RapidArc, intensity modulated photon and proton techniques for recurrent prostate cancer in previously irradiated patients: a treatment planning comparison study

BACKGROUND: A study was performed comparing volumetric modulated arcs (RA) and intensity modulation (with photons, IMRT, or protons, IMPT) radiation therapy (RT) for patients with recurrent prostate cancer after RT. METHODS: Plans for RA, IMRT and IMPT were optimized for 7 patients. Prescribed dose was 56 Gy in 14 fractions. The recurrent gross tumor volume (GTV) was defined on (18)F-fluorocholine PET/CT scans. Plans aimed to cover at least 95% of the planning target volume with a dose > 50.4 Gy. A maximum dose (D(Max)) of 61.6 Gy was allowed to 5% of the GTV. For the urethra, D(Max )was constrained to 37 Gy. Rectal D(Median )was < 17 Gy. Results were analyzed using Dose-Volume Histogram and conformity index (CI(90)) parameters. RESULTS: Tumor coverage (GTV and PTV) was improved with RA (V(95% )92.6 ± 7.9 and 83.7 ± 3.3%), when compared to IMRT (V(95% )88.6 ± 10.8 and 77.2 ± 2.2%). The corresponding values for IMPT were intermediate for the GTV (V(95% )88.9 ± 10.5%) and better for the PTV (V(95%)85.6 ± 5.0%). The percentages of rectal and urethral volumes receiving intermediate doses (35 Gy) were significantly decreased with RA (5.1 ± 3.0 and 38.0 ± 25.3%) and IMPT (3.9 ± 2.7 and 25.1 ± 21.1%), when compared to IMRT (9.8 ± 5.3 and 60.7 ± 41.7%). CI(90 )was 1.3 ± 0.1 for photons and 1.6 ± 0.2 for protons. Integral Dose was 1.1 ± 0.5 Gy*cm(3 )*10(5 )for IMPT and about a factor three higher for all photon's techniques. CONCLUSION: RA and IMPT showed improvements in conformal avoidance relative to fixed beam IMRT for 7 patients with recurrent prostate cancer. IMPT showed further sparing of organs at risk.