Patient positioning in prostate radiotherapy: is prone better than supine?

PURPOSE: To assess potential dose reductions to the rectum and to the bladder with three-dimensional conformal radiotherapy (3D-CRT) to the prostate in the prone as compared with the supine position; and to retrospectively evaluate treatment position reproducibility without immobilization devices. METHODS AND MATERIALS: Eighteen patients with localized prostate cancer underwent pelvic CT scans and 3D treatment planning in prone and supine positions. Dose-volume histograms (DVHs) were constructed for the clinical target volume, the rectum and the bladder for every patient in both treatment positions. "Comparative DVHs" (cDVHs) were defined for the rectum and for the bladder: cDVH was obtained by subtracting the organ volume receiving a given dose increment in the prone position from the corresponding value in the supine position. These values were then integrated over the entire dose range. The prescribed dose to the planning target volume (PTV) was 74 Gy using a 6-field technique. To evaluate reproducibility, portal films were subsequently reviewed in 12 patients treated prone and 10 contemporary patients treated supine (controls). No immobilization devices were used. Deviations in the anterio-posterior (X) and cranio-caudal (Y) axes were measured. Mean treatment position variation, total setup variation, systematic setup variation, and random setup variation were obtained. RESULTS: Prone position was associated with a higher dose to the rectum or to the bladder in 6 (33%) and 7 (39%) patients, respectively. A simultaneously higher dose to rectum and bladder was noted in 2 (11%) patients in prone and in 7 (39%) patients in supine. Rectal and bladder volumes were frequently larger in prone than in supine: mean prone/supine volume ratios were 1.21 (SD, 0.68) and 1.03 (SD, 1.32), respectively. In these cases cDVH analysis more often favored the prone position. Mean treatment position variation and total setup variation were similar for both prone and supine plans. A higher systematic setup variation was observed in prone positioning: 2.7 mm vs. 1.9 mm (X axis) and 4.1 mm vs. 2.2 mm (Y axis). The random variation was similar for both prone and supine: 4. 0 mm vs. 3.6 mm (X axis) and 3.7 mm vs. 3.6 mm (Y axis). CONCLUSIONS: Prone position 3D-CRT is frequently, but not always, associated with an apparent dose reduction to the rectum and/or to the bladder for prostate cancer patients. As suggested by the increased mean prone/supine rectal volume ratio, the advantage of prone positioning for the rectum may be artifactual, at least partly reflecting a position-dependent rectal air volume, which may significantly vary from treatment to treatment. In the absence of immobilization devices, daily setup reproducibility appears less accurate for the prone position, primarily due to systematic setup variations.     

Influence of patient positioning on dose-volume histogram and normal tissue complication probability for small bowel and bladder in patients receiving pelvic irradiation: a prospective study using a 3D planning system and a radiobiological model

Purpose: A prospective study was undertaken to evaluate the influence of patient positioning (prone position using a belly board vs. supine position) on the dose-volume histograms (DVHs) of organs of risk, and to analyze its possible clinical relevance using radiobiological models.

Methods and Materials: From November 1996 to August 1997 a computed tomography (CT) scan was done in the prone position using a belly board and in supine position in 20 consecutive patients receiving postoperative pelvic irradiation because of rectal cancer. Using a three-dimensional (3D) planning system (Helax, TMS®) the DVH for small bowel, bladder, a standard planning target volume (PTV) of postoperative irradiation of rectal cancer, the intersection of volume of PTV and small bowel (PTV ∩ V_SB), respectively, of PTV and bladder (PTV ∩ V_B) were defined in each axial CT slice. The normal tissue complication probability (NTCP) was determined by the radiobiological model of Lyman and Kutcher using the tolerance data of Emami. For evaluation of late toxicity /β ratio was 2.5; for evaluation of acute toxicity, it was 10. Total dose was 50.4 Gy (1.8 Gy/fraction) (ICRU 50).

Results: Using the prone position compared to the supine position, the median volume of PTV ∩ V_B was reduced by 18.5 cm³ (62%). Median dose (related to the reference dose) to the bladder was 44.5% (22.4 Gy) in prone and 66.05% (33.3 Gy) in supine position (p < 0.001). Median V_B within the 90% (45.4 Gy), 80% (40.3 Gy), 60% (30.2 Gy), and 40% (20.2 Gy) isodose was significantly lower in the prone position when compared to the supine position. Using the radiobiological models, however, there was no difference of NTCP between prone position or supine position. In the prone position, median volume of PTV ∩ V_SB was reduced by 32.5 cm³ (54%). The median dose to small bowel was 30.85% (15.4 Gy) in the prone position and 47.35% (23.9Gy) in the supine position (p < 0.001). Significant differences between prone and supine position were found for median V_SB within the 90% (45.4 Gy), 80% (40.3 Gy), 60% (30.2 Gy), and 40% (20.2 Gy) isodose. According to the method of Lyman, median NTCP of small bowel was significant lower in prone than in supine position.

Conclusion: The prone position with a standard belly board should be the standard positioning technique for patients receiving adjuvant postoperative radiation therapy following surgery of rectal cancer. Both irradiated volume and total dose to the organs of risk can be reduced significantly. As a consequence of this, radiation induced toxicity will be minimized.     

子宫颈癌调强放射治疗中不同体位的剂量学研究

 目的　比较分析子宫颈癌调强放射治疗（IMRT）中不同治疗体位对相邻正常器官受照剂量分布和受照体积的影响。方法　11例子宫颈鳞癌ⅡB～ⅢB患者在CT模拟定位机下分别行俯卧位和仰卧位定位扫描,将定位资料传输至治疗计划系统（TPS）,勾画两种不同体位下的临床靶区（CTV）和计划靶区（PTV）,并分别设计两种不同体位IMRT计划。处方剂量：95 %的PTV接受46 Gy（2 Gy／次,23次）,通过剂量体积直方图（DVH）分析比较两种治疗体位下,小肠等器官的不同受照剂量和体积的差别。结果　在符合PTV剂量要求的前提下,采用俯卧位体位小肠的受照体积在46～30 Gy剂量范围内比仰卧位体位时的受照体积明显减小（P＜0.05）,在低剂量范围内（＜20 Gy）,小肠的受照体积减小不明显（P＞0.05）。对膀胱、直肠、股骨头、脊髓两种体位的剂量体积差异无统计学意义（P＞0.05）。结论　子宫颈癌行IMRT时采用俯卧位能更好地保护小肠,建议对子宫颈癌行IMRT时采用俯卧位。     

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.     

A randomized trial of supine vs. prone positioning in patients undergoing escalated dose conformal radiotherapy for prostate cancer.

BACKGROUND AND PURPOSE: The optimal treatment position for patients receiving radical radiation therapy for prostate cancer has been a source of controversy. To resolve this issue, we conducted a randomized trial to evaluate the effects of supine and prone positioning on organ motion, positioning errors, and dose to critical organs during escalated dose conformal irradiation for localized prostate cancer and patient and therapist satisfaction with setup technique. PATIENTS AND METHODS: Twenty eight patients were randomized to commence treatment immobilized in the supine or prone position and were subsequently changed to the alternate positioning for the latter half of their treatment. Patients underwent CT simulation and conformal radiotherapy planning and treatment in both positions. The clinical target volume encompassed the prostate gland. Alternate day lateral port films were compared to corresponding simulator radiographs to measure the isocentre positioning errors (IPE). Prostate motion (PM) and total positioning error (TPE) were measured from the same films by the displacements of three implanted fiducial markers. Dose volume histograms (DVHs) for the two treatment positions were compared at the 95, 80 and 50% dose (D%) levels. The patients and radiation therapists completed weekly questionnaires regarding patient comfort and ease of setup. RESULTS: Seven patients, who started in the supine position, subsequently refused prone position and received their whole treatment supine. Small bowel in the treatment volume, not present in the supine position, prevented one patient from being treated prone. PM in anterior posterior direction was statistically significantly less in the supine position (P<0.05). There was no significant difference in superior inferior PM for the two treatment positions. No statistically significant difference between supine and prone positioning was observed in isocentre positioning error (IPE) or total positioning error (TPE) due to a policy of daily pre-treatment correction. However, more pre-treatment corrections were required for patients in the prone position. The DVH analysis demonstrated larger volumes of the bladder wall, rectal wall and small bowel within the D95, D80 and D50% when comparing the planning target volumes (PTVs) actually treated for prone positioning. When the prone PTV was expanded to account for the greater PM encountered in that position, a statistically significant difference (P<0.007) was observed in favour of the supine position at all dose levels. In the prone position, four patients had small bowel within the 60 Gray (Gy) isodose and in the supine position, no patients had small bowel in the 60 or 38Gy volumes. Supine position was significantly more comfortable for the patients and setup was significantly easier for the radiation therapists. The median patient comfort score was 0.79 (Standard deviation (SD) 0.03) supine and 0.45 (SD 0.05) prone (P<0.001) The therapist convenience of setup was 0.80 (SD 0.016) supine and 0.54 (SD 0.025) prone (P<0.005). No statistically significant difference was seen for the other parameters studied. CONCLUSIONS: We demonstrated significantly less PM in the supine treatment position. There was no difference for either treatment position in IPE or TPE, however, more pre-treatment corrections were required in the prone position. Prone position required a larger PTV with resulting increased dose to critical organs. There were statistically significant improvements at all dose levels for small bowel, rectal wall and bladder wall doses in the supine position once corrections were made for differences in organ motion. Linear analogue scores of patient comfort and radiation therapist convenience demonstrated statistically significant improvement in favour of the supine position. Supine positioning has been adopted as the standard for conformal prostatic irradiation at our centre.     

直肠癌放疗不同技术和体位对小肠受照剂量的比较

目的:分析直肠癌放射治疗过程中,不同放疗技术和不同治疗体位对小肠受照射体积的影响。方法:选取18例直肠癌患者,膀胱充盈的状态下,治疗体位为仰卧位和俯卧位下分别扫描两组定位CT图像,分别传输至计划系统。在两组CT图像上分别制作三维适形（3D-CRT）和调强放射治疗（IMRT）计划,比较小肠在接受不同剂量的受照绝对体积差异（V5~45）。结果:相同体位,IMRT相比3D-CRT,小肠V45明显降低,V15两者基本接近。采用相同放疗技术,俯卧位相比仰卧位小肠V45和V15均明显降低。结论:直肠癌放射治疗,相比放疗技术,治疗体位对小肠受照体积的影响更大。     

Radiation therapy of the pelvic and paraaortic lymph nodes in cervical carcinoma: a prospective three-dimensional analysis of patient positioning and treatment technique.

PURPOSE: Pelvic box fields in prone position are the standard treatment for patients with cervical carcinomas. The issue investigated in this report is whether this technique should also be used when extending the planning target volume to the paraaortic region. MATERIALS AND METHODS: In a prospective study of eight consecutive patients with cervical carcinomas, two patient positions (prone and supine) and three radiation techniques (A, anteroposterior/posteroanterior opposed fields; B, four-field box; and C, three-field technique) were examined concerning the dose to critical organs. The analysis was based on three-dimensional planning, dose-volume histograms and normal tissue complication probabilities (NTCP). RESULTS: Compared to the prone position, the supine position led to improved organ sparing in four of seven organs (liver, both kidneys, spinal canal). In two of seven organs (rectum and bladder) no difference between prone and supine position was observed. The best sparing of small bowel was achieved in prone position. Technique B followed by technique C in the supine position resulted in the best overall sparing of critical organs concerning the volumes receiving the respective TD(5/5) doses or more. Mean NTCP values for liver, rectum and bladder were below 1.0%. The highest values of up to 12% were found for both kidneys in prone position with C and for the spinal canal with A in the prone and supine position. CONCLUSION: According to this analysis, for the treatment of the pelvic and paraaortic lymph node regions together, supine position and technique B (alternatively C) should be preferred despite the advantages of prone position on belly boards for pelvic irradiation alone.     

Pilot study of conformal intensity modulated radiation therapy for localized prostate cancer]

PURPOSE:- To report our experience on treatment planning and acute toxicity in 16 patients suffering from clinically localized prostate cancer treated with high-dose intensity-modulated radiation therapy (IMRT). PATIENTS AND METHODS: - Between March 2001 and October 2002, 16 patients with clinically localized prostate cancer were treated with IMRT. Treatment planning included an inverse-planning approach, and the desired beam intensity profiles were delivered by dynamic multileaf collimation. All patients received the entire treatment course with IMRT to a prescribed dose of 78 Gy. All IMRT treatment plans were compared with a theoretical conventional three-dimensional conformal radiation therapy (3D-CRT). Acute lower gastro-intestinal (GI) and genito-urinary (GU) toxicity was evaluated in all patients and graded according to the Common Toxicity Criteria for Adverse Events version 3.0 (CTCAE v. 3.0). A relationship between dose volume and clinical toxicity was evaluated. RESULTS: - Ninety-five percent of the PTV2 received more than 76 Gy using IMRT or 3D-CRT with no difference between both methods. The dose-volume histogram mean obtained for the PTV2 was not different between IMRT and 3D-CRT. IMRT improved homogeneity of the delivered dose to the PTV2 as compared with 3D-CRT (7.5 vs 9%, respectively). Ninety-five percent of the PTV1 received 5 Gy more using IMRT with protection of the bladder and the rectum walls. The benefit was considered below 75 and 70 Gy for the wall of the bladder and the rectum, respectively. Grade 2 GI and GU toxicity was observed in four (25%) and five (31%) patients, respectively. No grade 3 toxicity was observed. There was a trend towards a relationship between the mean rectal dose and acute rectal toxicity but without statistical significant difference (P =0.09). CONCLUSION: - Dose escalation with IMRT is feasible with no grade 3 or higher acute GI or GU toxicity. Examination of a larger cohort and longer-term follow-up are warranted in the future.     

A dose-escalation trial with the adaptive radiotherapy process as a delivery system in localized prostate cancer: analysis of chronic toxicity

PURPOSE: To evaluate the validity of the chosen adaptive radiotherapy (ART) dose-volume constraints while testing the hypothesis that toxicity would not be greater at higher tumor dose levels. MATERIALS AND METHODS: In the ART dose escalation/selection trial, treatment was initiated with a generic planning target volume (PTV) formed as a 1-cm expansion of the clinical target volume (CTV). After the first week of therapy, the patient was replanned with a patient-specific PTV, constructed with CT and electronic portal images obtained in the first 4 days of treatment. A new multileaf collimator beam aperture was used. A minimum dose prescribed to the patient-specific PTV, ranging 70.2-79.2 Gy, was determined on the basis of the following rectal and bladder constraints: <5% of the rectal wall has a dose >82 Gy, <30% of the rectal wall has a dose >75.6 Gy, <50% of the bladder volume has a dose >75.6 Gy, and the maximum bladder dose is 85 Gy. A conformal four-field and/or intensity-modulated radiotherapy (IMRT) technique was used. Independent reviewers scored toxicities. The worst toxicity score seen was used as per the Common Toxicity Criteria grade scale (version 2). We divided the patients into three separate groups: 70.2-72 Gy, >72-75.6 Gy, and >75.6-79.2 Gy. Toxicities in each group were quantified and compared by the Pearson chi-squared test to validate our dose escalation/selection model. Grades 0, 1, 2, and 3 were censored as none vs. each category and none vs. any. RESULTS: We analyzed patients with follow-up greater than 1 year. The mean duration of follow-up was 29 months (range, 12-46 months). We report on 280 patients, mean age 72 years (range, 51-87 years). Only 60 patients received adjuvant hormones. Mean pretreatment prostate-specific antigen level was 9.3 ng/mL (range, 0.6-120 ng/mL). Mean Gleason score was 6 (range, 3-9). The lowest dose level was given to 49 patients, the intermediate dose to 131 patients, and 100 patients received the highest dose escalation. One hundred eighty-one patients (65%) were treated to a prostate field only and 99 patients (35%) to prostate and seminal vesicles. Chronic genitourinary and/or gastrointestinal categories were incontinence, persistent urinary retention, increased urinary frequency/urgency, urethral stricture, hematuria, diarrhea, rectal pain, bleeding, ulcer, fistula, incontinence, and proctitis. Toxicity at the high dose level was not different from toxicity at the intermediate or lower dose levels. No significant difference was observed in any of the individual toxicity categories. CONCLUSIONS: By applying the ART process--namely, developing a patient-specific PTV--to prostate cancer patients, significant dose escalation can be achieved without increases in genitourinary or gastrointestinal toxicity. Our data validate the rectal and bladder dose-volume constraints chosen for our three-dimensional conformal and IMRT prostrate radiotherapy planning.     

Comparison of biologically equivalent dose–volume parameters for the treatment of prostate cancer with concomitant boost IMRT versus IMRT combined with brachytherapy

BACKGROUND AND PURPOSE: The two main modalities to deliver high dose to the prostate and prevent high doses to neighboring organs are intensity modulated radiotherapy (IMRT) or external beam radiotherapy combined with brachytherapy. Because of the different biological effectiveness the physical dose distributions were converted to 3-dimensional linear quadratic dose at 2 Gy per fraction (EQD(2)). From the latter, cumulative EQD(2)-volume histograms were determined for comparison of the modalities. MATERIAL AND METHODS: An IMRT plan was made on the contoured planning target volume (PTV1) and organs at risk (OAR) of 20 patients (IMRT-only). A dose of 70 Gy was prescribed on the PTV1 with a concomitant boost to a total of 76 Gy on a subvolume (PTV2). Also a 46 Gy IMRT plan was made combined with either a pulsed dose-rate (PDR) or a high dose-rate (HDR) brachytherapy boost. The EQD(2) on the PTV1 of the combined IMRT-PDR and IMRT-HDR plans were made equivalent to the EQD(2) of the 70 Gy IMRT-only plan. The alpha/beta-ratio for prostate was set to 1.5 Gy and 10 Gy. For normal tissues an alpha/beta-ratio of 3.0 Gy was taken. Several EQD(2)-volume histogram parameters were calculated for comparison and analyzed by two-way ANOVA. RESULTS: The mean EQD(2) to 95% of the prostate volume was slightly higher for the IMRT-only plan than for the brachytherapy modalities (P<0.001), in contrast to the mean EQD(2) to 50% of the prostate volume in which the opposite was the case (P<0.001). Rectum and bladder doses for IMRT-only are significantly higher (P<0.001). The urethra dose for IMRT-HDR was much higher than the other modalities only when the alpha/beta-ratio for prostate was 10 Gy. CONCLUSION: Because of the high doses within an implant, the dose in 50% of the prostate volume is much higher with the brachytherapy modalities than IMRT-only which may have clinical consequences. With brachytherapy the doses to the OAR are lower or similar to IMRT-only. Dose escalation for prostate tumors is more easily achieved with brachytherapy than with IMRT alone. Therefore, brachytherapy might be the preferred modality to achieve further dose escalation.     

Dose-volume histogram evaluation of prone and supine patient position in external beam radiotherapy for cervical and endometrial cancer.

BACKGROUND AND PURPOSE: To evaluate the influence of patient positioning on dose-volume histograms of organs at risk in external beam radiotherapy for cervical and endometrial cancer. MATERIALS AND METHODS: In 20 patients scheduled for definitive (7) or postoperative (13) external beam radiotherapy of the pelvis treatment planning CT scans were performed in supine and prone (belly board) positions. After volume definition of target and organs at risk treatment plans were calculated applying the four-field box technique. The dose-volume histograms of organs at risk were compared. RESULTS: Radiotherapy in prone position causes a reduction of the bladder portion (mean 15%, p<0.001) and an increase of the rectum portion (mean 11%, p<0.001) within the 90% isodose. A reduction of the bowel portion could only be observed in postoperatively treated patients (mean 13%, p<0.001). In definitive radiotherapy the target volume increases in supine position (mean 7%, p=0.02) due to an anterior tumour/uterus movement, so that bowel portions within the 90% isodose are similar. The bladder filling correlates with a reduction of bladder and bowel (postoperatively treated patients) dose. CONCLUSIONS: External beam radiotherapy of the pelvis should be performed in prone position in postoperative patients because of best bowel protection. Considering the additional HDR brachytherapy rectum protection takes the highest priority in definitive treatment-the requirements are best met in supine position. An adequate bladder filling is important to reduce the irradiated bladder and bowel volumes.     

Dosimetric and toxicity comparison between prone and supine position IMRT for endometrial cancer

PURPOSE: To determine the dosimetric and toxicity differences between prone and supine position intensity-modulate radiotherapy in endometrial cancer patients treated with adjuvant radiotherapy. METHODS: Forty-seven consecutive endometrial cancer patients treated with adjuvant RT were analyzed. Of these, 21 were treated in prone position and 26 in the supine position. Dose-volume histograms for normal tissue structures and targets were compared between the two groups. Acute and chronic toxicity were also compared between the cohorts. RESULTS: The percentage of volume receiving 10, 20, 30, 40, 45, and 50 Gy for small bowel was 89.5%, 69%, 33%, 12.2%, 5%, and 0% in the prone group and 87.5%, 62.7%, 26.4%, 8%, 4.3%, and 0% in the supine group, respectively. The difference was not statistically significant. The dose-volume histograms for bladder and rectum were also comparable, except for a slightly greater percentage of volume receiving 10 Gy (1.5%) and 20 Gy (5%) for the rectum in the prone group. Acute small bowel toxicities were Grade 1 in 7 patients and Grade 2 in 14 patients in the prone group vs. Grade 1 in 6 patients and Grade 2 in 19 patients in the supine group. Chronic toxicity was Grade 1 in 7 patients and Grade 3 in 1 patient in the prone group and Grade 1 in 5 patients in the supine group. CONCLUSION: These preliminary results suggest that no difference exists in the dose to the normal tissue and toxicity between prone and supine intensity-modulated radiotherapy for endometrial cancer. Longer follow-up and more outcome studies are needed to determine whether any differences exist between the two approaches.     

A Feasibility Study of Automated Inverse Treatment Planning for Cancer of the Prostate

Purpose: The development of automated “inverse planning,” utilizing intensity-modulated radiation therapy (IMRT) raises the question of whether this new technique can provide a practical and efficient means of dose escalation in conformal treatment of cancer of the prostate. The purpose of this feasibility study was to determine a single set of inverse-planning parameters that can be used for a variety of different prostate patient geometries to automatically generate escalated dose (≥81 Gy) IMRT plans that satisfy normal tissue constraints for rectal and bladder walls.Methods: We studied a subset of the 46 patients who were previously treated at Memorial Sloan Kettering Cancer Center (MSKCC) to a total dose of 81 Gy using a 3D conformal approach. Six patients were selected for our study and replanned using an analytical inverse-planning algorithm (referred to as OPT3D) applied to 8 intensity modulated, co-axial radiation beams. A set of more than a dozen inverse planning parameters were adjusted by trial and error until the resulting dose distributions satisfied the critical organ dose–volume constraints imposed by our study rules (D30 ≤ 75.6 Gy and D10 ≤ 80 Gy for the rectal wall; D15 ≤ 80 Gy for the bladder wall) for the sample of patients selected. The OPT3D-generated plans were compared to hand-generated BEV plans using cumulative DVH analysis.Results: A single set of inverse-planning parameters was found that was able to automatically generate IMRT plans meeting all critical organ dose-volume constraints for all but one of the patients in our study. [The exception failed to meet bladder dose constraints for both IMRT and BEV methods, due to extensive overlap between the planning target volume (PTV) and bladder contours]. Based upon analysis of the cumulative dose-volume histogram (DVH) for the prostate PTV, the D95 (DX is defined such that x% of the volume receives a dose ≥ DX), averaged over all patients, was approximately 81 Gy. The average D90 and mean dose values were 85 Gy and 93 Gy, respectively. Although a similar D95 was achieved using the BEV-generated plans, the D90 and mean dose values were substantially higher for the inverse planning (OPT3D) method.Conclusion: This limited “paper study” shows IMRT with inverse planning to be a promising technique for the treatment of prostate cancer to high doses. We determined a small set of inverse-planning parameter values that was able to automatically design intensity-modulated radiotherapy (IMRT) plans for a subset of 6 patients previously treated at MSKCC to 81 Gy using BEV planning techniques. With one minor exception, the resulting plans succeeded in meeting predetermined dose-volume constraints while at the same time allowing an increase in the mean dose and D90 to the prostate PTV. These 8 field plans also resulted in reduced dosage to the femoral heads. This automated technique is efficient in terms of planning effort and, with proper software for computer-controlled MLC, may be appropriate for clinical use. The clinical feasibility of this approach for a larger group of patients is currently under study.     

Three-dimensional photon dosimetry: a comparison of treatment of the intact breast in the supine and prone position

PURPOSE: To compare the adequacy of target coverage, dose homogeneity, and volume of normal tissue irradiated in treatment of the intact breast in the supine and prone position. METHODS AND MATERIALS: Fifteen patients with early breast cancer who presented for treatment to the intact breast after excisional biopsy were studied. A specially designed device was used for the prone setup to displace the contralateral breast away from the tangential field borders. Treatment planning computed tomography was performed for each patient in both the supine and prone positions. Dosimetric data were obtained in both positions and isodose distributions were calculated for each patient in both positions. RESULTS: The volume of breast receiving greater than 5% of the prescribed dose was significantly less in the prone position. Medial wedges were either not used or their angles were reduced for all patients in the prone position compared with the supine position. The average volume of lung receiving >10 Gy and >20 Gy was significantly less in the prone positions. The volume of heart irradiated at critical dose levels did not vary consistently in the prone and supine positions. The integral dose delivered to the contralateral breast was not significantly different. CONCLUSION: Treatment of the intact breast in the prone position may result in improved dose homogeneity within the target volume as well as sparing of normal lung compared with treatment in the conventional supine position.     

Reduction of dose delivered to the rectum and bulb of the penis using MRI delineation for radiotherapy of the prostate

PURPOSE: The prostate volume delineated on MRI is smaller than on CT. The purpose of this study was to determine the influence of MRI- vs. CT-based prostate delineation using multiple observers on the dose to the target and organs at risk during external beam radiotherapy. MATERIALS AND METHODS: CT and MRI scans of the pelvic region were made of 18 patients and matched three-dimensionally on the bony anatomy. Three observers delineated the prostate using both modalities. A fourth observer delineated the rectal wall and the bulb of the penis. The planning treatment volume (PTV) was generated from the delineated prostates with a margin of 10 mm in three-dimensions. A three-field treatment plan with a prescribed dose of 78 Gy to the International Commission on Radiation Units and Measurements point was automatically generated from each PTV. Dose-volume histograms were calculated of all PTVs, rectal walls, and penile bulbs. The equivalent uniform dose was calculated for the rectal wall using a volume exponent (n = 0.12). RESULTS: The equivalent uniform dose of the CT rectal wall in plans based on the CT-delineated prostate was, on average, 5.1 Gy (SEM 0.5) greater than in the plans based on the MRI-delineated prostate. For the MRI rectal wall, this difference was 3.6 Gy (SEM 0.4). Allowing for the same equivalent uniform dose to the CT rectal wall, the prescribed dose to the PTV could be raised from 78 to 85 Gy when using the MRI-delineated prostate for treatment planning. The mean dose to the bulb of the penis was 11.6 Gy (SEM 1.8) lower for plans based on the MRI-delineated prostate. The mean coverage (volume of the PTV receiving > or =95% of the prescribed dose) was 99.9% for both modalities. The interobserver coverage (coverage of the PTV by a treatment plan designed for the PTV delineated by another observer in the same modality) was 97% for both modalities. The MRI rectum was significantly more ventrally localized than the CT rectum, probably because of the rounded tabletop and no knee support on the MRI scanner. CONCLUSIONS: The dose delivered to the rectal wall and bulb of the penis is significantly reduced with treatment plans based on the MRI-delineated prostate compared with the CT-delineated prostate, allowing a dose escalation of 2.0-7.0 Gy for the same rectal wall dose. The interobserver coverage was the same for CT and MRI delineation of the prostate. A statistically significant difference in position between the CT- and MRI-delineated rectum was observed, probably owing to a different tabletop and use of knee support.     

The effect of pressure from the table top and patient position on pelvic organ location in patients with prostate cancer

PURPOSE: To assess the impact of pressure from the table top and patient position on the relationship of the prostate, rectum, and bladder to the bony pelvis. METHODS AND MATERIALS: In 9 patients with prostate cancer (3 status postprostatectomy), computed tomography (CT) scans were obtained in four positions: supine with and without false table top under the buttocks, prone with and without false table top under the lower abdomen. In four patients, a fifth scan was obtained in the first position (supine with table top in place) to assess the impact of changes in bladder/rectal fullness over time. Urination and defecation were not permitted between scans. For each patient, the four (or five) CT scans were registered to each other. RESULTS: The anal canal and the rectum caudal to the coccyx shifted posteriorly in 7/9 patients when the support under the buttocks was removed in the supine position. When pressure from the table top was removed in the prone position, the anterior bladder extension increased. The superior rectum was adjacent to the prostate in all scans and the prostate/superior rectum/bladder generally moved together. Rectal fullness changed with time and rectal gas position was gravity-dependent and shifted with patient position. Bladder volume increased with time. Organs had shifted and/or changed fullness between the first and fifth scan obtained in the same patient position approximately 90 min apart, mostly due to increase in bladder volume. All patients found the supine position most comfortable. CONCLUSIONS: The bladder and rectal fullness vary with time, confounding the ability to attribute changes in organ location to positional factors. Pressure from the table top affects the relative location of pelvic organs and, in part, is responsible for changes previously attributed to position/gravity.     

Influence of organ motion on conformal vs. intensity-modulated pelvic radiotherapy for prostate cancer

PURPOSE: To compare an intensity-modulated radiotherapy (IMRT) planning approach for prostate pelvic RT with a conformal RT (CRT) approach taking into account the influence of organ-at-risk (OAR) motion. METHODS AND MATERIALS: A total of 20 male patients, each with one planning computed tomography scan and five to eight treatment computed tomography scans, were used for simulation of IMRT and CRT for delivery of a prescribed dose of 50 Gy to the prostate, seminal vesicles, and pelvic lymph nodes. Planning was done in Eclipse without correcting for OAR motion. Evaluation was performed using the CRT and IMRT dose matrices and the planning and treatment OAR outlines. The generalized equivalent uniform dose (gEUD) was calculated for 894 OAR volumes using a volume-effect parameter of 4, 12, and 8 for bowel, rectum and bladder, respectively. For the bowel, the gEUD was normalized to a reference volume of 200 cm(3). For each patient and each OAR, an average of the treatment gEUDs (gEUD(treat)) was calculated for CRT and IMRT. The paired t test was used to compare IMRT with CRT and gEUD(treat) with gEUD(plan). RESULTS: The mean gEUD(treat) was reduced from 43 to 40 Gy, 47 to 46 Gy, and 48 to 45 Gy with IMRT for the bowel, rectum, and bladder, respectively (p < 0.001). Differences between the gEUD(plan) and gEUD(treat) were not significant (p > 0.05) for any OAR but was >6% for the bowel in 6 of 20 patients. CONCLUSION: Intensity-modulated RT reduced the bowel, rectum, and bladder gEUDs also under influence of OAR motion. Neither CRT nor IMRT was robust against bowel motion, but IMRT was not less robust than CRT.