|Tomotherapy Treatment of the Prostate and
Pelvic Lymph Nodes With a Sequential Conedown
S. Chen, IJROBP Volume 69, Issue 3, Pages S692-S693 (1 November 2007)
Rush University Medical Center, Chicago, IL
External beam radiotherapy is a standard curative treatment for patients with prostate adenocarcinoma. It is a common practice in patients with intermediate to high risk prostate cancer to treat the draining pelvic lymph node regions and the prostate and proximal seminal vesicles (pSV) followed by conedown to the prostate and pSV alone. Currently, there is no clinically available package to perform multi-phase Tomotherapy planning. As a result, there have been no reports in the literature utilizing Tomotherapy in the treatment of pelvic lymph nodes and the prostate using a sequential conedown. This study examines this treatment paradigm.
The study population consisted of 15 patients with intermediate and high risk prostate cancer who were treated with standard 7-field IMRT to a total dose of 77.4 Gy. PTV45 consisted of the at-risk pelvic vessels with a 1 cm expansion and the prostate plus pSV with an 8 mm margin in all directions except 6 mm posteriorly. PTV77.4 consisted of the prostate and pSV with the same margins. The IMRT plans were previously developed with the Pinnacle planning system using a sequential conedown, with the conedown phase optimized accounting for dose from the pelvic phase. A Tomotherapy treatment plan was developed for each of these patients using the same PTVs and critical structures including rectum, bladder, and penile bulb. The initial volume and conedown were independently planned on the Tomotherapy system and subsequently combined and evaluated using a novel in-house software package. The prescription dose was set to cover 95% of the PTVs. The RTOG dose guidelines were scaled by 0.58 (45 Gy/77.4 Gy) for the pelvic treatment and 0.42 (32.4 Gy/77.4 Gy) for the prostate boost; these were used as constraints in the planning process. The Tomotherapy plans were compared to the IMRT plans using the following criteria: PTV V100%, PTV V105%, PTV maximum dose, and RTOG DVH guidelines for rectum, bladder, and penile bulb. Paired T-tests were performed.
TomoTherapy is superior to standard 7-field IMRT for dose homogeneity measured by PTV V105% and maximum dose. These differences are likely due to the helical delivery aspects of TomoTherapy in which dose is delivered over many angles, thereby decreasing “hot spots.” There were no significant differences in the DVH criteria for rectum and bladder. TomoTherapy was inferior for mean dose to the penile bulb, but conformed to the RTOG guideline. The difference can be reduced by decreasing the collimator size. In summary, TomoTherapy treatment of the pelvic lymph nodes and prostate with a sequential conedown is feasible.
Structure Guideline Tomo IMRT p-value
PTV77.4 V100% 95.8% 96.0% 0.684
PTV77.4 V105% 4.9% 19.3% 0.049
PTV77.4 Max Dose 105.6% 108.4% 0.012
Rectal V75 Gy <15% 11.5% 13.1% 0.118
Rectal V70 Gy <25% 19.0% 21.3% 0.135
Rectal V65 Gy <35% 27.3% 29.0% 0.392
Rectal V60 Gy <50% 38.4% 37.2% 0.651
Bladder V80 Gy <15% 2.8% 4.8% 0.187
Bladder V75 Gy <25% 20.1% 20.2% 0.968
Bladder V70 Gy <35% 29.8% 28.0% 0.321
Bladder V65 Gy <50% 39.0% 35.5% 0.106
Penile Bulb Mean Dose <5250 cGy 4886 2739 <0.001