A biological modeling based comparison of two strategies for adaptive radiotherapy of urinary bladder cancer

Abstract

Background Adaptive radiotherapy is introduced in the management of urinary bladder cancer to account for day-to-day anatomical changes. The purpose of this study was to determine whether an adaptive plan selection strategy using either the first four cone beam computed tomography scans (CBCT-based strategy) for plan creation, or the interpolation of bladder volumes on pretreatment CT scans (CT-based strategy), is better in terms of tumor control probability (TCP) and normal tissue sparing while taking the clinically applied fractionation schedules also into account. Material and methods With the CT-based strategy, a library of five plans was created. Patients received 55 Gy to the bladder tumor and 40 Gy to the non-involved bladder and lymph nodes, in 20 fractions. With the CBCT-based strategy, a library of three plans was created, and patients received 70 Gy to the tumor, 60 Gy to the bladder and 48 Gy to the lymph nodes, in 30-35 fractions. Ten patients were analyzed for each adaptive plan selection strategy. TCP was calculated applying the clinically used fractionation schedules, as well as a rescaling of the dose from 55 to 70 Gy for the CT-based strategy. For rectum and bowel, equivalent doses in 2 Gy fractions (EQD2) were calculated. Results The CBCT-based strategy resulted in a median TCP of 75%, compared to 49% for the CT-based strategy, the latter improving to 72% upon rescaling the dose to 70 Gy. A median rectum V30Gy (EQD2) of 26% [interquartile range (IQR): 8-52%] was found for the CT-based strategy, compared to 58% (IQR: 55-73%) for the CBCT-based strategy. Also the bowel doses were lower with the CT-based strategy. Conclusions Whereas the higher total bladder TCP for the CBCT-based strategy is due to prescription differences, the adaptive strategy based on CT scans results in the lowest rectum and bowel cavity doses.

Evaluation of clinical implications in the use of dose to water versus dose to medium by using NTCP and TCP models for urinary bladder tumours

“…Few other endpoints like small bowel toxicity and femoral head necrosis were evaluated for other OARs. For LQ Poisson model the TCPs 10 were calculated with the LQ model.…”

Take Action Protocol: A radiation therapist led approach to act on anatomical changes seen on CBCT

“…For predictable ACs, adaptive strategies can be very helpful to reduce the impact of ACs, e.g. prostate adaptive radiotherapy (ART) and Library of Plan (LoP) strategies for cervix and bladder cancer patients [7] , [8] , [9] , [10] , [11] . But for unexpected ACs a decision support protocol could help to determine whether for example unscheduled plan adaptation is required.…”

The promise of adaptive radiotherapy for pelvic tumors: “too high cost for too little result” or “a low cost for a significant result”?

“…Very interestingly, although this approach was the first to be implemented in the 1990s, as may be seen in Table 2 of the Thornqvist et al review [1], only eight series have been published (five for prostate and three for bladder cancer) with the majority of the data referring to patients treated in the 1990s and in the early 2000s. On the contrary, the second category (2), mainly represented by on-line plan selection approaches for cervix and bladder cancer seems to be currently quite ''vital'', as confirmed by the publication of significant new experiences during the time of preparation of the review [5][6][7]. The third category is the largest: the potential of adapting the brachytherapy boost to tumor regression drove several centers toward the implementation of adaptive brachytherapy for gynecological cancers [8].…”