Proton Radiotherapy Could Reduce the Risk of Fatal Second Cancers for Children with Intracranial Tumors in Low- and Middle-Income Countries

Abstract

Purpose To test our hypothesis that, for young young children with intracranial tumors, proton radiotherapy in a high-income country does not reduce the risk of a fatal subsequent malignant neoplasm (SMN) compared with photon radiotherapy in low- and middle-income countries. Materials and Methods We retrospectively selected 9 pediatric patients with low-grade brain tumors who were treated with 3-dimensional conformal radiation therapy in low- and middle-income countries. Images and contours were deidentified and transferred to a high-income country proton therapy center. Clinically commissioned treatment planning systems of each academic hospital were used to calculate absorbed dose from the therapeutic fields. After fusing supplemental computational phantoms to the patients' anatomies, models from the literature were applied to calculate stray radiation doses. Equivalent doses were determined in organs and tissues at risk of SMNs, and the lifetime attributable risk of SMN mortality (LAR) was predicted using a dose-effect model. Our hypothesis test was based on the average of the ratios of LARs from proton therapy to that of photon therapy Results Proton therapy reduced the equivalent dose in organs at risk for SMNs and LARs compared with photon therapy for which the for the cohort was 0.69 ± 0.10, resulting in the rejection of H0 (P < .001, α = 0.05). We observed that the younger children in the cohort (2-4 years old) were at a factor of approximately 2.5 higher LAR compared with the older children (8-12 years old). Conclusion Our findings suggest that proton radiotherapy has the strong potential of reducing the risk of fatal SMNs in pediatric patients with intracranial tumors if it were made available globally.

Modeling secondary cancer risk ratios for proton versus carbon ion beam therapy: A comparative study based on the local effect model

“…This simplification is however only allowed for active beam delivery methods, fully in line with the work of Moteabbed et al 46 . and Gallagher et al., 47 who also argue that the neutron dose can be considered negligible in the case of pencil beam scanning due to the absence of beam shaping devices.…”

“…Hence the effect of the absorbed neutron dose on the SC risk is expected to be very low and therefore was not considered in the risk calculations shown here. This simplification is however only allowed for active beam delivery methods, fully in line with the work of Moteabbed et al 46 and Gallagher et al, 47 who also argue that the neutron dose can be considered negligible in the case of pencil beam scanning due to the absence of beam shaping devices. Since on the other hand neutrons also exhibit increased RBE values, this could finally lead to some moderate contribution to the SC risk and further research is needed to clarify this fact.…”