Individualized planning target volumes for intrafraction motion during hypofractionated intensity-modulated radiotherapy boost for prostate cancer.
OBJECTIVE
The objective of the study was to access toxicities of delivering a hypofractionated intensity-modulated radiotherapy (IMRT) boost with individualized intrafraction planning target volume (PTV) margins and daily online correction for prostate position.


METHODS
Phase I involved delivering 42 Gy in 21 fractions using three-dimensional conformal radiotherapy, followed by a Phase II IMRT boost of 30 Gy in 10 fractions. Digital fluoroscopy was used to measure respiratory-induced motion of implanted fiducial markers within the prostate. Electronic portal images were taken of fiducial marker positions before and after each fraction of radiotherapy during the first 9 days of treatment to calculate intrafraction motion. A uniform 10-mm PTV margin was used for the first phase of treatment. PTV margins for Phase II were patient-specific and were calculated from the respiratory and intrafraction motion data obtained from Phase I. The IMRT boost was delivered with daily online correction of fiducial marker position. Acute toxicity was measured using National Cancer Institute Common Toxicity Criteria, version 2.0.


RESULTS
In 33 patients who had completed treatment, the average PTV margin used during the hypofractionated IMRT boost was 3 mm in the lateral direction, 3 mm in the superior-inferior direction, and 4 mm in the anteroposterior direction. No patients developed acute Grade 3 rectal toxicity. Three patients developed acute Grade 3 urinary frequency and urgency.


CONCLUSIONS
PTV margins can be reduced significantly with daily online correction of prostate position. Delivering a hypofractionated boost with this high-precision IMRT technique resulted in acceptable acute toxicity.
Cheung
Patrick
P
Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada. patrick.cheung@sw.ca
Sixel
Katharina
K
Morton
Gerard
G
Loblaw
D Andrew
DA
Tirona
Romeo
R
Pang
Geordi
G
Choo
Richard
R
Szumacher
Ewa
E
Deboer
Gerrit
G
Pignol
Jean-Philippe
JP
D000368:Aged; D000369:Aged, 80 and over; D019583:Dose Fractionation, Radiation; D005471:Fluoroscopy / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D020266:Radiotherapy, Conformal / Q000379:methods*; D012119:Respiration; D012669:Seminal Vesicles / Q000000981:diagnostic imaging; D014555:Urination Disorders / Q000209:etiology