Radiation Therapy for Stage IIA/B Seminoma: Modeling Secondary Cancer Risk for Protons and VMAT versus 3D Photons

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Research

Background:

• Radiation therapy (RT) is a standard treatment for stage II seminoma.
• Long-term survival in seminoma patients raises concerns about secondary cancers induced by RT.
• Evaluating advanced RT techniques is crucial for minimizing long-term risks.

Purpose of the Study:

• To compare secondary cancer risk following proton pencil-beam scanning (PBS) and photon VMAT versus 3D conformal photon RT in stage II seminoma.
• To assess organ at risk (OAR) dosimetry and quantify cancer risks using Excess Absolute Risk (EAR) and Lifetime Attributable Risk (LAR).

Main Methods:

• Generated three RT plans (PBS, VMAT, 3D-CRT) for ten stage II seminoma patients (five IIA, five IIB).
• Evaluated doses to organs at risk (OAR).
• Calculated secondary cancer risks (EAR and LAR) for each RT modality.

Main Results:

• Proton PBS reduced mean OAR dose by an average of 60% compared to 3D-CRT.
• PBS significantly decreased EAR and LAR for all OAR, notably the bowel, liver, and stomach.
• VMAT showed mixed results, reducing high doses but increasing low-dose exposure, leading to higher risks in some OAR.

Conclusions:

• Proton PBS offers superior OAR sparing compared to 3D-CRT and VMAT for stage II seminoma.
• The dosimetric advantages of PBS suggest a potential reduction in secondary cancer risk.
• Proton therapy holds promise for mitigating both acute and late side effects of RT in seminoma patients.