Purpose: To determine calibration factors for several diodes and TLD as a function of distance from the field edge. These can then be applied to measure dose at any out‐of‐field point. Method and Materials: Skin QED Diode has been used to estimate the radiation dose to patient's ICD outside the treatment fields. The ICDs from three major manufacturers have an outer case made of Titanium (Ti) ranging from 0.4– 0.6 mm thickness. With the correction of mass attenuation coefficients of Ti and tissue at 6‐MeV, it is estimated that 0.5‐ mm Ti is equivalent to 2.4‐mm tissue. The manufacturers recommend that the ICD be implanted subcutaneously underneath skin at 3–4 mm depth. Therefore, a 5‐mm bolus with skin diode 1‐mm inherent buildup is close to the true depth of the electronic device. The responses of the skin diode with and without bolus, an ISORAD photon diode, and TLD were measured per unit dose to water at off‐axis distances up to 10‐cm from the field edge. Dose at each point was measured by an ionization chamber located at 0.5‐cm and 1.5‐cm depth. Results: The calibration factor as a function of distance from the field edge, relative to its central axis value, changed very little for TLD and for the QED skin diode with 0.5‐cm bolus; decreased by a factor as large as 2 for the photon diode; increased by a factor as large as 3.4 for the QED diode without bolus. Conclusions: The use of diodes for out‐of‐field dose measurements requires knowing the calibration factor as a function of off‐axis distance. This can be readily done at each institution or the manufacturer can provide the pertinent relative response data. The skin QED diode is easy to use as an in‐vivo dosimeter, and, with 5‐mm bolus, its behavior is similar to TLD.
Extraskeletal chondrosarcoma of the leg is a rare, malignant neoplasm with very few cases having been reported in the literature. In this study we investigate the possibility of using intensity modulated radiotherapy (IMRT) for this type of disease and demonstrate its advantages over conventional three‐dimensional (3D) conformal treatment. A case was presented of a patient with extraskeletal chondrosarcoma of the lateral compartment of the leg in which the target volume was 50 cm in length and twisted around the surrounding bones. Both the 3D conformal plan and IMRT plan were designed using the Memorial Sloan‐Kettering Cancer Center planning system. The IMRT plan produced a superior dose distribution to the patient as compared to the 3D conformal plan both in terms of dose conformity and homogeneity in the target volumes, and reduction of the maximum dose to the bone. The planning time of the IMRT plan was about 3–5 times shorter than that of the 3D conformal plan. It was demonstrated that the IMRT technique can be used not just for small tumors, but also for large and spiral‐shaped tumors close to critical organs. The IMRT method requires less planning time, and provides better target coverage with more sparing of critical structures. When planning patients with multiple target volumes receiving different prescribed doses, the IMRT technique can more easily meet this requirement.PACS number(s): 87.53.–j, 87.90.+y
Intensity modulated radiation therapy (IMRT) is often used for the treatment of soft tissue sarcoma. Due to high radiation doses, many patients have high risk of suffering from a femoral bone fracture sometime following the IMRT treatment. The most common type of radiation treatment-related fracture is a stress fracture. The fracture risk rate may be as high as 24% in sarcoma patients who have undergone periosteal stripping and received chemotherapy. Thus, it is necessary to be able to identify those patients with high risk for IMRT treatment-related bone fracture. In this paper, we will first present IMRT treatment planning techniques. We will then discuss how bone system changes their stiffness and how the fracture risk develops after a certain period of time post radiation treatment. Finally, we will present our latest data on the femoral bone fracture risk factor assessment for patients with soft tissue sarcoma following IMRT treatment. We have developed a novel mathematical model of trabecular bone composed of a disordered cubic network. Based on our preliminary data, we believe that this new mathematical model could shed new light on the relationship between the femoral bone fracture risk factor and the radiation dose delivered by an IMRT plan and provide a valuable prognostic tool for these high-risk patients.
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