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Purpose: Advances in technology allow the creation of complex treatment plans with tightly conforming doses. However, variations in positioning of the organ/patient with respect to treatment beams necessitate the use of an appreciable margin, potentially limiting dose escalation in many patients. To (1) reduce this margin and (2) test the hypothesis that the achievable level of dose escalation is patient dependent, a patient-specific, confidence-limited planning target volume (cl-PTV) was constructed using an adaptive radiotherapy (ART) process for prostate cancer treatment developed in-house. The potential dose escalation achievable with this ART process is quantified for both conformal radiotherapy (CRT) delivery and intensity-modulated radiotherapy (IMRT) delivery. Material and Methods: Patients with organ confined prostate cancer were entered prospectively into an ART process developed in-house. This ART process has been designed to improve accuracy and precision of dose delivery, consequently enhancing dose escalation. In this process, a cl-PTV is constructed for each patient in the second week of treatment based upon on-line portal and CT images acquired during the first week of treatment. The treatment prescription dose, defined as the minimum dose to the cl-PTV, is selected based on predefined dose-volume constraints for rectum/bladder and derived from the pretreatment planning CT image. In addition, the treatment modality (CRT or IMRT) is determined based on the level of dose escalation achievable and the risk of inaccurate targeting. The potential for both dose escalation and the application of IMRT was evaluated by comparing the prescription doses delivered using the ART process, with the cl-PTV, to those in the traditional treatment process, with a conventional generic PTV. In addition, the distributions of potential geometric target underdosing and normal tissue overdosing were also calculated to evaluate the quality of the conventional treatment plans. Results: One hundred and fifty patients have been treated with the ART process. When compared to the treatment dose delivered with the conventional treatment process (generic PTV), an average 5% (2.5–10%) more dose could be delivered using the ART process with CRT, and 7.5% (2.5–15%) more dose could be delivered with IMRT. Of the 150 patients, 70% were treated to a minimum cl-PTV dose ≥ 77.4 Gy (81.3 Gy ICRU isocenter dose). Dosimetric analysis revealed that 81 Gy to the cl-PTV (or 86.7 Gy ICRU) could be prescribed to at least 50% of patients if IMRT was applied using the ART process. In contrast, IMRT did not yield an obvious dose escalation gain if patients were treated using the generic PTV. Our results also demonstrate that the cl-PTV is significantly smaller than the conventional generic PTV for most patients, with a mean volume reduction of 24% (range, 5–43%). Conclusion: These results support our hypothesis that the achievable level of dose escalation using ART is patient dependent. By using the ART process to develop a cl-PTV, one can (1) optimize the dose level, (2) increase the applicability of IMRT, and (3) improve the quality of dose delivery. The ART process provides the foundation to identify a suitable option (CRT or IMRT) for the delivery of a safe treatment and dose escalation. It is now our standard of practice for prostate cancer treatment.

Interfractional patient variation occurs regularly and considerably during the radiotherapy course. Consequently, a generic but large planning target margin has to be applied when patient treatment plan design based on a single pre-treatment computed tomography scan is used to guide multifraction radiation treatment, which creates a major limiting factor for radiotherapy improvement. Planning target margins can be significantly reduced using multiple (or 4-dimensional) image feedback management in the routine treatment process. The most effective method in multiple-image feedback management of radiotherapy is the adaptive control methodology. The adaptive radiotherapy technique aims to customize each patient's treatment plan to patient-specific variation by evaluating and characterizing the systematic and random variations through image feedback and including them in adaptive planning. Adaptive radiotherapy will become a new treatment standard, in which a predesigned adaptive treatment strategy, including the schedules of imaging and replanning, will eventually replace the predesigned treatment plan in the routine clinical practice.

Materials/Methods: From August 1999 to March 2002, 330 prostate cancer patients were treated on our clinic’s adaptive radiotherapy (ART) protocol. This protocol demands analysis of each patient’s setup error, discerned by way of electronic portal images (EPIs) acquired for each treatment field. Therefore, for the i patient in this population we have available both the systematic error i,k and standard deviation i,k of the random error, where the index k 1,2,3 indicates the coordinate direction. The estimate i,k includes a residual i,k, which is an upper bound on the uncorrected systematic error–due either to lack of statistical confidence, or to the uncertainty induced by out-of-plane rotations. A minimal k(N) exists and satisfies i,k Mk(N) for at least N% of our population. Define k(N) and k(N) similarly for the residuals and standard deviations, respectively.