729P - Profile of Doses to Organs at Risk Using 3-D Conformal Radiotherapy (3-DCRT) Versus Intensity Modulated Radiotherapy (IMRT) in Postoperative Radiotherapy of Periampullary Cancers: Implications for Radiation Dose Escalation

Abstract

ABSTRACT Introduction Periampullary cancers are treated with Whipple's surgery in combination with radiotherapy & chemotherapy. The common cause of treatment failure in these patients is recurrence in the tumor bed & regional lymph nodes. A treatment approach aiming to increase the local control rate, by escalating radiation dose is likely to translate into a better survival.The purpose of the present study was to do a dosimetric analysis of the doses to organs at risk in postoperative radiotherapy using a dose of 45Gy/25 fractions and to assess the feasibility of radiation dose escalation. Material & methods Ten patients of periampullary cancers in head of pancreas were selected. All patients had undergone Whipple's surgery. IMRT and 3DCRT plans were generated for each patient. IMRT contouring was done as per RTOG guidelines. 3DCRT planning was done using one anterior and two lateral fields. A dose of 45Gy/25 fractions was prescribed to the Planning Target volume. Dosimetric evaluation of doses to liver, kidneys, stomach, bowel bag, spinal cord was done using ‘QUANTAC' parameters. For statistical analysis the data was arranged in SPSSv18. ‘t' test was used to compare the mean doses. A ‘p' value of Results Dose to the bowel bag was less using IMRT versus 3-DCRT with a V45 of 80.91±57.40 cc (Mean volume ± Standard deviation) versus 212.28 ± 159.04cc (p = 0.03).The mean doses to liver, stomach, spinal cord, Rt kidney & Lt. kidney using 3-DCRT were 24.59± 3.90 Gy (Mean Dose ± Standard deviation), 21.90±6.73 Gy, 26.50±14.72 Gy, 14.14±3.90 Gy, 13.71±3.83 Gy respectively. With IMRT the doses to the above structures were 22.91 ± 3.14Gy (p = 0.32), 20.71±5.78 Gy (p = 0.69), 24.77 ± 7.93Gy (p = 0.76), 11.55±4.12 Gy (p = 0.19), 13.72±2.44 Gy (p = 0.99) respectively. Conclusions With a prescription of 45Gy/25# the dose to bowel bag is significantly reduced using IMRT compared to 3-DCRT. The doses received by other organs are lower with IMRT compared to 3-DCRT though not statistically significant. The profile of doses received by organs at risk leaves ample scope of dose escalation using IMRT. Disclosure All authors have declared no conflicts of interest.