Improving the therapeutic ratio by using proton therapy in patients with stage I or II seminoma

The goal of the present study was to evaluate possible dosimetric advantages of proton therapy (PT) compared with 3-dimensional conformal radiotherapy (3DCRT) or intensity-modulated radiotherapy (IMRT) in the treatment of patients with stage I and II seminoma.

Two representative patients (1 with left-sided and 1 with right-sided seminoma) underwent treatment planning for stage I seminoma (paraaortic lymph nodes alone) with 3DCRT (PA3d), IMRT (PAimrt) double-scatter protons (PAPds), and uniform-scanning protons (PAPus) and for stage II seminoma (paraaortics lymph nodes and iliac nodes) with 3DCRT (PI3d) , IMRT (PIimrt) double-scatter protons (PIPds), and uniform-scanning protons (PIPus). The doses to the organs at risk were compared for photons and protons.

For stage I seminoma, PT reduced the mean dose to the stomach, ipsilateral kidney, pancreas, bowel space, small bowel, and colon compared with 3DCRT and IMRT. For stage II seminoma, PT reduced the mean dose to the same organs as in stage I seminoma with additional reductions in mean dose to the bladder and rectum compared with 3DCRT and IMRT. Uniform-scanning protons further reduced the dose to the organs at risk compared with double-scatter protons.

PT may offer an improvement in the therapeutic ratio in patients with seminoma by reducing the dose to normal tissue. This improvement may translate into lower risks of acute gastrointestinal side effects, infertility, and secondary malignancies, which should be explored in a prospective study.