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

Abstract

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, DMaxwas constrained to 37 Gy. Rectal DMedianwas < 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%). CI90was 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. © 2009 Weber et al; licensee BioMed Central Ltd.