Field displacement during external radiotherapy in prostatic adenocarcinoma treated with radioactive 198Au implants and external irradiation

Four and five dimensional radiotherapy with reference to prostate cancer--definitions, state of the art and further directions--an overview

Radiotherapy (RT) always requires a compromise between tumor control and normal tissue side-effects. Technical innovation in radiation therapy (RT), such as three dimensional RT, is now established. Concerning prostate cancer (PC), it is reasonable to assume that RT of PC will increase in the future. The combination of small margins, a movable target (prostate), few fractions and high doses will probably demand dynamically positioning systems and in real time. This is called four dimensional radiotherapy (4DRT). Moreover, biological factors must be included in new treatments such as hypofractionation schedules. This new era is called five dimensional radiotherapy, 5DRT. In this paper we discuss new concepts in RT in respect to PC.

A review of prostate motion with considerations for the treatment of prostate cancer

The motion of the prostate gland can influence the efficacy of radiation therapy. This article examines the literature concerning prostate gland motion with considerations for the treatment of cancer. The objectives of this review include providing radiation oncologists, medical physicists, and dosimetrists with data to assist in determining the best treatment adaptation for individual patients. The prostate gland is not a static structure, but rather a dynamic structure and this should be a consideration in the treatment protocol. The treatment planning personnel must add a margin to the clinical treatment volume (CTV) radiation field to account for prostate motion and patient setup errors resulting in a planning treatment volume (PTV). The movement of the prostate in a radiation field with a small margin to protect the anterior rectum may allow the posterior aspect of the gland to escape the prescribed dose. Thus, an understanding of potential prostate movements in radiation therapy is critical to achieve tumor control and minimize radiation complications in patients.

Postoperative radiotherapy after prostatectomy--a review

PURPOSE

The management of prostate adenocarcinomas using postoperative irradiation is a controversial question. The purpose of this study was to review the literature on the subject.

MATERIAL AND METHODS

A total of 417 articles dealing with postoperative radiotherapy after radical prostatectomy in English literature (1990-2002) were reviewed in aspects of effect on survival, time of irradiation, risk factors, dose and technique and side effects.

RESULTS AND DISCUSSION

No randomised studies have been performed and therefore no definitive conclusive data can be made concerning the efficiency of the concept. However, postoperative radiotherapy appears to increase local control preferably in pT3/4 prostatic carcinomas with seminal vesicles involvement and/or positive margins and/or high Gleason score and high postoperative PSA level. It has not been shown to improve survival. Severe side effects are reported in a low frequency. However, postoperative irradiation can cause severe side effects and postoperative adjuvant/salvage treatments should be delivered earliest 3-6 months after surgery and the total dose delivered to the prostate bed should be 65-70 Gy. Postoperative radiotherapy induces improved local control in patients with positive surgical margins and in patients with a local relapse, preferably if the tumour is small (i.e. PSA <1-2 ng/mL).

Positioning errors and prostate motion during conformal prostate radiotherapy using on-line isocentre set-up verification and implanted prostate markers

PURPOSE

To evaluate treatment errors from set-up and inter-fraction prostatic motion with port films and implanted prostate fiducial markers during conformal radiotherapy for localized prostate cancer.

METHODS

Errors from isocentre positioning and inter-fraction prostate motion were investigated in 13 men treated with escalated dose conformal radiotherapy for localized prostate cancer. To limit the effect of inter-fraction prostate motion, patients were planned and treated with an empty rectum and a comfortably full bladder, and were instructed regarding dietary management, fluid intake and laxative use. Field placement was determined and corrected with daily on-line portal imaging. A lateral portal film was taken three times weekly over the course of therapy. From these films, random and systematic placement errors were measured by matching corresponding bony landmarks to the simulator film. Superior-inferior and anterior-posterior prostate motion was measured from the displacement of three gold pins implanted into the prostate before planning. A planning target volume (PTV) was derived to account for the measured prostate motion and field placement errors.

RESULTS

From 272 port films the random and systematic isocentre positioning error was 2.2 mm (range 0.2-7.3 mm) and 1.4 mm (range 0.2-3.3 mm), respectively. Prostate motion was largest at the base compared to the apex. Base: anterior, standard deviation (SD) 2.9 mm; superior, SD 2.1 mm. Apex: anterior, SD 2.1 mm; superior, SD 2.1 mm. The margin of PTV required to give a 99% probability of the gland remaining within the 95% isodose line during the course of therapy is superior 5.8 mm, and inferior 5.6 mm. In the anterior and posterior direction, this margin is 7.2 mm at the base, 6.5 mm at the mid-gland and 6.0 mm at the apex.

CONCLUSIONS

Systematic set-up errors were small using real-time isocentre placement corrections. Patient instruction to help control variation in bladder and rectal distension during therapy may explain the observed small SD for prostate motion in this group of patients. Inter-fraction prostate motion remained the largest source of treatment error, and observed motion was greatest at the gland base. In the absence of real-time pre-treatment imaging of prostate position, sequential portal films of implanted prostatic markers should improve quality assurance by confirming organ position within the treatment field over the course of therapy.

A prospective comparison of three systems of patient immobilization for prostate radiotherapy

PURPOSE

The study compared the setup reliability of 3 patient immobilization systems, a rubber leg cushion, the alpha cradle, and the thermoplastic Hipfix device, in 77 patients with cT1-T3, N0, M0 prostate cancer receiving conformal radiotherapy.

METHODS AND MATERIALS

Port films were analyzed and compared to simulation films to estimate the setup errors in the three coordinate axes (anterior-posterior, cranial-caudal, medial-lateral). A total vector error was calculated from these shifts.

RESULTS

The Hipfix was found significantly superior to the other two devices in reducing mean setup errors in all axes (p < 0.005). The average field-positioning error with the Hipfix ranged from 1.9 mm to 2.6 mm for all axes, whereas the deviation for the other two systems ranged from 2.7 to 3. 4 mm. Errors greater than 10 mm were virtually eliminated with the Hipfix system. There was a reduction in the mean total vector error in the alpha cradle and Hipfix patient cohorts over time, reflecting improved efficacy as a result of experience.

CONCLUSION

There was a significant difference in the performance of each immobilization device. The Hipfix was consistently more reliable in reducing setup errors than the other devices.

[Conformal radiotherapy of prostatic cancer: a general review]

Recent progress in radiotherapeutic management of localized prostate cancer is reviewed. Clinical aspects--including dose-effect beyond 70 Gy, relative role of conformal radiation therapy techniques and of early hormonal treatment--are discussed as well as technical components--including patient immobilization, organ motion, prostate contouring, beam arrangement, 3-D treatment planning and portal imaging. The local control and biological relapse-free survival rates appear to be improved by high dose conformal radiotherapy from 20 to 30% for patients with intermediate and high risk of relapse. A benefit of overall survival is expected but not yet demonstrated. Late reactions, especially the rectal toxicity, remain moderate despite the dose escalation. However, conformal radiotherapy demands a high precision at all steps of the procedure.

Patient positioning using magnetic implants and magnetic field sensors

A phantom study was conducted in order to evaluate the precision and reproducibility of a magnetic field positioning system using magnetic implants and magnetic field sensors. Three implants and three magnetic field sensors were used to position a phantom on a Simulix Y simulator; x-ray films were used as reference. The reproducibility of the position determination of the three magnetic field sensors was checked three times in five different positions in both the X and Y dimensions of the sensors. The phantom was then positioned by the system five times and the displacement errors of four markers in the periphery of the phantom were noted. A reference x-ray film was exposed before the positioning procedure. An error of one millimetre was permitted in each dimension in one sensor. Only the maximum displacement errors of one of the four markers were noted. In the first reproducibility test the system was found to miss 1 mm in one reading out of 90 position readings. In the second part, the mean for the maximum displacement error was 0.46 and 0.6 mm for the maximum frontal and lateral displacements respectively, with a maximal error of 1.3 mm.

Irradiation of localized prostatic carcinoma with a combination of high dose rate iridium-192 brachytherapy and external beam radiotherapy with three target definitions and dose levels inside the prostate gland

PURPOSE

Localized prostate cancer was treated with combined external beam radiotherapy and high dose rate Ir-192 brachytherapy with the purpose of a high dose. The technical aspects of a modified treatment are described.

METHODS

The brachytherapy was given in two sessions preceded and succeeded by external beam radiation. The radioactive source was temporarily implanted by a remote afterloading device through six to 15 needles inserted transperineally guided by transrectal ultrasound. The entire prostate gland was included in the clinical target volume. The urethra and the tumour volume could be defined and irradiated to different dose levels in more than 90% of the patients.

RESULTS

Fifty-four patients were treated. The total dose to the prostate was approximately 70 Gy and to the tumour volume 80 Gy. By calculating the corresponding dose given by 2.0 Gy fractions, considering the radiobiology by using the LQ formula and assuming an alpha/beta value for prostate tissue of 10, the dose to the prostate was approximately 84 Gy and to the tumour volume 112 Gy. For the late effects to the urethra an alpha/beta value of 3 was used, which corresponds to 85 Gy. The brachytherapy could be given with accuracy except when the dorsal border of the prostate was concave. The dose distribution then tended to be less satisfactory. Post-treatment calculations showed that the maximum dose to the rectum was 67 Gy (radiobiologically corrected to 88 Gy), given in a small volume. The early side effects from the brachytherapy were minimal. The treatment could not be performed as intended in four patients; three patients had a narrow pelvis and in one patient the prostate was unusually resilient, preventing the needles from being positioned properly.

CONCLUSIONS

This modification of a previously reported brachytherapy technique for prostate carcinoma permits a high radiation dose to the tumour and to the prostate gland, which ultimately may improve local control.