Critical appraisal of treatment techniques based on conventional photon beams, intensity modulated photon beams and proton beams for therapy of intact breast

Exploring Helium Ions' Potential for Post-Mastectomy Left-Sided Breast Cancer Radiotherapy

Proton therapy presents a promising modality for treating left-sided breast cancer due to its unique dose distribution. Helium ions provide increased conformality thanks to a reduced lateral scattering. Consequently, the potential clinical benefit of both techniques was explored. An explorative treatment planning study involving ten patients, previously treated with VMAT (Volumetric Modulated Arc Therapy) for 50 Gy in 25 fractions for locally advanced, node-positive breast cancer, was carried out using proton pencil beam therapy with a fixed relative biological effectiveness (RBE) of 1.1 and helium therapy with a variable RBE described by the mMKM (modified microdosimetric kinetic model). Results indicated that target coverage was improved with particle therapy for both the clinical target volume and especially the internal mammary lymph nodes compared to VMAT. Median dose value analysis revealed that proton and helium plans provided lower dose on the left anterior descending artery (LAD), heart, lungs and right breast than VMAT. Notably, helium therapy exhibited improved ipsilateral lung sparing over protons. Employing NTCP models as available in the literature, helium therapy showed a lower probability of grade ≤ 2 radiation pneumonitis (22% for photons, 5% for protons and 2% for helium ions), while both proton and helium ions reduce the probability of major coronary events with respect to VMAT.

Proton Beam Therapy for Breast Cancer

Given the radiobiological and physical properties of the proton, proton beam therapy has the potential to be advantageous for many patients compared with conventional radiotherapy by limiting toxicity and improving patient outcomes in specific breast cancer scenarios.

The use of Hybrid Techniques in Whole-Breast Radiotherapy: A Systematic Review

Objectives The development of new techniques in radiotherapy (RT) provides a better planned target volume (PTV) dose distribution while further improving the protection of organs at risk (OARs). The study aims to present the dosimetric results of studies using hybrid techniques in whole-breast radiotherapy (WBRT). Methods: This systematic literature review was conducted by scanning the relevant literature in PubMed, Scopus, and Web of Science following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Among the parameters are dose values for PTV and OARs beam contribute ratios, the value of monitors, and treatment times for different RT techniques. Initially, 586 articles were identified; 196 duplicate articles were removed leaving 391 articles for screening. Three-hundred and thirty-seven irrelevant articles were excluded, leaving 54 studies assessed for eligibility. A total of 22 articles met the search criteria to evaluate dosimetric results of hybrid and other RT techniques in WBRT. Results: According to the dosimetric data of the studies, hybrid intensity-modulated RT (H-IMRT) and hybrid volumetric-modulated arc therapy (H-VMAT) techniques give dosimetrically advantageous results in WBRT compared to other RT techniques. Conclusion: Hybrid techniques using appropriate beams contribute value and show great promise in improving dosimetric results in WBRT. However, there is a need for new studies showing the long-term clinical results of hybrid RT.

Proton Therapy for Breast Cancer: A Consensus Statement From the Particle Therapy Cooperative Group Breast Cancer Subcommittee

Radiation therapy plays an important role in the multidisciplinary management of breast cancer. Recent years have seen improvements in breast cancer survival and a greater appreciation of potential long-term morbidity associated with the dose and volume of irradiated organs. Proton therapy reduces the dose to nontarget structures while optimizing target coverage. However, there remain additional financial costs associated with proton therapy, despite reductions over time, and studies have yet to demonstrate that protons improve upon the treatment outcomes achieved with photon radiation therapy. There remains considerable heterogeneity in proton patient selection and techniques, and the rapid technological advances in the field have the potential to affect evidence evaluation, given the long latency period for breast cancer radiation therapy recurrence and late effects. In this consensus statement, we assess the data available to the radiation oncology community of proton therapy for breast cancer, provide expert consensus recommendations on indications and technique, and highlight ongoing trials' cost-effectiveness analyses and key areas for future research.

Dosimetric Comparison of Whole Breast Radiotherapy Using Field-in-Field and Volumetric Modulated Arc Therapy Techniques in Left-Sided Breast Cancer Patients

Introduction

The radiotherapy of left-sided breast cancers is challenging because of neighboring critical organs, posing an increased risk of complications. Various radiation delivery techniques have been used to deliver the desired dose of radiation to the target area while keeping the doses to nearby structures within constraints.

The main aim of this study is to quantify doses delivered to the organs at risk (OARs) including heart, left lung, spinal cord, and contralateral breast, and to the planning target volume (PTV) using Field-in-Field (FIF) and Volumetric Modulated Arc Therapy (VMAT).

Patients and methods

A retrospective review of 15 left-sided breast cancer patients was done. All the patients underwent breast-conserving surgery and adjuvant radiation. For every patient, two different radiation treatment plans were formulated and compared for the PTV coverage and doses to OARs, including heart, ipsilateral lung, spinal cord, and contralateral breast.

The radiation treatment techniques utilized for this purpose were FIF and VMAT. The homogeneity index (HI), and conformity index (CI) required for the treatment planning were also calculated. Data was analyzed using Statistical Package for the Social Sciences (IBM Corp., Armonk, USA). An Independent T-test was used for statistical analysis.

Results

The mean age was 41 years and the majority of them were stage II. Total nine patients were given 4005centi Gray (cGy) in 15 fractions (fr) followed by 10Gy boost, hence receiving a total dose of 5005cGy in 20fr. While remaining six patients were given a total dose 4005cGy in 15fr without any boost.

All patients were hypofractionated and the dose was delivered at a rate of 267cGy per fr. The FIF technique utilized in breast cancer radiation significantly reduced the mean doses to OARs: mean heart dose (3.81cGy), ipsilateral lung dose (V16- 15cGy), mean contralateral breast dose (0.03cGy), and maximum spinal cord dose (0.18cGy); as compared to VMAT technique which delivered comparatively higher doses: mean heart dose (8.85cGy), ipsilateral lung dose (V16- 19.82cGy), mean contralateral breast dose (4.59cGy), and maximum spinal cord dose (7.14cGy).

There was a significant mean difference between doses of OARs and all p-values were statistically significant (p<0.005). Moreover, the FIF technique also improves the dose distribution of PTV in terms of dose homogeneity. However, the conformity index is more enhanced with VMAT as opposed to FIF.

Conclusion

The FIF technique is more advantageous than the VMAT planning technique because it provides better dose distribution in terms of PTV coverage and significantly lower doses to OARs in radiotherapy to left-sided breast cancer.

Future Perspectives of Proton Therapy in Minimizing the Toxicity of Breast Cancer Radiotherapy

The toxicity of radiotherapy is a key issue when analyzing the eligibility criteria for patients with breast cancer. In order to obtain better results, proton therapy is proposed because of the more favorable distribution of the dose in the patient’s body compared with photon radiotherapy. Scientific groups have conducted extensive research into the improved efficacy and lower toxicity of proton therapy for breast cancer. Unfortunately, there is no complete insight into the potential reasons and prospects for avoiding undesirable results. Cardiotoxicity is considered challenging; however, researchers have not presented any realistic prospects for preventing them. We compared the clinical evidence collected over the last 20 years, providing the rationale for the consideration of proton therapy as an effective solution to reduce cardiotoxicity. We analyzed the parameters of the dose distribution (mean dose, Dmax, V5, and V20) in organs at risk, such as the heart, blood vessels, and lungs, using the following two irradiation techniques: whole breast irradiation and accelerated partial breast irradiation. Moreover, we presented the possible causes of side effects, taking into account biological and technical issues. Finally, we collected potential improvements in higher quality predictions of toxic cardiac effects, like biomarkers, and model-based approaches to give the full background of this complex issue.

Particle Therapy for Breast Cancer: Benefits and Challenges

Hadron therapy with protons and carbon ions is widely attracting interest as a potential competitor of conventional photon radiotherapy. Exquisite dose distribution of charged particles allows for a higher local control of the tumor and lower probability of damage to nearby healthy tissues. Heavy ions have presumed biological advantages rising from their high-linear energy transfer (LET) characteristics, including greater cell-killing effectiveness and reduced heterogeneity dependence of radiation response. Although these advantages are clear and supported by data, only 18.0% of proton and carbon ion radiotherapy (CIRT) facilities in Europe are treating breast cancers. This review summarizes the physical and radiobiological properties of charged particles, clinical use of particle beam for breast cancer, and suggested approaches to overcome technical and financial challenges.

Impact of Breast Size on Dosimetric Indices in Proton Versus X-ray Radiotherapy for Breast Cancer

Deep inspiration breath hold (DIBH) radiotherapy is a technique used to manage early stage left-sided breast cancer. This study compared dosimetric indices of patient-specific X-ray versus proton therapy DIBH plans to explore differences in target coverage, radiation doses to organs at risk, and the impact of breast size. Radiotherapy plans of sixteen breast cancer patients previously treated with DIBH radiotherapy were re-planned with hybrid inverse-planned intensity modulated X-ray radiotherapy (h-IMRT) and intensity modulated proton therapy (IMPT). The total prescribed dose was 40.05 Gy in 15 fractions for all cases. Comparisons between the clinical, h-IMRT, and IMPT evaluated doses to target volumes, organs at risk, and correlations between doses and breast size. Although no differences were observed in target volume coverage between techniques, the h-IMRT and IMPT were able to produce more even dose distributions and IMPT delivered significantly less dose to all organs at risk than both X-ray techniques. A moderate negative correlation was observed between breast size and dose to the target in X-ray techniques, but not IMPT. Both h-IMRT and IMPT produced plans with more homogeneous dose distribution than forward-planned IMRT and IMPT achieved significantly lower doses to organs at risk compared to X-ray techniques.

Estimating the second primary cancer risk due to proton therapy compared to hybrid IMRT for left sided breast cancer

BACKGROUND AND PURPOSE

Proton therapy has been proposed as a technique to improve the long-term quality of life of breast cancer patients. This is due to its ability to reduce the dose to healthy tissue compared to conventional X-ray therapy. The aim of this study was to investigate the risk of secondary carcinogenesis due to proton therapy compared to hybrid IMRT for breast treatments.

MATERIAL AND METHODS

In this study, the Pinnacle treatment planning system was used to simulate treatment plans for 15 female left-sided whole breast cancer patients with deep inspiration breath hold scans. Two treatment plans were generated for each patient: hybrid intensity modulated radiotherapy (h-IMRT) and intensity modulated proton therapy (IMPT). Using the dose-volume histograms (DVHs) from these plans, the mean lifetime attributed risk (LAR) for both lungs and the contralateral breast were evaluated using the BEIR VII and Schneider full risk models.

RESULTS

The results from both risk models show lower LAR estimates for the IMPT treatment plan compared to the h-IMRT treatment plan. This result was observed for all organs of interest and was consistent amongst the two separate risk models. For both treatment plans, the organs from most to least at risk were: ipsilateral lung, contralateral breast, and contralateral lung. In all cases, the risk estimated via the BEIR VII model was higher that the Schneider full risk model.

CONCLUSION

The use of proton therapy for breast treatments leads to reduced risk estimates for secondary carcinogenesis. Therefore, proton therapy shows promise in improving the long term treatment outcome of breast patients.

Proton Accelerated Partial Breast Irradiation: Clinical Outcomes at a Planned Interim Analysis of a Prospective Phase 2 Trial

PURPOSE

To perform a planned interim analysis of acute (within 12 months) and late (after 12 months) toxicities and cosmetic outcomes after proton accelerated partial breast irradiation (APBI).

METHODS AND MATERIALS

A total of 100 patients with pTis or pT1-2 N0 (≤3cm) breast cancer status after segmental mastectomy were enrolled in a single-arm phase 2 study from 2010 to 2019. The clinically determined postlumpectomy target volume, including tumor bed surgical clips and operative-cavity soft-tissue changes seen on imaging plus a radial clinical expansion, was irradiated with passively scattered proton APBI (34 Gy in 10 fractions delivered twice daily with a minimum 6-hour interfraction interval). Patients were evaluated at protocol-specific time intervals for recurrence, physician reports of cosmetic outcomes and toxicities, and patient reports of cosmetic outcomes and satisfaction with the treatment or experience.

RESULTS

Median follow-up was 24 months (interquartile range [IQR], 12-43 months). Local control and overall survival were 100% at 12 and 24 months. There were no acute or late toxicities of grade 3 or higher; no patients experienced fat necrosis, fibrosis, infection, or breast shrinkage. Excellent or good cosmesis at 12 months was reported by 91% of patients and 94% of physicians; at the most recent follow-up, these were 94% and 87%, respectively. The most commonly reported late cosmetic effect was telangiectasis (17%). The total patient satisfaction rate for treatment and results at 12 and 24 months was 96% and 100%, respectively. Patients' mean time away from work was 5 days (IQR, 2-5 days), and the median out-of-pocket cost was $700 (IQR, $100-$1600). The mean left-sided heart dose was 2 cGy (range, 0.2-75 cGy), and the mean ipsilateral lung dose was 19 cGy (range, 0.2-164 cGy).

CONCLUSIONS

Proton APBI is a maturing treatment option with high local control, favorable intermediate-term cosmesis, high treatment satisfaction, low treatment burden, and exceptional heart and lung sparing.

Potential skin morbidity reduction with intensity-modulated proton therapy for breast cancer with nodal involvement

Background: Different modern radiation therapy treatment solutions for breast cancer (BC) and regional nodal irradiation (RNI) have been proposed. In this study, we evaluate the potential reduction in radiation-induced skin morbidity obtained by intensity modulated proton therapy (IMPT) compared with intensity modulated photon therapy (IMXT) for left-side BC and RNI. Material and Methods: Using CT scans from 10 left-side BC patients, treatment plans were generated using IMXT and IMPT techniques. A dose of 50 Gy (or Gy [RBE] for IMPT) was prescribed to the target volume (involved breast, the internal mammary, supraclavicular, and infraclavicular nodes). Two single filed optimization IMPT (IMPT₁ and IMPT₂) plans were calculated without and with skin optimization. For each technique, skin dose-metrics were extracted and normal tissue complication probability (NTCP) models from the literature were employed to estimate the risk of radiation-induced skin morbidity. NTCPs for relevant organs-at-risk (OARs) were also considered for reference. The non-parametric Anova (Friedman matched-pairs signed-rank test) was used for comparative analyses. Results: IMPT improved target coverage and dose homogeneity even if the skin was included into optimization strategy (HI_IMPT2 = 0.11 vs. HI_IMXT = 0.22 and CI_IMPT2 = 0.96 vs. CI_IMXT = 0.82, p < .05). A significant relative skin risk reduction (RR = NTCP_IMPT/NTCP_IMXT) was obtained with IMPT₂ including the skin in the optimization with a RR reduction ranging from 0.3 to 0.9 depending on the analyzed skin toxicity endpoint/model. Both IMPT plans attained significant OARs dose sparing compared with IMXT. As expected, the heart and lung doses were significantly reduced using IMPT. Accordingly, IMPT always provided lower NTCP values. Conclusions: IMPT guarantees optimal target coverage, OARs sparing, and simultaneously minimizes the risk of skin morbidity. The applied model-based approach supports the potential clinical relevance of IMPT for left-side BC and RNI and might be relevant for the setup of cost-effectiveness evaluation strategies based on NTCP predictions, as well as for establishing patient selection criteria.

Dosimetric evaluation and systematic review of radiation therapy techniques for early stage node-negative breast cancer treatment

Radiation therapy (RT) is essential in treating women with early stage breast cancer. Early stage node-negative breast cancer (ESNNBC) offers a good prognosis; hence, late effects of breast RT becomes increasingly important. Recent literature suggests a potential for an increase in cardiac and pulmonary events after RT. However, these studies have not taken into account the impact of newer and current RT techniques that are now available. Hence, this review aimed to evaluate the clinical evidence for each technique and determine the optimal radiation technique for ESNNBC treatment. Currently, six RT techniques are consistently used and studied: 1) prone positioning, 2) proton beam RT, 3) intensity-modulated RT, 4) breath-hold, 5) partial breast irradiation, and 6) intraoperative RT. These techniques show dosimetric promise. However, limited data on late cardiac and pulmonary events exist due to challenges in long-term follow-up. Moving forward, future studies are needed to validate the efficacy and clinical outcomes of these current techniques.

Proton therapy for breast cancer: progress & pitfalls

As the number of patients cured from breast cancer increases with improvements in multidisciplinary care, emphasis on reducing late toxicities of treatment has increased, in order to improve long-term quality of life. Proton beam therapy (PBT) is a form of radiotherapy that uses particles with unique physical properties that enable treatment delivery with minimal dose deposition beyond the treatment target. Therefore, PBT has emerged as an exciting radiotherapy modality for breast cancer due to the ability to minimize exposure to the heart, lungs, muscle, and bone. Herein, we review the rationale for PBT in breast cancer, potential clinical applications, and the available clinical data supporting its use. We also address some of the technical and logistical challenges and areas of ongoing research that will ultimately establish the role for PBT for breast cancer in the years ahead.

Dosimetric trade-offs in breast treatment with VMAT technique

OBJECTIVE

Breast planning with volumetric modulated arc therapy (VMAT) has been explored, especially for left-sided breast treatments, with the primary intent of lowering the heart dose and improving target dose homogeneity. As a trade-off, larger healthy tissue volumes would receive low dose levels, with the potential risk of increasing late toxicities and secondary cancer induction, although no clinical data are available today to confirm the risk level. The scope of this work is to explore the dosimetric trade-offs using two different VMAT plans.

METHODS

Two planning strategies for dual-partial-arc VMAT, RA_avoid and RA_full, with and without avoidance sectors, were explored in a cohort of 20 patients, for whole left breast irradiation for 40.05 Gy to the mean target dose in 15 fractions. Common dose objectives included a stringent dose homogeneity, mean dose to the heart <5 Gy, ipsilateral lung (I_lung) <8 Gy, contralateral lung (C_lung) <2 Gy and contralateral breast (C_breast) <3 Gy.

RESULTS

RA_full showed a better dose conformity, lower high-dose spillage in the healthy tissue and lower skin dose. RA_avoid presented a reduction of the mean doses for all critical structures: 51% to the heart, 12% to the I_lung, 81% to the C_lung and 73% to the C_breast. All differences were significant with p < 0.0001.

CONCLUSION

The adaptation of VMAT options to planning objectives reduced significantly the healthy tissue dose levels at the price of some high-dose spillage. Evaluation of the trade-offs for application to the different critical structures should drive in improving the usage of the VMAT technique for breast cancer treatment. Advances in knowledge: Different planning strategies in the same VMAT technique could give significant variations in dose distributions. The choice of the trade-offs would affect the possible future late toxicity and secondary cancer induction risk.

Intensity modulated radiotherapy with simultaneous integrated boost vs. conventional radiotherapy with sequential boost for breast cancer - A preliminary result

PURPOSE

This study was aimed to assess the acute dermatological adverse effect from two distinct RT techniques for breast cancer patients. We compared intensity-modulated radiotherapy with simultaneous integrated boost (IMRT-SIB) and conventional radiotherapy followed by sequential boost (CRT-SB).

METHODS

The study population was composed of 126 consecutive female breast cancer patients treated with breast conserving surgery. Sixty-six patients received IMRT-SIB to 2 dose levels simultaneously. They received 50.4 Gy at 1.8 Gy per fraction to the whole breast and 60.2 Gy at 2.15 Gy per fraction to the tumor bed by integral boost. Sixty patients in the CRT-SB group received 50 Gy in 25 fractions to the whole breast followed by a boost irradiation to tumor bed in 5-7 fractions to a total dose of 60-64 Gy. Acute skin toxicities were documented in agreement with the Common Terminology Criteria for Adverse Events version 3 (CTCAE v.3.0).

RESULTS

Ninety-eight patients had grade 1 radiation dermatitis while 14 patients had grade 2. Among those with grade 2, there were 3 patients in IMRT-SIB group (4.5%) while 11 in CRT-SB group (18.3%). (P = 0.048) There was no patient with higher than grade 2 toxicity. Three year local control was 99.2%, 3-year disease free survival was 97.5% and 3-year overall survival was 99.2%.

CONCLUSIONS

A significant reduction in the severity of acute radiation dermatitis from IMRT-SIB comparing with CRT-SB is demonstrated.

Assessing radiation exposure of the left anterior descending artery, heart and lung in patients with left breast cancer: A dosimetric comparison between multicatheter accelerated partial breast irradiation and whole breast external beam radiotherapy

BACKGROUND AND PURPOSE

This study aims to quantify dosimetric reduction to the left anterior descending (LAD) artery, heart and lung when comparing whole breast external beam radiotherapy (WBEBRT) with multicatheter accelerated partial breast irradiation (MCABPI) for early stage left breast cancer.

MATERIALS AND METHODS

Planning CT data sets of 15 patients with left breast cancer receiving multicatheter brachytherapy post breast conserving surgery were used to create two independent treatment plans - WBEBRT prescribed to 50 Gy/25 fractions and MCABPI prescribed to 34 Gy/10 fractions. Dose parameters for (i) LAD artery, (ii) heart, and (iii) ipsilateral lung were calculated and compared between the two treatment modalities.

RESULTS

After adjusting for Equivalent Dose in 2 Gy fractions(EQD2), and comparing MCAPBI with WBEBRT, the largest dose reduction was for the LAD artery whose mean dose differed by a factor of 7.7, followed by the ipsilateral lung and heart with a factor of 4.6 and 2.6 respectively. Compared to WBEBRT, the mean MCAPBI LAD was significantly lower compared to WBEBRT (6.0 Gy vs 45.9 Gy; p<0.01). Mean MCAPBI heart D(0.1cc) (representing the dose received by the most highly exposed 0.1 cc of the risk organ, i.e. the dose peak) was significantly lower (16.3 Gy vs 50.6 Gy; p<0.01). Likewise, the mean heart dose (MHD) was significantly lower (2.3 Gy vs 6.0 Gy; p<0.01). Peak dose and mean lung dose (MLD) for ipsilateral lung was also lower for MCAPBI compared to WBEBRT (Peak dose: 22.2 Gy vs 52.0 Gy; p<0.01; MLD: 2.3 Gy vs 10.7 Gy; p<0.01).

CONCLUSION

Compared to WBEBRT, MCAPBI showed a significant reduction in radiation dose for the LAD, heart and lung. This may translate into better cardiac and pulmonary toxicities for patients undergoing MCAPBI.

Assessment and quantification of patient set-up errors in nasopharyngeal cancer patients and their biological and dosimetric impact in terms of generalized equivalent uniform dose (gEUD), tumour control probability (TCP) and normal tissue complication probability (NTCP)

OBJECTIVE

The aim of this study is to assess and quantify patients' set-up errors using an electronic portal imaging device and to evaluate their dosimetric and biological impact in terms of generalized equivalent uniform dose (gEUD) on predictive models, such as the tumour control probability (TCP) and the normal tissue complication probability (NTCP).

METHODS

20 patients treated for nasopharyngeal cancer were enrolled in the radiotherapy-oncology department of HCA. Systematic and random errors were quantified. The dosimetric and biological impact of these set-up errors on the target volume and the organ at risk (OARs) coverage were assessed using calculation of dose-volume histogram, gEUD, TCP and NTCP. For this purpose, an in-house software was developed and used.

RESULTS

The standard deviations (1SDs) of the systematic set-up and random set-up errors were calculated for the lateral and subclavicular fields and gave the following results: ∑ = 0.63 ± (0.42) mm and σ = 3.75 ± (0.79) mm, respectively. Thus a planning organ at risk volume (PRV) margin of 3 mm was defined around the OARs, and a 5-mm margin used around the clinical target volume. The gEUD, TCP and NTCP calculations obtained with and without set-up errors have shown increased values for tumour, where ΔgEUD (tumour) = 1.94% Gy (p = 0.00721) and ΔTCP = 2.03%. The toxicity of OARs was quantified using gEUD and NTCP. The values of ΔgEUD (OARs) vary from 0.78% to 5.95% in the case of the brainstem and the optic chiasm, respectively. The corresponding ΔNTCP varies from 0.15% to 0.53%, respectively.

CONCLUSION

The quantification of set-up errors has a dosimetric and biological impact on the tumour and on the OARs. The developed in-house software using the concept of gEUD, TCP and NTCP biological models has been successfully used in this study. It can be used also to optimize the treatment plan established for our patients.

ADVANCES IN KNOWLEDGE

The gEUD, TCP and NTCP may be more suitable tools to assess the treatment plans before treating the patients.

Combined photon-electron beams in the treatment of the supraclavicular lymph nodes in breast cancer: A novel technique that achieves adequate coverage while reducing lung dose

Radiation pneumonitis is a well-documented side effect of radiation therapy for breast cancer. The purpose of this study was to compare combined photon-electron, photon-only, and electron-only plans in the radiation treatment of the supraclavicular lymph nodes. In total, 13 patients requiring chest wall and supraclavicular nodal irradiation were planned retrospectively using combined photon-electron, photon-only, and electron-only supraclavicular beams. A dose of 50Gy over 25 fractions was prescribed. Chest wall irradiation parameters were fixed for all plans. The goal of this planning effort was to cover 95% of the supraclavicular clinical target volume (CTV) with 95% of the prescribed dose and to minimize the volume receiving ≥ 105% of the dose. Comparative end points were supraclavicular CTV coverage (volume covered by the 95% isodose line), hotspot volume, maximum radiation dose, contralateral breast dose, mean total lung dose, total lung volume percentage receiving at least 20 Gy (V(20 Gy)), heart volume percentage receiving at least 25 Gy (V(25 Gy)). Electron and photon energies ranged from 8 to 18 MeV and 4 to 6 MV, respectively. The ratio of photon-to-electron fractions in combined beams ranged from 5:20 to 15:10. Supraclavicular nodal coverage was highest in photon-only (mean = 96.2 ± 3.5%) followed closely by combined photon-electron (mean = 94.2 ± 2.5%) and lowest in electron-only plans (mean = 81.7 ± 14.8%, p < 0.001). The volume of tissue receiving ≥ 105% of the prescription dose was higher in the electron-only (mean = 69.7 ± 56.1 cm(3)) as opposed to combined photon-electron (mean = 50.8 ± 40.9 cm(3)) and photon-only beams (mean = 32.2 ± 28.1 cm(3), p = 0.114). Heart V(25 Gy) was not statistically different among the plans (p = 0.999). Total lung V(20 Gy) was lowest in electron-only (mean = 10.9 ± 2.3%) followed by combined photon-electron (mean = 13.8 ± 2.3%) and highest in photon-only plans (mean = 16.2 ± 3%, p < 0.001). As expected, photon-only plans demonstrated the highest target coverage and total lung V(20 Gy). The superiority of electron-only beams, in terms of decreasing lung dose, is set back by the dosimetric hotspots associated with such plans. Combined photon-electron treatment is a feasible technique for supraclavicular nodal irradiation and results in adequate target coverage, acceptable dosimetric hotspot volume, and slightly reduced lung dose.

Cardiac dose sparing and avoidance techniques in breast cancer radiotherapy

Breast cancer radiotherapy represents an essential component in the overall management of both early stage and locally advanced breast cancer. As the number of breast cancer survivors has increased, chronic sequelae of breast cancer radiotherapy become more important. While recently published data suggest a potential for an increase in cardiac events with radiotherapy, these studies do not consider the impact of newer radiotherapy techniques commonly utilized. Therefore, the purpose of this review is to evaluate cardiac dose sparing techniques in breast cancer radiotherapy. Current options for cardiac protection/avoidance include (1) maneuvers that displace the heart from the field such as coordinating the breathing cycle or through prone patient positioning, (2) technological advances such as intensity modulated radiation therapy (IMRT) or proton beam therapy (PBT), and (3) techniques that treat a smaller volume around the lumpectomy cavity such as accelerated partial breast irradiation (APBI), or intraoperative radiotherapy (IORT). While these techniques have shown promise dosimetrically, limited data on late cardiac events exist due to the difficulties of long-term follow up. Future studies are required to validate the efficacy of cardiac dose sparing techniques and may use surrogates for cardiac events such as biomarkers or perfusion imaging.

Nonisocentric treatment strategy for breast radiation therapy: a proof of concept study

PURPOSE

To propose a nonisocentric treatment strategy as a special form of station parameter optimized radiation therapy, to improve sparing of critical structures while preserving target coverage in breast radiation therapy.

METHODS AND MATERIALS

To minimize the volume of exposed lung and heart in breast irradiation, we propose a novel nonisocentric treatment scheme by strategically placing nonconverging beams with multiple isocenters. As its name suggests, the central axes of these beams do not intersect at a single isocenter as in conventional breast treatment planning. Rather, the isocenter locations and beam directions are carefully selected, in that each beam is only responsible for a certain subvolume of the target, so as to minimize the volume of irradiated normal tissue. When put together, the beams will provide an adequate coverage of the target and expose only a minimal amount of normal tissue to radiation. We apply the nonisocentric planning technique to 2 previously treated clinical cases (breast and chest wall).

RESULTS

The proposed nonisocentric technique substantially improved sparing of the ipsilateral lung. Compared with conventional isocentric plans using 2 tangential beams, the mean lung dose was reduced by 38% and 50% using the proposed technique, and the volume of the ipsilateral lung receiving ≥ 20 Gy was reduced by a factor of approximately 2 and 3 for the breast and chest wall cases, respectively. The improvement in lung sparing is even greater compared with volumetric modulated arc therapy.

CONCLUSIONS

A nonisocentric implementation of station parameter optimized radiation therapy has been proposed for breast radiation therapy. The new treatment scheme overcomes the limitations of existing approaches and affords a useful tool for conformal breast radiation therapy, especially in cases with extreme chest wall curvature.

Accelerated partial-breast irradiation using intensity-modulated proton radiotherapy: do uncertainties outweigh potential benefits?

OBJECTIVE

Passive scattering proton beam (PSPB) radiotherapy for accelerated partial-breast irradiation (APBI) provides superior dosimetry for APBI three-dimensional conformal photon radiotherapy (3DCRT). Here we examine the potential incremental benefit of intensity-modulated proton radiotherapy (IMPT) for APBI and compare its dosimetry with PSPB and 3DCRT.

METHODS

Two theoretical IMPT plans, TANGENT_PAIR and TANGENT_ENFACE, were created for 11 patients previously treated with 3DCRT APBI and were compared with PSPB and 3DCRT plans for the same CT data sets. The impact of range, motion and set-up uncertainties as well as scanned spot mismatching between fields of IMPT plans was evaluated.

RESULTS

IMPT plans for APBI were significantly better regarding breast skin sparing (p<0.005) and other normal tissue sparing than 3DCRT plans (p<0.01) with comparable target coverage (p=ns). IMPT plans were statistically better than PSPB plans regarding breast skin (p<0.002) and non-target breast (p<0.007) in higher dose regions but worse or comparable in lower dose regions. IMPT plans using TANGENT_ENFACE were superior to that using TANGENT_PAIR in terms of target coverage (p<0.003) and normal tissue sparing (p<0.05) in low-dose regions. IMPT uncertainties were demonstrated for multiple causes. Qualitative comparison of dose-volume histogram confidence intervals for IMPT suggests that numeric gains may be offset by IMPT uncertainties.

CONCLUSION

Using current clinical dosimetry, PSPB provides excellent dosimetry compared with 3DCRT with fewer uncertainties compared with IMPT.

ADVANCES IN KNOWLEDGE

As currently delivered in the clinic, PSPB planning for APBI provides as good or better dosimetry than IMPT with less uncertainty.

External-beam accelerated partial breast irradiation using multiple proton beam configurations

PURPOSE

To explore multiple proton beam configurations for optimizing dosimetry and minimizing uncertainties for accelerated partial breast irradiation (APBI) and to compare the dosimetry of proton with that of photon radiotherapy for treatment of the same clinical volumes.

METHODS AND MATERIALS

Proton treatment plans were created for 11 sequential patients treated with three-dimensional radiotherapy (3DCRT) photon APBI using passive scattering proton beams (PSPB) and were compared with clinically treated 3DCRT photon plans. Monte Carlo calculations were used to verify the accuracy of the proton dose calculation from the treatment planning system. The impact of range, motion, and setup uncertainty was evaluated with tangential vs. en face beams.

RESULTS

Compared with 3DCRT photons, the absolute reduction of the mean of V100 (the volume receiving 100% of prescription dose), V90, V75, V50, and V20 for normal breast using protons are 3.4%, 8.6%, 11.8%, 17.9%, and 23.6%, respectively. For breast skin, with the similar V90 as 3DCRT photons, the proton plan significantly reduced V75, V50, V30, and V10. The proton plan also significantly reduced the dose to the lung and heart. Dose distributions from Monte Carlo simulations demonstrated minimal deviation from the treatment planning system. The tangential beam configuration showed significantly less dose fluctuation in the chest wall region but was more vulnerable to respiratory motion than that for the en face beams. Worst-case analysis demonstrated the robustness of designed proton beams with range and patient setup uncertainties.

CONCLUSIONS

APBI using multiple proton beams spares significantly more normal tissue, including nontarget breast and breast skin, than 3DCRT using photons. It is robust, considering the range and patient setup uncertainties.

Superficial doses in breast cancer radiotherapy using conventional and IMRT techniques: a film-based phantom study

BACKGROUND AND PURPOSE

Superficial doses in radiotherapy are affected by the treatment technique. The implications for breast cancer treatments were evaluated.

MATERIAL AND METHODS

Four treatment techniques relevant for breast cancer irradiation were evaluated; tangential standard, tangential IMRT, 7-field IMRT (arc-like field arrangement) and hybrid IMRT (an IMRT plan mixed with non-modulated fields). Only 6MV photons were used. GafChromic EBT film was used for dose measurements at the surface, in the skin (0-5mm depth) and in the superficial parts of CTV (5-10mm depth) of an anthropomorphic thorax phantom.

RESULTS

Only small differences in superficial doses were observed between tangential standard and tangential IMRT. Compared to the tangential standard plan, the surface and skin doses were reduced with the 7-field IMRT plan, on average by 20% and 5%, respectively, while hybrid IMRT reduced the surface and skin doses medially (by 44% and 8%, respectively) and increased the surface and skin dose laterally (by 40% and 15%, respectively). Minimum superficial CTV doses varied between regions, but were mainly between 90% and 95% of the target dose for all plans, only the hybrid IMRT plan resulted in a region with minimum dose below 90%.

CONCLUSIONS

Compared to tangential irradiation, skin sparing was achieved by the 7-field IMRT plan. The minimum dose in the superficial parts of the CTV was below 95% of the target dose for all plans investigated.

Forward planned intensity modulated radiotherapy (IMRT) for whole breast postoperative radiotherapy. Is it useful? When?

The purpose was to compare the dosimetric results observed in 201 breast cancer patients submitted to tangential forward intensity-modulated radiation therapy (IMRT) with those observed in 131 patients treated with a standard wedged 3D technique for postoperative treatment of whole breast, according to breast size and supraclavicular node irradiation. Following dosimetric parameters were used for the comparison: D(max), D(min), D(mean), V(95%) and V(107%) for the irradiated volume; D(max), D(mean), V(80%) and V(95%) for the ipsilateral lung; D(max), D(mean), V(80%) and V(95%) for the heart. Stratification was made according to breast size and supraclavicular (SCV) nodal irradiation. As respect to irradiated volume, a significant reduction of V(107%) (mean values: 7.0 ± 6.6 versus 2.4 ± 3.7, p < 0.001) and D(max) (mean % values: 111.2 ± 2.7 versus 107.7 ± 6.3, p < 0.001), and an increase of D(min) (mean % values: 65.0 ± 17.4 versus 74.9 ± 12.9, p < 0.001) were observed with forward IMRT. The homogeneity of dose distribution to target volume significantly improved with forward IMRT in all patient groups, irrespective of breast size or supraclavicular nodal irradiation. When patients treated with supraclavicular nodal irradiation were excluded from the analysis, forward IMRT slightly reduced V(80%) (mean values: 3.7 ± 2.6 versus 3.0 ± 2.4, p = 0.03) and V(95%) (mean values 1.9 ± 1.8 versus 1.2%± 1.5; p = 0.001) of the ipsilateral lung. The dose to the heart tended to be lower with IMRT but this difference was not statistically significant. Tangential forward IMRT in postoperative treatment of whole breast improved dosimetric parameters in terms of homogeneity of dose distribution to the target in a large sample of patients, independent of breast size or supraclavicular nodal irradiation. Lung irradiation was slightly reduced in patients not undergoing to supraclavicular irradiation.

Comparison of electron IMRT to helical photon IMRT and conventional photon irradiation for treatment of breast and chest wall tumours

BACKGROUND AND PURPOSE

Conventional irradiation of breast and chest wall tumours may cause high doses in underlying organs. Intensity-modulated radiation therapy (IMRT) with photons achieves high conformity between treated and tumour volume but is associated with considerable low-dose effects which may induce secondary malignancies. We compare treatment plans of electron IMRT to helical photon IMRT and conventional irradiation.

MATERIAL AND METHODS

Treatment planning for three patients (breast, chest wall plus lymph nodes, sarcoma of medial chest wall/sternum) was performed using XiO 4.3.3 (CMS) for conventional photon irradiation, Hi-Art 2.2.2.05 (TomoTherapy) for helical photon IMRT, and a self-designed programme for electron IMRT.

RESULTS

The techniques resulted in similar mean and maximum target doses. Target coverage by the 95%-isodose was best with tomotherapy. Mean ipsilateral lung doses were similar with all techniques. Electron IMRT achieved best sparing of heart, and contralateral breast. Compared with photon IMRT, electron IMRT allowed better sparing of contralateral lung and total healthy tissue.

CONCLUSIONS

Electron IMRT is superior to conventional irradiation, as it allows satisfying target coverage and avoids high doses in underlying organs. Its advantage over photon IMRT is better sparing of most organs at risk (low-dose effects) which reduces the risk of radiation-induced malignancies.

Do we have enough evidence to implement particle therapy as standard treatment in lung cancer? A systematic literature review

BACKGROUND

The societal burden of lung cancer is high because of its high incidence and high lethality. From a theoretical point of view, radiotherapy with beams of protons and heavier charged particles, for example, carbon ions (C-ions), should lead to superior results, compared with photon beams. In this review, we searched for clinical evidence to justify implementation of particle therapy as standard treatment in lung cancer.

METHODS

A systematic literature review based on an earlier published comprehensive review was performed and updated through November 2009.

RESULTS

Eleven fully published studies, all dealing with non-small cell lung cancer (NSCLC), mainly stage I, were identified. No phase III trials were found. For proton therapy, 2- to 5-year local tumor control rates varied in the range of 57%-87%. The 2- and 5-year overall survival (OS) and 2- and 5-year cause-specific survival (CSS) rates were 31%-74% and 23% and 58%-86% and 46%, respectively. Radiation-induced pneumonitis was observed in about 10% of patients. For C-ion therapy, the overall local tumor control rate was 77%, but it was 95% when using a hypofractionated radiation schedule. The 5-year OS and CSS rates were 42% and 60%, respectively. Slightly better results were reported when using hypofractionation, 50% and 76%, respectively.

CONCLUSION

The present results with protons and heavier charged particles are promising. However, the current lack of evidence on the clinical (cost-)effectiveness of particle therapy emphasizes the need to investigate the efficiency of particle therapy in an adequate manner. Until these results are available for lung cancer, charged particle therapy should be considered experimental.

Proton spot scanning radiotherapy of spontaneous canine tumors

Thirty dogs with spontaneous tumors were irradiated with proton therapy using a novel spot scanning technique to evaluate the safety and efficacy of the system, and to study the acute and late radiation reactions. Nasal tumors, soft tissue sarcomas, and miscellaneous tumors of the head were treated with a median total dose of 52.5 Gy given in 3.5 Gy fractions. Acute effects, late effects, tumor response, and outcome were analyzed. No unexpected radiation reactions were seen, however two dogs did develop in-field osteosarcoma, and one dog developed in-field bone necrosis. Complete response to therapy was seen in 40% (12/30), partial response in 47% (14/30), and no response in 13% (4/30). Median survival for all dogs was 385 days (range of 14-4583 days). Dogs with nasal cavity tumors had a median survival of 385 days (range of 131-1851 days) and dogs with soft tissue sarcomas had a median survival time of 612 days (range of 65-4588 days). Treatment outcome was similar to historical controls. This new proton spot scanning technique proved to be safe and reliable.

Simultaneous integrated boost radiotherapy for bilateral breast: a treatment planning and dosimetric comparison for volumetric modulated arc and fixed field intensity modulated therapy

Purpose

A study was performed comparing dosimetric characteristics of volumetric modulated arcs (RapidArc, RA) and fixed field intensity modulated therapy (IMRT) on patients with bilateral breast carcinoma.

Materials and methods

Plans for IMRT and RA, were optimised for 10 patients prescribing 50 Gy to the breast (PTVII, 2.0 Gy/fraction) and 60 Gy to the tumour bed (PTVI, 2.4 Gy/fraction). Objectives were: for PTVs V_90%>95%, D_max<107%; Mean lung dose MLD<15 Gy, V_{20 Gy}<22%; heart involvement was to be minimised. The MU and delivery time measured treatment efficiency. Pre-treatment dosimetry was performed using EPID and a 2D-array based methods.

Results

For PTVII minus PTVI, V_90% was 97.8 ± 3.4% for RA and 94.0 ± 3.5% for IMRT (findings are reported as mean ± 1 standard deviation); D_5%-D_95% (homogeneity) was 7.3 ± 1.4 Gy (RA) and 11.0 ± 1.1 Gy (IMRT). Conformity index (V_95%/V_PTVII) was 1.10 ± 0.06 (RA) and 1.14 ± 0.09 (IMRT). MLD was <9.5 Gy for all cases on each lung, V_{20 Gy} was 9.7 ± 1.3% (RA) and 12.8 ± 2.5% (IMRT) on left lung, similar for right lung. Mean dose to heart was 6.0 ± 2.7 Gy (RA) and 7.4 ± 2.5 Gy (IMRT). MU resulted in 796 ± 121 (RA) and 1398 ± 301 (IMRT); the average measured treatment time was 3.0 ± 0.1 minutes (RA) and 11.5 ± 2.0 (IMRT). From pre-treatment dosimetry, % of field area with γ <1 resulted 98.8 ± 1.3% and 99.1 ± 1.5% for RA and IMRT respectively with EPID and 99.1 ± 1.8% and 99.5 ± 1.3% with 2D-array (ΔD = 3% and DTA = 3 mm).

Conclusion

RapidArc showed dosimetric improvements with respect to IMRT, delivery parameters confirmed its logistical advantages, pre-treatment dosimetry proved its reliability.

Clinical experience in breast irradiation with intensity modulated photon beams

Since 2002, twenty-five patients affected by breast cancer, for whom extensive lung/heart involvement was expected from conventional techniques, were irradiated with intensity modulated photon beams (IMRT). For 10 patients the internal mammary lymphatic chain was included in the target, 6 patients received treatment of the thoracic wall after mastectomy and 9 patients were treated after breast conserving surgery. Dose prescription ranged between 48.6 and 50 Gy at 1.8 or 2 Gy per fraction. The target volume (PTV) ranged from 194 to 2121 cm3. For all cases a Dose Volume Histogram analysis has been conducted on omolateral lung, heart, contralateral lung and breast, healthy tissue and PTV. For PTV the volume receiving more than 90% of the prescribed dose (V90%) was 95.8+/-1.8% while V107% = 5.3+/-2.8%. The mean dose computed for the heart was 10.4+/-2.9 Gy, for the omolateral lung: 13.3+/-2.8 Gy, for the contralateral breast: 3.4+/-1.8 Gy, for the contralateral lung: 4.6+/-2.7 Gy. For the omolateral lung V20Gy = 23.1+/-7.0% and V45Gy = 0.8+/-0.9 Gy. With a short mean follow up of 10.4 months, no pulmonary or cardiac complications were observed. IMRT proved to be technically feasible on a clinical basis for the treatment of the whole breast, including internal mammary chain, or of the thoracic wall after mastectomy.

A pilot study to assess the utility of SPECT/CT-based lymph node imaging to localize lymph nodes that drain the arm in patients undergoing treatment for breast cancer

Image-guided treatment planning that minimizes irradiation of critical lymph nodes (LNs) may reduce the incidence and severity of long term complications following breast cancer treatment. This localization cannot be obtained with conventional imaging techniques and we undertook this proof of concept study to determine whether a coordinated use of SPECT and CT has sufficient precision to inform radiation planning and potentially lessen the incidental exposure of critical LNs. Thirty-two consecutive women with breast cancer were injected in the arm ipsilateral to their breast cancers prior to radiation treatment with 0.5 mCi of filtered (99m)Tc-sulfur colloid and underwent scanning with a hybrid device which combined a dual-head SPECT camera and a low-dose, single slice CT scanner. The number of visualized LNs as well as their locations, maximum counts, and total uptake were recorded. Coordinates derived from the SPECT/CT fusion images were used to map LN locations onto the 3D radiation treatment planning system. A mean of 3.4 (SD 2.0) lymph nodes were detected in each subject. Level I and II LNs were detected more often in patients who had sentinel node biopsies, and more supraclavicular nodes were detected in patients who had undergone axillary dissection (P < 0.001). SPECT-CT derived LN coordinates were successfully mapped onto radiation simulation CT scans for all patients. SPECT/CT fusion images localize the LNs draining the arm after breast cancer surgery. These finding suggest that SPECT/CT may be helpful in minimizing incidental LN irradiation and in directing breast cancer therapy to reduce long-term morbidity.

Particle therapy in lung cancer: where do we stand?

BACKGROUND

From a theoretical point of view, charged particles should lead to superior results compared to photons. In this review, we searched for clinical evidence that protons or C-ions are really beneficial to patients with lung cancer.

METHODS

A systematic literature review based on an earlier published comprehensive review was performed and updated until November 1st 2007.

RESULTS

Ten fully published series, all dealing with non-small cell lung cancer (NSCLC), mainly stage I, were identified. No phase III trials were found. On proton therapy, 2-5 year local tumor control rates varied between 87% and 57%. The 2 year/5 year overall survival and 2 year/5 year cause specific survival varied between 31-74%/23% and 58-86%/46%, respectively. Late side effects were observed in about 10% of the patients. For C-ion therapy, the local tumor control rate was 77%, while 95% when using a hypofractionated radiation schedule. The 5 year overall survival and cause specific survival rates were 42% and 60%, respectively. Slightly better results were reported when using hypofractionation, 50% and 76%, respectively. The reported late side effects for C-ions were 4%.

CONCLUSION

The results with charged particles, at least for stage I disease, seem to be promising. A gain can be expected in reduction of late side effects, especially after treatment with C-ions. Available data demonstrate that particle therapy in general is a safe and feasible treatment modality. Although current results are promising, more evidence is required before particle therapy can become internationally the standard treatment for (subsets of) lung cancer patients.

Skin-sparing radiation using intensity-modulated radiotherapy after conservative surgery in early-stage breast cancer: a planning study

PURPOSE

To evaluate the feasibility of skin-sparing by configuring it as an organ-at-risk (OAR) while delivering whole-breast intensity-modulated radiotherapy (IMRT) in early breast cancer.

METHODS AND MATERIALS

Archival computed tomography scan images of 14 left-sided early-breast tumor patients who had undergone lumpectomy were selected for this study. Skin was contoured as a 4- to 5-mm strip extending from the patient outline to anterior margin of the breast planning target volume (PTV). Two IMRT plans were generated by the helical tomotherapy approach to deliver 50 Gy in 25 fractions to the breast alone: one with skin dose constraints (skin-sparing plan) and the other without (non-skin-sparing plan). Comparison of the plans was done using a two-sided paired Student t test.

RESULTS

The mean skin dose and volume of skin receiving 50 Gy were significantly less with the skin-sparing plan compared with non-skin-sparing plan (42.3 Gy vs. 47.7 Gy and 12.2% vs. 57.8% respectively; p < 0.001). The reduction in skin dose was confirmed by TLD measurements in anthropomorphic phantom using the same plans. Dose-volume analyses for other OARs were similar in both plans.

CONCLUSIONS

By configuring the skin as an OAR, it is possible to achieve skin dose reduction while delivering whole-breast IMRT without compromising dose profiles to PTV and OARs.

Effective beam directions using radiobiologically optimized IMRT of node positive breast cancer

The purpose of this study was to investigate the optimal coplanar beam directions when treating an early breast cancer with locoregional lymphatic spread with a few radiobiologically optimized intensity modulated beams. Also to determine the increase in the probability of complication-free cure with the number of beam portals and the smallest number required to perform a close to optimal treatment for this tumour site. Four test patients with stage II left-sided breast cancer were studied with heart, lung and contralateral breast as principal organs at risk. The clinical target volume consisted of the breast tissue remaining after surgery, the axillary, the internal mammary as well as the supraclavicular lymph nodes. Through an exhaustive search of all possible beam directions the most effective coplanar beams with one to four intensity modulated photon beam portals were investigated. Comparisons with uniform beam treatment techniques and up to 12 intensity modulated beams were also made. The different plans were optimized using the probability of complication-free tumour cure, P(+), as biological objective function. When using two intensity modulated beam directions three major sets of suitable directions were identified denoted by A, P and T. A corresponds to an anterior oblique pair of beams around 25 degrees and 325 degrees , P is a perpendicular lateral pair at around 50 degrees and 130 degrees whereas T is a more conventional tangential pair at around 155 degrees and 300 degrees . Interestingly, these configurations identify simply three major effective beam directions namely at 30 degrees +/-20 degrees , 145 degrees +/-20 degrees and 310 degrees +/-15 degrees . For the three intensity modulated beam technique a combination of these three effective beam directions generally covered the global maximum of the probability of complication-free tumour control. The improvement in complication-free cure probability with two optimally selected intensity modulated beams is around 10% when compared to a uniform beam technique with three to four beam portals. This increase is mainly due to a reduction by almost 1% in the probability of injury to the heart and an increase of 6% in the probability of local tumour control. When three or four biologically optimized beam portals are used a further increase in the probability of complication-free cure of about 6% can often be obtained. This improvement is caused by a small decrease in the probability of injury to the heart, left lung and other surrounding normal tissue, as well as a slight further increase in the probability of tumour control. The increase in the treatment outcome is minimal when more than four intensity modulated beams are employed. A small increase in dose homogeneity in the target volume and a slight decrease in the normal tissue volume receiving high dose may be seen, but without appreciably improving the complication-free cure probability. For a stage II breast cancer, three and in more complex cases four optimally oriented beams are sufficient to reach close to the maximum probability of complication-free tumour control when biologically optimized intensity modulated dose delivery is used. Angle of incidence optimization may then be advantageous starting from the given most effective three beam directions.

A Dosimetric Comparison of Electronic Compensation, Conventional Intensity Modulated Radiotherapy, and Tomotherapy in Patients With Early-Stage Carcinoma of the Left Breast

PURPOSE

Intensity modulated radiation therapy (IMRT) has been shown to significantly reduce dose to normal tissue while maintaining coverage of the clinical target volume (CTV) in patients with intact breast cancer. We compared delivery of whole breast irradiation utilizing three techniques: electronic tissue compensation (ECOMP), inverse-planned dynamic multileaf collimation IMRT (DMLC), and tomotherapy (TOMO).

PATIENTS AND METHODS

Ten patients with early stage, left-sided breast cancer were selected for planning. CTV was defined as breast encompassed in a standard tangent field minus the superficial 5 mm from the skin edge. Normal tissue contours included the heart, lungs, and contralateral breast. Plans included delivery of 45 Gy in 25 fractions and were normalized to ensure > or =95% coverage of the CTV. Isodose distributions and dose-volume histograms for CTV and normal tissue were compared between plans. The time it took to plan each patient excluding contouring, as well as number of monitor units (MUs) required to execute each plan were additionally tabulated.

RESULTS

The TOMO plans resulted in significantly greater heterogeneity (CTV V(115)) versus ECOMP (p = 0.0029). The ECOMP plans resulted in significantly lower doses to heart, lung, and contralateral breast when compared with TOMO plans. The ECOMP plans were generated in the shortest time (12 min) and resulted in the lowest number of MUs when compared with DMLC (p = 0.002, p < 0.0001) and TOMO (p = 0.0015, p < 0.0001).

CONCLUSIONS

The ECOMP plans produced superior dose distributions in both the CTV and normal tissue when compared with TOMO or DMLC plans. In addition, ECOMP plans resulted in the lowest number of MUs and labor cost.

Equivalent uniform dose concept evaluated by theoretical dose volume histograms for thoracic irradiation

BACKGROUND AND PURPOSE

The goal of our study was to quantify the limits of the EUD models for use in score functions in inverse planning software, and for clinical application.

MATERIALS AND METHODS

We focused on oesophagus cancer irradiation. Our evaluation was based on theoretical dose volume histograms (DVH), and we analyzed them using volumetric and linear quadratic EUD models, average and maximum dose concepts, the linear quadratic model and the differential area between each DVH.

RESULTS

We evaluated our models using theoretical and more complex DVHs for the above regions of interest. We studied three types of DVH for the target volume: the first followed the ICRU dose homogeneity recommendations; the second was built out of the first requirements and the same average dose was built in for all cases; the third was truncated by a small dose hole. We also built theoretical DVHs for the organs at risk, in order to evaluate the limits of, and the ways to use both EUD(1) and EUD/LQ models, comparing them to the traditional ways of scoring a treatment plan. For each volume of interest we built theoretical treatment plans with differences in the fractionation.

CONCLUSION

We concluded that both volumetric and linear quadratic EUDs should be used. Volumetric EUD(1) takes into account neither hot-cold spot compensation nor the differences in fractionation, but it is more sensitive to the increase of the irradiated volume. With linear quadratic EUD/LQ, a volumetric analysis of fractionation variation effort can be performed.