Adjuvant radiation therapy for bladder cancer: a dosimetric comparison of techniques.
Trials of adjuvant radiation after cystectomy are under development. There are no studies comparing radiation techniques to inform trial design. This study assesses the effect on bowel and rectal dose of 3 different modalities treating 2 proposed alternative clinical target volumes (CTVs). Contours of the bowel, rectum, CTV-pelvic sidewall (common/internal/external iliac and obturator nodes), and CTV-comprehensive (CTV-pelvic sidewall plus cystectomy bed and presacral regions) were drawn on simulation images of 7 post-cystectomy patients. We optimized 3-dimensional conformal radiation (3-D), intensity-modulated radiation (IMRT), and single-field uniform dose (SFUD) scanning proton plans for each CTV. Mixed models regression was used to compare plans for bowel and rectal volumes exposed to 35% (V35%), 65% (V65%), and 95% (V95%) of the prescribed dose. For any given treatment modality, treating the larger CTV-comprehensive volume compared with treating only the CTV-pelvic sidewall nodes significantly increased rectal dose (V35% rectum, V65% rectum, and V95% rectum; p < 0.001 for all comparisons), but it did not produce significant differences in bowel dose (V95% bowel, V65% bowel, or V35% bowel). The 3-D plans, compared with both the IMRT and the SFUD plans, had a significantly greater V65% bowel and V95% bowel for each proposed CTV (p < 0.001 for all comparisons). The effect of treatment modality on rectal dosimetry differed by CTV, but it generally favored the IMRT and the SFUD plans over the 3-D plans. Comparison of the IMRT plan vs the SFUD plan yielded mixed results with no consistent advantage for the SFUD plan over the IMRT plan. Targeting a CTV that spares the cystectomy bed and presacral region may marginally improve rectal toxicity but would not be expected to improve the bowel toxicity associated with any given modality of adjuvant radiation. Using the IMRT or the SFUD plans instead of the 3-D conformal plan may improve both bowel and rectal toxicity.
Department of Radiation Oncology at the University of Pennsylvania, Philadelphia, PA.
Brian C
BC
Baumann
Department of Radiation Oncology at the University of Pennsylvania, Philadelphia, PA.
Kate
K
Noa
Department of Biostatistics and Epidemiology at the University of Pennsylvania, Philadelphia, PA.
E Paul
EP
Wileyto
Department of Radiation Oncology at the University of Pennsylvania, Philadelphia, PA.
Justin E
JE
Bekelman
Department of Radiation Oncology and Molecular Radiation Sciences at Johns Hopkins University School of Medicine, Baltimore, MD.
Curtiland
C
Deville
Department of Radiation Oncology at the University of Pennsylvania, Philadelphia, PA.
Neha
N
Vapiwala
Department of Radiation Oncology at the University of Pennsylvania, Philadelphia, PA.
Maura
M
Kirk
Department of Radiation Oncology at the University of Pennsylvania, Philadelphia, PA.
Stefan
S
Both
Department of Radiation Oncology at the University of Pennsylvania, Philadelphia, PA.
Derek
D
Dolney
Department of Radiation Oncology at the University of Pennsylvania, Philadelphia, PA.
Ali
A
Kassaee
Department of Radiation Oncology at the University of Pennsylvania, Philadelphia, PA. Electronic address: christojo@uphs.upenn.edu.
John P
JP
Christodouleas
D002277:Carcinoma / Q000532:radiotherapy*; D006801:Humans; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012007:Rectum; D012189:Retrospective Studies; D001749:Urinary Bladder Neoplasms / Q000532:radiotherapy*
Adjuvant radiation; Bladder cancer; Dosimetric analysis; IMRT; Proton therapy