A Dosimetric Analysis Comparing TomoTherapy and IMRT in the Treatment of Prostate Cancer

A.P. Shah, Volume 69, Issue 3, Page S383 (1 November 2007)

Intensity modulated radiation therapy (IMRT) has been established as a preferred method of external beam radiation in the treatment of prostate cancer. TomoTherapy is a newer method of IMRT which allows the delivery of radiation along a helix using thousands of beamlets, as well as the ability to perform daily CT localization of the prostate. Limited information is available comparing these two modalities. We present our dosimetric comparison of IMRT and TomoTherapy in the treatment of prostate cancer.

The study population consisted of 15 patients with low or intermediate risk prostate cancer. For each patient both a TomoTherapy plan and an IMRT plan were generated based on the same planning objectives. The PTV for both plans was the prostate and proximal seminal vesicles plus an 8-mm margin in all directions and a 6-mm margin posteriorly. The prescription dose was 7740 cGy in 43 fractions. RTOG normal tissue guidelines were followed, and the PTV coverage was statistically equal between the two plans. Established benchmark DVH values for the rectum and bladder and mean dose to the penile bulb were recorded for the 15 patients for IMRT and TomoTherapy plans. In addition, the volume of the PTV receiving ≥105% of the prescription dose was recorded in an effort to compare the homogeneity of the plans.

The mean DVH values for each of the RTOG constraints were significantly improved using TomoTherapy as compared to IMRT (Table 1). The volume of the PTV receiving ≥105% of the prescribed dose was higher in the IMRT plans (11.7% vs. 0.2%, p ≤ 0.001). The mean dose to the penile bulb was higher in the TomoTherapy plans (40.4 Gy vs. 27.4 Gy, p = 0.005).

Using established RTOG criteria, TomoTherapy allows decreased radiation dose to the rectum and bladder compared to IMRT. The TomoTherapy plans showed improved dose homogeneity as measured by the percentage of the PTV that received ≥105% of the prescription dose. The mean dose received by the penile bulb was higher with TomoTherapy compared to IMRT; however, no patient exceeded the RTOG guidelines for mean penile bulb dose.