A Dosimetric study Comparing Outcome Advantages of Intensity Modulated Radiotherapy versus 3D-CRT versus Arc Therapy doses to Organs at Risk and Target in Gastric adenocarcinoma. Single Institution

Background: Gastric adenocarcinoma worldwide is the 4th common cause of 
death. The corner stone in treatment is surgery followed by radiotherapy to 
improve survival and decrease local recurrence which ≥ 80%. Low radiation 
tolerance of liver and kidney can subsequently cause life threatening damage. 
Our goal is to investigate the optimal radiation technique offering best target 
coverage, preventing recurrence and preserving nearby sensitive risk organs.
Materials and Methods: This is a dosimetric study including 10 patients with 
gastric cancer referred to our hospital for adjuvant chemoradiotherapy after total 
or subtotal gastrectomy. Three‑dimensional (3D-CRT) conformal radiotherapy, 
intensity‑modulated therapy (IMRT), volumetric modulated arc therapy 
(VMAT) plans were created for each patient. For the 30 plans, comparative 
dosimetric analyses of target volume (Dmean, D95, D98, D2), Homogeneity
(HI) and conformity (CI). Organs at risk (OAR) were compared by dose-volume 
histogram, Dmean, Dmax, V20,35, V45 for the three techniques.
Results: IMRT and VMAT were more homogeneous than 3D-CRT (p<0.05). 
However, the best conformal plans were yielded with VMAT (p = 0.033). IMRT 
and VMAT were significantly better protecting OARs than 3D-CRT. The lowest 
Dmax to the heart was obtained with VMAT with statistically different than 
IMRT and 3D-CRT(p=0.00). The mean liver doses were not statistically 
different between the 3 techniques. However, liver V35 and V45 were 
significantly lower in IMRT (p= 0.003 and p=0.006, respectively) and VMAT
(p=0.002 and p=0.003, respectively) than 3D-CRT. Both kidneys were better 
preserved with IMRT and VMAT. The adjacent left kidney was better spared 
with significant lower (Dmax, Dmean, V20, and V35) in IMRT and VMAT than 
3D-CRT plans. Dmean and V35doses of spinal cord were significantly higher in 
3D plans while the doses of other two techniques were lower.
Conclusions: In comparison to 3D-CRT both IMRT, VMAT is preferable 
techniques for conformity of target volume and preserving the left kidney and 
the heart. However, for better HI & CI regarding PTV coverage, and for less 
toxicity to OAR, VMAT is preferable and more advantageous than IMRT 
&3DRT in adjuvant gastric adenocarcinoma.