigated.</p> <p><b>Material and methods</b> For 13 cervical cancer patients, full and empty bladder planning computed tomography (CT) images and weekly CTs were acquired. Based on both primary clinical target volumes (pCTVs) [i.e. gross tumor volume (GTV), cervix, corpus-uterus and upper part of the vagina] on planning CTs, the pretreatment observed full range primary internal target volume (pITV) was interpolated to derive pITV subranges. Given corresponding ITVs (i.e. pITVs including lymph nodes), patient-specific photon and proton plan libraries were generated. Using all weekly CTs, IGART and IGAPT treatments were simulated by selecting library plans and recalculating the dose. For each recalculated IGART and IGAPT fraction, CTV (i.e. pCTV including lymph nodes) coverage was assessed and differences in fractionated substitutes of dose-volume histogram (DVH) parameters (V_15Gy, V_30Gy, V_45Gy, D_mean, D_2cc) for bladder, bowel and rectum were tested for significance (Wilcoxon signed-rank test). Also, differences in toxicity-related DVH parameters (rectum V_30Gy, bowel V_45Gy) were approximated based on accumulated dose distributions.</p> <p><b>Results</b> In 92% (96%) of all recalculated IGAPT (IGART) fractions adequate CTV coverage (V_95% >98%) was obtained. All dose parameters for bladder, bowel and rectum, except the fractionated substitute for rectum V_45Gy, were improved using IGAPT. Also, IGAPT reduced the mean dose to bowel, bladder and rectum significantly (p < 0.01). In addition, an average decrease of rectum V_30Gy and bowel V_45Gy indicated reductions in toxicity probabilities when using IGAPT.</p> <p><b>Conclusion</b> This study demonstrates the feasibility of IGAPT in cervical cancer using a plan-library based plan-of-the-day approach. Compared to photon-based IGART, IGAPT maintains target coverage while significant dose reductions for the bladder, bowel and rectum can be achieved.</p