P-0112 - Evaluation of bowel doses in patients undergoing dose escalated post operative Intensity Modulated Radiotherapy in Perimapullary Cancers
|Date||28 June 2014|
|Event||World GI 2014|
|Topics|| Hepatobiliary Cancers
Surgery and/or Radiotherapy of Cancer
|Citation||Annals of Oncology (2014) 25 (suppl_2): ii14-ii104. 10.1093/annonc/mdu165|
A. Bahl1, T. Bhattacharya2, R. Kapoor2, T. Parsee2, A. Singh2, R. Gupta2, S. Sharma2
Post operative radiotherapy is indicated in perimapullary cancer patients having high risk features like nodal positivity, close or involved margins, poorly differentiated histology and pancreatic involvement. Conventionally doses of 40-50 Gy have been used often using a split course regimen. The common cause of treatment failure in these patients is recurrence in the tumor bed and regional lymph nodes. Dose escalation to tumor bed was not possible using conventional radiotherapy due to surrounding critical organs particularly the bowel. The aim of the present dosimetric study is to evaluate dose escalation up to 60Gy/33#/4.5 weeks using Intensity Modulated Radiotherapy (IMRT) and its impact on bowel and surrounding critical structures.
Ten Patients of periampullary cancer in the head of pancreas were selected for this prospective dosimetric study. All patients had undergone Whipples surgery. CT scan images of slice thickness 2.5mm acquired and transferred to Eclipse Treatment Planning system (v8.6 Varian associates, Palo Alto, USA). IMRT contouring was done using the new RTOG guidelines. IMRT plans were generated using seven coplanar beams. An escalated dose of 60Gy/33#/4.5 weeks was prescribed to the Planning Treatment Volume. Individual bowel loops were contoured for the analysis. The dose constraint used for bowel was V45 < 195cc. Dosimetric evaluation of doses to bowel and other organs at risk like liver, kidneys, stomach, bowel bag and spinal cord was done. 3D Conformal Radiotherapy plans were also generated for the patients using the same prescription of 60 Gy/33#/4.5 weeks using one anterior and two lateral wedged fields to make comparative analysis. 6 MV photons were used for all treatment planning. For statistical analysis the data was arranged in SPSSv17. Summary statistics were generated for all variables. ‘T' test was used to compare the mean doses between the groups. A ‘p' value of <0.05 was considered significant.
Dose to the bowel was less using IMRT versus 3-DCRT with a V45 of 193.84 ± 116.50 cc (Mean volume ± Standard deviation) versus 550.02 ± 221.27cc (p = 0.01). The mean doses to liver, stomach, spinal cord, Right kidney & Left kidney using 3-DCRT were 37.32 ± 6.48 Gy (Mean Dose ± Standard deviation), 42.57 ± 6.78 Gy, 20.85± 8.26 Gy, 19.71± 8.69 Gy, 17.42± 8.41 Gy respectively. With IMRT the doses to the above structures were 28.76 ±4.72 Gy (p = 0.04), 29.42± 8.96 Gy (p = 0.03), 27.64± 9.85Gy (p = 0.27), 16.69± 5.92 Gy (p = 0.53), 18.28± 6.88 Gy (p = 0.86) respectively.
With dose escalation up to 60 Gy/33#/4.5 weeks, the dose received by bowel is significantly reduced with IMRT compared to 3DCRT (p = 0.01). The mean doses to other critical organs are also well within tolerance limits and lower with IMRT. Dose escalation up to 60 Gy/33# can be safely implemented with IMRT and is likely to improve local control and improve survival in periampullary cancer patients.