Clinical implementation of intensity modulated proton therapy for testicular seminoma

Background and purpose: We have previously shown that proton therapy results in considerable reduced doses to abdominal organs at risk (OAR) which likely reduces the patient’s risk of a second malignant tumor, which is vital for this young population with favourable prognosis. Here, we present dosimetric results after implementing intensity modulated proton therapy (IMPT) as a national standard for seminoma. Patient/material and methods: Thirty patients with stage IIA and IIB (< 3 cm) seminoma were treated with five-field robustly multi-field optimised (MFO) proton therapy to 20–24 Gy (relative biological effectiveness [RBE]) to the dog-leg retroperitoneal volume followed by a boost of 10–16 Gy (RBE) to the nodal metastasis. Control CTs were performed routinely, and target coverage evaluated. A standard two cone-beam CT (CBCT) set-up strategy with four match structures was developed, enabling implementation of a standard adaptive scheme. Results: The median clinical target volume (CTV-E) length in the craniocaudal direction was 26.9 cm, with a median volume of 551.4 cm3. Target coverage V95% = 100% for the nominal plan and V95% ≥ 98% for worst-case scenarios were fulfilled for all treatment plans and the 46 recalculated plans on control CTs. Kidney V17Gy was 0–6% and mean kidney dose 0–6 Gy across all plans. Bowel bag V15Gy was 194–698 cm3. All other OAR showed low doses. Four patients had replans (1–2 per patient). The median time for our image guidance (IG) strategy was 14:07 min across all patients with two CBCTs. Interpretation: We have established a robust setup for treatment planning, IG strategy, treatment delivery and adequate response to replanning. Therefore, we suggest considering IMPT for testicular seminoma whenever available.