Comparison of treatment techniques for conformal radiotherapy of the prostate using dose-volume histograms and normal tissue complication probabilities

The efficacy of conventional external beam, three-dimensional conformal, intensity-modulated, particle beam radiation, and brachytherapy for localized prostate cancer

Technologic advances in radiation treatment planning and delivery have generated popular interest in the different radiation therapy techniques used in treating patients with localized prostate cancer. Throughout the past decade, high-energy (> 4 MV) linear accelerators have largely replaced Cobalt machines in external beam radiation therapy (EBRT) delivery. Conventional EBRT has been used to treat prostate cancer successfully since the 1950s. By switching to computed tomography-based planning, three-dimensional conformal radiation therapy provides better relative conformality of dose than does conventional EBRT. Intensity-modulated radiation therapy (IMRT) has further refined dose conformality by spreading the low-dose region to a larger volume. However, the potential long-term risks of larger volumes of normal tissues receiving low doses of radiation in IMRT are unknown. Particle-beam radiation therapy offers unique dose distributions and characteristics with higher relative biologic effect and linear energy transfer. Transperineal prostate brachytherapy offers the shortest treatment time with equivalent efficacy without significant risk of radiation exposure. The addition of hormonal therapy to radiation therapy has been shown to improve the outcome of radiation therapy.

Simplified intensity-modulated arc therapy for dose escalated prostate cancer radiotherapy

Simplified intensity-modulated arc therapy (SIMAT) employs forward planned, conformal, and avoidance arc combinations with dynamic multileaf collimation (MLC) as a simpler alternative to other forms of intensity-modulated radiotherapy (IMRT). In this work, we compare SIMAT with 4-field (4F) and 6-field (6F) 3D conformal radiation therapy (CRT) for prostate cancer treatment. Prostate, seminal vesicle, bladder, and rectum were contoured on the CT images of 10 patients being planned for radiotherapy. Two planning target volumes (PTV) were defined: PTV1 (prostate + seminal vesicles + 1.0-cm margin) and PTV2 (prostate + 1.0-cm margin). SIMAT, 4F, and 6F plans were generated with a prescription dose of 78 Gy to prostate and 54 Gy to the seminal vesicles. Differences in the 3 techniques in terms of target and rectal coverage were compared. In addition, dose distributions of the SIMAT plans were verified with measurements in a phantom. Mean dose to PTV2 (4F, 76 Gy; 6F, 78 Gy; SIMAT, 76 Gy) and the dose delivered to 95% of the target volume (D(95)) were similar between the 3-techniques. Target conformity was better with SIMAT. Mean dose and calculated NTCP for the rectum were lower for SIMAT than those for 4F and 6F plans (4F 55.6 Gy vs. 6F 49.0 Gy vs. SIMAT 42.7 Gy). Mean dose to femoral heads was lower for the 4F technique vs. 6F and SIMAT techniques (4F 44.5 Gy vs. 6F 48.9 Gy vs. SIMAT 49.5 Gy). In-phantom measurement demonstrated good agreement between the plans and SIMAT treatments delivered in phantom. We concluded that SIMAT demonstrates advantages over 4F and 6F in terms of target conformity mean rectal dose and NTCP with good reproducibility in phantom. On the basis of this analysis, we have commenced a clinical pilot study of SIMAT for prostate cancer radiotherapy.

Prospective evaluation of urinary and intestinal side effects after BeamCath stereotactic dose-escalated radiotherapy of prostate cancer

BACKGROUND

New data suggest that a higher radiation dose will improve outcome in treatment of localized prostate cancer. External beam radiotherapy (EBRT) may on the other hand induce disturbances in the patient's urinary and intestinal function. Since 1997, 195 patients have been treated with a stereotactic boost of 4-8 Gy added to conventional 70 Gy EBRT. Late side effects were prospectively evaluated 3 years after dose-escalated EBRT.

METHODS

Urinary and intestinal problems were prospectively evaluated with a validated self-assessment questionnaire, the Prostate Cancer Symptom Scale (PCSS). Two hundred and eighty-seven patients completed the questionnaire at the 1 year follow-up, and 153 at 3 years after treatment. Pre-treatment mean age was 66 years. One hundred and sixty-eight patients were treated with the conformal technique and 195 were treated with the dose-escalated stereotactic BeamCath technique. Mean total dose in the conformal group (< or =70 Gy) was 66 Gy (60.8-70.4 Gy). The dose-escalated group consists of three dose levels, 74 Gy (n = 68), 76 Gy (n = 74), and 78 Gy (n = 53).

RESULTS

Analyzing the whole population 3 years after treatment, urgency and starting problems decreased in comparison to pre-treatment. A minor increase in urinary incontinence was reported 3 years after treatment in comparison to pre-treatment. No increases in other urinary symptoms were reported. Intestinal symptoms were slightly increased during the follow-up period in comparison to pre-treatment. Dose escalation with stereotactic EBRT (74-78 Gy) did not increase gastrointestinal or genitourinary late side effects at 1 year or 3 years in comparison to doses < or =70 Gy.

CONCLUSIONS

The stereotactic BeamCath EBRT technique facilitates safe dose escalation of patients with prostate cancer.

2-CAT: 2-concentric arc technique

We used conventional three-dimensional (3D) planning software and blocking to design a radiation dose distribution in the shape of a hollow sphere. The technique, known as 2-CAT, employs arcing beams with blocking of the center of the field, along with partial transmission blocking of the poles of the portal. The central core can subsequently be irradiated to deliver a relatively even dose to the entire volume. The technique differs from conventional planning in that the central portion of the tumor, while surrounded, is not included in the initial treatment volume. The clinical usefulness of the method will require future testing, as the technique has not yet been clinically proven.

Radiotherapy of prostate cancer with or without intensity modulated beams: a planning comparison

PURPOSE

To evaluate whether intensity modulated radiotherapy (IMRT) by static segmented beams allows the dose to the main portion of the prostate target to escalate while keeping the maximal dose at the anterior rectal wall at 72 Gy. The value of such IMRT plans was analyzed by comparison with non-IMRT plans using the same beam incidences.

METHODS AND MATERIALS

We performed a planning study on the CT data of 32 consecutive patients with localized adenocarcinoma of the prostate. Three fields in the transverse plane with gantry angles of 0 degrees, 116 degrees, and 244 degrees were isocentered at the center of gravity of the target volume (prostate and seminal vesicles). The geometry of the beams was determined by beam's eye view autocontouring of the target volume with a margin of 1.5 cm. In study 1, the beam weights were determined by a human planner (3D-man) or by computer optimization using a biological objective function with (3D-optim-lim) or without (3D-optim-unlim) a physical term to limit target dose inhomogeneity. In study 2, the 3 beam incidences mentioned above were used and in-field uniform segments were added to allow IMRT. Plans with (IMRT-lim) or without (IMRT-unlim) constraints on target dose inhomogeneity were compared. In the IMRT-lim plan, target dose inhomogeneity was constrained between 15% and 20%. After optimization, plans in both studies were normalized to a maximal rectal dose of 72 Gy. Biological (tumor control probability [TCP], normal tissue complication probability [NTCP]) and physical indices for tumor control and normal tissue complication probabilities were computed, as well as the probability of the uncomplicated local control (P+).

RESULTS

The IMRT-lim plan was superior to all other plans concerning TCP (p < 0.0001). The IMRT-unlim plan had the worst TCP. Within the 3D plans, the 3D-optim-unlim had the best TCP, which was significantly different from the 3D-optim-lim plan (p = 0.0003). For rectal NTCP, both IMRT plans were superior to all other plans (p < 0.0001). The IMRT-unlim plan was significantly better than the IMRT-lim plan (p < 0.0001). Again, 3D-optim-unlim was superior to the other 3D plans (p < 0. 0007). Physical endpoints for target showed the mean minimal target dose to be the lowest in the IMRT-unlim plan, caused by a large target dose inhomogeneity (TDI). Medial target dose, 90th percentile, and maximal target dose were significantly higher in both IMRT plans. Physical endpoints for the rectum showed the IMRT-unlim plan to be superior compared to all other plans. There was a strong correlation between the 65th percentile (Rp65) and rectal NTCP (correlation coefficient > or =89%). For bladder, maximal bladder dose was significantly higher in the IMRT-unlim plan compared to all other plans (p < or = 0.0001).P+ was significantly higher in both IMRT-plans than in all other plans. The 3D-optim-unlim plan was significantly better than the two other 3D plans (p < 0.0001).

CONCLUSION

IMRT significantly increases the ratio of TCP over NTCP of the rectum in the treatment of prostate cancer. However, constraints for TDI are needed, because a high degree of TDI reduced minimal target dose. IMRT improved uncomplicated local control probability. In our department, IMRT by static segmented beams is planned and delivered in a cost-effective way. IMRT-lim has replaced non-modulated conformal radiotherapy as the standard treatment for prostate cancer.

The effect of patient position and treatment technique in conformal treatment of prostate cancer

PURPOSE

The relative value of prone versus supine positioning and axial versus nonaxial beam arrangements in the treatment of prostate cancer remains controversial. Two critical issues in comparing techniques are: 1) dose to critical normal tissues, and 2) prostate stabilization.

METHODS AND MATERIALS

Ten patients underwent pretreatment CT scans in one supine and two prone positions (flat and angled). To evaluate normal tissue exposure, prostate/seminal vesicle volumes or prostate volumes were expanded 8 mm and covered by the 95% isodose surface by both 6-field axial and 4-field nonaxial techniques. A total of 280 dose-volume histograms (DVHs) were analyzed to evaluate dose to rectal wall and bladder relative to patient position and beam arrangement. A CT scan was repeated in each patient after 5 weeks of treatment. Prostate motion was assessed by comparing early to late scans by three methods: 1) center of mass shift, 2) superior pubic symphysis to anterior prostate distance, and 3) deviation of the posterior surface of the prostate.

RESULTS

For prostate (P) or prostate/seminal vesicle (P/SV) treatments, prone flat was advantageous or equivalent to other positions with regard to rectal sparing. The mechanism of rectal sparing in the prone position may be related to a paradoxical retraction of the rectum against the sacrum, away from the P/SV. Although there was no clear overall preference for beam arrangement, substantial improvements in rectal sparing could be realized for individual patients. In this limited number of patients, there was no convincing evidence prostate position was stabilized by prone relative to supine position.

CONCLUSIONS

Prone flat positioning was advantageous over other positions and beam arrangements in rectal sparing. This study suggests that patient position is a more critical a factor in conformal therapy than beam arrangement, and may improve the safety of dose escalation.