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Chest wall irradiation with intensity- and energy-modulated electron beams
S312
I. J. Radiation Oncology
1085
● Biology ● Physics
Volume 57, Number 2, Supplement, 2003
Chest Wall Irradiation with Intensity- and Energy-Modulated Electron Beams
1
C. Chui, L. Hong,1 N. Lee2 Medical Physics, MSKCC, New York, NY, 2Radiation Oncology, MSKCC, New York, NY
1
Purpose/Objective: To develop a method for chest wall (CW) irradiation with intensity- and energy-modulated electron beams. Materials/Methods: The CT images of the patient were acquired and contours of CW target volumes were entered by the treating physician. Enface electron beam parameters and the nominal beam energy were selected by the planner. Electron pencil beams were traced from the source towards the skin. Each pencil beam was traced until it exited the CW target volumes. The CW target thickness was calculated by pixel integration along the pencil beam to the exit point. This thickness determined the energy of the pencil beam to give the prescribed coverage (e.g. 90% dose level) to the target exit point. The distance to the exit point from the source was also calculated. This determined the pencil beam intensity to achieve the same dose along the posterior edge of the target volume. Energy modulation of electron beams can be achieved by adding 5mm spoilers to the beam. Each layer of spoiler reduced the nominal beam energy by approximately 1-MeV. Intensity modulation ideally can be delivered with a multileaf collimator (MLC). This, however, is currently not available in the clinical mode. Alternatively, individual cutouts for each intensity level can be made to deliver in step-and-shoot mode. This can be used as a proof of principle, but would not be practical for routine clinical implementation. Results: A case using a nominal 9-MeV electron beam is shown as an example. The intensity distributions of beams with energies ranging from 5-MeV to 8-MeV were determined by the above method (Figure 1). Note that the intensity was higher in the periphery of the 8-MeV beam to account for the surface curvature sloping away from the source. In the middle of the treatment area, lower energies were needed due to the smaller CW thickness. The dose distribution was highly conformal to the CW with full skin dose coverage, as seen by the 90% isodose curves (Figure 2). The calculation took only a few seconds on a 233 MHz computer. Conclusions: We have developed a method for CW irradiation with intensity and energy modulated electron beams. The method is simple and robust. Highly conformal dose distribution to the CW can be obtained in a few seconds. Energy modulation can be achieved with spoilers and intensity modulation can be delivered with an MLC. When these capabilities are made available on the machine by the vendors, this method can be implemented for routine clinical use.
I. J. Radiation Oncology
1085
● Biology ● Physics
Volume 57, Number 2, Supplement, 2003
Chest Wall Irradiation with Intensity- and Energy-Modulated Electron Beams
1
C. Chui, L. Hong,1 N. Lee2 Medical Physics, MSKCC, New York, NY, 2Radiation Oncology, MSKCC, New York, NY
1
Purpose/Objective: To develop a method for chest wall (CW) irradiation with intensity- and energy-modulated electron beams. Materials/Methods: The CT images of the patient were acquired and contours of CW target volumes were entered by the treating physician. Enface electron beam parameters and the nominal beam energy were selected by the planner. Electron pencil beams were traced from the source towards the skin. Each pencil beam was traced until it exited the CW target volumes. The CW target thickness was calculated by pixel integration along the pencil beam to the exit point. This thickness determined the energy of the pencil beam to give the prescribed coverage (e.g. 90% dose level) to the target exit point. The distance to the exit point from the source was also calculated. This determined the pencil beam intensity to achieve the same dose along the posterior edge of the target volume. Energy modulation of electron beams can be achieved by adding 5mm spoilers to the beam. Each layer of spoiler reduced the nominal beam energy by approximately 1-MeV. Intensity modulation ideally can be delivered with a multileaf collimator (MLC). This, however, is currently not available in the clinical mode. Alternatively, individual cutouts for each intensity level can be made to deliver in step-and-shoot mode. This can be used as a proof of principle, but would not be practical for routine clinical implementation. Results: A case using a nominal 9-MeV electron beam is shown as an example. The intensity distributions of beams with energies ranging from 5-MeV to 8-MeV were determined by the above method (Figure 1). Note that the intensity was higher in the periphery of the 8-MeV beam to account for the surface curvature sloping away from the source. In the middle of the treatment area, lower energies were needed due to the smaller CW thickness. The dose distribution was highly conformal to the CW with full skin dose coverage, as seen by the 90% isodose curves (Figure 2). The calculation took only a few seconds on a 233 MHz computer. Conclusions: We have developed a method for CW irradiation with intensity and energy modulated electron beams. The method is simple and robust. Highly conformal dose distribution to the CW can be obtained in a few seconds. Energy modulation can be achieved with spoilers and intensity modulation can be delivered with an MLC. When these capabilities are made available on the machine by the vendors, this method can be implemented for routine clinical use.