ABSTRACT
Stereotactic radiosurgery and image-guided radiotherapy (IGRT) place enhanced demands on treatment delivery machines. In this study, we describe a high-dose-rate output accelerator as a part of our stereotactic IGRT delivery system. The linac is a Siemens Oncor without a flattening filter, and enables dose rates to reach 1000 monitor units (MUs) per minute. Even at this high-dose-rate, the linac dosimetry system remains robust; constancy, linearity, and beam energy remain within 1% for 3 to 1000 MU. Dose profiles for larger field sizes are not flat, but they are radially symmetric and, as such, able to be modeled by a treatment planning system. Target localization is performed via optical guidance utilizing a 3-dimensional (3D) ultrasound probe coupled to an array of 4 infrared light-emitting diodes. These diodes are identified by a fixed infrared camera system that determines diode position and, by extension, all objects imaged in the room coordinate system. This system provides sub-millimeter localization accuracy for cranial applications and better than 1.5 mm for extracranial applications. Because stereotactic IGRT can require significantly longer times for treatment delivery, the advantages of the high-dose-rate design and its direct impact on IGRT are discussed.
Subject(s)
Neoplasms/radiotherapy , Particle Accelerators/instrumentation , Radiosurgery/instrumentation , Ultrasonography/instrumentation , Humans , Neoplasms/diagnostic imaging , Radiotherapy DosageSubject(s)
Appointments and Schedules , Kidney Neoplasms/radiotherapy , Placebos , Radiotherapy, Adjuvant , Unnecessary Procedures , Wilms Tumor/radiotherapy , Adolescent , Anesthesia, General , Carcinoma, Renal Cell/diagnosis , Carcinoma, Renal Cell/surgery , Child , Child, Preschool , Combined Modality Therapy , Female , Humans , Infant , Infant, Newborn , Kidney Neoplasms/diagnosis , Kidney Neoplasms/surgery , Male , Multicenter Studies as Topic , Nephrectomy , Nephroma, Mesoblastic/diagnosis , Nephroma, Mesoblastic/surgery , Neuroblastoma/diagnosis , Neuroblastoma/surgery , Neuroectodermal Tumors, Primitive/diagnosis , Neuroectodermal Tumors, Primitive/surgery , Randomized Controlled Trials as Topic/standards , Sarcoma, Clear Cell/diagnosis , Sarcoma, Clear Cell/surgery , Time Factors , Wilms Tumor/diagnosis , Wilms Tumor/surgeryABSTRACT
PURPOSE: Intensity-modulated radiotherapy (IMRT) has been shown to reduce the radiation dose to small bowel in pelvic RT in gynecology patients. Prone positioning has also been used to decrease small bowel dose by displacement of small bowel from the RT field in these patients. The purpose of this study was to determine whether the combination of both IMRT and prone positioning on a belly board can reduce small bowel dose further in gynecologic cancer patients undergoing pelvic RT. METHODS AND MATERIALS: IMRT plans for pelvic RT were computed in 16 patients with gynecologic cancer who had undergone planning CT scans in both the supine and the prone positions on a belly board. For the gross tumor volume, the uterus, cervix, and tumor (or postoperative region) were traced. The clinical target volume was defined as the vessels and lymph nodes from the obturator level to the aortic bifurcation, presacral region, and upper 4 cm of the vagina, in addition to gross tumor volume. The planning target volume was defined as a 2-cm margin in addition to the gross tumor volume and upper 4 cm of the vagina, and 1.5 cm for lymph nodes and vessels. Normal tissue regions of interest included small bowel, large bowel, and bladder. IMRT plans using (1) the limited arc technique (180 degrees arc length) and (2) the extended arc technique (340 degrees arc length) were computed. Dose-volume histograms for normal tissue structures and target were compared between the supine and prone IMRT plans using the paired t test. RESULTS: Prone positioning on a belly board decreased the small bowel dose in gynecologic pelvic IMRT, and the magnitude of improvement depended on the specific IMRT technique used. With the limited arc technique, prone positioning significantly decreased the irradiated small bowel volume at the 25-50-Gy dose levels compared with supine positioning. Small bowel volumes receiving > or =45 Gy decreased from 19% to 12.5% (p = 0.005) with prone positioning. With the extended arc technique, the decrease in irradiated small bowel volume was less marked, but remained detectable in the 35-45-Gy dose levels. Small bowel volumes receiving > or =45 Gy decreased from 13.6% to 10.1% (p = 0.03) with prone positioning. The effect of prone positioning on large bowel and bladder was variable. Large bowel volumes receiving > or =45 Gy increased with prone positioning from 16.5% to 20.6% (p = 0.02) in the limited arc technique and was unaffected in the extended arc technique. CONCLUSION: These preliminary data suggest that prone positioning on a belly board can reduce the small bowel dose further in gynecology patients treated with pelvic RT, and that the dose reduction depends on the IMRT technique used.
