SummaryThe lack of specific treatment planning tools limits the spread of Intraoperative Electron Radiation Therapy. An innovative simulation and planning tool is presented. Applicator positioning, isodose curves, and dose volume histograms can be estimated for previously segmented regions to treat/protect. Evaluation by three radiation oncologists on 15 patients showed high parameter agreement in nine cases, demonstrating the possibilities in cases involving different anatomical locations, and Purpose: Intraoperative electron beam radiation therapy (IOERT) involves a modified strategy of conventional radiation therapy and surgery. The lack of specific planning tools limits the spread of this technique. The purpose of the present study is to describe a new simulation and planning tool and its initial evaluation by clinical users. Methods and Materials: The tool works on a preoperative computed tomography scan. A physi cian contours regions to be treated and protected and simulates applicator positioning, calcu lating isodoses and the corresponding doseevolume histograms depending on the selected electron energy. Three radiation oncologists evaluated data from 15 IOERT patients, including different tumor locations. Segmentation masks, applicator positions, and treatment parameters were compared. Results: High parameter agreement was found in the following cases: three breast and three rectal cancer, retroperitoneal sarcoma, and rectal and ovary monotopic recurrences. All radiation oncologists performed similar segmentations of tumors and high risk areas. The average appli cator position difference was 1.2 AE 0.95 cm. The remaining cancer sites showed higher devia tions because of differences in the criteria for segmenting high risk areas (one rectal, one pancreas) and different surgical access simulated (two rectal, one Ewing sarcoma).
Conclusions:The results show that this new tool can be used to simulate IOERT cases involving different anatomic locations, and that preplanning has to be carried out with specialized surgical input.
The reality of intraoperative radiation therapy (IORT) practice is consistent with an efficient and highly precise radiation therapy technique to safely boost areas at risk for local recurrence. Long-term clinical experience has shown that IORT-containing multi-modality regimens appear to improve local disease control, if not survival in many diseases. Research with IORT is a multidisciplinary scenario that covers knowledge from radiation beam adapted development to advance molecular biology for bio-predictability of outcome. The technical parameters employed in IORT procedures are important information to be recorded for quality assurance and clinical results analysis. In addition, specific treatment planning systems for IORT procedures are available, to help in the treatment decision-making process. A systematic revision of opportunities for research and innovation in IORT is reported including radiation beam modulation, delivery, dosimetry and planning; infrastructure and treatment factors; experimental and clinical radiobiology; clinical trials, innovation and translational research development.
In vivo dosimetry is recommended in intraoperative electron radiotherapy (IOERT). To perform real-time treatment monitoring, action levels (ALs) have to be calculated. Empirical approaches based on observation of samples have been reported previously, however, our aim is to present a predictive model for calculating ALs and to verify their validity with our experimental data. We considered the range of absorbed doses delivered to our detector by means of the percentage depth dose for the electron beams used. Then, we calculated the absorbed dose histograms and convoluted them with detector responses to obtain probability density functions in order to find ALs as certain probability levels. Our in vivo dosimeters were reinforced TN-502RDM-H mobile metal-oxide-semiconductor field-effect transistors (MOSFETs). Our experimental data came from 30 measurements carried out in patients undergoing IOERT for rectal, breast, sarcoma, and pancreas cancers, among others. The prescribed dose to the tumor bed was 90%, and the maximum absorbed dose was 100%. The theoretical mean absorbed dose was 90.3% and the measured mean was 93.9%. Associated confidence intervals at P ¼ .05 were 89.2% and 91.4% and 91.6% and 96.4%, respectively. With regard to individual comparisons between the model and the experiment, 37% of MOSFET measurements lay outside particular ranges defined by the derived ALs. Calculated confidence intervals at P ¼ .05 ranged from 8.6% to 14.7%. The model can describe global results successfully but cannot match all the experimental data reported. In terms of accuracy, this suggests an eventual underestimation of tumor bed bleeding or detector alignment. In terms of precision, it will be necessary to reduce positioning uncertainties for a wide set of location and treatment postures, and more precise detectors will be required. Planning and imaging tools currently under development will play a fundamental role.
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