ABSTRACT
To verify that the calculated dose distribution is delivered accurately during intensity-modulated radiation therapy (IMRT), we have implemented an automated plan/film validation protocol. The cubic polystyrene film phantom provided with the Peacock IMRT system and the Radiation Imaging Technology (RIT) film dosimetry system were used to compare planned and delivered dose distributions. The calculated dose matrix from CORVUS was transferred to RIT and analyzed. The analysis included dose-difference histograms, dose comparison in low-gradient areas, distance to agreement in high-gradient areas, dose profiles, and isodose comparisons. Dose differences of up to 5% were commonly observed in the high-dose and low-gradient areas between verification films and treatment plans for prostate patients. The most prominent discrepancies were detected in the high-gradient areas of dose distributions. The automated protocol is an efficient technique that provides information about spatial differences between calculated and delivered doses.
Subject(s)
Electronic Data Processing/instrumentation , Electronic Data Processing/methods , Film Dosimetry/instrumentation , Film Dosimetry/methods , Neoplasms/radiotherapy , Phantoms, Imaging , Radiotherapy, Computer-Assisted/instrumentation , Radiotherapy, Computer-Assisted/methods , Humans , Models, Biological , Quality Control , Radiotherapy DosageABSTRACT
BACKGROUND: Multicystic benign lymphoepithelial lesions of the parotid gland (BLL) seen in patients with human immunodeficiency virus (HIV) can produce considerable cosmetic deformity as well as physical discomfort. We previously reported our preliminary results with low-dose radiotherapy in this disease, and all 8 patients were satisfied with the initial improvement in their appearance. We now report the long-term follow-up of those patients and additional patients. METHODS: Twelve HIV-positive patients with BLL were treated with 8-10 Gy of external radiation using 2-Gy daily fractions. Objective responses and subjective duration of patient-defined cosmetic control were recorded. RESULTS: All 12 patients (100%) had at least a 50% decrease in the size of their parotid masses. Five of 12 (42%) had a complete response and 7 (58%) had a partial response. Persisting complete response was achieved in only 1 patient, however, with relapse in the other 11 patients. Cosmetic palliation, as judged by the patients, was achieved for a median of 9.5 months. Eight patients were subsequently retreated with doses of 6-16 Gy (median and mode: 10 Gy). None (0%) of the 8 patients retreated achieved local control. CONCLUSIONS: Very low-dose radiation (8-10 Gy) provides reliable but temporary cosmetic palliation for BLL. Retreatment was unsatisfactory, and we are now investigating higher initial doses of radiation to prolong palliation and eliminate recurrences.
