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Scatter Contributions to the Dose/MU in the Treatment of Lung Lesions Using Proton Beams

R Simpson*, A Ghebremedhin , V Ugarte , S Gadoue , B Patyal , Loma Linda university Medical Center, Loma Linda, CA


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To improve proton MU modeling for lung lesion cases, where the chest wall interface can create additional scattering conditions in treatment fields that traverse large amounts of lung tissue.

Methods: Proton SBRT lung treatments use two to four fields typically to treat lung lesions. To account for changes that can occur in secondary scattering for these fields, measurements were collected in Plastic Water (PW), with similar setup conditions as the patient, to determine the extent the additional scattering conditions affect the dose/MU in proton lung fields. To simulate a lung treatment, PW was placed at three locations in the beam line: the position of the patient bolus, the position of the patient chest wall, and the location of the tumor and surrounding patient tissue. The gap (foam filled) between the PW representing the patient chest wall and PW representing the patient tumor was varied from 8cm to 0cm, where 8cm represented a typical maximum amount of lung tissue and 0cm represented no lung tissue.

Results: Similar to the proton MU model bolus gap factor, the additional scattering from the chest wall and lung tissue was dependent upon the thickness of the chest wall, size of the field, and the amount of lung tissue traversed. The results indicate that for such fields the proton MU model can be improved by including a factor for additional scatter. Model results were compared with in-house TPS and Monte Carlo simulations.

Conclusion: The results indicate an opportunity to improve the model dose/MU for proton fields treating lung lesions. The improvement is significant for beams traversing longer distances in lung tissue. With an increase in the use of the SBRT modality for lung treatments, accurate determination of the dose/MU is a crucial step to ensure that the physician prescribed dose is correctly delivered.


Not Applicable / None Entered.


IM- Particle (e.g., proton) CT: Monte Carlo, modeling

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