Program Information
Achieving Desirable Lung Doses in Total Body Irradiation Based On in Vivo Dosimetry and Custom Tissue Compensation
G Cui*, A Shiu , S Zhou , J Cui , and L Ballas , Univ Southern California, Los Angeles, CA
Presentations
SU-E-T-92 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To achieve desirable lung doses in total body irradiation (TBI) based on in vivo dosimetry and custom tissue compensation.
Methods: The 15 MV photon beam of a Varian TrueBeam STx linac was used for TBI. Patients were positioned in the lateral decubitus position for AP/PA treatment delivery. Dose was calculated using the midpoint of the separation distance across the patient’s umbilicus. Patients received 200 cGy twice daily for 3 days. The dose rate at the patient’s midplane was approximately 10 cGy/min. Cerrobend blocks with a 5-HVL thickness were used for the primary lung shielding. A custom styrofoam holder for rice-flour filled bags was created based on the lung block cutouts. This was used to provide further lung shielding based on in vivo dose measurements. Lucite plates and rice-flour bags were placed in the head, neck, chest, and lower extremity regions during the treatment to compensate for the beam off-axis output variations. Two patients were included in the study. Patients 1 and 2 received a craniospinal treatment (1080 cGy) and a mediastinum treatment (2520 cGy), respectively, before the TBI. During the TBI nanoDot dosimeters were placed on the patient skin in the forehead, neck, umbilicus, and lung regions for dose monitoring. The doses were readout immediately after the treatment. Based on the readings, fine tuning of the thickness of the rice-flour filled bags was exploited to achieve the desirable lung doses.
Results: For both patients the mean lung doses, which took into consideration all treatments, were controlled within 900 +/- 10% cGy, as desired. Doses to the forehead, neck, and umbilicus were achieved within +/- 10% of the prescribed dose (1200 cGy).
Conclusion: A reliable and robust method was developed to achieve desirable lung doses and uniform body dose in TBI based on in vivo dosimetry and custom tissue compensator.
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