Rapidarc, Intensity Modulated Photon and Proton Techniques for Recurrent Prostate Cancer after Radiotherapy: A Treatment Planning Comparison Study

Article Outline

• Purpose/Objective(s)
• Materials/Methods
• Results
• Conclusions
• Copyright

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Purpose/Objective(s) 

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.

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Materials/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 (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 (CI₉₀) parameters.

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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%). 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.

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Conclusions 

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.