Evaluation of adequacy of conventional radiotherapy fields based on bony landmarks in cervical cancer patients using contrast enhanced computed tomography scan- A regional cancer centre experience

Objective: Knowing that there is a wide variation in pelvic anatomy worldwide, it was an instinctive query that whether radiotherapy planning in cancer cervix by four field box technique based on GOG (gynaecologic oncology group) defined field carries adequacy and justification in our region. A prospective trial was conducted at a Regional Cancer Centre located in Northern India, from August 2014 to July 2015. CECT (contrast enhanced computed tomography) abdomen and pelvis was done in newly diagnosed 64 patients of cervical cancer with stage IB to IIIB. Using vessels as surrogates for lymph nodes, adequacy of radiation portals using bony landmarks defined by GOG were assessed. Materials and Methods: 2D (two dimensional) radiation portals were designed on conventional simulator ”Acuity” as per GOG recommendations. CECT pelvis from L1(first lumbar) to mid femur was done in the same position along with same immobilization accessories used during conventional simulation. Three parameters D1, D2 and D3 were defined for adequacy of superior, lateral, and anterior portals respectively. Results: Increasing the length of AP:PA portal cranially by 4.5 cm will cover the proximal common iliac nodes adequately. The width of the AP: PA portal needs to be increased by 3.6 cm to cover the distal external iliac nodes adequately. Conclusions: Conventional pelvic fields failed to cover all of pelvic lymph nodes in majority of this study population. Diagnostic CT and MRI are suggested to be referenced to plan pelvic fields precisely when CT simulation is not available. Keywords: Cancer cervix, Conventional simulator, Bony landmarks.