Inter- and intrafractional movement-induced dose reduction of prostate target volume in proton beam treatment.
OBJECTIVE
To quantify proton radiotherapy dose reduction in the prostate target volume because of the three-dimensional movement of the prostate based on an analysis of dose-volume histograms (DVHs).


METHODS
Twelve prostate cancer patients underwent scanning in supine position, and a target contour was delineated for each using a proton treatment planning system. To simulate target movement, the contour was displaced from 3 to 15 mm in 3-mm intervals in the superior-to-inferior (SI), inferior-to-superior (IS), anterior-to-posterior (AP), posterior-to-anterior (PA), and left-to-right (LR) directions.


RESULTS
For both intra- and interfractional movements, the average coverage index and conformity index of the target were reduced in all directions. For interfractional movements, the magnitude of dose reduction was greater in the LR direction than in the AP, PA, SI. and IS directions. Although the reduction of target dose was proportional to the magnitude of intrafractional movement in all directions, a proportionality between dose reduction and the magnitude of interfractional target movement was clear only in the LR direction. Like the coverage index and conformity index, the equivalent uniform dose and homogeneity index showed similar reductions for both types of target movements.


CONCLUSIONS
Small target movements can significantly reduce target proton radiotherapy dose during treatment of prostate cancer patients. Attention should be given to interfractional target movement along the longitudinal direction, as image-guided radiotherapy may be ineffective if margins are not sufficient.
Yoon
Myonggeun
M
Proton Therapy Center, National Cancer Center, Goyang, Republic of Korea.
Kim
Dongwook
D
Shin
Dong Ho
DH
Park
Sung Yong
SY
Lee
Se Byeong
SB
Kim
Dae Yong
DY
Kim
Joo Young
JY
Pyo
Hong Ryull
HR
Cho
Kwan Ho
KH
D006801:Humans; D008297:Male; D009068:Movement; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D011522:Protons
D011522:Protons