Head and Neck Radiotherapy with Tele-Cobalt Machine- Efficacy and Need for Tissue Compensation

Abstract

External Beam Radiotherapy (EBRT) remains the mainstay for radical treatments, in malignancies in head and neck regions. Head and Neck malignancies form around 50% of radiotherapy patients in the north eastern parts of the Indian subcontinent. Because of less inter-field separations, the penetration requirements of the treatment plans makes the telecobalt beam sufficient for executing radiotherapy, with proper immobilization and use of wedges if required. Inter-field thickness variations and irregular contour affect uniformity in delivered doses, and adverse reactions are encountered because of skewed isodose curves seriously affecting the volume dose variations in treatment planning. Normal tissue reactions affect effectiveness of the treatment and therefore deter the Quality of Life (QOL). EBRT with a telecobalt machine (Theratron 780C) started in 2006 and completed a decade at our centre. About 15 patients per day receive radiotherapy for head and neck treatments. To overcome skin reactions and excess dose due to small contour of neck, a need was felt to introduce tissue compensation. Ellis type tissue compensation using 1 cm thick Aluminum metal is introduced. The tissue deficiency is measured by an L shaped gridded type Lucite frame work. For individual patients the custom type compensator tray is prepared on a Lucite plate, mountable in the shadow tray of the cobalt machine. The attenuation coefficient of metal rods μ=0.1462cm-1 (1cm Al=2.57cm water). A simple type of POP immobilization is prepared in place of thermoplastic immobilization shell. The Lucite mounting tray has attenuation about 4%. Lateral opposing fields with compensation reduced resultant iso doses 180% and 170% in neck and chin levels to 150% with uniform tumor volume homogeneous dose of 160%. Portal radiographs with and without compensator showed uniform tissue irradiation, also a method to verify field positions. If this method is applied to all the head and neck radiotherapy patients both for AP-PA and Lateral fields, the morbidity up to epidermis, and overdose effects could be brought down, making tele cobalt treatments more effective. In the era of high technology radio-therapy, these types of innovations at hospital level promote cost-effective radical treatments to cancer patients, because cancer care all over the globe becomes unaffordable.