Comparison and evaluation of dosimetric and radiobiological parameters in two different treatment plans in stomach cancer by use of 3D CRT

Introduction: In 3DCRT the number of therapeutic fields has dramatic impact on treatment results especially in stomach cancer. Traditionally, for radiotherapy of stomach cancer the therapeutic procedure was using two fields (AP- PA or AP Lateral with wedge) to achieve smooth and homogeneous dose distribution in tumor. But nowadays, adding lateral or oblique fields to aforementioned techniques lead to reducing dose to organ at risks (OARs) like spinal cord, liver, both kidneys and better dose distribution in tumor. Moreover, there are a several ways to evaluate traditional and novel techniques in 3DCRT for stomach cancer. for example, Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP) from radiobiological point of view and Homogeneity Index (HI), Conformity Index (CI) as a dosimetric parameters. Thus, the aim of this study is to assess and compare two different plans in stomach cancer by using homogeneity Index, conformity index, TCP and NTCP as guidance criteria in 3DCRT.   Materials and Methods: In this study, 10 patients with stomach cancer were chosen. Two different of treatment plans; three fields (AP, PA, and lateral) and four fields (AP, PA and two laterals) were prepared. A photon beam of 6MV quality was used for both treatment plans in PCRT 3D as treatment planning system. Prescribed dose was 5o.4 Gy for tumor. Therapeutic aim for all treatment plans was to deliver at least 95% of prescribed dose to 97% of target volume while sparing organ at risks. The normalization of each plan followed the recommendation of ICRU report 50. The tumor volume selected for calculating the HI, CI and TCP and OARs for NTCP.   Results:Average ratio of the calculated parameters in treatment plans of four fields over three fields with standard deviation (Mean /SD) was 1.05±0.13 for CI and 0.99±0.01 for HI. In addition, Treatment ratio for four fields over three fields was 1±0.02. Damage ratio to spinal cord and liver was 0.57±0.18 and 2.09±0.93 respectively for treatment plans with four fields in comparison of treatment plans by using of three therapeutic fields.   Conclusion: Results show that, HI and CI parameters are approximately equal in two treatment plans. Therefore, both of the treatment plans are acceptable for clinical use. Assessment TCP and NTCP radiobiology parameter determined that, tumor control probability for both treatment plans are same but, damage probability of liver in three field treatment plan is less than over four fields while damage probability of spinal cord in four field treatment plan is lower than three fields treatment planning.