Potential role of intensity modulated proton beams in prostate cancer radiotherapy

Purpose: The present study was undertaken to assess the potential benefit o f intensity modulated (IM) proton beams in optimizing the dose distribution to safely escalate the tumor dose in prostate cancer radiotherapy. Methods and Materials: Four treatment plans were compared in a prostate can cer patient aiming to deliver 81 Gy to the target: 1) conformal 18 MV X-ray s, 6-fields; 2) 214 MeV protons, 2-fields; 3) IM 15 MV X-rays, 5-fields; an d 4) 177-200 Mev IM protons, 5-fields as in Plan 3. In addition, IM methods were used to further escalate the tumor dose to 99 Gy, Dose-volume histogr ams (DVH) were used to physically compare the treatment plans. DVH data wer e also used to obtain normal tissue complication probabilities (NTCP) for t he rectum, bladder, femoral heads, and tumor control probabilities. Results: Although the planning target volume dose distribution was satisfac tory with the four treatment plans, the homogeneity was slightly reduced in both X-ray plans (IM and standard) and the low-to-medium doses delivered t o all organs at risk, and other normal tissues were significantly reduced b y both proton plans. For a prescribed dose of 81 Gy, only the IM X-ray and IM proton plans both succeeded in predicting an acceptably low NTCP for the rectum (< 5 %, Grade 3). The integral nontarget dose was significantly red uced with IM proton beams (i.e., 3.1, 1.3, and 1.7 times less than Plans 1, 2, and 3,respectively). When escalating the dose to 99 Gy, no additional i mprovement between IM protons and LM X-ray beams was observed. Conclusions: Both WI X-ray and proton beams were able to optimize the dose distribution and comply with the goal of delivering the highest dose to the target while reducing the risk of severe morbidity to acceptable levels. T he main advantage compared to IM X-rays was that WI protons succeeded in si gnificantly reducing the low-to-medium dose to the nontarget tissues and ac hieved a small improvement in planning target volume (PTV) dose heterogenei ty. (C) 2001 Elsevier Science Inc.