ICTR 2000
Intensity modulated radiation therapy (IMRT) following prostatectomy: more favorable acute genitourinary toxicity profile compared to primary IMRT for prostate cancer

Presented at ICTR 2000, Lugano, Switzerland, March 5–8, 2000.
https://doi.org/10.1016/S0360-3016(00)01474-7Get rights and content

Abstract

Purpose: To report our initial experience on postprostatectomy IMRT (PPI), addressing acute genitourinary (GU) toxicity in comparison to primary IMRT (PI) for prostate cancer.

Methods and Materials: From April 1998 to December 1999, 40 postprostatectomy patients were treated with intensity modulated radiation therapy (IMRT) to a median prescribed dose of 64 Gy (mean dose of 69 Gy). The Radiation Therapy Oncology Group (RTOG) scoring system was used to assess acute GU toxicity. Target volume and maximum and mean doses were evaluated. The mean doses to the bladder and irradiated bladder volume receiving >65 Gy were assessed. These were compared to those of 125 patients treated with PI to a prescribed dose of 70 Gy (mean dose of 76 Gy).

Results: The acute GU toxicity profile is more favorable in the PPI group with 82.5% of Grade 0–1 and 17.5% of Grade 2 toxicity compared to 59.2% and 40.8%, respectively, in the PI group (p < 0.001). There was no Grade 3 or higher toxicity in either group. The target volume was larger in the PPI group, while the maximum and mean doses to the target were higher in the PI group. The mean dose delivered to the bladder was higher in the PPI group. The irradiated bladder volume receiving >65 Gy was significantly larger in the PI group (p < 0.001).

Conclusions: PPI can be delivered with acceptable acute GU toxicity. The larger PPI target volume may be related to the difficulty in delineating prostatic fossa. Despite a larger target volume and a higher mean dose to the bladder, PPI produced a more favorable acute GU toxicity profile. This may be related to a combination of lower mean and maximum doses and smaller bladder volumes receiving >65 Gy in the PPI group, as well as urethral rather than bladder irradiation. The findings have implications in the evaluation of IMRT treatment plan for prostate cancer, whereby the irradiated bladder volumes above 65 Gy may be more meaningful than the mean dose to the bladder. Longer term toxicity results are awaited.

Introduction

The advances of radiation oncology technology have led to the implementation of three-dimensional conformal radiotherapy (3D-CRT) in the clinics. 3D-CRT has been shown to reduce treatment-related toxicity and to improve biochemical control (1). Intensity modulated radiation therapy (IMRT) combines two advanced concepts to deliver 3D-CRT: (1) Inverse treatment planning with optimization by computer, and (2) Computer-controlled intensity modulation of the radiation beam during treatment 2, 3.

There are many studies (randomized and nonrandomized) addressing acute toxicity following primary 3D-CRT for prostate cancer 1, 4. However, acute toxicity related to postprostatectomy radiotherapy is not as well studied, especially in the 3D-CRT era. To date, there are no data on postprostatectomy IMRT (PPI). We report our initial experience on PPI addressing acute genitourinary (GU) toxicity and treatment planning dosimetric parameters in comparison to primary IMRT (PI) for prostate cancer.

Section snippets

Patient characteristics

From April 1998 to December 1999, 40 patients were treated with IMRT using a commercially available inverse planning system (Peacock, NOMOS Corporation, Sewickley, PA) following initial radical prostatectomy. Patient characteristics are shown in Table 1. Twenty patients had established extracapsular extension, while 19 had positive surgical margin. Five patients had involvement of seminal vesicles. The patients could be broadly divided into two groups:

  • 1.

    Adjuvant radiotherapy: 9 patients (22.5%)

Treatment planning dosimetry

Fig. 1, Fig. 2, Fig. 3 show axial (two separate levels) and sagittal images of dose distribution for PPI. Dose coverage of the prostatic fossa and doses delivered to the surrounding normal structures, especially bladder and rectum, are depicted. Please note that the patient was treated in the prone position with an air-filled rectal balloon in place. A comparison of target volumes (prostatic fossa vs. prostate with or without seminal vesicles) is shown in Table 3. The target volume was

Discussion

This report is the first to demonstrate the clinical implementation of IMRT with inverse treatment planning in patients following radical prostatectomy. We have previously shown that PI with prostate immobilization using a rectal balloon has significantly reduced acute toxicity when compared to conventional and six-field conformal radiotherapy (5). Before implementing this technique in the postprostatectomy setting, we noted two inherent problems. First, it is more difficult to define the

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