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SU‐FF‐T‐73: Effects of Beam Energies On IMRT Treatments of Large‐Sized Prostate Patients
Author(s) -
Sun M,
Ma L
Publication year - 2005
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1997744
Subject(s) - nuclear medicine , prostate , prostate cancer , radiation treatment planning , rectum , medicine , dosimetry , intensity (physics) , beam (structure) , intensity modulation , volume (thermodynamics) , percentage depth dose curve , radiation therapy , materials science , ionization chamber , cancer , optics , physics , radiology , surgery , ion , quantum mechanics , phase modulation , phase noise , ionization
Purpose: The energy dependence of intensity modulated beams for prostate cancer treatments has been extensively reported for regular sized patients. In this study, we evaluate whether 6‐MV intensity modulated beams can be used for treating large sized patients (⩾ 25 cm in anterior‐posterior separation and ⩾ 35 cm in lateral separation). Method and Materials: Five prostate patients with AP separations of 25 to 34 cm and lateral separations of 35 to 47 cm were planned for IMRT treatments. Each patient was planned with 6‐MV and 18‐MV beams for comparison. The plans were optimized using identical dose volume constraints on a commercial treatment planning system (Pinnacle, Phillips Medicals). To limit dose streaking effects outside of the PTV, we imposed the optimization constraints to the surrounding normal tissue extending from PTV with ∼1 cm margin to the skin surface. Dose volume histograms (DVH) of 6‐MV and 18‐MV plans were analyzed. Results: The DVH curves for PTV, GTV, rectum and bladder were found to be nearly indistinguishable between 6‐MV and 18‐MV treatment plans. The dose hot spots were marginally lower (0–2%) for the 6‐MV plans. The integral dose to the surrounding normal tissue was slightly (< 1% – 10%) higher for the 6‐MV plans. Considering the large volume of the surrounding normal tissue, such small difference suggested that the low entrance dose from the 18‐MV beam is mostly balanced out by the higher exit dose of the beam. Conclusion: Intensity modulated beams of 6 MV are equivalent to 18 MV for large prostate patient treatments.