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Japanese Journal of Clinical Oncology Advance Access originally published online on January 22, 2008
Japanese Journal of Clinical Oncology 2008 38(2):158-163; doi:10.1093/jjco/hym167
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© The Author (2008). Published by Oxford University Press. All rights reserved

Performance Evaluation of Field-In-Field Technique for Tangential Breast Irradiation

Jeong-Woo Lee1,2, Semie Hong1,, Kyoung-Sik Choi3, Yon-Lae Kim1, Byung-Moon Park1, Jin-Beom Chung2,4, Doo-Hyun Lee2,5 and Tae-Suk Suh2

1 Department of Radiation Oncology, School of Medicine, Konkuk University, Konkuk University Hospital, Seoul, Republic of Korea
2 Department of Biomedical Engineering, School of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
3 Department of Radiation Oncology, College of Medicine, Ajou University Hospital, Gyeonggi-do, Republic of Korea
4 Department of Radiation Oncology, Seoul National University Bundang Hospital, Gyeonggi-do, Republic of Korea
5 Department of Radiation Oncology, National Cancer Center, Gyeonggi-do, Republic of Korea

For reprints and all correspondence: Semie Hong, Department of Radiation Oncology, School of Medicine, Konkuk University, Konkuk University Hospital 4-12 Hwayang-dong, Gwangjin-gu, Seoul, 143-729, Republic of Korea. E-mail: semiehong{at}kuh.ac.kr

Received October 2, 2007; accepted November 21, 2007


   Abstract
TOP
 Abstract
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION AND CONCLUSION
 References
 
Conventional hard or dynamic wedge systems are commonly applied to reduce the dose inhomogeneity associated with whole breast irradiation. We evaluated the dosimetric benefits of the field-in-field (FIF) technique by comparing it with the electronic compensator (EC), Varian enhanced dynamic wedge (EW) and conventional hard wedge (HW) techniques. Data were obtained from 12 patients who had undergone breast-conserving surgery (six left-sided and six right-sided). For these patients, the average breast planning target volume (PTV) was 447.4 cm3 (range, 211.6–711.8 cm3). For the experiments, a 6 MV photon beam from a Varian 21 EX was used, the HW and EW angles were applied from 15 to 45 degrees, while 40–50% isodose values were chosen to achieve the best dose distribution for electronic compensation. In applying the FIF technique, we used two or three subfields for each portal. To evaluate the performance for each planning technique, we analysed a dose-volume histogram (DVH) for the PTV and organs-at-risk (OARs). To evaluate the effects of these techniques on dose inhomogeneity, we defined the PTV Dose Improvement (PDI) index, which was derived from a PTV volume between 97–103% of the differential DVHs. In addition, we compared the average monitor units (MUs) for each technique. The average PDI index with FIF is 76.4%, while the PDI indices for other treatments were 65.8, 41.8 and 50.9% for EC, EW and HW, respectively. This study demonstrated an improved performance using the FIF technique compared with the conventional HW/EW system, as well as a new modality for EC. We demonstrated that FIF is a very useful technique for improving PTV conformity, while protecting the OARs from breast tangential irradiation.

Key Words: breast irradiation • field-in-field technique • dose compensation • PTV Dose Improvement Index (PDI index)


   INTRODUCTION
TOP
 Abstract
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION AND CONCLUSION
 References
 
Whole breast radiation therapy has been widely used after breast-conserving surgery to prevent local recurrence in patients with early breast cancer. A tangential parallel-opposed pair technique is generally used for whole breast radiation therapy. A three-dimensional analysis of this technique demonstrated that there could be a large dose inhomogeneity inside the target volume (1,2). Achieving an acceptable dose homogeneity across the whole breast volume is difficult because of the continuous change in breast shape across multiple planes and the effect of the low-density lung tissues that are included in the irradiated volume. Also, tangential breast irradiation involves several organs-at-risk (OARs) such as the heart, ipsilateral lung, contralateral breast as well as breast planning target volume (PTV). The existence of low-density tissues in the lung causes a lower attenuation rate for the primary beam. This dose inhomogeneity is believed to cause many side effects such as poorer cosmetic results, breast pain and pneumonitis (3–6). Various techniques have been tested in an attempt to decrease the dose and volume to a safe level, while improving the dose distribution in the PTV. Conventional hard wedge (HW) systems are commonly applied to reduce dose inhomogeneity due to severe breast surface irregularity and tissue heterogeneity (1,2).

Several groups have reported that using intensity modulating techniques, such as field-in-field (FIF), can reduce dose inhomogeneity (7–9). In this study, we evaluated the dosimetric benefits of FIF technique compared with electronic compensator (EC), Varian enhanced dynamic wedge (EW) and conventional HW techniques.


   MATERIALS AND METHODS
TOP
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION AND CONCLUSION
 References
 
Six consecutive patients from both the left- and right-sided treatment site groups were included in this study. All patients had undergone breast-conserving surgery. All patients had CT scans while immobilized with the breast tilting board. The images were transferred to the commercial radiation treatment planning system (Varian Eclipse version 7.3.10, Varian Medical System, Palo Alto, CA), and the Clinical target volume (CTV) and contralateral breast were delineated by the same radiation oncologist using standard window level (0 HU) and width (500 HU), which is in our institution considered optimal for visibility of the glandular breast tissue. A PTV was generated by expanding the CTV 7 mm in all direction but in the direction of the skin surface, for compensating set-up uncertainty. We excluded the pulmonary trunk, the ascending aorta, and the superior vena cava for delineating the heart. The contour of the ipsilateral lung was contoured automatically. Figure 1 shows the scheme of the axial CT for breast tangential irradiation. The physiological information and geometric parameters used to determine the radiation treatment plan for the 12 patients are presented in Table 1. The average volume for the breast PTV was 447.4 cm3 (range, 211.6–711.8 cm3) for the 12 patients. The mean values for maximum breast height, breast separation and chest wall-to-lung distance were 4.3 cm (range, 2.7–5.8 cm), 19.1 cm (range, 16.2–21.8 cm) and 1.7 cm (range, 0–2.7 cm), respectively. The total dose was 50.4 Gy, which was defined at the normalization point in the inner PTV low dose gradient region to avoid the low dose penumbra field junction. One physicist individually performed all treatments. Five plans, including naked open-beam irradiation, were generated for each patient to evaluate the dose distribution according to various optimizing techniques. Each treatment plan was optimized for tangential irradiation with the same beam geometries, with the same angles and field sizes, and with positions appropriate for each patient. The field parameters for each plan and the physiological information of the patients are presented in Table 1. In this study, a 6 MV photon beam (CL 21EX, Varian Medical System, Palo Alto, CA) was used for each of the plans. HW and EW are conventional tangential breast techniques and the applied HW and EW angles were from 15 to 30 degrees and 20 to 45 degrees, respectively. EW technique can be described the appropriate composite method of open beam and 60° wedged beam proportionally to generate an intended wedged-angled beam in the specific depth (normally 10 cm) of medium. Through simple trial and error processes, the optimum wedge angle was determined for each patient. Electronic compensating is quite similar to physical compensating using conventional compensating materials such as plastic or aluminium. To make dose more homogeneous, EC was used by automatic multileaf collimator (MLC) substituting to manual plastic or aluminium. In the case of EC, the Eclipse planning system allowed the planner to easily choose the isodose line for electronic compensation using the Varian Millennium 120 MLC. For repetition, the compensating value was set at 40–50% to achieve the best dose distribution. FIF is generally regarded as manual-based forward intensity modulated radiotherapy. To use the FIF technique, we first made a dose distribution without any beam modifier. A dose distribution based on open beam fields has been shown to eliminate the hot spot volume. Hot spot volume blocking subfields were then determined in order to improve the dose homogeneity for the PTV. The optimized FIF plans were developed and evaluated based on the 3D dose distribution as well as the dose-volume histograms (DVHs). Main fields and subfields were merged in one portal, including several MLC segments for sequential irradiation. We used two or three subfields for each portal. Figure 2 shows one of the FIF portals, which consists of one main field (a) and three subfields (b–d). To evaluate the performance of each planning technique, we analysed the DVH of the PTV, the irradiated volume except PTV (non-PTV), ipsilateral lung, heart and contralateral breast for each of the four techniques. In the case of PTV, a differential DVH was used for analysis between 97 and 103%, which was used to evaluate the effect of dose improvement. In this study, we defined a parameter, the PTV Dose Improvement (PDI) index, which we calculated using the following equation:


Formula 167M1

(1)


Figure 1
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  		Figure 1. Scheme of axial image for breast tangential irradiation.

 

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  		Table 1. Physiological information and geometrical parameter for radiation treatment planning associated with six left and right patients

 

Figure 2
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  		Figure 2. Right-anterior oblique portal views of FIF technique. (a) Main field without multileaf collimator (MLC) blocking. (b) Drawing MLC to block out 112% isodose cloud. (c) Drawing MLC to block out 106%. (d) Drawing MLC block out 102%. After finishing the opposite left-posterior oblique portal FIF, the dose distribution was re-calculated for the optimization repeatedly. FIF, Field-In-Field.

 
Vptv97–103: Volume of PTV between 97 and 103% by four different plans

Voptv97–103: Volume of PTV between 97 and 103% by open beam plan

The modified Batho power law was used as the tissue inhomogeneity correction method for the dose calculation. The 2.5 mm grid size was applied for the calculation in all plans. Volumes over 20 Gy in the ipsilateral lung, 40 Gy in the heart and 2 Gy in the contralateral breast were used to establish the extent of the high dose received by the OARs. To evaluate treatment efficiency as well as differential and cumulative DVHs, we compared the total average MUs for the four plans from the 12 patients.


   RESULTS
TOP
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION AND CONCLUSION
 References
 
Figure 3 shows the differential DVHs in the range of 80–120% of breast PTV from the 12 patients' average treatment results using the four different tangential irradiation techniques. It shows that FIF has a narrower histogram in the range of 97–103% compared with the other three techniques. Analyses from the differential DVHs of the PTV demonstrated that the FIF technique can improve dose conformity of the breast target. Table 2 summarizes the PDI index comparisons, which represent the quantitative analyses of target conformity for the 12 patients and four different techniques. The average PDI index with FIF is 76.4%, indicating an improvement in PTV dose homogeneity relative to the application of only an open naked beam, while the PDI indices for other treatments were 65.8% (P = 0.05), 41.8% (P < 0.01) and 50.9% (P < 0.01) for EC, EW and HW, respectively (paired t-test). The dose reduction with the open beam plan was in the range of 2.4–6.1% for the maximum doses to the PTV, while the doses to the OARs fluctuated among the five different plans. There was little difference among the mean maximum doses for the OARs except for the maximum dose to the PTV. As shown in Table 3, a volume over 20 Gy in the ipsilateral lung and over 40 Gy in the heart also show that there is little dependence of the treatment techniques, including the open beam technique. But relative to the open beam technique, volumes over 103% in the PTV showed a dose reduction of 18.6, 9.3, 26.7 and 31.4% for the HW, EW, EC and FIF techniques, respectively. With a dose over 2 Gy applied to the contralateral breast, HW showed a 1.7% higher dose than that of the open beam plan, and other plans were similar. There are cumulative DVHs (dose range, 80–110%) for non-PTV in Fig. 4a, which show a relative reduction in dose compared with the volumes in the FIF technique, while the other techniques were similar. Figure 4b shows that there was little difference among EW, EC and FIF, while HW clearly showed that the increased ipsilateral lung volume received a higher dose than the others. The DVHs (dose range, 80–110%) for the heart are graphically shown in Fig. 4c. The heart volumes to high doses reveal that EC is even worse than HW, and FIF is superior to other plans. The cumulative DVHs for the contralateral breast from the average treatment (dose range, 0–6%) results for the 12 patients are presented in Fig. 4d. Based on the histograms, the HW plan is worse than the other plans, while the other three techniques yielded similar results. The total MUs from the 12 patients for the four different treatments are shown in Table 4. Compared with the open beam technique, the mean % increase in MUs was 63, 7, 27 and 2% for HW, EW, EC and FIF, respectively. The differences between MUs from FIF and EW in comparison to the open beam treatment were not significant but there was a great difference between the MUs from HW and EC.


Figure 3
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  		Figure 3. Differential dose volume histograms of PTV from twelve patients' average planning results by four different tangential irradiation techniques. (HW, Hard wedge; EW, Enhanced dynamic wedge; EC, Electronic compensator; PTV, Planning target volume).

 

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  		Table 2. Comparison of PTV dose improvement index

 

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  		Table 3. The percentage volumes of doses over 103% in PTV and the volumes over the constraint dose level to OARs

 

Figure 4
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  		Figure 4. Cumulative dose volume histograms of (a) non-PTV, (b) ipsilateral lung, (c) heart and (d) contralateral breast from the average planning results by four different tangential irradiation techniques, respectively.

 

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  		Table 4. Total MU setting for four treatment planning techniques of 12 patients

 

   DISCUSSION AND CONCLUSION
TOP
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION AND CONCLUSION
References
 
Although the beneficial effects of postoperative radiation therapy is established for patient undergoing breast conserving surgery, radiation therapy for intact breast may be related to number of complications including cardiac toxicity such as accelerated atherosclerosis, pericarditis, pulmonary toxicity and rib fracture. Risk of these complications particularly increases with suboptimal irradiation technique (10). There have been many efforts to decrease these complications, and FIF technique is one of those efforts (1,2,7–9). FIF technique consists of creating fields using MLC leaves that are strategically placed in areas so that the dose to the breast is considerably higher than the prescription dose. This systematic collimation of the beam contributes to the reduction of undesirable hot spots, thus resulting in an acceptably even dose distribution over the irradiated volume. Therefore, this technique allows for better dose uniformity and the elimination of hot spots (11).

In this study, we evaluated four different whole breast irradiation techniques using HW or EW system, an EC and FIF. Four clinically relevant factors were evaluated: PDI index, average maximum dose in PTV and OARs, volumes over 103% in the PTV and total MU setting. We set the isodose level at 97–103% rather than at 95–107% for the PTV dose improvement index because we think a more homogeneous dose distribution may give better local control and cosmetic results; inhomogeneous dose distribution may cause unexpected skin toxicity and poor cosmetic results. Vicini et al. showed that breast volumes receiving more than 105 or 110% of the prescribed dose of 45 Gy were the only significant factors (excluding surgery) associated with increased skin toxicity (12).

We found that FIF gave favourable results for all aspects when compared with other treatment plans.

There are many excellent reports on the use of intensity modulated-radiation therapy (IMRT) to improve dose distributions with whole breast irradiation (13,14). However, considering the significant cost and requirement of human resources demanded by the implementation of the most advanced intensity modulation techniques, these techniques must be evaluated for clinical relevance. In this case, the FIF technique did not require a lot of resources for treatment planning and delivery. Furthermore, the FIF technique does not require a pretreatment QA procedure, which is essential for IMRT. We think the FIF technique can be used as the standard whole breast irradiation technique, even in busy departments.

In conclusion, the use of the FIF technique showed improvements in performance when compared with the conventional HW or EW techniques. We have shown that the use of FIF effectively improves PTV conformity, while saving the OARs from tangential irradiation during whole breast irradiation treatment.

Conflict of interest statement

None declared.


   References
TOP
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION AND CONCLUSION
 References
 
1 Aref A, Thornton D, Youssef E, He T. Dosimetric improvements following 3D planning of tangential breast irradiation. Int J Radiat Oncol Biol Phys (2000) 48:1569–74.[CrossRef][ISI][Medline]

2 Buchholz TA, Gurogze E, Bice WS. Dosimetric analysis of intact breast irradiation in off-axis planes. Int J Radiat Oncol Biol Phys (1997) 39:361–7.[CrossRef][ISI][Medline]

3 Neal AJ, Torr M, Heyler S. Correlation of breast heterogeneity with breast size using 3D CT planning and dose volume histograms. Radiother Oncol (1995) 34:210–8.[CrossRef][ISI][Medline]

4 Taylor ME, Perez CA, Halverson KJ. Factors influencing cosmetic results after conservation therapy for breast cancer. Int J Radiat Oncol Biol Phys (1995) 31:753–64.[CrossRef][ISI][Medline]

5 Moody AM, Mayles WPM, Bliss JM. The influence of breast size on late radiation effects and association with radiotherapy dose inhomogeneity. Radiother Oncol (1994) 33:106–12.[CrossRef][ISI][Medline]

6 Gagliardi G, Bjohle J, Lax I. Radiation pneumonitis after breast cancer irradiation: analysis of the complication probability using the relative seriality model. Int J Radiat Oncol Biol Phys (2000) 46:373–81.[CrossRef][ISI][Medline]

7 Chang SX, Deschesne KM, Cullip TJ, Parker SA, Earmhart J. A comparison of different intensity modulation treatment techniques for tangential breast irradiation. Int J Radiat Oncol Biol Phys (1999) 45:1305–14.[CrossRef][ISI][Medline]

8 Donovan EM, Johnson U, Shentall G, Evans PM, Neal AJ, Yarnold JR. Evaluation of compensation in breast radiotherapy: a planning study using multiple static field. Int J Radiat Oncol Biol Phys (2000) 46:671–9.[CrossRef][ISI][Medline]

9 Lo YC, Yasuda G, Fitzgerald TJ, Urie MM. Intensity modulation for breast treatment using static multileaf collimators. Int J Radiat Oncol Biol Phys (2000) 46:187–94.[CrossRef][ISI][Medline]

10 Senkus-Konefka E, Jassem J. Complications of breast cancer radiotherapy. Clin Oncol (R Coll Radiol) (2006) 18:229–35.[Medline]

11 Torre N, Figueroa CT, Martinez K, Riley S, Chapman J. A comparative study of surface dose and dose distribution for intact breast following irradiation with field in field technique vs. the use of conventional wedges. Med Dosim (2004) 29:109–14.[CrossRef][Medline]

12 Vicini FA, Sharpe M, Kestin LL. Optimizing breast cancer treatment efficacy with intensity modulated radiotherapy. Int J Radiat Oncol Biol Phys (2002) 54:1336–44.[CrossRef][ISI][Medline]

13 Mayo CS, Urie MM, Fitzgerald TJ. Hybrid IMRT plans-concurrently treating conventional and IMRT beams for improved breast irradiation and reduced planning time. Int J Radiat Oncol Biol Phys (2005) 61:922–32.[CrossRef][ISI][Medline]

14 Hurkmans CW, Meijer GJ, Viliet-Vroegindeweij C, Sangen MJ, Cassee J. High dose simulataneously integrated breast boost using intensity modulated radiotherapy and inverse optimization. Int J Radiat Oncol Biol Phys (2006) 66:923–30.[ISI][Medline]


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This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
38/2/158    most recent
hym167v1
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