Main Session
Sep 28
PQA 03 - Digital Health Innovation and Informatics, Patient Safety & Quality, and Radiation and Cancer Biology

2584 - Fetal Neutron Dose Reduction by a Novel Planning Modification in Proton Pencil Beam Scanning

10:45am - 12:00pm ET
Poster Hall - Exhibit Hall A
Screen: 31
POSTER

Presenter(s)

David Alicia, CMD, BS - Maryland Proton Treatment Center, Baltimore, MD

R. Rahimi1, K. T. Griffin2, D. Alicia3, J. Shin4, E. M. Nichols5, M. J. Ferris5, C. Lee2, and B. Y. Yi6; 1University of Maryland School of Medicine, Baltimore, MD, 2National Cancer Institute, National Institutes of Health, Rockville, MD, 3Department of Radiation Oncology, Maryland Proton Treatment Center, Baltimore, MD, 4National Cancer Institute/National Institutes of Health, Rockville, MD, 5Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, 6Maryland Proton Treatment Center, Baltimore, MD

Purpose/Objective(s):

Strict control of radiation exposure to the fetus is critically important. Proton pencil beam scanning (PBS) reduces integral dose compared with photon therapy and may be considered for pregnant patients when radiation treatment is necessary. For superficial targets, a range shifter (RS) is commonly required for proximal dose coverage. In standard clinical workflow, the RS is retained for the entire field once required for any portion of the target, including deeper regions that do not require it. Because secondary neutrons in PBS are predominantly generated in beam-modifying devices such as the RS, this practice may increase out-of-field neutron exposure.

We hypothesized that restricting RS use to only superficial target regions would reduce fetal neutron dose without compromising the plan dosimetric quality.

Materials/Methods:

Clinically acceptable PBS plans were created for two treatment techniques requiring superficial target coverage: treatment to the left breast and treatment to the head and neck area. Both treatments were planned with two independent strategies:

  1. RS-Full: RS applied for the entire field
  2. RS-Split: RS applied only for superficial target regions
Plans were generated with identical prescriptions, optimization objectives, and robustness settings and were dosimetrically equivalent in terms of tumor coverage, hotspot control, and organ-at-risk constraints. Secondary neutron dose was evaluated using a commissioned Monte Carlo PBS beam model. Neutron physical dose to the uterus (fetal surrogate structure; ~45 cm and ~30 cm from field edges for head and neck and breast plans, respectively) was calculated and compared between the strategies.

Results:

Both RS-Full and RS-Split plans achieved equivalent target coverage and robustness. The RS-Split strategy reduced modeled neutron dose to the uterus in both treatment sites, with an estimated neutron dose reduction factor of between 20 to 50%. Neutron doses to the maternal organs were similarly reduced. No degradation in plan quality was observed.

Conclusion:

Restricting RS use to superficial target regions significantly reduces modeled fetal neutron dose in PBS proton therapy without compromising target coverage or robustness. This cost-minimal workflow modification represents a practical strategy to enhance proton therapy safety for pregnant patients and other scenarios where minimizing fetal neutron exposure is critical.