Proton therapy for seminoma: Case report describing the technique, efficacy, and advantages of proton-based therapy for seminoma

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

Radiation therapy (RT) is an effective treatment for stage IIA and select stage IIB seminomas. However, given the long life expectancy of seminoma patients, there are concerns about the risk of secondary cancers from RT. This study assessed differences in secondary cancer risk for stage II seminoma patients following proton pencil-beam scanning (PBS) and photon VMAT, compared to 3D conformal photon RT. Ten seminoma patients, five with a IIA staging who received 30 GyRBE and five with a IIB staging who received 36 GyRBE, had three RT plans generated. Doses to organs at risk (OAR) were evaluated, and secondary cancer risks were calculated as the Excess Absolute Risk (EAR) and Lifetime Attributable Risk (LAR). PBS reduced the mean OAR dose by 60% on average compared to 3D, and reduced the EAR and LAR for all OAR, with the greatest reductions seen for the bowel, liver, and stomach. VMAT reduced high doses but increased the low-dose bath, leading to an increased EAR and LAR for some OAR. PBS provided superior dosimetric sparing of OAR compared to 3D and VMAT in stage II seminoma cases, with models demonstrating that this may reduce secondary cancer risk. Therefore, proton therapy shows the potential to reduce acute and late side effects of RT for this population.

Treatment de-escalation for stage II seminoma

International Germ Cell Cancer Collaborative Group good-risk metastatic seminoma has cure rates of >95%. Within this risk group, patients with stage II disease exhibit the best oncological outcomes with the standard-of-care treatment strategies of radiotherapy or combination chemotherapy. However, these treatments can be associated with substantial early and late toxic effects. Therapy de-escalation aims to reduce treatment morbidity whilst preserving oncological outcomes. The evidence supporting such approaches is largely from non-randomized institutional data, and therefore this strategy is not recognized as standard of care. Current de-escalation approaches for stage II seminoma include single-agent chemotherapy, radiotherapy and surgery based on early data from clinical studies. Increased recognition of emerging data on treatment modification to reduce morbidity whilst maintaining cure rates and consideration of therapy de-escalation could improve patient survivorship outcomes.

Proton Therapy for Stage IIA-B Seminoma: A New Standard of Care for Treating Retroperitoneal Nodes

Currently there has been no published report describing the use of proton beam therapy for stage II testicular seminoma. A 31-year-old man presenting with a right testicular mass and a 2.7-cm aortocaval lymph node received a diagnosis of stage IIB testicular seminoma. He was treated with scanning proton beam therapy, as a means of improving the therapeutic ratio of radiation therapy over conventionally used x-ray radiation therapy. The patient achieved a complete response and remained free of relapse at 15 months post proton beam therapy. The advantageous dose deposition characteristics of proton beam, allowing much lower radiation doses to normal tissues, should be exploited when radiation therapy is applied for stage II testicular seminoma or for an isolated retroperitoneal lymph node relapse of stage I disease initially managed with surveillance.