ALPHA CRADLE® DEVICES WITH PELVIC IRRADIATION REDUCE POSITIONING ERRORS
Laura W. Jones, BSRT, T, CMD
Deborah Fuller, RTT
John Devine, MD
Rhonda Jones, RTT
Kermit Quesinberry, RTT, Nancy Ramsey, RTT
Clint Wynn, MRT
South Georgia Medical Center
Valdosta, Georgia
INTRODUCTION
Consistent positioning accuracy is an important factor in the delivery of quality radiation therapy treatments. Conventionally, 4-field. pelvic irradiation, for prostate cancer was delivered to the tumor and surrounding area to a total of 4500 cGy. The tumor was then boosted 2000-2400 cGy with a smaller 4-field. technique or 120° lateral arcs. In order to reduce complication, current trends replace the arc technique with a reduced 4-field. plan utilizing extremely small (8 x 8 cm) fields.1 Concern arose regarding the reproducibility of these small fields especially when utilized to treat obese patients. Techniques to improve accuracy and reproducibility were considered.2 The intent of this particular study was to answer the question, “Does the use of an ALPHA CRADLE® brand device with pelvic irradiation reduce positioning errors?”
METHODS AND MATERIALS
Port film accuracy data was collected for 44 consecutive patients undergoing 4-fd. Pelvic irradiation during the time period 1990-1991 when ALPHA CRADLE® Forms were not routinely used for pelvic immobilization. This data was compared with data from 44 consecutive patients receiving 4-fd. Pelvic irradiation during the time period 1992-1993 when ALPHA CRADLE® brand devices were routinely used for immobilization. This data was organized according to Table I. Each film was rated as follows:
Good: needing no changes
Minor: needing minimal change of field alignment
Major: needing significant change such as a geographic miss of the tumor
Technical Error: film suboptional due to incorrect exposure, processor jam, etc.
By dividing the data into these categories, repeats caused by positioning errors could be isolated from the total number of repeated port films.
Table 1
The ALPHA CRADLE® devices were fabricated during the simulation process and used throughout the patient’s entire course of treatment. Although Smithers Medical Products, Inc. does have a pelvic device available, all the ALPHA CRADLE® devices in this study were made using the revised ALPHA CRADLE® MOLD MAKER II (Fig. 1) and ACMM FOAMING AGENTS.3
Fig. 1 Alpha Cradle® Mold Maker II
In order to make these custom ALPHA CRADLE® devices structurally stable, a 10” x 10” x 1” piece of Styrofoam® was placed inside the polyfoam bag in the weight-bearing area of cradle. After the chemicals were poured and patient positioned, a piece of 3” x 3” x 3” Styrofoam® was placed between the legs to facilitate the foaming agent to form around each leg separately. When the ALPHA CRADLE® device was completed (Fig. 2) the MOLD MAKER II was removed and the simulation continued. After fields were localized, the central ray (CR) extensions or laser lines were drawn on the patient and the ALPHA CRADLE® device. If the CR itself fell on the form, the form was trimmed down so the CR fell on the patient’s skin.
Fig. 2 Pelvis Alpha Cradle®
When the patient was positioned in the treatment room, the table was raised to comply with a pre-determined tabletop to lateral CR measurement, the form was aligned with lasers, and patient was aligned with ALPHA CRADLE® device and lasers. All measurements were verified and recorded and initial port films were approved. Port films were taken on all fields weekly for the remaining course of treatment.
DICUSSION / CONCLUSION
The collected port film data was organized into the format of Table II. With the addition of ALPHA CRADLE® brand devices, repeat ports due to minor positioning errors decreased from 12.8% to 9.6%. Statistically overall, this represented a 25% decrease in minor positioning errors (12.8 – 9.6%. Statistically overall, this represented a 25% decrease in minor positioning errors (12.8 – 9.6 / 12.8 x 100 = 25%).
This data was collected over a two year time period during which there were several staff change-overs. Once a stable staff was in place the technique errors dropped dramatically. There were no major position errors noted for any of the set ups.
Since all parameters (with the exception of ALPHA CRADLE® device use and personnel change) remained the same, the use of ALPHA CRADLE® devices was determined to be a major factor in the 25% decrease in minor positioning errors. The study showed that the use of ALPHA CRADLE® devices for immobilization during 4-fd. pelvic irradiation is a valuable tool for positioning reproducibility.
Table 2
