Dosimetry and field matching for radiotherapy to the breast and supraclavicular fossa

Improved treatment robustness of postoperative breast cancer radiotherapy including supraclavicular nodes

A combination of a three-dimensional conformal radiation therapy (3D-CRT) plan with a dose gradient of the chest wall area and a volumetric modulated arc therapy (VMAT) plan of the supraclavicular area might improve the dose distribution robustness in the junction. To investigate the impact of patient motion on the dose distribution, hybrid 3D-CRT and VMAT plans were recalculated by shifting the isocenter of the VMAT plan. Compared to the nominal plan, the target D_98% for high- vs low-dose gradients decreased by 24% vs 12%. Hybrid VMAT with a low-dose gradient 3D-CRT plan was found to be robust towards patient motion.

Investigation of dose profile across the junction of deep inspiration breath hold, breast with supra-clavicle fossa treatments

Breast with supraclavicular fossa (Br+SCF) radiotherapy treatments can utilise a monoisocentric technique to concurrently treat the breast area (tangent fields) and supraclavicular area (opposing fields). The region where these treatment areas adjoin is known as the junction region, field junction, or match line. Dose variations that may occur about the junction region, due to geometrical inaccuracies, are typically feathered out in patient free-breathing treatments. However, there is limited information on how dose at the junction is influenced in deep inspiration breath hold (DIBH) treatments. This study aims to investigate dose variation at the field junction for a patient population undertaking a DIBH Br+SCF treatment course. GAFChromic EBT3 film was used to record the dose across the junction at skin surface for approximately one third of the 25 fraction treatment course for 11 patients undergoing DIBH Br+SCF treatment. Single fraction and summated fraction profiles for each patient were compared to profiles in the treatment planning system and assessed the: (1) local dose variations, (2) position of the 50% dose gradient, and (3) relative dose at the nominal junction. Local dose variations of 10% or greater, position displacement of the junction greater than 5 mm, and relative dose differences at the match line greater than 10% can be found within single fraction dose profiles. When these single fractions are summed over the treatment course, the position variations reduce to 2 mm and dose variations reduced to within 10% for 10 of the 11 patients. Only one of 11 patients recorded a summed dose difference greater than ±10% over their treatment, recording 76% ± 8% of the planned dose in this region. This was due to a small overall position displacement of 1.8 ± 1.6 mm from the nominal junction. A feathering of the dose at the junction is present for DIBH Br+SCF patient treatments. The feathering effect is sufficient, in the majority of cases studied, to reduce any differences in dose and displacement present in single fractions. This work also demonstrates that there may be exceptions from this observed behavior that should be considered. Further study in this area using a larger patient cohort is recommended.

Dosimetric comparison between different tangential field arrangements during left-sided breast cancer radiotherapy

This study aimed to evaluate variations in dose distribution within the target volume and dose received by the organs at risk (OARs) for different tangential field arrangements during three-dimensional (3D) conformal treatment planning for left-sided breast cancer. Computed tomography (CT) images of 25 breast cancer patients were included, and three different mono-isocentric half-block (MIHB) treatment plans-parallel central axis technique (PCAXT), posterior border parallel technique (PBPT), and parallel quadrant technique (PQUDT)-were considered for each patient. The dosimetric and geometric parameters related to each followed plan were then extracted for the planning target volume (PTV) and the OARs, and compared. The results showed no significant differences among the extracted dosimetric and geometric parameters of the OARs for the different plans, while the D_max, V_95%, homogeneity index (HI), and conformity index (CI) values related to the PTV were significantly different (P < 0.05). The lowest D_max and V_95% values inside the PTV were related to the PCAXT plan. The best HI was achieved with the PBPT plan, whereas the best CI was observed for the PCAXT plan. The best correlation between the geometric and dosimetric parameters of the OARs was between V_5Gy-central lung distance for the ipsilateral lung and the V_5Gy-maximum heart distance for the heart in all plans. These results demonstrate that variations in the tangential field arrangement at the posterior border for optimal coverage of the PTV may not considerably affect the dose received by the OARs.

Verification of the junctional dose for irradiation of the chest wall and supraclavicular regions under the circumstances of advanced technologies

A single-isocenter half-beam technique is commonly used when irradiating the chest wall and supraclavicular regions in patients with high-risk breast cancer. However, several studies have reported that underdosage can occur at the junction of the chest wall and supraclavicular regions due to a "tongue-and-groove" effect. This study verified the efficacy of an open leaf technique (OL-tech) that involves placing a multileaf collimator 5 mm outside from the beam central axis to remove the effect of the multileaf collimator in a single-isocenter half-beam technique. We compared the junction doses of the OL-tech with those of a conventional technique (C-tech) in square and clinical plans, using 4 and 10 MV x-rays in the Clinac iX and 6 and 10 MV x-rays in the Trilogy accelerators (Varian Medical Systems, Palo Alto, CA). EBT3 radiochromic films were used for measurements. Measurements were performed at a depth of 3 cm when verifying field matching. The EBT3 films in the square plan indicated junction doses for the C-tech of 78.3% with the Clinac iX accelerator and 73.6% with the Trilogy accelerator. By contrast, the corresponding doses for the OL-tech were 107.2% and 99.8%, respectively. In the clinical plan, the junction doses for the C-tech were 76.5% with the Clinac iX accelerator and 72.6% with the Trilogy accelerator; the corresponding doses for the OL-tech were 108.3% and 101.7%, respectively. As with the square plan, variations in the junction dose were much smaller using the OL-tech than using the C-tech. Our results suggest that the OL-tech can be useful for improving dose homogeneity at the junction of the chest wall and supraclavicular regions.

Using Cherenkov imaging to monitor the match line between photon and electron radiation therapy fields on biological tissue phantoms

SIGNIFICANCE

Due to patients' respiratory movement or involuntary body movements during breast cancer radiotherapy, the mismatched adjacent fields in surface exposure regions could result in insufficient dosage or overdose in these regions, which would lead to tissue injury, excessive skin burns, and potential death. Cherenkov luminescence imaging (CLI) could be used to effectively detect the matching information of adjacent radiation fields without extra radiation or invasive imaging.

AIM

Our objective was to provide a biological experimental basis for monitoring matching of adjacent radiation fields between photon and electron fields due to introduced shifts during radiotherapy by CLI technique.

APPROACH

A medical accelerator was used to generate photon and electron fields. An industrial camera system was adopted to image the excited CLI signal during irradiation of chicken tissue with yellow (group A and group C experiments) or black color (group B experiment). The following introduced shifts were tested: 10, 5, 2, and 0 mm toward superior or inferior direction. A model was introduced to deal with matching error analysis of adjacent radiation fields due to introduced shifts with adapted plans used to treat neoplasms of the right breast with supraclavicular nodes or internal mammary lymph node.

RESULTS

The matching values between photon and electron fields were consistent with the tested introduced shifts during yellow chicken irradiation. In group A, average discrepancies were 0.59  ±  0.35  mm and 0.68  ±  0.37  mm for photon fields and electron fields in anterior/posterior (AP) direction, with 87% and 75% of measurement within 1 mm, respectively. In group C, average discrepancies were 0.80  ±  0.65  mm and 1.07  ±  0.57  mm for oblique photon field with gantry angles of 330 deg and 150 deg, with 66% and 65% of measurement within 1 mm, respectively. The average discrepancies were 0.44  ±  0.30  mm for electron field in the AP direction, with 94% of measurement within 1 mm. The matching error introduced by the proposed method was less than 1.5 mm for AP fields and 2 mm for oblique incidence fields. However, the field matching could not be monitored with black chicken tissue irradiation due to a weak CLI signal that could hardly be extracted from background noise in group B.

CONCLUSIONS

CLI is demonstrated for the quantitative monitoring of the field match line on light biological tissue phantoms and has potential for monitoring of field matching in surface tissue during breast cancer radiotherapy.

Comparison of Photon-electron and Photon Radiotherapy for Supraclavicular Lymph Nodes of Mastectomy Patients with Left-sided Breast Cancer

The aim of radiotherapy is to deliver the highest possible radiation dose to the tumor and the lowest radiation to normal tissues surrounding the tumor. In the present study, lymph nodes of the supraclavicular region were treated using two therapeutic techniques, namely photon technique (PT) and combinatory photon-electron technique (CPET). We recruited 50 patients with local lymph node metastasis. The photon energies were 6-15 MV. Furthermore, the electron beam energy was 18 MeV in CPET. The study findings revealed that the mean delivered dose to target volume was 41.12 ± 2.98Gy for PT and 44.56 ± 1.90Gy for CPET. The percentage of the target volume irradiated to 90% of the prescribed dose (V90) was calculated as 74.61% ± 9.30% and 82.06% ± 9.70% for PT and CPET, respectively. The mean dose delivered to the heart and lungs was not significantly different between the two groups. Furthermore, the maximum doses delivered to the spinal cord were 12.55Gy in PT and 8.89Gy in CPET. The mean doses delivered to the thyroid gland were 39.26 and 34.89Gy in PT and CPET. According to the study results, the maximum doses delivered to the spinal cord, head of the humerus bone, and thyroid were reduced significantly as measured the CPET technique. In contrast, no significant difference was observed regarding the dose delivered to the heart and lung. The dose delivered to the supraclavicular region determined by the CPET was significantly augmented. Furthermore, the coverage of the tumor mass was optimized using the new method.

HALFMOON TomoTherapy (Helical ALtered Fractionation for iMplant partial OmissiON): implant-sparing post-mastectomy radiotherapy reshaping the clinical target volume in the reconstructed breast

PURPOSE

To report the dosimetric feasibility of the radiation technique HALFMOON (Helical ALtered Fractionation for iMplant partial OmissiON) for post-mastectomy radiation therapy (PMRT) in intermediate-high-risk breast cancer patients with implant-based immediate breast reconstruction, where the clinical target volume (CTV) does not include the whole implant (implant-sparing approach).

METHODS

In the HALFMOON technique, the CTV consisted of skin, subcutaneous tissues, and pectoralis major muscle, excluding the implant, chest wall muscles, and rib plane. The HALFMOON plans were compared with conventionally contoured CTV plans, in which the whole implant, chest wall muscles, and ribs plane were included in the CTV, in a ratio 1:3. All patients underwent hypofractionated treatment of 40.05 Gy/15 fractions, using helical Tomotherapy^®.

RESULTS

Eighteen patients undergoing HALFMOON technique were compared to 54 subjects treated with conventionally contoured CTV plans. No difference was found in the planning target volume coverage between the two groups. Conversely, a statistically relevant dose reduction in HALFMOON patients was observed for ipsilateral lung (D_15%, p < 0.0001; D_20%, p < 0.0001; D_35%, p = 0.003), contralateral lung (D_20%, p = 0.048), contralateral breast (D_15%, p = 0.031; D_20%, p = 0.047), and stomach (D_mean, p = 0.011). Regarding the implant, V_90% and D_50% decreased by 46% and 8%, respectively, in the HALFMOON plans (p < 0.0001).

CONCLUSION

The HALFMOON approach is technically feasible and resulted in high-dose conformity of the target with a significant reduction of radiation dose delivered to implant and other organs. A clinical study is needed to assess the impact on reconstruction cosmetic outcome and local control.

Jaw position uncertainty and adjacent fields in breast cancer radiotherapy

Locoregional treatment of breast cancer involves adjacent, half blocked fields matched at isocenter. The objective of this work is to study the dosimetric effects of the uncertainties in jaw positioning for such a case, and how a treatment planning protocol including adjacent field overlap of 1 mm affects the dose distribution. A representative treatment plan, involving 6 and 15 photon beams, for a patient treated at our hospital is chosen. Monte Carlo method (EGSnrc/BEAMnrc) is used to simulate the treatment. Uncertainties in jaw positioning of ± 1 mm are addressed, which implies extremes in reality of 2 mm field gap/overlap when planning adjacent fields without overlap and 1 mm gap or 3 mm overlap for a planning protocol with 1 mm overlap. Dosimetric parameters for PTV, lung and body are analyzed. Treatment planning protocol with 1 mm overlap of the adjacent fields does not considerably counteract possible underdosage of the target in the case studied. PTV-V95% is for example reduced from 95% for perfectly aligned fields to 90% and 91% for 2 mm and 1 mm gap, respectively. However, the risk of overdosage in PTV and in healthy soft tissue is increased when following the protocol with 1 mm overlap. A 3 mm overlap compared to 2 mm overlap results in an increase in maximum dose to PTV, PTV-D2%, from 113% to 121%. V120% for 'Body-PTV' is also increased from 5 cm(3) to 14 cm(3). A treatment planning protocol with 1 mm overlap does not considerably improve the coverage of PTV in the case of erroneous jaw positions causing gap between fields, but increases the overdosage in PTV and doses to healthy tissue, in the case of overlapping fields, for the case investigated.

Inter-departmental dosimetry audits - development of methods and lessons learned

External dosimetry audits give confidence in the safe and accurate delivery of radiotherapy. In the United Kingdom, such audits have been performed for almost 30 years. From the start, they included clinically relevant conditions, as well as reference machine output. Recently, national audits have tested new or complex techniques, but these methods are then used in regional audits by a peer-to-peer approach. This local approach builds up the radiotherapy community, facilitates communication, and brings synergy to medical physics.

A three-field monoisocentric inverse breast treatment planning technique without half-beam blocking

The purpose of this study was to introduce a three‐field monoisocentric inverse treatment planning method without half‐beam blocks for breast cancer radiation treatments. Three‐field monoisocentric breast treatment planning with half‐beam blocks limits the tangential field length to 20 cm. A dual‐isocenter approach accommodates patients with larger breasts, but prolongs treatment time and may introduce dose uncertainty at the matching plane due to daily setup variations. We developed a novel monoisocentric, three‐field treatment planning method without half‐beam blocking. The new beam‐matching method utilizes the full field size with a single isocenter. Furthermore, an open/IMRT hybrid inverse optimization method was employed to improve dose uniformity and coverage. Geometric beam matching was achieved by rotating the couch, collimator, and gantry together. Formulae for three‐field geometric matching were derived and implemented in Pinnacle scripts. This monoisocentric technique can be used for patients with larger breast size. The new method has no constraints on the length of tangential fields. Compared with the dual‐isocenter method, it can significantly reduce patient setup time and uncertainties.

PACS number: 87.55.D‐

Comparing the monoisocentric and dual isocentric techniques in chest wall radiotherapy of mastectomy patients

The monoisocentric (MIT) and dual isocentric (DIT) techniques are compared for the mastectomy patients undergoing chest wall radiotherapy, and a new practical method is suggested for determining the dose calculation reference point to be used in the MIT. Data of 18 mastectomy patients having chest wall radiotherapy were used. To find the appropriate dose calculation reference point for the MIT, the target tissue was divided into nine regions with 17 points as the appropriate candidates. After finding the best reference point for the MIT, dose calculations were made for each patient based on the MIT and DIT to determine the dose distributions of the target volume and organs at risk. The lateral component of the dose calculation reference point was found to be located at one-third of the distance between the geometrical center and the lateral border of the chest wall in the lateral direction toward the outer border. The longitudinal component of this point was found to be located at the geometrical center of the chest wall with a depth located around 2-3 cm under the patients' skin. There was no significant difference between the two radiotherapy planning techniques (MIT and DIT) regarding the dose distributions in the organs at risk and the 95% of the prescribed dose coverage of the target tissue. However, a significant difference for the 105% of the prescribed dose coverage, maximum dose delivered to the target tissue, and the level 2 lymph nodes dose was found, with the DIT showing higher values. Because of the good matching and no superposition observed between the treatment fields in the MIT, it was expected and confirmed that the hot and cold regions (with higher and lower doses than the prescribed dose) with the MIT are significantly fewer than that of the DIT. Therefore, to perform a better conformal radiotherapy for the patients having mastectomy, it could be recommended to use the MIT instead of the DIT and other conventional techniques.

Dosimetric analysis of the brachial plexus among patients with breast cancer treated with post-mastectomy radiotherapy to the ipsilateral supraclavicular area: report of 3 cases of radiation-induced brachial plexus neuropathy

Background

The purpose of this study was to evaluate the brachial plexus (BP) dose of postmastectomy radiotherapy (PMRT) to the ipsilateral supraclavicular (ISCL) area, and report the characteristics of radiation-induced brachial plexus neuropathy (RIBPN).

Methods

The BP dose of 31 patients who received adjuvant PMRT to the ISCL area and chest wall using three-dimensional conformal radiotherapy (3DCRT) and the records of 3 patients with RIBPN were retrospectively analyzed based on the standardized Radiation Therapy Oncology Group-endorsed guidelines. The total dose to the ISCL area and chest wall was 50 Gy in 25 fractions.

Results

Patients with a higher number of removed lymph nodes (RLNs) had a higher risk of RIBPN (hazard ratio [HR]: 1.189, 95% confidence interval [CI]: 1.005-1.406, p = 0.044). In 31 patients treated with 3DCRT, the mean dose to the BP without irradiation to the ISCL area was significantly less than that with irradiation to the ISCL area (0.97 ± 0.20 vs. 44.39 ± 4.13 Gy, t = 136.75, p <0.001). In the 3DCRT plans with irradiation to the ISCL area and chest wall, the maximum dose to the BP was negatively correlated with age (r = −0.40, p = 0.026), body mass index (BMI) (r = −0.44, p = 0.014), and body weight (r = −0.45, p = 0.011). Symptoms of the 3 patients with RIBPN occurred 37–65 months after radiotherapy, and included progressive upper extremity numbness, pain, and motor disturbance. After treatment, 1 patient was stable, and the other 2 patients’ symptoms worsened.

Conclusions

The incidence of RIBPN was higher in patients with a higher number of RLNs after PMRT. The dose to the BP is primarily from irradiation of the ISCL area, and is higher in slim and young patients. Prevention should be the main focus of managing RIBPN, and the BP should be considered an organ-at-risk when designing a radiotherapy plan for the ISCL area.

Influence of Individualized Stabilization on the Consistency of Supraclavicular Fossa Positioning in Breast Radiation Therapy: A Retrospective Study

INTRODUCTION

The accurate stabilization of breast patients who are also undergoing supraclavicular fossa treatment is essential and can be challenging. Discrepancy in setup error for these patients often lies with the position of the clavicle in relationship with other anatomic structures. This study was performed to assess how individualized stabilization can improve patient's stability and reproducibility.

METHODS

Thirty patients stabilized with an individualized vacfix located on a Civco wing board (Civco Medical Solutions, Kalona, IA) were compared with 30 patients stabilized in the traditional manner on a Civco breast board (Civco Medical Solutions). Each of these patients underwent daily imaging using the Varian Clinac iX On-board Imaging System (Varian Medical Systems, Palo Alto, CA), and image mismatch data for each session were collected. Additionally, the relationship between the clavicle and vertebrae was assessed for each stabilization solution on a daily basis. Statistical analysis of this data was then performed using a mixed effects approach to take account of data grouping by patient specifically for the displacement error in each direction.

RESULTS

The use of an individualized vacfix decreased the overall systematic and random setup errors and displayed a reduction in the standard deviation of setup error. Patients positioned using breast board stabilization with the clavicle as the match method were exposed in the longitudinal direction to a systematic error of a 95% confidence interval (CI) of 2.6-4.5 mm and a random error of a 95% CI of 2.7-3.2 mm. This was significantly reduced for vacfix stabilization with a systematic error of a 95% CI of 1.2-2.3 mm and a random error of a 95% CI of 1.8-2.3 mm. These data amount to a reduction of the systematic error by 40% (P = .02) and a random error by 25% (P = .003) when using the vacfix method compared with the breast board. The data displaying the relationship between the clavicle and other anatomy within the treatment volume appear to be more consistent with the individualized vacfix approach.

CONCLUSIONS

Reproducible and consistent stabilization for the breast/supraclavicular fossa technique is vital in terms of ensuring accurate patient position. Analysis of the setup error for clavicle and spinous process matching strongly indicates a reduction in both the systematic and random setup error achieved by the vacfix. This illustrates the increased stability and reproducibility of patient positioning when an individualized vacfix is used.

Comparison of three-dimensional versus intensity-modulated radiotherapy techniques to treat breast and axillary level III and supraclavicular nodes in a prone versus supine position

BACKGROUND AND PURPOSE

To determine the optimal method of targeting breast and regional nodes in selected breast cancer patients after axillary dissection, we compared the results of IMRT versus no IMRT, and CT-informed versus clinically-placed fields, in supine and prone positions.

MATERIALS AND METHODS

Twelve consecutive breast cancer patients simulated both prone and supine provided the images for this study. Four techniques were used to target breast, level III axilla, and supraclavicular fossa in either position: a traditional three-field three-dimensional conformal radiotherapy (3DCRT) plan, a four-field 3DCRT plan using a posterior axillary boost field, and two techniques using a CT-informed target volume consisting of an optimized 3DCRT plan (CT-planned 3D) and an intensity-modulated radiotherapy (IMRT) plan. The prescribed dose was 50 Gy in 25 fractions.

RESULTS

CT-planned 3D and IMRT techniques improved nodal PTV coverage. Supine, mean nodal PTV V50 was 50% (3-field), 59% (4-field), 92% (CT-planned 3D), and 94% (IMRT). Prone, V50 was 29% (3-field), 42% (4-field), 97% (CT-planned 3D), and 95% (IMRT). Prone positioning, compared to supine, and IMRT technique, compared to 3D, lowered ipsilateral lung V20.

CONCLUSIONS

Traditional 3DCRT plans provide inadequate nodal coverage. Prone IMRT technique resulted in optimal target coverage and reduced ipsilateral lung V20.

Managing supraclavicular disease from breast cancer with brachial plexus-sparing techniques using helical tomotherapy

AIMS

Managing supraclavicular fossa (SCF) disease in patients with breast cancer can be challenging, with brachial plexopathy recognised as a complication of high-dose radiotherapy to the SCF. Local control of SCF disease is an important end point. Intensity-modulated radiotherapy (IMRT) techniques provide a steep dose gradient and improve the therapeutic index, making it possible to escalate dose to planning target volumes (PTVs), while reducing the dose to organs at risk (OAR). We explored image-guided IMRT techniques using helical tomotherapy to dose escalate SCF lymph nodes with a view to restrict the dose to the brachial plexus.

MATERIALS AND METHODS

Three cases with SCF nodal disease in varying clinical stages of breast cancer were planned and treated using helical tomotherapy-IMRT to assess the feasibility and safety of radiotherapy dose escalation to improve the chances of local control in SCF while restricting the dose to the brachial plexus. Consultant clinical oncologists were asked to define the PTVs and OARs as per agreed inhouse policy. The brachial plexus was outlined as a separate OAR in all three cases. In case 1 the left breast and SCF were treated with adjuvant radiotherapy (40 Gy in 15 fractions) with a sequential boost (10 Gy in five fractions) to the SCF PTV. In case 2, local recurrence was salvaged using a simultaneous integrated boost to the gross tumour plus a 3 mm margin to 63 Gy and 54 Gy to the entire SCF. Case 3 was to control nodal disease with re-irradiation of the SCF to a median dose of 44 Gy, while maintaining a low dose to the brachial plexus. Inverse planning constraints (helical tomotherapy) were applied to the PTV and OARs with the brachial plexus allowed a maximum biologically effective dose (BED) of 120 Gy.

RESULTS

It was possible to treat the SCF to a higher dose using helical tomotherapy-IMRT. The treatment was successful in controlling disease in the SCF. No patients reported symptoms suggestive of brachial plexopathy.

CONCLUSION

Sequential or simultaneous integrated boost to the SCF was safe and feasible. This is the first publication of dose escalation to the SCF when treating breast cancer with brachial plexus-sparing IMRT techniques. The feasibility of such techniques warrants a multicentre phase II study of dose escalation with IMRT to improve local control in isolated SCF disease.

Clinical applications of geometrical field matching in radiotherapy based on a new analytical solution

A new analytical formalism has been published recently that provides all the parameters necessary for geometrical field matching in radiotherapy. The present work applies the general expressions for craniospinal irradiation, breast irradiation with a supraclavicular half-field, and breast irradiation with a supraclavicular full-field. We also explore the formalism as a tool to analyze and compare different techniques. Field matching is achieved by imposing both parallelism and coincidence between the side planes of adjacent fields. The rotation angles and either the field aperture for a certain isocenter position or the isocenter coordinates for a given field aperture are supplied. All of the already known exact solutions are reproduced. New expressions for the field aperture and for the isocenter coordinates, which were not previously available, are also computed. If tangential fields at a fixed source-to-skin distance are used together with a supraclavicular full-field, different apertures for each tangential field are required to achieve a correct match. If an isocentric technique for the tangential fields or a supraclavicular half-field is used, this complication is avoided. The breast technique with the supraclavicular half-field is recommended, because it presents several advantages with respect to the supraclavicular full-field. This formalism provides a useful tool in cases where matching of adjacent fields is necessary.