Initial dosimetric experience using simple three-dimensional conformal external-beam accelerated partial-breast irradiation

PURPOSE: Several accelerated partial-breast irradiation (APBI) techniques are being investigated in patients with early-stage breast cancer. We present our initial experience using three-dimensional conformal radiation therapy (3D-CRT). METHODS AND MATERIALS: Sixty-one patients with tumors of 2 cm or less and negative axillary nodes were treated with 3D-CRT accelerated partial-breast irradiation (APBI) between August 2003 and March 2005. The prescribed radiation dose was 32 Gy in 4-Gy fractions given twice daily. Efforts were made to minimize the number of beams required to achieve adequate planning target volume (PTV) coverage. RESULTS: A combination of photons and electrons was used in 85% of patients. A three-field technique that consisted of opposed, conformal tangential photons and enface electrons was employed in 43 patients (70%). Nine patients (15%) were treated with a four-field arrangement, which consisted of three photon fields and enface electrons. Mean PTV volumes that received 100%, 95%, and 90% of the prescribed dose were 93% +/- 7%, 97% +/- 4%, and 98% +/- 2%, respectively. Dose inhomogeneity exceeded 10% in only 7 patients (11%). Mean doses to the ipsilateral lung and heart were 1.8 Gy and 0.8 Gy, respectively. CONCLUSIONS: Simple 3D-CRT techniques of APBI can achieve appropriate PTV coverage while offering significant normal-tissue sparing. Therefore, this noninvasive approach may increase the availability of APBI to patients with early-stage breast cancer.     

Dosimetric Evaluation of 3-D Conformal and Intensitymodulated Radiotherapy for Breast Cancer after Conservative Surgery

Background: Breast cancers are becoming more frequently diagnosed at early stages with improved longterm outcomes. Late normal tissue complications induced by radiotherapy must be avoided with new breastradiotherapy techniques being developed. The aim of the study was to compare dosimetric parameters of planningtarget volume (PTV) and organs at risk between conformal (CRT) and intensity-modulated radiation therapy(IMRT) after breast-conserving surgery. Materials and Methods: A total of 20 patients with early stage leftbreast cancer received adjuvant radiotherapy after conservative surgery, 10 by 3D-CRT and 10 by IMRT, witha dose of 50 Gy in 25 sessions. Plans were compared according to dose-volume histogram analyses in terms ofPTV homogeneity and conformity indices as well as organs at risk dose and volume parameters. Results: The HIand CI of PTV showed no difference between 3D-CRT and IMRT, V95 gave 9.8% coverage for 3D-CRT versus99% for IMRT, V107 volumes were recorded 11% and 1.3%, respectively. Tangential beam IMRT increasedvolume of ipsilateral lung V5 average of 90%, ipsilateral V20 lung volume was 13%, 19% with IMRT and3D-CRT respectively. Patients treated with IMRT, heart volume encompassed by 60% isodose (30 Gy) reducedby average 42% (4% versus 7% with 3D-CRT), mean heart dose by average 35% (495cGy versus 1400 cGywith 3D-CRT). In IMRT minimal heart dose average is 356 cGy versus 90cGy in 3D-CRT. Conclusions: IMRTreduces irradiated volumes of heart and ipsilateral lung in high-dose areas but increases irradiated volumes inlow-dose areas in breast cancer patients treated on the left side.     

胃癌术后放疗方式对肾脏剂量学影响的比较研究

目的:比较胃癌术后三维适形放疗(3D-CRT)与调强适形放疗(IMRT)对肾脏剂量学的分布影响.方法:选择9例根治术后的进展期胃癌患者,应用Pinnacal三维计划系统(TPS)分别为每例患者设计4野3D-CRT和5、7野IMRT,所有计划给予处方剂量95％的计划靶体积(PTV)＞45 Gy; IMRT同时要求99％的PTV体积＞42.75 Gy.应用等剂量曲线及剂量体积直方图(DVH)比较各个计划之间靶区剂量的分布和肾脏的剂量受量差异.结果:4野3D-CRT和5、7野IMRT的靶区V45分别为0.96±0.03、0.95±0.02和0.95±0.02.所有计划靶区均满足处方剂量,与4野3D-CRT相比,IMRT明显提高靶区的剂量的均匀性(HI)和适形度(CI),并且降低双侧肾脏18 Gy的剂量体积百分比(V18),但在低剂量(10 Gy)体积百分比(V10)3种放射方式之间差异无统计学意义,P＞0.05.5和7野IMRT之间不论在靶区剂量分布还是危及器官的剂量受量上均差异无统计学意义,P＞0.05.结论:与3D-CRT比较,IMRT明显提高靶区均匀性,降低肾脏剂量受量和剂量体积百分比,但在V10上3种计划间差异无统计学意义.     

A treatment planning study using non-coplanar static fields and coplanar arcs for whole breast radiotherapy of patients with concave geometry.

PURPOSE: A treatment planning study was performed to evaluate the performance of new radiotherapy techniques based on non-coplanar multiple fields or on dynamic conformal arcs for early stage breast treatments. METHODS AND MATERIALS: CT datasets of 7 different patients that were deemed unsuitable for tangential beam treatment due to a large volume of lung in the treatment fields were used as input for the study. Standard tangential field plans and inversely modulated IMRT plans were used as benchmark to evaluate performances of conformal plans with 3 non-coplanar fields (3F-NC), with 2 short dynamic conformal arcs (2-Arc) or hybrid plans with one static conformal field and one dynamic conformal arc (P-Arc). All plans were designed to achieve the higher target coverage and minimum ipsilateral lung involvement depending on the planning technique with a key objective to avoid involvement of the contralateral breast. The following planning objectives were selected. For PTV: D(1%) (maximum significant dose) lower than 110% and D(99%) (minimum significant dose) higher than 90%. For the ipsilateral lung a mean dose lower than 15 Gy and/or a volume receiving more than 20 Gy lower than 22%. For contralateral breast, all techniques but IMRT were set to have no beam impinging this organ at risk, while for IMRT plans were further designed to keep the mean dose lower than 5 Gy and to minimise the volume receiving a dose higher than 70% of the prescribed dose. RESULTS: P-Arc resulted to be on average a better technique, as it provides a PTV dose distribution highly conformal (Conformity index 1.45), homogeneous (D(5%)-D(95%)=15.6%), with adequate coverage (V(90%)=96.4%) and a limited involvement of the ipsilateral lung (MLD approximately 9 Gy, V(5 Gy) approximately 36%, NTCP<2%) when compared to four other treatment techniques. 3F-NC presented similar but slightly worse performances on target: Conformity index 1.57, D(5%)-D(95%)=18.1%, V(90%)=95.7%). 3F-NC on ipsilateral lung resulted as the P-Arc. The tangential approach, the 2-Arc or the IMRT techniques, resulted to be inferior to the previous in either conformality (tangentials), ipsilateral lung sparing (tangentials, 2-Arc and IMRT) and in contralateral or healthy tissue involvement (IMRT). CONCLUSION: For early stage breast cancer when high sparing of lung tissues is required and no involvement of contralateral breast is allowed, the P-Arc or the 3F-NC techniques might be recommended in terms of dosimetric expectations.     

Assessment of extended-field radiotherapy for stage IIIC endometrial cancer using three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, and helical tomotherapy

PURPOSE: To perform a dosimetric comparison of three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and helical tomotherapy (HT) plans for pelvic and para-aortic RT in postoperative endometrial cancer patients; and to evaluate the integral dose (ID) received by critical structures within the radiation fields. METHODS AND MATERIALS: We selected 10 patients with Stage IIIC endometrial cancer. For each patient, three plans were created with 3D-CRT, IMRT, and HT. The IMRT and HT plans were both optimized to keep the mean dose to the planning target volume (PTV) the same as that with 3D-CRT. The dosimetry and ID for the critical structures were compared. A paired two-tailed Student t test was used for data analysis. RESULTS: Compared with the 3D-CRT plans, the IMRT plans resulted in lower IDs in the organs at risk (OARs), ranging from -3.49% to -17.59%. The HT plans showed a similar result except that the ID for the bowel increased 0.27%. The IMRT and HT plans both increased the IDs to normal tissue (see Table 1 and text for definition), pelvic bone, and spine (range, 3.31-19.7%). The IMRT and HT dosimetry showed superior PTV coverage and better OAR sparing than the 3D-CRT dosimetry. Compared directly with IMRT, HT showed similar PTV coverage, lower Ids, and a decreased dose to most OARs. CONCLUSION: Intensity-modulated RT and HT appear to achieve excellent PTV coverage and better sparing of OARs, but at the expense of increased IDs to normal tissue and skeleton. HT allows for additional improvement in dosimetry and sparing of most OARs.     

Dosimetric comparison of proton and photon three-dimensional, conformal, external beam accelerated partial breast irradiation techniques

PURPOSE: To compare the dosimetry of proton and photon-electron three-dimensional, conformal, external beam accelerated partial breast irradiation (3D-CPBI). METHODS AND MATERIALS: Twenty-four patients with fully excised, Stage I breast cancer treated with adjuvant proton 3D-CPBI had treatment plans generated using the mixed-modality, photon-electron 3D-CPBI technique. To facilitate dosimetric comparisons, planning target volumes (PTVs; lumpectomy site plus 1.5-2.0 cm margin) and prescribed dose (32 Gy) were held constant. Plans were optimized for PTV coverage and normal tissue sparing. RESULTS: Proton and mixed-modality plans both provided acceptable PTV coverage with 95% of the PTV receiving 90% of the prescribed dose in all cases. Both techniques also provided excellent dose homogeneity with a dose maximum exceeding 110% of the prescribed dose in only one case. Proton 3D-CPBI reduced the volume of nontarget breast tissue receiving 50% of the prescribed dose by an average of 36%. Statistically significant reductions in the volume of total ipsilateral breast receiving 100%, 75%, 50%, and 25% of the prescribed dose were also observed. The use of protons resulted in small, but statistically significant, reductions in the radiation dose delivered to 5%, 10%, and 20% of ipsilateral and contralateral lung and heart. The nontarget breast tissue dosimetric advantages of proton 3D-CPBI were not dependent on tumor location, breast size, PTV size, or the ratio of PTV to breast volume. CONCLUSIONS: Compared to photon-electron 3D-CPBI, proton 3D-CPBI significantly reduces the volume of irradiated nontarget breast tissue. Both approaches to accelerated partial breast irradiation offer exceptional lung and heart sparing.     

乳腺癌保乳术后行IMRT和3D-CRT治疗的剂量学参数及靶区适形度比较

目的:通过配对比较早期乳腺癌保乳术后IMRT和3D-CRT两种放疗技术模式下靶区的适形度和肺组织的受照体积-剂量参数,探索早期乳腺癌保乳术后的最佳放疗模式。方法:选取20例 I-II期（T1-2N0M0）乳腺癌保乳术后行全乳腺放疗者,对同一患者分别设计IMRT和3D-CRT两套放射计划方案,配对分析PTV及PGTVbed靶区剂量分布适形度,患侧肺组织的受照体积-剂量参数,包括V5、V10、V20、V25、V30及肺组织和心脏平均受照剂量。结果:对比3D-CRT,IMRT使肺组织平均受照剂量降低了1.34 Gy,高剂量受照区域V20体积降低了2.89%,V25体积降低了5.57%,V30体积降低了7.45%;同时提高了PTV及PGTVbed靶区内的剂量分布适形度,差异均具有统计学意义（P<0.05）。两组的心脏平均受照剂量分别为（4.01±0.38）Gy和（4.61±0.42）Gy,差异无统计学意义（P>0.05）。结论:在早期乳腺癌保乳术后的辅助放疗中,采用IMRT模式比3D-CRT模式能够获得更好的靶区适形度,靶区内的剂量分布更均匀,有利于提高局控率,同时减少了肺组织的高剂量受照区域和平均受照剂量,对正常肺组织的保护更好,值得临床上应用和推广。     

A dosimetric comparison of accelerated partial breast irradiation techniques: multicatheter interstitial brachytherapy, three-dimensional conformal radiotherapy, and supine versus prone helical tomotherapy

PURPOSE: To compare dosimetrically four different techniques of accelerated partial breast irradiation (APBI) in the same patient. METHODS AND MATERIALS: Thirteen post-lumpectomy interstitial brachytherapy (IB) patients underwent imaging with preimplant computed tomography (CT) in the prone and supine position. These CT scans were then used to generate three-dimensional conformal radiotherapy (3D-CRT) and prone and supine helical tomotherapy (PT and ST, respectively) APBI plans and compared with the treated IB plans. Dose-volume histogram analysis and the mean dose (NTD(mean)) values were compared. RESULTS: Planning target volume coverage was excellent for all methods. Statistical significance was considered to be a p value <0.05. The mean V100 was significantly lower for IB (12% vs. 15% for PT, 18% for ST, and 26% for 3D-CRT). A greater significant differential was seen when comparing V50 with mean values of 24%, 43%, 47%, and 52% for IB, PT, ST, and 3D-CRT, respectively. The IB and PT were similar and delivered an average lung NTD(mean) dose of 1.3 Gy(3) and 1.2 Gy(3), respectively. Both of these methods were statistically significantly lower than the supine external beam techniques. Overall, all four methods yielded similar low doses to the heart. CONCLUSIONS: The use of IB and PT resulted in greater normal tissue sparing (especially ipsilateral breast and lung) than the use of supine external beam techniques of 3D-CRT or ST. However, the choice of APBI technique must be tailored to the patient's anatomy, lumpectomy cavity location, and overall treatment goals.     

Comparison of inverse-planned three-dimensional conformal radiotherapy and intensity-modulated radiotherapy for non-small-cell lung cancer

PURPOSE: Lungs are the major dose-limiting organ during radiotherapy (RT) for non-small-cell lung cancer owing to the development of pneumonitis. This study compared intensity-modulated RT (IMRT) with three-dimensional conformal RT (3D-CRT) in reducing the dose to the lungs. METHODS: Ten patients with localized non-small-cell lung cancer underwent computed tomography (CT). The planning target volume (PTV) was defined and the organs at risk were outlined. An inverse-planning program, AutoPlan, was used to design the beam angle-optimized six-field noncoplanar 3D-CRT plans. Each 3D-CRT plan was compared with a series of five IMRT plans per patient. The IMRT plans were created using a commercial algorithm and consisted of a series of three, five, seven, and nine equidistant coplanar field arrangements and one six-field noncoplanar plan. The planning objectives were to minimize the lung dose while maintaining the dose to the PTV. The percentage of lung volume receiving >20 Gy (V20) and the percentage of the PTV covered by the 90% isodose (PTV90) were the primary endpoints. The PTV90/V20 ratio was used as the parameter accounting for both the reduction in lung volume treated and the PTV coverage. RESULTS: All IMRT plans, except for the three-field coplanar plans, improved the PTV90/V20 ratio significantly compared with the optimized 3D-CRT plan. Nine coplanar IMRT beams were significantly better than five or seven coplanar IMRT beams, with an improved PTV90/V20 ratio. CONCLUSION: The results of our study have shown that IMRT can reduce the dose to the lungs compared with 3D-CRT by improving the conformity of the plan.     

Dosimetric comparison of two different three-dimensional conformal external beam accelerated partial breast irradiation techniques

PURPOSE: We compare the dosimetry of two techniques for three-dimensional, conformal, external beam, accelerated partial breast irradiation (3D-CPBI) in the supine position. METHODS AND MATERIALS: Sixteen patients with Stage I breast cancer had PBI treatment plans generated using the multiple, noncoplanar photon field technique and the three-field, mixed-modality technique. Planning target volumes (PTVs; lumpectomy site plus 1.5-2.0 cm margin) and total dose (32 Gy) were held constant to facilitate dosimetric comparisons. Plans were optimized for conformality and PTV coverage. RESULTS: Mixed-modality plans employed fewer fields than multiple, noncoplanar photon field plans (mean 3.2 vs. 4.1). Both techniques provided comparable PTV coverage and in all cases, 95% of the PTV received 90% of the prescribed dose. Volumes of ipsilateral breast receiving greater than 16 Gy were similar; however, the mean volume of ipsilateral breast receiving 8 Gy was significantly lower for mixed-modality plans (58% vs. 66%). No differences in the volumes of ipsilateral lung or heart receiving greater than 5 Gy were observed, however, the mixed-modality technique delivered 2.5 Gy to larger volumes of these organs. CONCLUSIONS: Both techniques for supine position, 3D-CPBI provides excellent normal tissue sparing with adequate PTV coverage. The multiple, noncoplanar photon field technique exposes smaller volumes of ipsilateral lung and heart to low dose radiation at the expense of increased plan complexity and larger irradiated breast volumes.     

Minimising contralateral breast dose in post-mastectomy intensity-modulated radiotherapy by incorporating conformal electron irradiation

Purpose

To assess the potential benefit of incorporating conformal electron irradiation in intensity-modulated radiotherapy (IMRT) for loco-regional post-mastectomy RT.

Patients and methods

Ten consecutive patients that underwent left-sided mastectomy were selected for this comparative planning study. Three-dimensional conformal radiotherapy (3D-CRT) photon-electron dose plans were compared to photon-only IMRT (IMRT_p) and photon IMRT with conformal electron irradiation (IMRT_p/e). The planning target volume (PTV) was prescribed 50 Gy and included the chest wall and the internal mammary and supra-clavicular lymph node regions. It was attempted to minimise dose delivered to heart, lungs and contralateral breast (CB), while maintaining adequate PTV coverage.

Results

All plans complied with objectives for PTV coverage. IMRT_p/e eliminated volumes receiving ?70 Gy (V70) that were present in 3D-CRT at the junction of photon and electron beams. Both IMRT strategies reduced heart V30 significantly below 3D-CRT levels. Mean heart dose with IMRT_p/e was the lowest and was equal to that with 3D-CRT. Minimising heart dose with IMRT_p resulted in irradiated CB volumes much larger than that with 3D-CRT. With IMRT_p/e, CB dose was only slightly increased when compared to 3D-CRT. Mean lung dose values were similar for IMRT and 3D-CRT. With IMRT, lung V20 was smaller, whereas V5 values for heart, lung and CB were higher than those with 3D-CRT.

Conclusions

Incorporation of conformal electron irradiation in post-mastectomy IMRT_p/e enables a heart dose reduction which can only be obtained with IMRT_p when allowing large irradiated volumes in the contralateral breast.     

A four-dimensional CT-based evaluation of techniques for gastric irradiation

PURPOSE: To evaluate three-dimensional conformal (3D-CRT), intensity-modulated (IMRT) and respiration-gated radiotherapy (RGRT) techniques for gastric irradiation for target coverage and minimization of renal doses. All techniques were four-dimensional (4D)-CT based, incorporating the intrafractional mobility of the target volume and organs at risk (OAR). METHODS AND MATERIALS: The stomach, duodenal C-loop, and OAR (kidneys, liver, and heart) were contoured in all 10 phases of planning 4D-CT scans for five patients who underwent abdominal radiotherapy. Planning target volumes (PTVs) encompassing all positions of the stomach (PTV(all phases)) were generated. Three respiratory phases for RGRT in inspiration and expiration were identified, and corresponding PTV(inspiration) and PTV(expiration) and OAR volumes were created. Landmark-based fields recommended for the Radiation Therapy Oncology Group (RTOG) 99-04 study protocol were simulated to assess PTV coverage. IMRT and 3D-CRT planning with and without additional RGRT planning were performed for all PTVs, and corresponding dose volume histograms were analyzed. RESULTS: Use of landmark-based fields did not result in full geometric coverage of the PTV(all phases) in any patient. IMRT significantly reduced mean renal doses compared with 3D-CRT (15.0 Gy +/- 0.9 Gy vs. 20.1 Gy +/- 9.3 Gy and 16.6 Gy +/- 1.5 Gy vs. 32.6 Gy +/- 7.1 Gy for the left and right kidneys, respectively; p = 0.04). No significant increase in renal sparing was seen when adding RGRT to either 3D-CRT or IMRT. Tolerance doses to the other OAR were not exceeded. CONCLUSIONS: Individualized field margins are essential for gastric irradiation. IMRT plans significantly reduce renal doses, but the benefits of RGRT in gastric irradiation appear to be limited.