ESTRO 38 Abstract book

S1000 ESTRO 38

plan parameters including planned MF, actual MF, couch speed, gantry period, average leaf open time (LOT), pitch and jaw width were analyzed. Pearson correlation coefficient was calculated between the actual MF and the gantry period. Results The distribution of actual MF for total cases is plotted in figure 1(a) and detailed data are listed in table 1. The mean value of actual MF didn’t show much difference for different treatment regions. As shown in figure 1(b)-(c), the actual MF correlates with the gantry period with Pearson correlation coefficients of 0.70 and 0.84 for BCW(2.5D) and BCW(5D) respectively while p<0.01. The minimum rotation time of 12s was not reached for any BCW case. If the gantry period less than 13s was taken as the end point for a conventional 2Gy/fr treatment when optimizing treatment efficiency, the current planned MF for BCW could be further decreased. Besides, the planning efficiency might also be improved by reducing the iteration based on the large discrepancy between planned and actual MF. Figure 1(d)-(e) show the correlation for HN(2.5D) and abdomen(2.5D) as well. A few HN cases with the maximum gantry speed indicated the current lower limit of 2 for the planned MF was proper, which had to be increased to 3 for some critical cases. However, the linear trend in figure 1(d) indicated the upper limit should be decreased and a value of 3.4 could be reasonable. Those outliers with gantry period larger than 20s were caused by large prescription dose. The same conclusions were drawn for thorax and pelvis region. For abdomen and brain cases, no linear correlation could be observed which meant the current planned MF had a reasonable range from 1.8 to 3.6 and 1.4 to 3.2, respectively.

Results The wish list for prostate IMRT/VMAT comprised of 10 priority levels (see table 1). The first few levels focused on target coverage, followed by target homogeneity and conformity. The subsequent priority levels mainly accounted for organ sparing. The lowest priority further reduced the average organ at risk dose as much as possible. Studying ATP-IMRT an ATP-VMAT plans of the eight evaluation patients, we found similar target coverage (all ATP plans: V95>98.2% for PTV 77 and PTV 70 ), target conformity (range: CI95% PTV_70 = 0.64 – 0.81), target homogeneity (range: HI98% PTV_77 = 0.92 – 0.94) as compared to the dosimetrist-optimized VMAT plans. Furthermore, ATP resulted in an averaged dose reduction of 3.3 Gy (range: Gy -0.8 – 11.9 Gy) to the bladder and 4.6 Gy (range: -2.6 – 6.3 Gy) to the rectum (representative case in figure 1). Preparation and post-processing took approximately 45 minutes for the ATP plans. All plans were approved by an experienced radiation-oncologist in prostate cancer treatments.

Conclusion The prioritized clinical-goal based ATP algorithm led to high quality IMRT and VMAT plans for prostate cancer patients. The plans were fully automatically optimized in the background resulting in an increased departmental efficiency (approx. 135 minutes reduction per prostate case). EP-1843 Evaluation of treatment efficiency for helical tomotherapy with TomoEdge technology B. Yang 1 , W.W. Lam 1 , H. Geng 1 , K.Y. Cheung 1 , S.K. Yu 1 1 Hong Kong Sanatorium & Hospital, Medical Physics and Research Department, Happy Valley, Hong Kong SAR China Purpose or Objective Some previous studies analyzed the impact of modulation factor (MF) on both plan quality and treatment time by varying MF and pitch. Those studies usually drew conclusions based on a series of reference plans and focused on specific treatment region, e.g. head and neck. This study aims to evaluate the treatment efficiency based on large amount of clinical plans in different treatment regions by analyzing the treatment plan parameters of helical tomotherapy with TomoEdge technology, especially the correlation between actual modulation factor (MF) and gantry period. Material and Methods A total number of 303 patients treated in head and neck (HN), breast/chest wall (BCW), brain, thorax, abdomen (ABD) and pelvis regions in our hospital using tomotherapy with TomoEdge technique were retrospectively studied. All treatment plans involved in this study were approved by oncologists with clinical goals achieved. The treatment