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 18F-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 (DMax) of 61.6 Gy was allowed to 5% of the GTV. For the urethra, DMax was constrained to 37 Gy. Rectal DMedian was < 17 Gy. Results were analyzed using Dose-Volume Histogram and conformity index (CI90) parameters. RESULTS Tumor coverage (GTV and PTV) was improved with RA (V95% 92.6 +/- 7.9 and 83.7 +/- 3.3%), when compared to IMRT (V95% 88.6 +/- 10.8 and 77.2 +/- 2.2%). The corresponding values for IMPT were intermediate for the GTV (V95% 88.9 +/- 10.5%) and better for the PTV (V95%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%). CI90 was 1.3 +/- 0.1 for photons and 1.6 +/- 0.2 for protons. Integral Dose was 1.1 +/- 0.5 Gy*cm3 *105 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.