ANALYSIS OF BENEFITS OF RAPIDARC / VMAT RADIOTHERAPY TREATMENT

WRITTEN BY MELISSA MCCLEMENT, APPLICATION SPECIALIST, TECMED AFRICA

DECEMBER 2011

INTRODUCTION

The first RapidArc or VMAT treatment in South Africa was given on the 11th of November 2010, at the Radiotherapy Department of Netcare Unitas Hospital. Since then, this speciality radiotherapy treatment has only gone from strength to strength, with over 400 patients in South Africa treated with this technique by the end of 2011.

But the main question is what exactly is the benefit of this particular treatment technique, in comparison to the conformal treatment techniques, to the patient and ultimately to the radiotherapy department?

This document aims to prove the benefit of RapidArc / VMAT treatment in comparison to conformal radiotherapy treatment techniques. A description of this treatment technique and comparative studies will also be included.

WHAT IS RAPIDARC OR VMAT TREATMENT EXACTLY?

RapidArc is the term coined by Varian Medical Systems for Volumetric Modulated Arc Therapy (VMAT). As an employee of Tecmed Africa, distributors of Varian Radiation equipment, I will use RapidArc as my term of preference. The two centres in South Africa (Netcare Unitas and Addington Hospital) doing Volumetric Modulated Arc Therapy are also Varian / Tecmed departments.

RapidArc radiotherapy technology advances the standard of care with uncompromised treatment in two minutes or less (www.varian.com).

The Cancer Centre at Lake Manassas in Virginia, US, explains RapidArc in the following manner:

“RapidArc shapes and modulates a highly focussed treatment beam so that it targets the tumour precisely, sparing surrounding healthy tissues. It treats the entire tumour with pinpoint accuracy and is easier on the patient, who does not have to hold still for long periods of time. RapidArc treatment allows your clinician to deliver a more targeted dose of radiation, with potentially fewer side effects and less damage to healthy surrounding tissue.”

One needs to put this in laymen’s terms though.

Cancer cells grow and divide more rapidly than many of the normal cells around them. High doses of radiation can kill cells or keep them from growing and dividing, and they have proven to be particularly effective in killing cancer cells and shrinking tumours – cells that divide and grow quickly. Although some normal cells are affected by radiation, most normal cells recover more fully from the effects of radiation than do cancer cells. Weekend rest breaks allow normal cells to recover. The total dose of radiation and the number of treatments a patient needs depend on the size and location of the cancer, they type of tumour, the patient’s general health and other factors. (www.cancer-radiation.com).

Where conventional radiotherapy techniques treat one shaped field at a certain angle and then move on to the next angle to treat, RapidArc rotates 360 degrees around the patient at once, whilst enabling the very small beams with varying intensity to be aimed at the tumour from multiple angles. This means that higher doses of radiation are delivered to hit the tumour harder, and less radiation is delivered to surrounding healthy tissue. RapidArc treatments are planned using sophisticated computer programs that analyze diagnostic image data and calculate the best way of delivering the radiation dose to minimize impact on healthy tissue for each patient. As mentioned before, treatments are fast. With RapidArc, the treatment time is reduced by about 80% in comparison to conventional treatment techniques. (www.altabatessummit.org).

During a RapidArc treatment the radiation beam is continually shaped and reshaped according to the size, shape, and position of the tumour in the body. The specialized software algorithms (mentioned earlier as well) vary three parameters simultaneously: the speed of rotation around the patient, the shape of the MLC aperture (in other words the shape of the beam), and the dose delivery rate (in other words the dose delivered at specific times). (www.trinitascancercenter.org).

THE FACTS

Now that we know exactly what RapidArc is, we can compare the RapidArc plans to the more conventional radiotherapy plans and even to IMRT (Intensity Modulated Radiation Therapy) plans. IMRT was the big precursor to RapidArc, and an enormous step up from conventional radiotherapy plans.

All of the following studies are attached under APPENDIX A.

1) VUmc in Amsterdam compared RapidArc to IMRT planning for Head and Neck, glioma and pancreatic cancers. They found that RapidArc accurately delivers the planned dose distributions. Plans of 2 arcs were superior to IMRT for tumour volume homogeneity and for sparing of the organs at risk. Given the low number of MU’s and short delivery times, RapidArc has replaced IMRT in their department.

2) In another study by VUmc, where RapidArc for highly conformal irradiation of vestibular schwannoma’s were investigated, they concluded that with RapidArc, a higher conformity index, a decrease in low dose area and shorter treatment delivery times were shown. That indicates RapidArc to be a patient-friendly, non-invasive alternative to “conventional” 5-arc radiosurgery for vestibular schwannoma. (Radiosurgery is a single high dose treatment with pencil thin beams for very small sized tumours in the brain).

3) In the first six months of going clinical with RapidArc, the Oncology Institute of Southern Switzerland in Bellinzona found that the target coverage is D₉₈ > 93% with high sparing of organs at risk. The beam on time was around 1 minute 20 seconds, and the average time a patient spent in the treatment room was 7.5 minutes. They expect that RapidArc would progressively replace IMRT in most of their clinical indications.

4) The same institute found that simultaneously treating an integrated boost for bilateral breast carcinoma with RapidArc showed dosimetric improvements with respect to IMRT and that delivery parameters confirmed its logistical advantages. Treating breast carcinoma in this way would decrease the amount of treatment fractions, as with conventional treatment the whole breast is treated first, followed by the boost.

5) In another study by the Oncology Institute of Southern Switzerland, RapidArc was investigated for anal canal cancer in comparison to IMRT. They found that although excellent dosimetric results were achieved with IMRT, RapidArc with double arcs improved the sparing of organs at risk and had uncompromised target (tumour volume) coverage.

6) When a study between three departments (Oncology Institute of Southern Switzerland, University of Lausanne and Tata Memorial Hospital in Mumbai) were done on cervix uteri treatments, the conclusion was that statistically highly significant improvements in organs at risk and healthy tissue sparing with uncompromised target coverage was found with RapidArc, which lead to avoidance of treatments with conventional IMRT.

7) The department of Radiation Oncology in Montpellier, France, also found that treatment to the head and neck using RapidArc reduces treatment time and the number of monitor units. They also found that the dose delivery to both parotids was significantly decreased.

8) The same department also compared plans using RapidArc and IMRT for anal cancer treatment. Their conclusion was that RapidArc was able to deliver an equivalent treatment plan to IMRT in terms of tumour volume coverage and sparing of organs at risk. But, the significant reduction in MU’s and treatment time per fraction may decrease the risk of secondary malignancy compared to IMRT.

As mentioned before, all of the above studies are included in APPENDIX A.

THE REASONING

There are many centres that came to the same conclusions:

- Less time for the patient on the bed, means less movement, which would increase the accuracy of the treatment (www.cancer-radiation.com).

Significance to a department:

1) Patient movement on the bed whilst irradiating does not only mean missing the target volume (tumour volume), but also increasing the dose delivered to the normal or healthy tissues. Under dosing the target volume would lead to recurrence, over dosing the normal tissues would lead to increased side effects (both early and late side effects). The next domino to fall in the line would be that any of the resulting issues would lead to an increase in the use of medical resources.

2) The less the time per patient spends on the treatment bed, the more patients can be treated in one day. Thus leading to eliminating waiting lists.

- The significant decrease in the amount of monitor units (MU) needed per treatment.

Significance to a department:

As the last mentioned study confirmed, a RapidArc treatment needs less MU than an IMRT treatment with essentially the same conformity to the tumour volume (again leading to less irradiation of normal tissues). An increase amount of MU could possibly lead to a secondary tumour developing – leading, yet again, to the use of more medical resources.

- The ability to treat a large field and a boost to the same area simultaneously.

The above was not mentioned in any of the studies included in this document. It is possible to treat multiple small tumours, located in the same anatomical area, to a higher dose, within a larger anatomical tumour volume. For example: The boost area of a breast patient can be treated to the higher dose whilst the whole of the breast is being treated to a lower dose; Including para-aortic nodes in a pelvic treatment volume; Multiple brain metastases included in one brain treatment volume.

Significance to a department:

The more fractions added to a treatment volume, the longer the patient is being treated. Treating more than one volume at one time or parts of a volume to a higher dose at once, will decrease the amount of treatment fractions needed, thus decreasing the total time the patient occupies the slot on the treatment unit. In departments where there is a backlog of patients to be treated, this is very significant. That treatment slot will then be filled with a new patient quicker and more often, thus resulting in more patients being treated per day, or per month, or per year.

- The dose to the organs at risk was decreased in all of the studies mentioned. The organs at risk are usually treated differently to ‘normal tissue’. Organs at risk are those organs which has a threshold dose limit before irreversible damage is caused. For a treatment to the brain, one of the organs at risk would be the lenses of the eyes, as they can handle only very little amounts of radiation before causing permanent blindness. Another organ at risk would be the brainstem, which can also only handle a certain amount of dose before causing major side effects. The spine can only handle a certain amount of radiation before irreversible paralysis is caused.

Significance to a department:

It is obvious that serious damage, such as paralysis or blindness or emphysema caused by ‘overdosing’ an organ at risk, will increase the future financial pressure put on medical resources.

APPENDIX B includes an indication of the extensive clinical applications of RapidArc.

CONCLUSION

In conclusion, one has to admit that providing the best, most relevant and most effective radiotherapy treatment available to a patient is of the utmost importance. The long term benefits that result from a highly advanced treatment such as RapidArc or VMAT are priceless to a patient. The departmental benefits can of course also not be overlooked – more patients can be treated in a given amount of time than that with conventional treatment or IMRT. RapidArc is the future of Radiation therapy.

APPENDIX A: STUDIES MENTIONED WITHIN TEXT

IN ORDER OF DISCUSSION WITHIN TEXT

APPENDIX B: ILLUSTRATION OF EXTENSIVE CLINICAL APPLICATION OF RAPIDARC