An IMRT class solution for patients with skin lesions of the temple region that have spread to the parotid gland

Patients with skin lesions of the temple region that have spread to the parotid gland are commonly treated with three-dimensional conformal radiation therapy (3DCRT). 3DCRT has associated limitations when treating this disease. 3DCRT requires this disease site to be treated with two junction regions, resulting in poor dose conformity to the tumour target. Proximity of critical structures to the target volume can make dosimetry difficult, "especially for concave-shaped targets in close proximity to sensitive normal structures" (Saw.C et al., 2002, p76). Intensity modulated radiation therapy (IMRT) is a relatively new treatment technology that has potential to overcome limitations associated with 3DCRT (Garden.A et al., 2004). IMRT has been reported to have significant advantages over conventional 3DCRT treatment, by improving dose to the tumour and lowering doses to critical structures (Adams.E et al., 2001). Research has been conducted into the optimal IMRT treatment for specific head and neck carcinomas. They are identified as class solutions. "A class solution can be defined as the historical experience in designing RT plans for a particular site" (Intensity Modulated Radiation Therapy Collaborative Working, 2001, p913). This study was performed to establish an optimal IMRT class solution for patients with skin lesions of the temple region that have spread to the parotid gland, and to determine if it is the superior treatment option over 3DCRT treatment. Dosimetry planning was performed on computerised tomography data sets of nine patients with this disease site. One optimised 3DCRT dosimetry plan and eight optimised IMRT plans with specific beam arrangements were calculated. Clinical and statistical analysis was performed on; critical structures, conformity indices (CI) and dose volume histogram (DVH) range analysis of the planning target volume (PTV). Analysis of IMRT plans revealed that the 7-beam arrangement and 4-beam ipsilateral arrangement produced significantly lower doses to the majority of critical structures (P < 0.05). The 7-beam IMRT arrangement produced the best and second best CI and DVH PTV results, but these were not significantly different to the majority of other beam arrangements. This indicates that the 7-beam arrangement with defined beam angles of; 40°,120°,160°,200°,240°,300°,0°, is the superior IMRT treatment plan, and thus class solution for this disease site. Clinical analysis confirmed results. Analysis was performed on IMRT class solution results compared with 3DCRT results. CI was significance higher and DVH PTV range was significantly lower for the IMRT class solution (P < 0.05). The class solution delivered significantly higher doses to the majority of critical structures in comparison to the 3DCRT plan (P < 0.05). This indicates that the IMRT class solution is superior to 3DCRT in terms of PTV conformity and homogeneity, but not in terms of doses to critical structures. Skin lesions of the temple region with tumour extension to the parotid gland, is a complicated disease site. Investigations into current and potential radiation therapy treatments will guide treatment options and facilitate outcomes for patients with this disease