An estimated 180,400 new prostate cancer cases will be diagnosed in the United States this year, and many of these patients will be diagnosed and treated at community cancer centers.
For patients receiving radiation therapy, intensity modulated radiation therapy (IMRT) achieves greater conformity than conventional three-dimensional conformal plans.
IMRT uses complex mathematical models to generate treatment plans that optimize the dose to the tumor while minimizing the radiation dose to normal tissues.
New integrated systems for the planning and delivery of IMRT allow its use even at smaller institutions, such as the Monmouth Medical Center, a community-based center in Long Branch, New Jersey.
At Monmouth, we have performed IMRT on 15 patients, mostly prostate cancer patients, including the case study described below, as well as some head and neck cancer patients.
The Patient
The patient is a retired 64 year old man with an abnormality found on digital rectal exam. Pathologic review of the dissected tissue revealed a Gleason score of 3 + 3 = 6/10 involving 15% of the core biopsy in the right midgland and Gleason score of 3 + 4 = 7/10 involving 20% of the core biopsy specimen in the right apex. The clinical stage is T2a, N0, M0. The prostate-specific antigen (PSA) level is 2.7 ng/mL.
The IMRT plan for this patient was designed to deliver 7,560 cGy to 95% of the planning target volume. The prescription rules were based on the ICRU 50 dosimetry guidelines for the planning target volume.
Figure 1 shows the magnified 3D structures for the prostate and the nearby critical organ structures used in treatment planning.
Once the dose prescription was determined and entered into the computer, an optimal treatment plan was devised using the NOMOS Corvus inverse planning system, integrated with the Siemens IMFAST planning module. IMFAST generates the minimum number of segments required and can also arrange the order of segment delivery to minimize the setup time between segments.
Treatment Delivery
The plan was approved and imported into the Siemens LANTIS Oncology Information Management System, an integrated database that provides instant access to all administrative and clinical data on the patient.
The SIMTEC field autosequencing module, located inside the PRIMUS PRIMEVIEW workstation, was then used to group the individual treatment segments to form sequential treatment fields for automated delivery of radiation therapy, the so-called step-and-shoot technique of radiation therapy delivery.
Treatment was then delivered on the Siemens PRIMUS Linear Accelerator using an 18 MV photon beam. A total of 26 treatment segments were delivered in about 7½ minutes with five different gantry angles (as shown in Figure 2).
The rationale for using IMRT lies in the better critical organ sparing and tumor coverage achieved. IMRT generally can deliver the same radiation dosage as conventional techniques, while dramatically reducing toxicity to critical organs such as the rectum and bladder.
Dose uniformity can be an issue for some IMRT plans; however, in this case, the hot spots fall inside the target volume.
Figure 3 shows a dose volume histogram analysis indicating rectal sparing in this case. The radiation dose to the bladder and femoral heads is also much lower than the dose received at the treatment target.
Conclusion
Delivery of IMRT with a streamlined, efficient integrated planning and delivery system opens a new era for radiation oncology departments. These systems make it clinically feasible for a smaller-scale department with limited manpower in a nonacademic institution to provide a relatively difficult treatment approach to its cancer patients.
