IMRT to Escalate the Dose to the Prostate while Treating the Pelvic Nodes |
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Authors: | Email author" target="_blank">Matthew?L?CaveyEmail author John?E?Bayouth Martin?Colman Eugene?J?Endres Giuseppe?Sanguineti |
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Institution: | (1) Department of Radiation Oncology, University of Texas Medical Branch, Galveston, TX, USA;(2) Department of Medical Physics, University of Texas Medical Branch, Galveston, TX, USA;(3) Department of Radiation Oncology, University of Texas Medical Branch, 301 University Blvd., Galveston, Texas 775555-0711, USA |
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Abstract: | Background and Purpose: To assess and quantify the benefit of introducing intensity–modulated radiotherapy (IMRT) over conventional
approaches to cover the pelvic nodes while escalating the dose to the prostate gland.Material and Methods: The pelvic lymphatics were planned to receive 50 Gy at 2 Gy per fraction by four–field box (4FB) technique
and standard field blocks drawn on digitally reconstructed radiographs (DRR), 4FB with field blocks according to the position
of pelvic nodes as contoured on serial planning CT slices, or IMRT. The lateral fields included three different variations of field
blocks to assess the role of various degrees of rectal shielding. The boost consisted in 26 Gy in 13 fractions delivered via six–field
three–dimensional conformal radiotherapy (3DCRT) or IMRT. By the combination of a pelvic treatment and boost, several plans
were obtained for each patient, all normalized to be isoeffective with regard to prostate–planning target volume (PTV–P) coverage.
Plans were compared with respect to dose–volume histogram (DVH) of pelvic nodes/seminal vesicles–PTV (PTV–PN/SV), rectum,
bladder and intestinal cavity. Reported are the results obtained in eight patients.Results: Pelvic IMRT with a conformal boost provided superior sparing of both bladder and rectum over any of the 4FB plans with
the same boost. For the rectum the advantage was around 10% at V70 and even larger for lower doses. Coverage of the pelvic
nodes was adequate with initial IMRT with about 98% of the volume receiving 100% of the prescribed dose. An IMRT boost provided
a gain in rectal sparing as compared to a conformal boost. However, the benefit was always greater with pelvic IMRT followed
by a conformal boost as compared to 4FB with IMRT boost. Finally, the effect of utilizing an IMRT boost with initial pelvic
IMRT was greater for the bladder than for the rectum (at V70, about 9% and 3% for the bladder and rectum, respectively).Conclusion: IMRT to pelvic nodes with a conformal boost allows dose escalation to the prostate while respecting current dose
objectives in the majority of patients and it is dosimetrically superior to 4FB. An IMRT boost should be considered for patients
who fail to meet bladder dose objectives. |
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Keywords: | IMRT Whole– pelvis radiotherapy Dose escalation |
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