def getTOFgamma(ins, dsp):
    """get TOF peak profile gamma
    
    :param dict ins: instrument parameters with at least 'X', 'Y' & 'Z'
      as values only
    :param float dsp: d-spacing of peak
    
    :returns: float getTOFgamma: peak gamma
    
    """
    return ins['Z'] + ins['X'] * dsp + ins['Y'] * dsp ** 2
