High Dose Zone Research Articles

Microscopic and Macroscopic Tumor and Parenchymal Effects of Liver Stereotactic Body Radiotherapy

To describe the histologic and volumetric changes in normal liver tissue after stereotactic body radiotherapy (SBRT) for liver metastases. Pre- and post-SBRT imaging studies were analyzed to evaluate the effect of SBRT on normal liver volume (NLV) in 15 patients treated in a prospective clinical trial. Two other patients underwent exploratory surgery after SBRT and histologic analyses of the irradiated liver were performed to characterize the pathologic effects of SBRT. In the 15 patients studied quantitatively, the total NLV had decreased transiently at 2-3 months after SBRT and then began to regenerate at 3-8 months after SBRT. The median NLV reduction at the maximal observed effect was 315 cm(3) (range, 125-600) or 19% (range, 13-33%). Among the several dosimetric parameters evaluated, the strongest linear correlation was noted for the NLV percentage receiving 30 Gy as a predictor of maximal NLV reduction (r(2) = 0.72). The histologic changes observed 2 and 8 months after SBRT demonstrated distinct zones of tissue injury consistent with localized veno-occlusive disease. The well-demarcated focal parenchymal changes after liver SBRT (demonstrated both radiographically and histologically) within the high-dose zone are consistent with a threshold dose-induced set of phenomena. In contrast, the more global effect of NLV reduction, which is roughly proportional to whole organ dose parameters, resembles more closely an effect determined from radiobiologically parallel architecture. These observations suggest that modeling of normal tissue effects after liver SBRT might require different governing equations for different classes of effects.

Management of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a distinctly radiosensitive and chemosensitive tumor. Best quality radiotherapy is demanded to build up the complex concave high-dose zone for this critical location. Intensity-modulated (IMRT) technique is advocated, image guidance to ensure setup precision and adaptive re-planning if major deviations from intended dose distribution occur during the treatment course are useful improvements if resources allow. Stringent dose constraint to organs at risk should be attempted to minimize late toxicities. Addition of cisplatin-based concurrent-adjuvant chemotherapy is recommended for patients with stages III–IVB and high-risk stage IIB diseases. More contemporary series using IMRT together with extensive use of chemotherapy and acceleration reported very encouraging early results with locoregional control in excess of 90% at 2–4 years; the key remaining problem is distant failure. Further improvement of efficacy by changing chemotherapy sequence to induction-concurrent is being explored.The plasma level of Epstein–Barr Viral Deoxyribonucleic Acid is an additional tool for nonkeratinizing carcinoma for prognostication and monitoring disease progress. Integrated fluorodeoxyglucose positron emission tomography and computed tomography is useful for excluding distant metastases and posttreatment persistent/recurrent disease. Early detection of failure is critical for increasing the chance of salvage; aggressive treatment should be attempted as far as possible, long survival can be achieved for patients with limited failure or metastasis. Different salvage methods and reported results are summarized.

An isocentric technique for treatment of carcinoma of the prostate in large patients.

An isocentric technique for treatment of carcinoma of the prostate of a large patient was investigated for a 4-MV linear accelerator. A split course, two four-field technique was found to deliver an appropriate high-dose zone while not exceeding tissue tolerances.