Impact of heterogeneities on lateral penumbra in uniform scanning proton therapy

Suresh Rana, Hardev Singh


Purpose: In the treatment planning of uniform scanning proton therapy, an aperture block is designed for each beam with a margin, which typically includes the lateral penumbra measured in water (homogenous) medium. However, during real proton therapy treatment, protons may pass through tissues of different densities within the patient's body before they are stopped. The main aim of this study was to investigate the dependency of lateral penumbra on low- and high-density heterogeneities placed in the plateau and spread-out Bragg peak (SOBP) regions.

Method: The measurements were performed by placing radiographic films at the isocenter (center of SOBP), and each proton beam was delivered with 150 monitor units using standard beam conditions of the institution.

Results and Conclusion: The preliminary results from this study showed that the lateral penumbra of uniform scanning proton beams was less sensitive to the inhomogeneities introduced in the protons beam path. The low-density heterogeneity in the plateau region had more impact on the lateral penumbra when compared to the low-density in the SOBP region. In contrast, the placement of high-density heterogeneity (whether in the plateau or SOBP region) produced a very minimal difference. The overall difference in lateral penumbra among different phantoms was within ±1 mm.


Cite this article as:
Rana S, Singh H. Impact of heterogeneities on lateral penumbra in uniform scanning proton therapy. Int J Cancer Ther Oncol 2013; 1(2):01026.



Lateral penumbra; Uniform scanning proton therapy; Inhomogeneity; SOBP

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International Journal of Cancer Therapy and Oncology (ISSN 2330-4049)

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