Extent of extracapsular extension: Implications for planning for conformal radiotherapy and brachytherapy

Brachytherapy for carcinoma of the prostate: techniques, patient selection, and clinical outcomes

Brachytherapy for prostate carcinoma has developed as either low dose rate permanent implants or high dose rate afterloading. Both approaches offer unsurpassed dose escalation and, particularly with permanent implants, the convenience of a single outpatient treatment. These therapies have now entered the mainstream of treatment options and are in the refinement phase of development. Techniques of implantation, treatment planning approaches, innovative fractionation schemes, and appropriate patient selection are the subject of current investigation. Treatment results are available beyond 10 years and appear equivalent or superior to other modalities. Although short term morbidity can be significant with brachytherapy, most current series report low long-term urinary and rectal complications. Meaningful quality of life studies and randomized cooperative group trials are now underway and should help define the role of brachytherapy in the near future.

Standardization of prostate brachytherapy treatment plans

PURPOSE

Whereas custom-designed plans are the norm for prostate brachytherapy, the relationship between linear prostate dimensions and volume calls into question the routine need for customized treatment planning. With the goal of streamlining the treatment-planning process, we have compared the treatment margins (TMs) achieved with one standard plan applied to patients with a wide range of prostate volumes.

METHODS AND MATERIALS

Preimplant transrectal ultrasound (TRUS) images of 50 unselected University of Washington patients with T1-T2 cancer and a prostate volume between 20 cc and 50 cc were studied. Patients were arbitrarily grouped into categories of 20-30 cc, 30-40 cc, and 40-50 cc. A standard 19-needle plan was devised for patients in the 30- to 40-cc range, using an arbitrary minimum margin of 5 mm around the gross tumor volume (GTV), making use of inverse planning technology to achieve 100% coverage of the target volume with accentuation of dose at the periphery and sparing of the central region. The idealized plan was applied to each patient's TRUS study. The distances (TMs) between the prostatic edge (GTV) and treated volume (TV) were determined perpendicular to the prostatic margin.

RESULTS

Averaged over the entire patient group, the ratio of thickness to width was 1.4, whereas the ratio of length to width was 1.3. These values were fairly constant over the range of volumes, emphasizing that the prostate retains its general shape as volume increases. The idealized standard plan was overlaid on the ultrasound images of the 17 patients in the 30- to 40-cc group and the V100, the percentage of target volume receiving 100% or more of the prescription dose, was 98% or greater for 15 of the 17 patients. The lateral and posterior TMs fell within a narrow range, most being within 2 mm of the idealized 5-mm TM. To estimate whether a 10-cc volume-interval stratification was reasonable, the standard plan generated from the 30- to 40-cc prostate model was applied to 5 patients each from the 20- to 30-cc group and the 40- to 50-cc group. Using the standard plan designed for the 30- to 40-cc group, the TMs were closer to 10 mm than to 5 mm for the smaller volume glands and too small for the larger volume ones, assuming an ideal margin of 5 mm.

CONCLUSION

The application of standardized plans to prostate brachytherapy is feasible. Stratifying the volume in 10-cc intervals appears to be adequate, suggesting that the majority of cases appropriate for treatment with brachytherapy might be treated with three standard plans. While the authors believe that the use of a limited number of standard treatment plans is feasible, practical, and medically acceptable, it should be emphasized that the use of a standard plan should always be previewed by computer-aided application to the particular patient's planning images.

Short-course intensity-modulated radiotherapy for localized prostate cancer with daily transabdominal ultrasound localization of the prostate gland

PURPOSE

To present our initial observations on the clinical feasibility of the technique of short-course intensity-modulated radiotherapy (SCIM-RT) in the treatment of localized prostate cancer coupled with daily transabdominal ultrasound localization of the prostate. The proposed regimen consists of a hypofractionated course delivering 70.0 Gy in 28 fractions.

METHODS AND MATERIALS

The treatment data of the first 51 patients treated with SCIM-RT at the Cleveland Clinic Foundation are presented in this report. The technique consisted of intensity-modulated radiotherapy using 5 static fields (anterior, 2 laterals, and 2 anterior obliques). Inverse plans were generated by the Corvus treatment-planning system. The treatment delivery was performed with a Varian Dynamic Multileaf Collimator. The target was the prostate only in patients with low-risk disease (stage T1-T2, pretreatment PSA < or =10, and biopsy Gleason < or =6). The target was the prostate and seminal vesicles in patients with high-risk disease (stage T3 or pretreatment PSA > 10 or biopsy Gleason > or =7). In the Corvus planning system, the margins for the planning target volume (PTV) were 4 mm posteriorly, 8 mm laterally, and 5 mm in all other directions. A total of 70.0 Gy (mean prostate dose approximately 75 Gy) was prescribed in all cases at 2.5 Gy per fraction to be delivered in 28 fractions over 5 1/2 weeks. Prior to treatment delivery, the patients were minimally immobilized on the treatment table, only using lasers and skin marks. The location of the prostate gland was verified daily with the BAT transabdominal ultrasound system and patient position adjustments were performed accordingly. Fifty-one patients completed therapy between October 1998 and May 1999.

RESULTS

The dose was prescribed to an isodose line ranging from 82.0% to 90.0% (mean: 87.2%). The range of the individual prostate mean doses was 73.5 to 78.5 Gy (average: 75.3 Gy). The range of the maximum doses was 77.4 to 84.5 Gy (average: 80.2 Gy). The range of the minimum doses was 64.3 to 69.2 Gy (average: 67.5 Gy). The average time for the prostate position verification and alignment of the prostate using the BAT system was 5 minutes. The entire localization/alignment process was performed by the radiation therapists. The daily alignment images were automatically saved and reviewed by the radiation oncologist, a process similar to port film checks. The total treatment (beam-on) time was around 6 minutes using the 5 static intensity-modulated fields. The mean and standard deviation (SD) of bladder volumes irradiated to 50, 60, and 70 Gy were as follows: 24 +/- 11 cc, 16 +/- 8 cc, and 8 +/- 6 cc. The mean and SD of rectal volumes irradiated to 50, 60, and 70 Gy were as follows: 22 +/- 11 cc, 15 +/- 8 cc, and 7 +/- 5 cc. The RTOG acute bladder toxicity scores were as follows: 0 in 3 (6%), 1 in 38 (74%), and 2 in 10 (20%). The RTOG acute rectal toxicity scores for SCIM-RT cases were as follows: 0 in 10 (20%), 1 in 33 (65%), and 2 in 8 (16%). No Grade 3 or 4 acute toxicities were observed.

CONCLUSION

The delivery of our proposed hypofractionated-schedule SCIM-RT in combination with daily target localization/alignment with the BAT transabdominal ultrasound system is clinically feasible. It is an alternative method of dose escalation in the treatment of localized prostate cancer. The proposed schedule would significantly increase convenience to patients due to the decrease in overall treatment time. Preliminary acute toxicity results are extremely encouraging. Long-term follow-up is needed to assess late complications and treatment efficacy.