P-0119 - Adjuvant Radiotherapy in periampullary carcinomas: Dosimetric comparison of 3DCRT, IMRT and Rapid Arc plans
|Date||28 June 2014|
|Event||World GI 2014|
|Topics|| Pancreatic Cancer
Surgery and/or Radiotherapy of Cancer
|Citation||Annals of Oncology (2014) 25 (suppl_2): ii14-ii104. 10.1093/annonc/mdu165|
M. Nandi, M. Gazi, J. Bhattacharya, S. Biswal, S. Pramanik, S. Mitra
This study was done to compare dosimetric characteristics between Rapid arc (RA), IMRT and 3DCRT plans with a view to assess the doses to organs at risk.
Five patients of peri ampullary carcinoma requiring adjuvant radiotherapy were treated with Rapid Arc plans. The IMRT and 3DCRT plans were generated for dosimetric comparison. Contrasts enhanced 3mm planning scans were acquired from carina to iliac crest. Rapid arc plans were generated with two simultaneously optimized volumetric partial arcs, IMRT planning was done with a 5/7-field coplanar sliding window technique, and 3DCRT plans used one anterior and two lateral fields. All plans were done on Eclipse treatment planning system (version 11.0.42). The clinical target volume included the postoperative tumour bed and draining lymph nodal areas. The dose prescribed was 50.4Gy in 28 fractions over 5 weeks in all the cases. The planning objective was to achieve >95% coverage to >95% of the Planning Target Volume (PTV) while meeting the normal-tissue dose constraints. The plans were evaluated on the basis of Homogeneity Index [HI (D5%/D95%)], Conformity Index [CI (VDP) PTV/ (VDP) BODY], mean doses to the organs at risk (OARs) expressed as [Gy ± SD (standard deviation)], and monitor units (MUs) needed to deliver the dose. Data was analysed using ANOVA. Comparison of means was performed using Paired t test for the normally distributed data and Wilcoxon signed rank test for the rest.
Mean PTV volume (±SD) was (527 ± 73) cm3. The mean CI for RA plans (0.98) was significantly better compared to IMRT (0.80, p = 0.007), and 3DCRT plans (1.10, p = .0001). RA plans showed better homogeneity with mean HI of 1.04 over IMRT (1.03, p = 0.03) or 3DCRT [1.10(p = 0.0001)]. The mean dose to right kidney was lower in RA plans (11.47 ± 2.0) Gy compared to IMRT (13.79 + /-4.3) Gy or 3DCRT (14.20 ± 4.5) Gy; though not statistically significant. The mean dose to left kidney was significantly reduced in RA (12.76 ± 3.4) Gy in comparison to IMRT [14.17 ± 3.9) Gy, p = 0.03]; though not with 3DCRT (13.17 ± 5.5, p = 0.8). There was significant reduction of V30mean of right kidney in RA plans (2.11 ± 1.6)% compared to IMRT [(4.81 ± 3.8)%, p = 0.003] or 3DCRT [(11.38 ± 3.7)%, p = 0.001]. V20mean (10.8 ± 2.9)% was also reduced in comparison to [IMRT (28 ± 18.2)%, p = .04] and 3DCRT [(20.51 ± 5.7)%, p = .03]. V20mean of left kidney in RA (10.5 ± 10.4) significantly lessened in comparison to IMRT [(18.6 ± 13.1)%, p = 0.03] and V30mean with 3DCRT [(13.24 ± 9.1)%, p = 0.03]. Mean liver dose was minimised in RA plans (11.47 ± 1.8) Gy compared to IMRT [13.79 ± 2.0) Gy, p = .04], or 3DCRT [14.4 + /-1.6) Gy, p = 0.04]. Mean dose to duodenum and gut was significantly less in RA [(44.44 ± 5.6) Gy, (15.24 ± 7.2) Gy] compared to 3DCRT respectively [(47.57 ± 5.2) Gy, p = 0.001, (19.71 ± 8.4) Gy, p = 0.01]. The mean number of MUs per fraction could be reduced from (881 ± 125) MUs in IMRT to (481 ± 26) MUs in RA (p = 0.001).
Rapid Arc plans could provide slight improvements in OARs sparing and lower MUs with improved target coverage compared to IMRT and significantly better to 3D-CRT for adjuvant radiotherapy in periampullary carcinomas.