Purpose. High-risk prostate cancer patients often receive radiotherapy (RT) to pelvic lymphatics (PLs). The aim of this study was to determine the safety margin around clinical target volume for PL (PL-CTV) to construct planning target volume for PL (PL-PTV) and for planning elective PL irradiation. Methods and Materials. Six patients who received RT to PL as part of prostate cancer treatment were identified. To determine average daily shifts of PL, the right and left IVs were contoured at 3 predetermined slices on the daily MV scans and their daily shifts were measured at these 3 levels using a measuring tool. Results. A total of 1,932 observations were made. Daily shifts of IV were random in distribution, and the largest observed shift was 13.6？mm in lateral and 15.4？mm in AP directions. The mean lateral and AP shifts of IV were 2.1？mm (±2.2) and 3.5？mm (±2.7), respectively. The data suggest that AP and lateral margins of 8.9？mm and 6.5？mm are necessary. Conclusions. With daily alignment to the prostate, we recommend an additional PL-CTV to PL-PTV conversion margin of 9？mm (AP) and 7？mm (lateral) to account for daily displacement of PL relative to the prostate. 1. Introduction High-risk status in prostate cancer as defined by T stage, Gleason score, or presenting PSA confers a high probability of extraprostatic and lymphatic spread of cancer [1]. Radiotherapy (RT) in conjunction with neoadjuvant and concurrent long-term androgen suppression has been demonstrated to improve outcomes in such patients [2, 3]. The role of irradiating the pelvic lymphatics (PLs) is controversial [4, 5]. However, current NCCN guidelines suggest that patients with high-risk prostate cancer are candidates for RT to prostate, seminal vesicles, and PL. Technological advances have allowed for higher doses to be delivered to the target, while minimizing the potential for interfraction variations which could result from positioning errors or organ motion [6–10]. During IGRT of high-risk prostate cancers, image guidance is accomplished by aligning the prostate contour with the daily image of the prostate. Though there is potential for day-to-day movement of the PL relative to the prostate, the PL field is not subjected to daily imaging for a number of reasons. Most RT institutions make use of radioopaque fiducials implanted within the prostate gland and daily kV orthogonal imaging for image guidance. Even when imaging systems such as cone-beam CT is available, the whole pelvis is not imaged daily as the procedure is time consuming and exposes the patient to unnecessary radiation.
References
[1]
D. F. Gleason, G. T. Mellinger, and L. J. Ardving, “Prediction of prognosis for prostatic adenocarcinoma by combined histological grading and clinical staging,” Journal of Urology, vol. 111, no. 1, pp. 58–64, 1974.
[2]
G. E. Hanks, T. F. Pajak, A. Porter et al., “Phase III trial of long-term adjuvant androgen deprivation after neoadjuvant hormonal cytoreduction and radiotherapy in locally advanced carcinoma of the prostate: the radiation therapy oncology group protocol 92-02,” Journal of Clinical Oncology, vol. 21, no. 21, pp. 3972–3978, 2003.
[3]
A. V. D'Amico, J. Manola, M. Loffredo, A. A. Renshaw, A. DellaCroce, and P. W. Kantoff, “6-Month androgen suppression plus radiation therapy vs radiation therapy alone for patients with clinically localized prostate cancer: a randomized controlled trial,” Journal of the American Medical Association, vol. 292, no. 7, pp. 821–827, 2004.
[4]
M. Roach 3rd, M. DeSilvio, C. Lawton et al., “Phase III trial comparing whole-pelvic versus prostate-only radiotherapy and neoadjuvant versus adjuvant combined androgen suppression,” Journal of Clinical Oncology, vol. 21, no. 10, pp. 1904–1911, 2003.
[5]
C. A. Lawton, M. DeSilvio, M. Roach 3rd, et al., “An update of the phase III trial comparing whole pelvic to prostate only radiotherapy and neoadjuvant to adjuvant total androgen suppression: updated analysis of RTOG 94-13, with emphasis on unexpected hormone/radiation interactions,” International Journal of Radiation Oncology, Biology, Physics, vol. 69, no. 3, pp. 646–655, 2007.
[6]
C. Thilmann, S. Nill, T. Tücking et al., “Correction of patient positioning errors based on in-line cone beam CTs: clinical implementation and first experiences,” Radiation Oncology, vol. 1, no. 1, article 16, 2006.
[7]
C. E. Noel, L. Santanam, J. R. Olsen, K. W. Baker, and P. J. Parikh, “An automated method for adaptive radiation therapy for prostate cancer patients using continuous fiducial-based tracking,” Physics in Medicine and Biology, vol. 55, no. 1, pp. 65–82, 2010.
[8]
A. A. Martinez, D. Yan, D. Lockman et al., “Improvement in dose escalation using the process of adaptive radiotherapy combined with three-dimensional conformal or intensity-modulated beams for prostate cancer,” International Journal of Radiation Oncology Biology Physics, vol. 50, no. 5, pp. 1226–1234, 2001.
[9]
R. K. Ten Haken and T. S. Lawrence, “The clinical application of intensity-modulated radiation therapy,” Seminars in Radiation Oncology, vol. 16, no. 4, pp. 224–231, 2006.
[10]
A. L. Zietman, M. L. DeSilvio, J. D. Slater et al., “Comparison of conventional-dose vs high-dose conformal radiation therapy in clinically localized adenocarcinoma of the prostate: a randomized controlled trial,” Journal of the American Medical Association, vol. 294, no. 10, pp. 1233–1239, 2005.
[11]
H. A. Shih, M. Harisinghani, A. L. Zietman, J. A. Wolfgang, M. Saksena, and R. Weissleder, “Mapping of nodal disease in locally advanced prostate cancer: rethinking the clinical target volume for pelvic nodal irradiation based on vascular rather than bony anatomy,” International Journal of Radiation Oncology Biology Physics, vol. 63, no. 4, pp. 1262–1269, 2005.
[12]
C. A. F. Lawton, J. Michalski, I. El-Naqa et al., “RTOG GU radiation oncology specialists reach consensus on pelvic lymph node volumes for high-risk prostate cancer,” International Journal of Radiation Oncology Biology Physics, vol. 74, no. 2, pp. 383–387, 2009.
[13]
A. Wang-Chesebro, P. Xia, J. Coleman, C. Akazawa, and M. Roach, “Intensity-modulated radiotherapy improves lymph node coverage and dose to critical structures compared with three-dimensional conformal radiation therapy in clinically localized prostate cancer,” International Journal of Radiation Oncology Biology Physics, vol. 66, no. 3, pp. 654–662, 2006.
[14]
A. Pollack, G. K. Zagars, L. G. Smith et al., “Preliminary results of a randomized radiotherapy dose-escalation study comparing 70 Gy with 78 Gy for prostate cancer,” Journal of Clinical Oncology, vol. 18, no. 23, pp. 3904–3911, 2000.
[15]
J. A. Lyons, P. A. Kupelian, D. S. Mohan, C. A. Reddy, and E. A. Klein, “Importance of high radiation doses (72 Gy or greater) in the treatment of stage T1-T3 adenocarcinoma of the prostate,” Urology, vol. 55, no. 1, pp. 85–90, 2000.
[16]
R. McCammon, K. E. Rusthoven, B. Kavanagh, S. Newell, F. Newman, and D. Raben, “Toxicity assessment of pelvic intensity-modulated radiotherapy with hypofractionated simultaneous integrated boost to prostate for intermediate and high-risk prostate cancer,” International Journal of Radiation Oncology Biology Physics, vol. 75, no. 2, pp. 413–420, 2009.
[17]
H. A. McNair, S. A. Mangar, J. Coffey et al., “A comparison of CT- and ultrasound-based imaging to localize the prostate for external beam radiotherapy,” International Journal of Radiation Oncology Biology Physics, vol. 65, no. 3, pp. 678–687, 2006.
[18]
C. Beltran, M. G. Herman, and B. J. Davis, “Planning target margin calculations for prostate radiotherapy based on intrafraction and interfraction motion using four localization methods,” International Journal of Radiation Oncology Biology Physics, vol. 70, no. 1, pp. 289–295, 2008.
[19]
A. Hsu, T. Pawlicki, G. Luxton, W. Hara, and C. R. King, “A study of image-guided intensity-modulated radiotherapy with fiducials for localized prostate cancer including pelvic lymph nodes,” International Journal of Radiation Oncology Biology Physics, vol. 68, no. 3, pp. 898–902, 2007.
[20]
P. J. Rossi, E. Schreibmann, A. B. Jani, V. A. Master, and P. A. S. Johnstone, “Boost first, eliminate systematic error, and individualize CTV to PTV margin when treating lymph nodes in high-risk prostate cancer,” Radiotherapy and Oncology, vol. 90, no. 3, pp. 353–358, 2009.
