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 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.
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.
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.