Prostate DVH Benchmark Study With Helical TomoTherapy

Guo. F, IJROBP 2006:66:Issue 3, Page S667 (1 November 2006)

During our clinic’s initial implementation of segmental MLC (SMLC) IMRT technique for prostate cancer, we developed benchmark dose-volume histograms (DVHs) for bladder and rectum based on our clinical experience with 31 patients treated with 3D-CRT and IMRT. In order to explore the potential of helical tomotherapy in the treatment of prostate cancer, a planning study comparing our previous SMLC IMRT experience with helical tomotherapy was conducted.

Six patients with prostate cancers were planned and treated using the TomoTherapy Hi·Art System® (TomoTherapy Inc., Madison, WI). Patients were positioned supine and we use daily imaging guidance from TomoTherapy’s MVCT system to track the location of the prostate for setup verification. A full bladder requirement was employed but there were no requirements for the rectum. For each patient, a CT scan (Picker PQ2000, Philips Medical Systems) was obtained with a slice thickness of 3 mm from the level of the L4 vertebral body to at least 5 cm below the ischial tuberosities. Rectal and urethral contrast media were not applied due to the TomoTherapy planning system requirement. All plans were using 2.5 cm jaw, 0.3 pitch, and 2.0 cm initial modulation and achieved to cover 98% volume of PTV by the prescription dose which is 74 Gy for a single phase treatment in which PTV is formed by CTV/GTV (prostate) plus 8 mm margin. For a two phase treatment, 54 Gy is prescribed to PTV1 (prostate and proximal seminal vesicle plus 8 mm margin), which is followed by a boost prescription of 24 Gy to PTV2 (prostate plus 8 mm margin except 5 mm posterior). Dose volume histograms were exported, processed and averaged using MatLab/Excel. The averaged DVH data were compared to the benchmark DVHs for the SMLC IMRT (planned on Eclipse TPS, Varian Medical System, Palo Alto, CA). Currently there is no capability to combine total doses from two TomoTherapy plans on the same patient. Therefore, PTV1 and PTV2 have to be compared separately.

Results. In all six cases, TomoTherapy plans show a rectum DVH that is comparable or better than the SMLC IMRT plan, particularly in the high dose region. In all 6 cases, TomoTherapy plans show a bladder DVH that is comparative to the SMLC IMRT benchmark.