Planning study for Merkel cell carcinoma based on the relapse pattern.

PURPOSE: To develop a technique for radiation (RT) of in-transit path ways (IT) in Merkel cell carcinoma. METHOD: In the planning study, IT were ink-marked on the skin during sentinel lymphscintigraphy and wire-marked in planning-CT. Pre- and post-operative planning-CTs were acquired. The clinical target volume (CTV) included tumor bed plus safety margin, IT and draining nodes, the planning volume (PTV) the CTV plus 0.5-1cm margin. VMAT plans with 2-3 arcs were analyzed. RESULTS: A planning study was performed for five pts. including two pts. with primary tumor (PT) in head and neck, 1 pt. each with PT of elbow, forearm and upper leg respectively. Plans showed satisfactory PTV coverage: Dmean 100%±0%, D98% 92.4%±2.24%, homogeneity index (HI) 0.095±0.01, conformation number (CN) 0.84±0.01 and conformality index (CI) 0.95±0.01. CONCLUSION: The planning study confirms feasibility of highly conformal irradiation of IT pathways based on individualized target delineation. Currently, patients referred for non-metastatic MCC are encouraged to enroll in a prospective clinical study that evaluates the feasibility of radiation of IT pathways.

Influence of organ at risk definition on rectal dose-volume histograms in patients with prostate cancer undergoing external-beam radiotherapy.

PURPOSE: To evaluate rectal dose-volume relations during three-dimensional conformal radiotherapy of patients with prostate cancer by means of different rectal volume contours. PATIENTS AND METHODS: 55 patients with prostate cancer underwent three-dimensional conformal external-beam radiotherapy. Rectal dose-volume histograms were calculated for four separately contoured rectal volumes in all patients resulting in four groups. In group 1 the outer rectal wall was contoured two CT slices above and below the planning target volume. The rectal contour of group 2 was drawn from the anal verge up to the sigmoid. Furthermore, the posterior half of the rectum was contoured for both volumes mentioned above (groups 1a and 2a). Statistical analysis was then performed using nonparametric Wilcoxon tests. RESULTS: The mean target dose was 72.9 Gy (standard deviation [SD] +/- 2.1 Gy). The minimum target dose was 70.2 Gy. Mean rectum dose (+/- SD) over all patients was 50.7 Gy (+/- 4.6 Gy), 45.2 Gy (+/- 5.4 Gy), 43.2 Gy (+/- 4.2 Gy), and 38.7 Gy (+/- 5.5 Gy) for group 1, 2, 1a, and 2a, respectively. The corresponding volumes receiving > or = 70 Gy for groups 1 and 2 were 14.0% (+/- 5.3%) and 11.9% (+/- 4.5%). These differences were statistically significant. Comparison of minimum and mean rectal dose also revealed a statistically significant difference toward higher doses in groups 1 and 1a (p < 0.001). Maximum rectal doses for groups 1 and 2 as well as for groups 1a and 2a revealed no statistically significant difference (p = 1.0). CONCLUSION: Data from the literature on normal-tissue complication probability (rectal bleeding) refer to different rectal contours. When applying dose restrictions to the rectum, contouring becomes a significant factor that determines the risk of rectal toxicity. The results of this study show that different ways of rectal contouring significantly influence doses to the rectum. The influence of organ at risk contouring should be considered thoroughly in conformal radiotherapy of prostate cancer patients, especially in dose escalation studies. It is recommended to calculate the doses for absolute rectal volumes and correlate these data with toxicity in order to be able to achieve comparable results among different institutions.

Testicular dose in prostate cancer radiotherapy: impact on impairment of fertility and hormonal function.

PURPOSE: To determine the dose received by the unshielded testicles during a course of 20-MV conventional external-beam radiotherapy for patients with localized prostate cancer. Critical evaluation of the potential impact on fertility and hormonal impairment in these patients according to the literature. PATIENTS AND METHODS: The absolute dose received by the testicles of 20 randomly selected patients undergoing radiotherapy of prostate cancer was measured by on-line thermoluminescence dosimetry. Patients were treated in supine position with an immobilization cushion under their knees. A flexible tube, containing three calibrated thermoluminescence dosimeters (TLDs) was placed on top or underneath the testicle closest to the perineal region with a day-to-day alternation. The single dose to the planning target volume was 1.8 Gy. Ten subsequent testicle measurements were performed on each patient. The individual TLDs were then read out and the total absorbed dose was calculated. RESULTS: The mean total dose (+/- standard deviation) measured in a series of 10 subsequent treatment days in all patients was 49 cGy (+/- 36 cGy). The calculated projected doses made on a standard series of 40 fractions of external-beam radiotherapy were 196 cGy (+/- 145 cGy). The results of this study are appraised with the available data in the literature. CONCLUSION: The dose received by the unshielded testes can be assessed as a risk for permanent infertility and impairment of hormonal function in prostate cancer patients treated with external-beam radiotherapy.

Virtual simulation of a boost field in adjuvant radiotherapy of the breast.

BACKGROUND AND PURPOSE: In CT-based adjuvant radiotherapy of the breast, virtual simulation techniques have been developed. This paper demonstrates a simple virtual simulation of a boost field. MATERIAL AND METHODS: 41 fields were planned virtually, 26 as electron beams, 15 as tangential photon beams. RESULTS: Depending on the user's expertise the geometric accuracy was high; possible sources of error are illustrated. Resulting field sizes tended to be slightly larger compared to conventional simulation when applying the same rules of field definition. Differences in focus-skin distances with consecutive divergence effects as well as partial volume effects were discussed to be causal. CONCLUSION: Virtual simulation of a boost field has the potential to elegantly link the simplicity of a conventional simulation with the accurate tumor bed identification provided by a CT data set. It was shown to be feasible and favorable with regard to the patient, the medical staff, and the simulator time. Moreover, it offers a visualization of dose distributions, which was found helpful in some cases.