Prostate brachytherapy
Optimal source distribution for focal boosts using high dose rate (HDR) brachytherapy alone in prostate cancer

https://doi.org/10.1016/j.radonc.2014.09.001Get rights and content

Abstract

Purpose

To investigate the optimal distribution of sources using high dose rate brachytherapy to deliver a focal boost to a dominant lesion within the whole prostate gland based on multi-parametric magnetic resonance imaging (mpMRI).

Methods

Sixteen patients with prostate cancer underwent mpMRI each of which demonstrated a dominant lesion. There were single lesions in 6 patients, two lesions in 4 and 3 lesions in 6 patients. Two dosimetric models and parameters were compared in each case. The first model used 10 mm intervals between needles, and the second model used additional needles at 5 mm intervals between each needle in the boost area.

Results

Three of thirty-two plans did not achieve the plan objectives. These three plans were in the first model. A higher median urethral volume was seen in the ‘unsuccessful’ group (2.7 cc, and 1.9 cc, respectively, p-value = 0.12). Conformity indices of the second model were also better than the first model (COIN index; 0.716 and 0.643, respectively).

Conclusions

Focal monotherapy based on mpMRI achieves optimal dosimetry by individualizing the needle positions using 5 mm spacing rather than 10 mm spacing within the boost volume. A larger urethral volume may have an adverse effect on this distribution. Formal clinical evaluation of this approach is currently underway.

Section snippets

Case selection and imaging

Sixteen patients with prostate cancer, who were to receive HDR prostate brachytherapy, also underwent mpMRI as part of their initial staging using a GE 3.0 Tesla scanner. The MRI sequences consisted of T2 weighted, DWI, DCE, and MRS. The scans were assessed by a radiologist with a specialist interest in prostate MRI (AP).

Contouring

The diagnostic MR images were imported into the Eclipse treatment planning system (Eclipse v. 10.0, Varian Medical System, Inc., Palo Alto, CA, USA). The entire prostate gland

Results

Patient characteristics are shown in Table 2. Six patients had one lesion, four patients had two lesions and six patients had three lesions in the prostate gland. There were 33 of 36 lesions in the peripheral zone. The median volumes of prostate gland and boost area were 59.3 cc and 1.6 cc, respectively; while the median of organ at risk volumes (rectum and urethra) were 34.95 cc and 1.9 cc, respectively. In addition, the median number of needles for the two plans was 21.5 (15–28) for Model A, and

Discussion

This study is the first to explore the optimum dosimetric model for a focal monotherapy boost using HDR brachytherapy in localized prostate cancer based on multi-parametric MR. One study has evaluated the feasibility of HDR brachytherapy for the dominant intra-prostatic tumor region defined with functional images, including endorectal MRI or PET-CT imaging in 20 cases using hemi-gland HDR brachytherapy boost [13]. External beam radiotherapy delivering 64 Gy was followed by an HDR brachytherapy

Conclusion

Focal boosts using HDR brachytherapy in prostate cancer can successfully achieve a 10% dose escalation to the boost volume while maintaining a lower dose to the remaining gland. Optimal dosimetry is achieved by individualizing the needle positions using 5 mm spacing rather than 10 mm spacing within the boost volume. Good differential dosimetry is more difficult to achieve in smaller glands and those with a larger urethra. Clinical evaluation of this approach is currently underway.

Conflicts of interest

No potential conflict of interests.

Acknowledgements

P. Dankulchai at Mount Vernon Cancer Centre (the United Kingdom) was supported by a grant of the Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand.

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