Abstract
Purpose: To compare target coverage and organ at risk (OAR) sparing in the supine and prone positions with 3-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) in low- and high-risk prostate radiotherapy cases. Materials and Methods: Using magnetic resonance images of five healthy volunteers, six treatment plans (supine 3DCRT, prone 3DCRT, supine IMRT, prone IMRT, supine VMAT and prone VMAT) were generated. Planning target volume 1 (PTV1) was defined as the prostate gland plus the seminal vesicles with adequate margins in a high-risk setting, while PTV2 was defined as prostate only with margins in a low-risk setting. The mean dose for both PTV1 and PTV2 was set at 78 Gy. Plans generated by each of the 3 techniques were compared between the supine and prone positions using dose-volume histograms (DVHs). Results: For PTV1, prone 3DCRT provided a significantly higher D98% than did supine 3DCRT, and its homogeneity index (HI) was significantly better. IMRT and VMAT values did not differ significantly between the prone and supine positions. For PTV2, no values differed significantly between the supine and prone positions under any treatment plan. With respect to OAR, the rectal D mean, D2%, V50, and V60 values of PTV1 were statistically higher in supine 3DCRT than in prone 3DCRT, while there were no significant differences in rectal values between the supine and prone positions with IMRT or VMAT. The rectal Dmean, V50, V60, V70, and V75 values of prone 3DCRT were significantly higher than those of supine IMRT or supine VMAT. There were no significant differences in any values for the rectum and bladder for PTV2. Conclusion: Although prone 3DCRT was found to be superior to supine 3DCRT in terms of rectal sparing in high-risk prostate cancer, IMRT and VMAT techniques could possibly cover this disadvantage.
Highlights
External beam radiation therapy (RT) for prostate cancer has been widely used as an important option for radical treatment, and higher dose delivery to the prostate has been known to improve outcome
The aim of the present study was to compare target coverage and organ at risk (OAR) sparing in the supine and prone positions with 3-dimensional conformal RT (3DCRT), intensity-modulated RT (IMRT) and volumetric modulated arc therapy (VMAT) in low- and high-risk cases in order to determine whether differences in the spatial relationship between the critical organs and the target would have an impact on dosimetric improvement in treatment planning
For Planning target volume 1 (PTV1) (Table 2(a)), prone 3DCRT provided a significantly higher D98% than did supine 3DCRT, and homogeneity index (HI) was significantly better in prone 3DCRT
Summary
External beam radiation therapy (RT) for prostate cancer has been widely used as an important option for radical treatment, and higher dose delivery to the prostate has been known to improve outcome. Advanced radiation treatment techniques are available, such as 3-dimensional conformal RT (3DCRT), intensity-modulated RT (IMRT), and volumetric modulated arc therapy (VMAT), rectal toxicity is amplified with increased radiation doses. The selection of treatment position is a critical choice in RT. The choice of position can alter the external contour of the treated area and has the potential to alter the spatial relationship between internal organs. In most previous reports, rectal doses were evaluated in patients treated with 3DCRT, and the effect of patient position on normal tissue doses in IMRT or VMAT is not well known
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