A prospective comparison of the effects of interfractional variations on proton therapy and IMRT for prostate cancer

Publication date: Available online 29 December 2015
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): M. Moteabbed, A. Trofimov, G.C. Sharp, Y. Wang, A.L. Zietman, J. Efstathiou, H.-M. Lu
PurposeTo quantify and compare the impact of interfractional setup and anatomy variations on proton therapy (PT) and intensity modulated radiotherapy (IMRT) for prostate cancer.Methods and MaterialsTwenty patients with low- or intermediate-risk prostate cancer randomized to receive passive-scattering PT (n=10) and IMRT (n=10) were selected. For both modalities, clinical treatment plans included 50.4 Gy(RBE) to prostate and proximal seminal vesicles, and prostate-only boost to 79.2 Gy(RBE) in 1.8 Gy(RBE) per fraction. Implanted fiducials were used for prostate localization, and endorectal balloons for immobilization. Patients in PT and IMRT arms received weekly CT and cone-beam CT (CBCT) scans, respectively. The planned dose was re-calculated on each weekly image, scaled and mapped onto the planning CT using deformable registration. The resulting accumulated dose distribution over the entire treatment course was compared with the planned dose using dose-volume histogram (DVH) and gamma analysis.ResultsThe target conformity index remained acceptable after accumulation. The largest decrease in the average prostate D98 was 2.2 and 0.7 Gy for PT and IMRT, respectively. On average, the mean dose to bladder increased by 3.26±7.51 Gy and 1.97±6.84 Gy for PT and IMRT, respectively. These values were 0.74±2.37 and 0.56±1.90 for rectum. Differences between changes in DVH indices were not statistically significant between the two modalities. All volume indices remained within the protocol tolerances after accumulation. The average pass rate in gamma analysis, assuming tolerances of 3 mm and 3%, for PT/IMRT for CTV, bladder, rectum and whole patient were 100/100, 92.6/99, 99.2/100 and 97.2/99.4, respectively.ConclusionThe difference in target coverage and OAR dose deviations for PT and IMRT was not statistically significant under the guidelines of this protocol.

Teaser

The impact of setup and anatomy variations on the dose distribution was compared between proton therapy and IMRT for prostate cancer. Although both modalities were robust to interfractional variations with no statistically significant differences, it is desirable to minimize the remaining sources of uncertainty mainly in setup accuracy and bladder size consistency.


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