Elsevier

Radiotherapy and Oncology

Volume 93, Issue 2, November 2009, Pages 234-240
Radiotherapy and Oncology

Prostate radiotherapy
Carbon-11 acetate PET/CT based dose escalated IMRT in prostate cancer

https://doi.org/10.1016/j.radonc.2009.08.010Get rights and content

Abstract

Purpose

To demonstrate the theoretical feasibility of [11C]acetate PET/CT in delineating the malignant intraprostatic lesions (IPL’s) in prostate cancer and to use the data in external beam radiotherapy to boost the biologically defined target volume (BTV).

Methods and materials

Twelve men with intracapsular prostate carcinoma were imaged with [11C]acetate PET/CT and the data were used to delineate the BTV. Six dynamic IMRT plans were generated to each patient: a standard IMRT (sIMRT) plan with a 77.9 Gy dose to PTV (prostate gland with a 6-mm margin) and a simultaneous integrated boost IMRT (SIBIMRT) plan to deliver 77.9 Gy, 81 Gy, 84 Gy, 87 Gy and 90 Gy to the BTV and 72 Gy to the rest of PTV. To study the theoretical dose escalation based on the delineation of BTV, tumor control probabilities (TCPs) and normal tissue complication probabilities (NTCPs) of bladder and rectum were calculated and compared between the treatment plans.

Results

[11C]Acetate was used to delineate the IPL’s of all 12 patients. With every patient the TCP was increased with SIBIMRT without increasing the NTCP of the bladder or rectum. The probability of uncomplicated control (PUC) was increased on average by 28% with the SIBIMRT treatment plans. The highest PUC was achieved with an average dose of 82.1 Gy to the BTV.

Conclusions

Our study indicates that [11C]acetate can be used to define the IPL’s and in combination with SIBIMRT the defined areas can theoretically be treated to ultra high doses without increasing the treatment toxicity. These results motivate the formal validation of [11C]acetate PET for biological dose planning in prostate cancer.

Section snippets

Patients

Twelve patients with histologically confirmed adenocarcinoma of prostate and WHO performance status 2 or better referred to external beam radiotherapy were enrolled between January 22 and October 30, 2008. Routine diagnostic workup included serum prostatic specific antigen (PSA), multiple (6–10) bilobal prostatic biopsies, transrectal ultrasound, pelvic computed tomography and bone scan. The median time from biopsy to PET imaging was 4 months (range, 2–6 months). No prior treatment of PCa was

Results

The patient characteristics are listed out in Table 1. All 12 patients were imaged with PET/CT and the injected activity of [11C]acetate was on the average 593 MBq (range 221–786 MBq). In all patients at least one IPL could be detected and 10 patients (83%) had more than one IPL (Table 1). The uptake of the tracer superimposed on fused CT-images of the first six patients is shown in Fig. 1. The maximum SUV ranged from 2.3 to 5.9 g/ml and the total volume of the BTV was on average 4.5 cm3 (0.8–13.9

Discussion

In this study PET/CT imaging with ACE was used to delineate the BTV of 12 patients with PCa. We demonstrated the theoretical feasibility of using the ACE based BTV as a target volume for the dose escalation treatment plans up to 90 Gy by calculating the TCP and NTCP of the rectum and the bladder and by comparing them to a standard IMRT plan.

Preexisting studies of the local progression of PCa suggest that the recurrences after radiotherapy are due to underdosage of the primary tumor area rather

Conclusion

PET/CT imaging with ACE was used to delineate the IPL’s with all 12 patients studied. With SIBIMRT we were able to escalate the dose in the BTV and with all patients the studied TCP was increased without increasing the NTCP of rectum or bladder. By the means of PUC, we determined the optimal dose to be 82.1 Gy to the BTV. Although some non-cancerous tissues such as hyperplasia will receive a high dose as well this should not compromise the improved therapeutic ratio potentially achievable with

Acknowledgments

This study was supported by an EVO grant of the Hospital District of Southwest Finland. The staff of Turku PET centre and Department of Oncology and Radiotherapy are gratefully acknowledged.

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