Conventional vs. conformal radiotherapy for prostate cancer: preliminary results of dosimetry and acute toxicity

Results of 3D conformal radiotherapy in the treatment of localized prostate cancer

PURPOSE

3D conformal radiotherapy (3D CRT) has been shown to decrease acute morbidity in the treatment of prostate cancer. Therapeutic outcome and late morbidity data have been accumulating. To evaluate the results of 3D CRT for the treatment of prostate cancer, we analyzed the outcome of a large series of patients treated with conformal techniques.

MATERIAL AND METHODS

From January 1987 through June 1994, 707 patients with localized prostate cancer were treated with 3D CRT. Patients with pathologically-confirmed pelvic lymph node metastasis, treated with pre-irradiation (preRT) androgen ablation, or treated post-prostatectomy were excluded. All had CT obtained specifically for treatment planning, multiple structures contoured on the axial images, and beam's-eye view conformal beams edited to provide 3D dose coverage. Median follow-up is 36 mos; 70 patients have been followed longer than 5.5 years. Six hundred three had T1-T2 tumors. PreRT prostate specific antigen (PSA) was available for 649 patients: median preRT PSA was 12.9 ng/ml, 209 patients had preRT PSA > 20 ng/ml. The median dose of radiation was 69 Gy; 102 patients received > or = 69 Gy. Biochemical failure was defined as: 1) two consecutive PSA rises over 2.0 ng/ml if nadir PSA < or = 2.0 ng/ml, 2) two consecutive PSA rises over nadir if nadir PSA > 2.0 ng/ml, or 3) initiation of hormonal therapy after RT. Complications were graded using the RTOG system.

RESULTS

PreRT PSA and Gleason score emerged as independent indicators of biochemical control (bNED). Patients with preRT PSA > 10 had a significantly worse bNED at 5 years than patients with preRT PSA < or = 10. Five-year bNED was determined according to preRT PSA: PSA < or = 4, 88%; PSA > 4 < or = 10, 72%; PSA > 10 < or = 20, 43%; and PSA > 20, 30%. Patients with Gleason score > or = 7 also had a significantly worse bNED than patients with Gleason score < 7. Patients were divided into two prognostic groups: a favorable group with PSA < or = 10, Gleason score < 7, and T1-T2 tumors, and an unfavorable group with PSA > 10, Gleason score > or = 7 or T3-T4 tumors and studied for the effect of dose on bNED status. The bNED at 5 years was 75% for the favorable group and 37% for the unfavorable group. In addition, a group that might be considered a surgical subset was reviewed: patients with PSA < or = 10, Gleason score < or = 7, and T1-T2 tumors who were < 70 years old. This subset had an 84% 5-year bNED rate and 98% 5-year overall survival. Complications with the techniques used here are very low: 3% risk at 7 years of Grade 3-4 complications and 1% risk at 7 years of Grade 3 bladder complications (no Grade 4).

CONCLUSION

3D CRT allows for treatment of prostate cancers with a very low risk of complications. Patients with relatively early disease as defined by preRT PSA, Gleason score < 7, and T1-2 tumors and patients who are candidates for radical prostatectomy have excellent 5-year bNED rates. Patients with adverse prognostic factors have a high risk of biochemical recurrence and are candidates for innovative therapy.

[Planned 3-dimensional low-volume conformal irradiation of a local prostatic carcinoma]

AIM

Recent data have shown a significant reduction of acute side effects by means of a three-dimensional planned conformal radiotherapy of carcinoma of the prostate compared to treatment techniques used before. Theoretically, an optimized field coverage of the planning target volume should result in a reduction of treated bladder and rectum volumes. We studied the effects of individualized blocks on treatment volumes, planning target volumes, irradiated bladder and rectum volumes on basis of three-dimensional treatment planning by means of beam's-eye-view technique.

PATIENTS AND METHOD

We compared dose-volume-histograms of 2 different planning models, a (fictitious) open 4-field-box-technique and a technique with conformal blocked fields designed from the beam's-eye-view display (prescribed dose 66 Gy, daily single fraction 2 Gy). Plans of 115 patients with localized prostate cancer treated from January 1994 to February 1996 were analyzed.

RESULTS

Using individualized fields treatment volume (covered by the 90%-isodose) was reduced by 23% on the average in comparison to the planning model without blocks. The averaged difference of treated volume and planning target volume, as a grade of efficiency of conformation, was reduced by 38% (496 cm3 303 cm3) using individualized blocks. 23% of the treated bladder volume and 13% of the treated rectum volume had been saved on the average. Nevertheless, at least 11.5% of the bladder volume and 27.6% of the contoured rectum volume were treated with the prescribed dose (55 Gy = 100%).

CONCLUSIONS

The comparison of dose-volume-histogram-data showed that especially high dose volumes of organs at risk had been saved by means of individualized blocks created from the beam's-eye-view. The blocks did not affect the dose distribution of the planning target volume adversely. Consequently the impact of these data on the extent of side effects and local tumor control has to be proven.

Prostate-specific antigen cancer volume: a significant prognostic factor in prostate cancer patients at intermediate risk of failing radiotherapy

PURPOSE

Although the pretreatment serum prostate-specific antigen level (PSAL) is the single-most significant predictor of local and biochemical control in prostate cancer patients treated with radiotherapy, it is relatively insensitive for patients with a PSAL in the intermediate range (4-20 ng/ml). PSA density (PSAD) has been shown to be slightly more predictive of outcome than PSAL for this intermediate risk group; however, this improvement is small and of little use clinically. PSA cancer volume (PSACV), an estimate of cancer volume based on PSA, has recently been described and has been purported to be more significant than PSAL in predicting early biochemical failure after radiotherapy. We report a detailed comparison between this new prognostic factor, PSAL, and PSAD.

METHODS AND MATERIALS

The records of 356 patients treated with definitive external beam radiotherapy for regionally localized (T1-4,Nx,M0) adenocarcinoma of the prostate were reviewed. Each patient had a PSAL, biopsy Gleason score, and pretreatment prostate volume by transrectal ultrasonography. The median PSAL was 9.3 ng/ml and 66% had Gleason scores in the 2-6 range. The median radiation dose was 66.0 Gy and the median follow-up for those living was 27 months. PSACV was calculated using a formula which takes into account PSAL, pretreatment prostate ultrasound volume, and Gleason score. The median PSACV was 1.43 cc. Biochemical failure was defined as increases in two consecutive follow-up PSA levels, one increase by a factor > 1.5, or an absolute increase of > 1 ng/ml. Local failure was defined as a cancer-positive prostate biopsy, obtained for evidence of tumor progression.

RESULTS

The distributions of PSACV and PSAL were similar and, when normalized by log transformation, were highly correlated (p < 0.0001, linear regression). There was a statistically significant relationship between PSACV and several potential prognostic factors including PSAL, PSAD, stage, Gleason score, and pretreatment prostatic acid phosphatase (PAP). In univariate analyses, PSACV, PSAL, and PSAD proved to be the most significant predictors of both biochemical and local control. In multivariate analyses using Cox proportional hazards models with PSAL, PSAD, PSACV, and PAP as continuous variables, PSAL, PSACV, and Gleason score were significant in predicting biochemical control. Only PSAL was significantly correlated with local control. However, when these analyses were restricted to patients with intermediate PSALs (4-20 ng/ml), only PSACV was significant for predicting both biochemical and local control.

CONCLUSION

PSACV was highly correlated with actuarial local and biochemical control and was superior to both PSAL and PSAD in predicting these outcomes in patients with PSALs between 4 and 20 ng/ml.

Prostate specific antigen density as a prognostic factor for patients with prostate carcinoma treated with radiotherapy

BACKGROUND

The pretreatment serum prostate specific antigen level (PSAL) is the most significant predictor of biochemical and local failure in patients treated with definitive radiotherapy. The role of prostate specific antigen (PSA) density (PSAD) relative to PSAL for such patients is controversial. In this article, we describe a comparative analysis of the prognostic value of PSAL and PSAD.

METHODS

The study was comprised of 365 patients who were treated with external beam radiotherapy for regionally localized (T1-T4, Nx, M0) adenocarcinoma of the prostate between 1987-1993 and in whom PSAL and pretreatment prostate volume by transrectal ultrasound were available. The mean and median doses were 66.8 Gy and 66 Gy. Median follow-up for those patients living was 27 months. The mean PSAL was 12.7 ng/mL with a median of 9.1 ng/mL. PSAD was calculated by dividing the PSAL by the pretreatment prostate transectal ultrasound volume (in cc). The mean PSAD was 0.44 and the median was 0.31. Biochemical failure was defined as two consecutive increases in follow-up PSAs, one increase by a factor of greater than 1.5 of an absolute increase of greater than 1 ng/mL.

RESULTS

The distributions of PSAD and PSAL were similar and were positively skewed. When log-transformed, the distributions of both parameters were normalized and linear regression revealed a high correlation (P < 0.0001). PSAD was significantly associated with several potential prognostic factors, including stage, Gleason score, PSAL, and pretreatment prostatic acid phosphatase. Univariate analyses of PSAD and PSAL revealed that these were the most significant correlates of local and biochemical control. By contrast, stage and Gleason score were the only factors predictive of freedom from distant metastasis. Multivariate analyses using Cox proportional hazards models were then performed to determine if PSAD provided prognostic information independent of PSAL. The manner in which PSAD and PSAL were categorized (four, three, of two groups) dramatically influenced the significance of these covariates. Optimization of these groups for significance showed grouped PSAD to be the stronger predictor of the local control and grouped PSAL to be the stronger predictor of biochemical control. However, when PSAD and PSAL were used as continuous variables, PSAL was the only independently significant prognostic factor for local or biochemical control.

CONCLUSIONS

PSAD was highly correlated with actuarial patient outcome in the univariate analyses and appeared to provide independent information when PSAL was between 4 and 20 ng/mL. However, the differences based on PSAD were relatively small and, therefore, not clinically useful.