Clinical Implementation of the World’s First Primatom, a Combi-nation of CT Scanner and Linear Accelerator, for Precise Tumor Targeting and Treatment*
J.R. Wong 1,4 , C.W. Cheng 1,2 , L. Grimm 1 , M. Uematsu 3
1. Department of Radiation Oncology,
Marristown Memorial Hospital/Atlantic Health System, NJ (USA)
2. Arizona Oncology Associates, Tucson, AZ (USA)
3. National Defense Medical College, Namiki, Tokorozawa
(Japan)
4. Columbic University, College of Physicians and Surgeons,
NY, NY, (USA)
Manuscript received: June 16, 2001; revised October 8, 2001
Accepted for publication: October 10, 2001
Abstract
A novel image guided radiation treatment technique by a CT-on-rail coupled with a linear accelerator (Primatom, Figure 1) was developed. The system is designed so that daily tumor target localization can be performed prior to each radiation treatment, and thus, reducing the extrinsic and intrinsic uncertainties that are associated with patient set up and organ motion respectively. The Primatom consists of a linear accelerator (PRImus) and a CT scanner (SOMATOM) that is movable on a pair of horizontal rails. Because the linear accelerator and the CT were installed in different times, the accuracy and effectiveness of each components (linear accelerator and CT) have to be checked and measured when they function together as a unit. To achieve this task, a Rando phantom study was performed prior to clinical implentation. Thirteen patients with biopsy proven prostate cancers were treated with the Primatom using 3D conformal radiation treatment. The clinical stages of these patients range from T1c to T3, with a Gleason range of 6-8, and a PSA range of 4.1-239. These patients are scanned by the CT which is movable on a pair of horizontal rails. During the scanning, there is no movement of the couch. The exact location of the prostate, seminal vesicles, and rectum can be identified and localized. These positions are then compared to the planned position. The daily movement of the prostate and rectum are corrected for, and a new isocenter derived. The patient is then treated immediately with the new isocenter. Rando phantom study showed that the Primatom is accurate and effective, with a positional acccuracy reproduced to within 2 mm. Of the 13 patients treated, a total of 63 consecutive daily CT scans were performed on the last part of the treatment. 32% of the treatment sessions required no new isocenter adjustment. 68% (43/63) required a shift of isocenter _3 mm in the APPA(anteroposterior and posteroanterior) direction. Among those adjustments, 17% (11/63) required a shift of >10 mm. The additional time for acquiring the CT scan, calculating and adjusting the shift of isocenter is about 20 minutes daily. By performing daily verification using CT scanning with the Primatom, target movement due to external set up variabilities/error, or due to intrinic internal organ movements can be minimized. This technique has significant implications for the radiation treatment of cancers, especially in terms of dose escalations, minimizing toxicities, and most importantly, maximizing the dose delivered to the tumor.
KEYWORDS: Image-Guided Radiation Therapy, Prostate Cancer, Radiation therapy, organ motion.