A three-field arc technique (3-FAT) for treating prostate cancer.
OBJECTIVE
We have previously designed two external beam radiotherapy techniques for treating prostate cancer. The seven-field, coplanar fixed beam technique resulted in dose distributions that were superior to other coplanar plans studied. The other technique using bilateral blocked arcs produced slightly higher doses to normal tissues but was far simpler to execute. We combined aspects of both these plans to produce a technique that was less complicated yet resulted in an improved dose distribution, i.e., to improve dose delivery to the clinical target volume (CTV) while minimizing doses to the rectum, bladder, and femoral heads.


METHODS
Twenty patients, previously treated at the University of California, San Francisco (UCSF) with radiotherapy for adenocarcinoma of the prostate, were studied. Each patient was treated with an immobilizer, urethrogram, and a preplanning CT scan. A previously employed, seven-field, coplanar, fixed beam technique was compared with a newly designed three-field, arc technique (3-FAT). This 3-FAT was designed using two equally weighted rotational beams, with nonuniform blocks, beginning in the lateral gantry position and spanning anteriorly 35 degrees. The two beams became noncoplanar by turning the table 20 degrees, bringing the patient's feet toward the gantry (inferior oblique arcs). An anterior inferior oblique (AIO), angled 20 degrees to the inferior of anterior was included for 10% of the daily treatment. Dose-volume histograms (DVH) were used to evaluate doses to adjacent critical structures. The dose to each critical structure was averaged and tabulated for the 20 patients. In addition, we compared normalized doses to adjacent structures using 3-FAT and seven-coplanar, fixed beams vs. a technique using four noncoplanar, fixed beams.


RESULTS
The three-field arc technique produced favorable dose distributions for the rectum, bladder, and femoral heads. Compared to the seven-field plan, employing the 3-FAT resulted in a 13% lower dose to 40% of the rectum, and 25% lower dose to 40% of the bladder. Compared to the four-field plan, employing the 3-FAT resulted in a 23% lower dose to 40% of the rectum, and 1% decrease in dose to 40% of the bladder. The three-field arc technique reduced the dose delivered to 40% of the femoral heads by approximately 45% when compared to the other techniques. Compared to other standard treatment techniques, the improvement in dose distribution was even greater.


CONCLUSIONS
The 3-FAT represents a technical improvement in the treatment of cancer of the prostate and seminal vesicles by minimizing the dose delivered to adjacent critical structures. The 3-FAT can incorporate the advances of multileaf collimation and digitally reconstructed radiographs to deliver treatment with cost effectiveness and technological efficiency.
Weil
M D
MD
Department of Radiation Oncology, University of California, San Francisco 94143, USA.
Pickett
B
B
Kuerth
S
S
Roach
M
M
D000230:Adenocarcinoma / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011878:Radiotherapy / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed