inverse planning system generates highly conformal dose deposition and dose avoidance patterns. These dose patterns allow the potential for dose escalation to the tumor while sparing the surrounding normal tissues. With marked dose fall-off seen on the IMRT isodose plans, certain caveats must be heeded. Motion may displace the target into much lower isodose lines than intended. The target needs to be immobilized to avoid underdosing; likewise, normal structures must maintain a consistent position to avoid overdosing. These necessities for target immobilization make IMRT for prostate cancer challenging. Organ motion has long been documented and is derived from many
sources. Langen and Jones have recently reviewed this issue(2). Without proper immobilization, the benefit of normal tissue avoidance—although increasing the dose to the target—may be lost. The emerging enthusiasm for dose escalation for IMRT must be tempered with consideration of target immobilization, patient setup error, and definition of subclinical extent of disease.
The authors’ premise in treating prostate cancer includes the following assumptions: (1) high degree of clinical understaging occurs; (2) subclinical extension must be treated as adequately as the gross tumor volume (GTV); (3) prostate motion exists, but can be sufficiently controlled to allow for margins of 5 mm, which serves to minimize the volume of normal tissue treated; and (4) dose escalation beyond 70 Gy is indicated in all patients for optimal local control of prostate cancer (i.e., dose escalation when performed cautiously and correctly has not yet resulted in intolerable acute or long-term toxicity). Prostate motion, prostate and patient immobilization, and setup error have been addressed previously at Baylor College of Medicine (3–7). The aims of the current study were (1) to quantify the extension of tumor beyond the prostatic capsule based on prostatectomy specimens and (2) to compare target volumes with the pathologic extent of disease to determine if the defined volumes preoperatively were
METHODS AND MATERIALS
Pathologic extension of disease beyond the prostate
Between August 1983 and September 1995, 712 consecutive prostates from radical prostatectomy were assessed from Baylor College of Medicine and were included in this study. None of the patients had prior radiation or hormonal manipulation with androgen receptor antagonists, 5--reductase inhibitors, or luteinizing hormone–releasing hormone agonists. The same pathologist (TMW) assessed all 712 prostate specimens to avoid any interobserver variations.
Definition of extension
Determination of the distance of extension of microscopic disease was made perpendicular to the surface of the prostate capsule and, in the case of multiple areas of extension, the focus of greatest distance was used for data collection.All the samples came from embedded whole mounts after allowing for fixation overnight in 10% formalin
solution assessed in 5-mm transverse slices. The process has been described in detail earlier .
Definition of the levels of prostatic capsular invasion is as follows and is shown in Fig. 1.
Level 0 (L0): Tumor confined to the prostatic stroma within the boundary of normal prostatic acini.
Level 1 (L1): Tumor confined to the prostatic stroma, but outside the boundary of normal prostatic acini.
Level 2 (L2): Tumor confined to the prostate but within a layer more fibrous than muscular (capsule).
Nonconfined (extracapsular extension)
Level 3 (L3): Tumor invasive to the periprostatic adipose tissue or smooth muscle of bladder neck.
Level 3 focal: Tumor outside the prostate to a depth of less than one high-powered field on no more than two separate sections.
Level 3 established: Any amount of extraprostatic tumor more than L3 focal.
The focus of this study was those patients considered to have L3 extension into the periprostatic tissue. 观察好久了，此文不知为何一直无人认领。后天就要坐火车回家去了。怎么办呢？罢了，我领回去学习学习。
作者:admin@医学,生命科学 2011-09-08 17:11