Radiotherapy of Breast Cancer in Laterally Tilted Prone vs. Supine Position: What about the Internal Mammary Chain?

BACKGROUND: In the multimodal breast-conserving curative therapy of some high-risk breast cancer patients, extended external beam radiotherapy (EBRT) not only to the breast but also to the supraclavicular fossa and the internal mammary chain (parasternal region (PSR)) is indicated. We report a dosimetric study on the EBRT of the breast ("B") and the breast including PSR ("B + PSR"), comparing the supine and the laterally tilted prone patient positions in free breathing. METHODS: The planning CT scans of 20 left- and 20 right-sided patients were analyzed. EBRT plans were calculated with 3D conformal EBRT (3D) and with intensity-modulated EBRT (IMRT) for "B" and "B + PSR" in the prone and supine positions. The mean and threshold doses were computed. The quality of EBRT plans was compared with an overall plan assessment factor (OPAF), comprising three subfactors, homogeneity, conformity, and radiogenic exposure of OAR. RESULTS: In the EBRT of "B", prone positioning significantly reduced the exposure of the OARs "heart" and "ipsilateral lung" and "lymphatic regions". The OPAF was significantly better in the prone position, regardless of the planning technique or the treated breast side. In the EBRT of "B + PSR", supine positioning significantly reduced the OAR "heart" exposure but increased the dose to the OARs "ipsilateral lung" and "lymphatic regions". There were no significant differences for the OPAF, independent of the irradiated breast side. Only the IMRT planning technique increased the chance of a comparatively good EBRT plan. CONCLUSION: Free breathing prone positioning significantly improves plan quality in the EBRT of the breast but not in the EBRT of the breast + PSR.

Comparison of different contouring definitions of the rectum as organ at risk (OAR) and dose-volume parameters predicting rectal inflammation in radiotherapy of prostate cancer: which definition to use?

OBJECTIVE: The objective of this retrospective planning study was to find a contouring definition for the rectum as an organ at risk (OAR) in curative three-dimensional external beam radiotherapy (EBRT) for prostate cancer (PCa) with a predictive correlation between the dose-volume histogram (DVH) and rectal toxicity. METHODS: In a pre-study, the planning CT scans of 23 patients with PCa receiving definitive EBRT were analyzed. The rectum was contoured according to 13 different definitions, and the dose distribution was correlated with the respective rectal volumes by generating DVH curves. Three definitions were identified to represent the most distinct differences in the shapes of the DVH curves: one anatomical definition recommended by the Radiation Therapy Oncology Group (RTOG) and two functional definitions based on the target volume. In the main study, the correlation between different relative DVH parameters derived from these three contouring definitions and the occurrence of rectal toxicity during and after EBRT was studied in two consecutive collectives. The first cohort consisted of 97 patients receiving primary curative EBRT and the second cohort consisted of 66 patients treated for biochemical recurrence after prostatectomy. Rectal toxicity was investigated by clinical investigation and scored according to the Common Terminology Criteria for Adverse Events. Candidate parameters were the volume of the rectum, mean dose, maximal dose, volume receiving at least 60 Gy (V60), area under the DVH curve up to 25 Gy and area under the DVH curve up to 75 Gy in dependence of each chosen rectum definition. Multivariable logistic regression considered other clinical factors such as pelvine lymphatics vs local target volume, diabetes, prior rectal surgery, anticoagulation or haemorrhoids too. RESULTS: In Cohort 1 (primary EBRT), the mean rectal volumes for definitions "RTOG", planning target volume "(PTV)-based" and "PTV-linked" were 100 cm3 [standard deviation (SD) 43 cm3], 60 cm3 (SD 26 cm3) and 74 cm3 (SD 31 cm3), respectively (p < 0.01; analysis of variance). The mean rectal doses according to these definitions were 35 Gy (SD 8 Gy), 48 Gy (SD 4 Gy) and 44 Gy (SD 5 Gy) (p < 0.01). In Cohort 2 (salvage EBRT), the mean rectal volumes were 114 cm3 (SD 47 cm3), 64 cm3 (SD 26 cm3) and 81 cm3 (SD 30 cm3) (p < 0.01) and the mean doses received by the rectum were 36 Gy (SD 8 Gy), 49 Gy (SD 5 Gy) and 44 Gy (SD 5 Gy) (p < 0.01). Acute or subacute rectal inflammation occurred in 69 (71.9%) patients in Cohort 1 and in 43 (70.5%) in Cohort 2. We did not find a correlation between all investigated DVH parameters and rectal toxicity, irrespective of the investigated definition. By adding additional variables in multivariate analysis, the predictive ability was substantially improved. Still, there was essentially no difference in the probability of predicting rectal inflammation occurrence between the tested contouring definitions. CONCLUSION: The RTOG anatomy-based recommendations are questionable in comparison with functional definitions, as they result in higher variances in several relative DVH parameters. Moreover, the anatomy-based definition is no better and no worse in the predictive value concerning clinical end points. Advances in knowledge: Functional definitions for the rectum as OAR are easier to apply, faster to contour, have smaller variances and do not offer less information than the anatomy-based RTOG definition.

Tangential vs. defined radiotherapy in early breast cancer treatment without axillary lymph node dissection: a comparative study.

PURPOSE: Recent studies have demonstrated low regional recurrence rates in early-stage breast cancer omitting axillary lymph node dissection (ALND) in patients who have positive nodes in sentinel lymph node dissection (SLND). This finding has triggered an active discussion about the effect of radiotherapy within this approach. The purpose of this study was to analyze the dose distribution in the axilla in standard tangential radiotherapy (SRT) for breast cancer and the effects on normal tissue exposure when anatomic level I-III axillary lymph node areas are included in the tangential radiotherapy field configuration. PATIENTS AND METHODS: We prospectively analyzed the dosimetric treatment plans from 51 consecutive women with early-stage breast cancer undergoing radiotherapy. We compared and analyzed the SRT and the defined radiotherapy (DRT) methods for each patient. The clinical target volume (CTV) of SRT included the breast tissue without specific contouring of lymph node areas, whereas the CTV of DRT included the level I-III lymph node areas. RESULTS: We evaluated the dose given in SRT covering the axillary lymph node areas of level I-III as contoured in DRT. The mean VD95% of the entire level I-III lymph node area in SRT was 50.28% (range, 37.31-63.24%), VD45 Gy was 70.1% (54.8-85.4%), and VD40 Gy was 83.5% (72.3-94.8%). A significant difference was observed between lung dose and heart toxicity in SRT vs. DRT. The V20 Gy and V30 Gy of the right and the left lung in DRT were significantly higher in DRT than in SRT (p<0.001). The mean heart dose in SRT was significantly lower (3.93 vs. 4.72 Gy, p=0.005). CONCLUSION: We demonstrated a relevant dose exposure of the axilla in SRT that should substantially reduce local recurrences. Furthermore, we demonstrated a significant increase in lung and heart exposure when including the axillary lymph nodes regions in the tangential radiotherapy field set-up.