A beam-specific planning target volume (PTV) design for proton therapy to account for setup and range uncertainties.

PURPOSE To report a method for explicitly designing a planning target volume (PTV) for treatment planning and evaluation in heterogeneous media for passively scattered proton therapy and scanning beam proton therapy using single-field optimization (SFO). METHODS AND MATERIALS A beam-specific PTV (bsPTV) for proton beams was derived by ray-tracing and shifting ray lines to account for tissue misalignment in the presence of setup error or organ motion. Range uncertainties resulting from inaccuracies in computed tomography-based range estimation were calculated for proximal and distal surfaces of the target in the beam direction. The bsPTV was then constructed based on local heterogeneity. The bsPTV thus can be used directly as a planning target as if it were in photon therapy. To test the robustness of the bsPTV, we generated a single-field proton plan in a virtual phantom. Intentional setup and range errors were introduced. Dose coverage to the clinical target volume (CTV) under various simulation conditions was compared between plans designed based on the bsPTV and a conventional PTV. RESULTS The simulated treatment using the bsPTV design performed significantly better than the plan using the conventional PTV in maintaining dose coverage to the CTV. With conventional PTV plans, the minimum coverage to the CTV dropped from 99% to 67% in the presence of setup error, internal motion, and range uncertainty. However, plans using the bsPTV showed minimal drop of target coverage from 99% to 94%. CONCLUSIONS The conventional geometry-based PTV concept used in photon therapy does not work well for proton therapy. We investigated and validated a beam-specific PTV method for designing and evaluating proton plans.

[1]  E Pedroni,et al.  The precision of proton range calculations in proton radiotherapy treatment planning: experimental verification of the relation between CT-HU and proton stopping power. , 1998, Physics in medicine and biology.

[2]  Hanne M Kooy,et al.  Target volume dose considerations in proton beam treatment planning for lung tumors. , 2005, Medical physics.

[3]  Marcel van Herk,et al.  The effect of set-up uncertainties, contour changes, and tissue inhomogeneities on target dose-volume histograms. , 2002, Medical physics.

[4]  J F Ziegler,et al.  Comments on ICRU report no. 49: stopping powers and ranges for protons and alpha particles. , 1999, Radiation research.

[5]  Riccardo Calandrino,et al.  Intensity-modulated proton therapy versus helical tomotherapy in nasopharynx cancer: planning comparison and NTCP evaluation. , 2008, International journal of radiation oncology, biology, physics.

[6]  P. Andreo,et al.  Calculation of stopping power ratios for carbon ion dosimetry , 2006, Physics in Medicine and Biology.

[7]  Alexei Trofimov,et al.  Radiotherapy treatment of early-stage prostate cancer with IMRT and protons: a treatment planning comparison. , 2007, International journal of radiation oncology, biology, physics.

[8]  M Goitein,et al.  Compensating for heterogeneities in proton radiation therapy. , 1984, Physics in medicine and biology.

[9]  Daniel W. Miller,et al.  Ion stopping powers and CT numbers. , 2010, Medical dosimetry : official journal of the American Association of Medical Dosimetrists.

[10]  E. Pedroni,et al.  The calibration of CT Hounsfield units for radiotherapy treatment planning. , 1996, Physics in medicine and biology.

[11]  H. Pyo,et al.  Inter- and intrafractional movement-induced dose reduction of prostate target volume in proton beam treatment. , 2008, International journal of radiation oncology, biology, physics.

[12]  A. Lomax,et al.  Intensity modulation methods for proton radiotherapy. , 1999, Physics in medicine and biology.

[13]  Daniel W. Miller,et al.  Methodologies and tools for proton beam design for lung tumors. , 2001, International journal of radiation oncology, biology, physics.

[14]  Radhe Mohan,et al.  Four-dimensional computed tomography-based treatment planning for intensity-modulated radiation therapy and proton therapy for distal esophageal cancer. , 2008, International journal of radiation oncology, biology, physics.

[15]  J C Stroom,et al.  Inclusion of geometrical uncertainties in radiotherapy treatment planning by means of coverage probability. , 1999, International journal of radiation oncology, biology, physics.

[16]  A. Lomax,et al.  Intensity modulated proton therapy and its sensitivity to treatment uncertainties 1: the potential effects of calculational uncertainties , 2008, Physics in medicine and biology.

[17]  A J Lomax,et al.  Intensity modulated proton therapy and its sensitivity to treatment uncertainties 2: the potential effects of inter-fraction and inter-field motions , 2008, Physics in medicine and biology.

[18]  Michael Gillin,et al.  Spot scanning proton beam therapy for prostate cancer: treatment planning technique and analysis of consequences of rotational and translational alignment errors. , 2010, International journal of radiation oncology, biology, physics.

[19]  M. V. van Herk,et al.  The probability of correct target dosage: dose-population histograms for deriving treatment margins in radiotherapy. , 2000, International journal of radiation oncology, biology, physics.

[20]  Christoph Bert,et al.  Respiratory motion management in particle therapy. , 2010, Medical physics.

[21]  J. Chavaudra,et al.  Prescribing, Recording, and Reporting Electron Beam Therapy , 2004, Journal of the ICRU.

[22]  Tae Hyun Kim,et al.  Characteristics of movement-induced dose reduction in target volume: a comparison between photon and proton beam treatment. , 2009, Medical dosimetry : official journal of the American Association of Medical Dosimetrists.